Heat stress: an overview of molecular responses in photosynthesis

CpHSFA2 isolated from a wild native Carica papaya genotype, with potential to confer tolerance to the combined effect of drought stress and heat shock

Many papaya producing regions are repeatedly affected by drought and high temperatures. In the present study, we investigated the individual effect of heat shock (HS), water deficit stress (WDS) and the combined effect of both types of stress (WD + HS), on the physiological performance of two contrasting papaya genotypes (Maradol and Wild). In all cases, water relations, membrane integrity, gas exchange, photochemical state of PSII and RELs of three Carica papaya transcription factors (CpHsfA1d, CpHsfA2 and CpHsfB3, in both a Wild-native genotype collected from an undisturbed site in its center of origin (Yucatán, Mexico; Wild), as well as in a commercial cultivar (Maradol). Results showed that both papaya genotypes have different physiological and molecular mechanisms to cope with individual stress and combined stresses. Wild (W) genotype exhibited greater tolerance to the three types of stresses than the commercial genotype (M), which correlates with the fact that W also showed higher relative expression levels (REL) in the three CpHsf studied: CpHsfA1d, CpHsfA2 and CpHsfB3 than M. REL of CpHsfA2 was particularly high in the HS and in the combined WD + HS treatment, as well as during the recovery phase of the WDS treatment. CpHSFA2 was then selected for further analysis of subcellular localization, finding that it accumulates in the membrane and nucleus. Taken together, it seems that CpHsfA2 plays an important role in the response to HS and WD + HS stress. Therefore, CpHsfA2 gene from the W genotype could be important to eventually improve tolerance to high temperatures and drought in commercial papaya cultivars.

Application of ATR-Fourier transform infrared spectroscopy in fast and simultaneous determination of leaf chemical and functional properties of forest herb species

ATR-Fourier transform infrared spectroscopy was used to determine the carbon and nitrogen content in the leaves of herbaceous forest plant species and functional traits associated with the leaf economic spectrum (one of the two-dimensional global spectrum of plant form and function), and monitoring plant physiological status under elevated temperature conditions. The content of carbon and nitrogen determined by traditional methods validated the accuracy of ATR-FTIR method. It was also shown that in the case of forest herbs, the ATR-FTIR method is an efficient tool for determining functional traits (such as specific leaf area (SLA) and leaf dry matter content (LDMC)) related to the leaf economics spectrum, and to diagnose the photophysiological state of plants after changes of temperature (changes of day/night temperature from 21/13 °C to 25/17 °C). Measuring the areas of three absorption bands of the ATR-FTIR spectra related to amides I and II (between 1700 cm-1 and 1500 cm-1), carbohydrates (cellulose and hemicellulose; between 1200 cm-1 - 850 cm-1) and amide III (between 1290 cm-1 and 1190 cm-1) allowed for determination of all analysed chemical and functional properties of leaves. Based on selected absorption bands accurately estimated C and N content, with coefficients of correlation (r) of 0.88 for C and 0.84 for N. SLA and LDMC were also predicted, with r values of 0.88 and -0.91, respectively. Moreover, ATR-FTIR proved to be a rapid, non-destructive tool for monitoring the plant physiological status, as demonstrated by the significant correlation (r = 0.99) between the chlorophyll fluorescence performance index (PI) and ATR-FTIR data. ATR-FTIR has been demonstrated as an efficient tool for simultaneous quantification of leaf carbon and nitrogen content, economic functional traits, and physiological status of forest herb plants.

Above-ground xylem genes and below-ground soil carbon genes analyses provide molecular insights into experimental warming in Phoebe chekiangensis

Phoebe chekiangensis C. B. Shang is an endemic and endangered species in China, and it is widely used for furniture, building materials and artwork due to its high-quality wood properties and high economic value. However, the impact of spring warming on P. chekiangensis growth molecular dynamics are poorly understood. In this study, we used a year-long warming control experiment (CK, +2 °C, +4 °C) to explore the molecular dynamics of aboveground xylem genes and belowground soil carbon genes. Transcriptome results indicated that spring warming primarily affects genes and pathways related to cell growth, lignin, photosynthesis, and cell wall macromolecules. Carbon fixation genes abundance increased significantly over time in the CK and + 2 °C groups, but no significant increase was observed in the +4 °C group. In addition, spring warming reduced the diversity of microbial communities which may be one of the reasons for reduced tree growth. These findings revealed the mechanisms underlying xylem and carbon cycling genes responses to varying temperature increases in P. chekiangensis. Our results provided valuable insights for future research on wood-related molecular mechanisms and offer a foundational basis for uniting aboveground xylem growth and belowground carbon genes to together influence seasonal development of wood.

Drought-Driven Divergence in Photosynthetic Performance Between Two Cunninghamia lanceolata Provenances: Insights from Gas Exchange and Chlorophyll Fluorescence Dynamics

Cunninghamia lanceolata, contributing 25% to China's commercial timber production, faces severe drought threats. However, provenance-specific photosynthetic adaptations remain poorly understood. Here, we compared gas exchange, prompt/delayed fluorescence (PF/DF), and modulated 820-nm reflection (MR) responses of two provenances (JXJJ and FJSM) under different drought treatment times. JXJJ maintained a higher net photosynthetic rate (Pn) and stomatal conductance (Gs) than FJSM under drought stress. The declining rates of FV/FM, φEO, ΨO, δRO, PIABS, TRO/CSM, and ETO/CSM were much more rapid in the FJSM than in the JXJJ. An MR kinetics analysis revealed significantly greater PSI impairment in FJSM, evidenced by a 60.2% reduction in P700+ re-reduction rate (Vred) compared to only 44.4% in JXJJ (p < 0.05) at 20 d drought treatment. Similarly, DF measurements demonstrated more pronounced PSII energy transfer disruption in FJSM, with the I2/I1 ratio increasing by 51.3% vs. 43.0% in JXJJ at 20 d drought treatment. These results demonstrate JXJJ's superior drought resilience through coordinated stomatal and non-stomatal regulation. Our findings provide actionable criteria for selecting drought-tolerant C. lanceolata provenances, which is essential for sustainable forestry as the climate changes. This study underscores the significance of photosynthetic activity in how C. lanceolata responds to drought and gives insights into boosting drought tolerance in forest species through genetic improvements.

Needle angle dynamics as a rapid indicator of drought stress in Larix kaempferi (Lamb.) Carrière: advancing non-destructive imaging techniques for resilient seedling production

Larix kaempferi (Lamb.) Carrière, a valuable species for timber production and reforestation, faces challenges in large-scale seedling propagation due to its slow growth cycle and high susceptibility to environmental stressors. Early detection of drought stress is critical for preparing seedlings for harsh field conditions and for optimizing irrigation strategies. This study aimed to detect drought stress at an early stage in L. kaempferi seedlings by integrating physiological traits with image-based phenotypic measurements, with a focus on needle angle dynamics under controlled drought and irrigation conditions. The apical needle angle of one-year-old seedlings was measured using ImageJ, while seedling-level analysis was conducted using PlantCV to collect data and extract relevant parameters. Statistical analyses were performed to evaluate temporal trends and to identify growth environment and physiological traits significantly influenced by drought stress. As a result, apical needle wilting and recovery, along with seedling-level image analysis (parameter: Center of Mass(y)), exhibited significant responses to drought stress as early as Day 2. This provides a non-destructive method for early detection, preceding observable changes in physiological traits such as chlorophyll fluorescence and needle temperature that responded to drought stress by Day 6, as well as before seedling mortality occurred. Multiple regression analysis indicated that, as drought stress progressed, solar radiation and thermal-related parameters (ФNPQ and needle temperature) emerged as key predictors of needle angle variation. Image-based approaches, including RGB and thermal imaging, proved effective for real-time stress monitoring, demonstrating their practical potential for nursery applications. In summary, this study lays the groundwork for needle-based phenomic approaches using imaging techniques in nursery systems and highlights the need for further research to optimize these methods for the large-scale, cost-effective production of high-quality, drought-resilient L. kaempferi seedlings.

Whey protein hydrolysates enhance grapevine resilience to abiotic and biotic stresses

Introduction

The growing need for sustainable viticulture has increased interest in biostimulants that enhance plant resilience to abiotic and biotic stresses. This study evaluates the efficacy of whey-derived protein hydrolysates (PHs) in improving Vitis vinifera cv. Cabernet Sauvignon tolerance to combined heat and drought stress and reducing pathogen infections.

Methods

Potted grapevines were subjected to 40°C heat stress without irrigation and treated with either water or PHs. Physiological parameters as well as key stress- and photosynthesis-related genes expression were monitored. The antimicrobial effects of PHs against Plasmopara viticola and Botrytis cinerea were also assessed.

Results

PHs-treated plants exhibited a faster recovery of photosynthetic activity than control plants and maintained normal sub-stomatal CO2 concentrations under combined abiotic stress. PHs treatment significantly upregulated heat stress-responsive genes (HSFA2, HSP101) and mitigated the stress-induced decline in photosynthesis-related genes (LHCA3, RbcS). Moreover, PHs significantly enhanced grapevine drought tolerance, as indicated by higher leaf water potential values and expression of drought-responsive genes (NCED1, TIP2;1). Additionally, PHs demonstrated a direct toxic effect on P. viticola, inhibiting zoospore germination and reducing sporulation on leaf discs, while reducing B. cinerea infection in berries when applied post-infection.

Conclusion

In the tested conditions, whey PHs serve as effective biostimulants, enhancing grapevine resilience to combined drought and heat stress while providing protection against grapevine pathogens. Although further validation in vineyard conditions is needed, this dual benefit of PHs may propose a potential sustainable alternative to reduce chemical inputs in viticulture, contributing to more environmentally friendly agricultural practices.

Alterations in physiological and biochemical characteristics of Prunus sibirica seedlings raised from spaceflight seeds

The aim was to explore the alterations in growth traits, physiological and biochemical characteristics of Prunus sibirica seedlings raised from spaceflight seeds. The seedlings cultivated by the "Shenzhou XII" spacecraft carrying the seeds of superior clones of P. sibirica were used to observe their growth traits and determine physiological indicators. The results showed that plant height of Prunus sibirica seedlings raised from spaceflight seeds increased by 18-34% and internode length increased by 8-26%, but the number of primary branches, secondary branches, and leaves showed no significant change compared to the ground control. Leaf length and width of Prunus sibirica seedlings raised from spaceflight seeds were significantly higher than those of the ground control, with leaf length, width, and area increasing to 1.21-1.80 times higher than that of the ground control. Furthermore, the antioxidant and osmoregulatory capacities of P. sibirica seedlings raised from spaceflight seeds were altered. The peroxidase (POD) activity and Malondialdehyde (MDA) content were increased in ST28, ST207, and ST507, while they were reduced in ST1 and ST453. Compared with the ground control, the content of soluble sugar(SS), starch (St), and free proline (Pro) were significantly or highly significantly increased in all lines. The content of soluble protein (SP) was significantly increased in ST1, ST28, ST207, and ST507, while there was no significant change in ST453. P. sibirica seedlings raised from spaceflight seeds exhibited increased leaf pigment content, the interstitial CO2 concentration (Ci), net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr). In conclusion, compared with the ground control, the growth indexes and physiological characteristics of Prunus sibirica seedlings raised from spaceflight seeds were changed, and the direction of change was different for different lines. This provided a foundation for subsequent germplasm improvement and variety selection.

How to improve the potential of microalgal biostimulants for abiotic stress mitigation in plants?

Abiotic stress is among the most critical factors limiting crop productivity worldwide and its importance is further exacerbated by climate change. In recent years, microalgal biostimulants have gained attention for their potential to enhance plant resilience towards abiotic stress. However, significant hurdles still persist, particularly regarding the unknown modes of action of microalgal biostimulants, which is a concern for stringent regulatory requirements and product reliability. The aim of this review is to improve the potential of microalgal biostimulants for abiotic stress mitigation in plants by addressing different key parameters shaping the efficacy of microalgal biostimulants, encompassing cultivation approaches, extraction techniques, and application methods. Furthermore, it also highlights how microalgal biostimulants modulate plant morphology, physiology and biochemistry under drought, salinity, and heat stress-three predominant stressors anticipated to intensify under climate change. Notably, these biostimulants consistently enhance drought stress tolerance by improving biomass accumulation, nutrient uptake, and water use efficiency through enhanced photosynthesis and stomatal regulation. These effects are largely driven by the accumulation of osmoprotectants and antioxidant compounds. In contrast, salt stress mitigation is highly species-dependent, with some microalgae enhancing stress tolerance through osmoprotectant and antioxidant accumulation, while others reduce these compounds, potentially lowering stress perception via unknown mechanisms. Despite the significance of the abiotic stress, heat stress mitigation by microalgal biostimulants remains an underexplored research area. Additionally, indirect applications of microalgae-ranging from biotechnological innovations to desalination-underscore the broader potential of these organisms in agricultural resilience. Collectively, this review identifies three key gaps in the existing literature-the diversity gap, the practical gap, and the research gap-while outlining promising avenues for future research in microalgal biostimulant development.

Systems analysis of long-term heat stress responses in the C4 grass Setaria viridis

Many C4 plants are used as food and fodder crops and often display improved resource use efficiency compared to C3 plants. However, the response of C4 plants to future extreme conditions such as heatwaves is less understood. Here, Setaria viridis, an emerging C4 model grass, was grown under long-term high-temperature stress for 2 wk (42 °C, compared to 28 °C). This resulted in stunted growth, but surprisingly had little impact on leaf thickness, leaf area-based photosynthetic rates, and bundle sheath leakiness. Dark respiration rates increased, and there were major alterations in carbon and nitrogen metabolism in the heat-stressed plants. Abscisic acid and indole-3-acetic acid-amino acid conjugates accumulated in the heat-stressed plants, consistent with transcriptional changes. Leaf transcriptomics, proteomics, and metabolomics analyses were carried out and mapped onto the metabolic pathways of photosynthesis, respiration, carbon/nitrogen metabolism, and phytohormone biosynthesis and signaling. An in-depth analysis of correlations between transcripts and their corresponding proteins revealed strong differences between groups in the strengths and signs of correlations. Overall, many stress signaling pathways were upregulated, consistent with multiple signals leading to reduced plant growth. A systems-based model of the plant response to long-term heat stress is presented based on the oxidative stress, phytohormone, and sugar signaling pathways.

Cotton under heat stress: a comprehensive review of molecular breeding, genomics, and multi-omics strategies

Cotton is a vital fiber crop for the global textile industry, but rising temperatures due to climate change threaten its growth, fiber quality and yields. Heat stress disrupts key physiological and biochemical processes, affecting carbohydrate metabolism, hormone signaling, calcium and gene regulation and expression. This review article explores cotton's defense mechanism against heat stress, including epigenetic regulations and transgenic approaches, with a focus on genome editing tools. Given the limitations of traditional breeding, advanced omics technologies such as GWAS, transcriptomics, proteomics, ionomics, metabolomics, phenomics and CRISPR-Cas9 offer promising solutions for developing heat-resistant cotton varieties. This review highlights the need for innovative strategies to ensure sustainable cotton production under climate change.

Differential effects of warming on carbon budget, photosynthetic yield and biochemical composition of cold-temperate and Arctic isolates of Laminaria digitata (Phaeophyceae)

Cold-temperate and Arctic hard bottom coastal ecosystems are dominated by kelp forests, which have a high biomass production and provide important ecosystem services, but are subject to change due to ocean warming. However, the photophysiological response to increasing temperature of ecologically relevant species, such as Laminaria digitata, might depend on the local thermal environment where the population has developed. Therefore, the effects of temperature on growth rate, biochemical composition, maximum quantum yield, photosynthetic quotient and carbon budget of young cultured sporophytes of Laminaria digitata from the Arctic at Spitsbergen (SPT; cultured at 4, 10 and 16 °C) and from the cold-temperate North Sea island of Helgoland (HLG; cultured at 10, 16 and 22 °C) were comparatively analyzed. Temperature significantly affected growth rates of L. digitata from SPT and HLG, with the highest rates occurring at 10 °C, but growth did not differ between both isolates neither at 10 °C nor at 16 °C. Nevertheless, maximum quantum yield and carbon fixation rate were highest at 4 °C for the Arctic and at 16 °C for the cold-temperate L. digitata. Significantly higher rates of oxygen production and carbon fixation were observed in the cold-temperate relative to the Artic L. digitata at 10 and 16 °C, respectively. Neither temperature nor biogeographic region of origin affected the photosynthetic quotient, and release rates of dissolved or particulate organic carbon. Total carbon and mannitol content were significantly higher in the Arctic compared to the cold-temperate L. digitata at 10 °C, revealing an increased accumulation of storage compounds in the high latitude L. digitata. We conclude that L. digitata from SPT and HLG differ in their sensitivity to increasing temperatures and that the Arctic population from Spitsbergen is likely to benefit from ocean warming, while the temperate population from Helgoland will be negatively affected by further increases in ambient temperature.

Application of ultra-weak photon emission imaging in plant stress assessment

The oxidative damage induced by abiotic stress factors such as salinity, drought, extreme temperatures, heavy metals, pollution, and high irradiance has been studied in Arabidopsis thaliana. Ultra-weak photon emission (UPE) is presented as a signature reflecting the extent of the oxidation process and/or damage. It can be used to predict the physiological state and general health of plants. This study presents an overview of a potential research platform where the technique can be applied. The results presented can aid in providing invaluable information for developing strategies to mitigate abiotic stress in crops by improving plant breeding programs with a focus on enhancing tolerance. This study evaluates the applicability of charged couple device (CCD) imaging in evaluating plant stress and degree of damage and to discuss the advantages and limitations of the claimed non-invasive label-free tool.

The thylakoid protein BCM1 sequesters antennae protein CP24 and CP29 within the grana cores thereby reducing their exposure to degradation under heat stress

Photosystem II (PSII) is one of the most thermosensitive components of photosynthetic apparatus in higher plants. Heat-inactivation of PSII may be followed by dissociation of antenna proteins, however, the fate and regulation mechanism of detached antenna proteins during this process remains unclear. Here, we investigate the regulation mechanism of two minor antenna proteins CP24 and CP29 during heat acclimation via the study on a thylakoid protein BCM1. BCM1 is distributed in both grana cores (GC) and stroma lamellae of thylakoids. However, heat stress induced its accumulation in grana cores but not stroma lamellae. Deficiency of BCM1 leads to the decline of plant resilience to heat stress, which results from the accelerated degradation of CP24 and CP29 in vivo. Heat stress induces a redistribution of CP24 and CP29 from the grana cores to the stroma lamellae, a shift that is exacerbated in bcm1 mutants, suggesting that migration of detached antennae proteins between thylakoid subcompartments may contribute to their degradation during heat acclimation. As an integral thylakoid protein, BCM1 physically interacts with CP24 and CP29. We propose that BCM1 serves as a stabilizing "anchor", effectively sequestering CP24 and CP29 within the grana cores thereby reducing their exposure to degradation in the stroma lamellae.

Exploring the Role of Non-Structural Carbohydrates (NSCs) Under Abiotic Stresses on Woody Plants: A Comprehensive Review

Global climate change has increased the severity and frequency of abiotic stresses, posing significant challenges to the survival and growth of woody plants. Non-structural carbohydrates (NSCs), including starch and sugars, play a vital role in enabling plants to withstand these stresses, helping to stabilize cellular functions by buffering plant energy demands and facilitating recovery on the alleviation of stress. Despite the recognized multiple functions of NSCs, the contrasting effects of multiple abiotic stresses on NSCs dynamics in woody plants remain poorly understood. This review aims to explore the current knowledge of the contrasting effects of abiotic stress conditions including drought, salinity, heat, water logging, and cold on NSCs dynamics. The roles of NSCs in regulating stress-resilience responses in woody plants are also discussed, along with the challenges in NSC measurement, and options for future research directions are explored. This review is based on comprehensive literature research across different search engines like Scopus, Web of Science, and Google Scholar (2000-2024) using targeted keywords. This study compiles the current research on NSCs functions and provides insights into the adaptive strategies of woody plants in response to changing climate conditions, providing groundwork for future research to improve stress tolerance in woody plants.

Differential biochemical responses of seven Indian wheat genotypes to temperature stress

BACKGROUND

Changes in the temperature induction response are potential tools for the empirical assessment of plant cell tolerance. This technique is used to identify thermotolerant lines in field crops. In the present investigation, ten-day-old seedlings of six wheat genotypes released by Dr. PDKV, Akola, Maharashtra, India were exposed to gradual increases in high temperature and duration (control 25 °C to 30 °C for 1 h, 34 °C for 1 h, 38 °C for 2 h and 42 °C for 3 h) to investigate their effects on some physiological and biochemical parameters to provide basic information for improving heat-tolerant cultivars.

RESULTS

Proline levels increased with increasing temperature up to 34 °C for 1 h but then decreased at higher temperatures (depending on genotype). Notably, proline levels decreased at 38 °C for 2 h in PDKV-Washim, AKAW-3722, and PDKV Sardar and at 42 °C for 3 h in all the genotypes. The relative leaf water content (RLWC) and chlorophyll 'b' content significantly decreased with increasing temperature. Hydrogen peroxide (H₂O₂) levels increased with temperature. The enzyme activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase also increased with temperature. However, these parameters, along with other biochemical indicators, generally decreased at 42 °C for 3 h.

CONCLUSION

This study revealed positive relationships between increasing temperatures. Hydrogen peroxide levels and the activities of SOD, APX, and peroxidase enzymes across all the genotypes. The AKAW-4627 genotype presented better maintenance of physiological and biochemical parameters and lower H₂O₂ levels, indicating greater heat tolerance. Compared with PDKV-Washim and AKAW-3722, which are more susceptible to high temperatures, the WSM-109-04, AKAW-4627 and PDKV Sardar genotypes presented better adaptability to heat stress. These findings suggest that selecting wheat genotypes with higher proline accumulation and better maintenance of physiological and biochemical parameters under heat stress, such as AKAW-4627, can help in the development of heat-tolerant wheat cultivars.

Estimation of light utilisation and antioxidative protection in an alpine plant species (Soldanella alpina L.) during the leaf life cycle at high elevation

Photosynthesis, electron transport to carbon assimilation, photorespiration and alternative electron transport, light absorption of the two photosystems, antioxidative protection and pigment contents were investigated in S. alpina leaves. S. alpina is an alpine snow-bed plant which can be found with green leaves after snowmelt. At least 24% of the leaves were formed at the beginning of the vegetation period in the previous year and survived two consecutive vegetation periods under contrasting environmental conditions. In leaves still covered by snow (SNOW), the parameters of antioxidative protection and carbon assimilation were lower than in leaves from the previous vegetation period (NEW) or several weeks after snowmelt (OLD). Directly after snowmelt, antioxidative protection was strongly but transitionally increased. The senescence of leaves did not depend on antioxidative scavenging capacity. Lower carbon assimilation was not related to increases in alternative electron flow (ETRalt) in SNOW leaves. In the second vegetation period, light absorption by PSII decreases in favour of PSI in OLD leaves. This allows OLD leaves to keep the electron transport chain more oxidised and to support photorespiration with increased ATP synthesis by cyclic electron transport around PSI. This study describes how the leaves of a unique plant can cope with contrasting environmental conditions.

Do Endangered Glacial Relicts Have a Chance for Effective Conservation in the Age of Global Warming? A Case Study: Salix lapponum in Eastern Poland

The abiotic stresses to which plants are exposed, especially in times of climate change, can result in the disruption of natural plant physiological processes. Sudden atmospheric phenomena may increase the risk of failure in protecting rare and extinction-threatened plant species by translocation. This study aimed to determine the effect of extreme ambient temperatures on the condition and physiological response of Salix lapponum plantlets used for their reintroduction into the natural habitat. Salix lapponum plants obtained by micropropagation methods at different stages of growth under laboratory conditions were subjected to a biological experiment. Plants were exposed for 12 h to temperature extremes (0 °C and 30 °C), after which the values of selected markers of the biochemical response were determined, such as photosynthetic pigments and anthocyanin content, guaiacol peroxidase and catalase activity, the presence of ROS and the RWC value. The study showed that plants at early growth stages were sensitive to low-temperature stress. In contrast, older ones showed a stronger response to high temperature, marked by an increased anthocyanin content and guaiacol peroxidase activity. It was also found that a short exposure to temperature extremes did not change the photosynthetic pigment content or catalase activity. The results of the study may be an important indication for the optimization of plant acclimatization methods in the process of their active protection by species translocation.

Tandemly duplicated Rubisco activase genes of cereals show differential evolution and response to heat stress

Heat stress affects various components of photosynthetic machinery of which Rubisco activation inhibition due to heat sensitive Rubisco activase (RCA) is the most prominent. Detailed comparison of RCA coding genes identified a tandem duplication event in the grass family lineage where the duplicated genes showed very different evolutionary pattern. One of the two genes showed high level of sequence conservation whereas the second copy, although present only 1.5 kb away, was highly variable among various plant species because of loss of introns, alternative splicing and loss of the last exon coding redox regulated C-terminal extension domain. Gene specific expression analysis, both at the transcription as well as the protein level, showed very different expression pattern of the two RCA copies. Expression of the highly conserved copy was higher under normal plant growing conditions that decreased many folds under heat stress with substantial genotypic variation, but the variable copy showed much higher expression under heat stress conditions across all grass species. The cultivated rice has only one functional gene as the second copy became nonfunctional due to multiple deletions but Oryza brachyantha and Oryza australiensis still have two functional Rca genes. Detailed analysis of the promoter region of the two copies among various plant species showed insertion of several transposable elements harboring heat responsive elements in the heat inducible copy of the gene. The conserved RCA copy of wheat didn't have any transposable insertions whereas in that of maize has one heat shock element and sorghum had two. It would be interesting to study if the higher level of heat stress tolerance observed in sorghum and maize is associated with the differences observed for RCA. Key message This manuscript is reporting a grass family-specific tandem duplication event in RCA genes of cereals. The duplicated copies underwent neo-functionalization to evolve novel function to deal with heat stress. One copy of the tandem duplication maintained a high level of conservation whereas the second copy showed tremendous divergence to evolve species specific function of the gene. Specific function to respond to heat stress likely evolved via the insertion of various heat responsive elements carried by transposable elements.

The effects of temperature and CO2 enrichment on the red seaweed Asparagopsis taxiformis from Southern California with implications for aquaculture

The red alga Asparagopsis taxiformis has recently been recognized for its unique ability to significantly reduce methane emissions from ruminant animals when fed in small quantities. The main obstacle in using this seaweed as a methane-mitigating feed supplement is the lack of commercially available biomass. Little is known about how best to grow this red alga on a commercial scale, as there are few published studies that have investigated the factors that influence growth, physiology, and overall performance. This study examined the effects of temperature and CO2 enrichment on the growth, photophysiology, and concentration of bromoform, the secondary metabolite largely responsible for methane reduction in A. taxiformis. A series of single and multifactor closed culture experiments were conducted on A. taxiformis collected, isolated, and cultured from populations in Southern California. We identified the optimal temperature range to be between 22 and 26°C, with significant short-term stress observed below 15°C and above 26°C. Carbon dioxide addition resulted in increased performance, when accounting for growth per CO2 use. In general, we observed the highest bromoform concentrations in algae with the highest growth rates, but these results varied among experiments. These findings indicate that through environmental control and by addressing limiting resources, significant increases in biomass production and quality can be achieved.

Warming and polymetallic stress induce proteomic and physiological shifts in the neurotoxic Alexandrium pacificum as possible response to global changes

Harmful Algal Blooms involving the dinoflagellate Alexandrium pacificum continue to increase in ecosystems suffering the climate warming and anthropogenic pressure. Changes in the total proteome and physiological traits of the Mediterranean A. pacificum SG C10-3 strain were measured in response to increasing temperature (24 °C, 27 °C, 30 °C) and trace metal contamination (Cu2+, Pb2+, Zn2+, Cd2+). Warming reduced the cell densities and maximal growth rate (μmax), but the strain persisted at 30 °C with more large cells. The polymetallic stress increased cell sizes, reduced cell growth at 24 °C-27 °C and it increased this at 30 °C. Toxin profiles showed a predominance of GTX4 (32-38 %), then C2 (11-34 %) or GTX6 (18-24 %) among the total Paralytic Shellfish Toxins, however these were modified under warming, showing increased contents in GTX1 (among the most toxic), GTX5, C1 and NeoSTX, while dc-NeoSTX and STX (among the most toxic) only appeared at 30 °C. Under polymetallic contamination, warming also increased contents in GTX5 and NeoSTX. In contrast, polymetallic stress, or warming had harmful effects on C2 contents. Proteins were more quantitatively produced by A. pacificum SG C10-3 under warming in accordance with the high levels of up-regulated proteins found in the total proteome in this condition. Polymetallic stress, only or combined with warming, led to low proteomic modifications (1 % or 4 %), whereas warming induced strong 52 % modified proteomic response, mainly based on up-regulated proteins involved in photosynthesis (light harvesting complex protein), carbohydrate metabolism (arylsulfatase) and translation (ribosomal proteins), and with the lesser down-regulated proteins principally associated with the lipid metabolism (type I polyketide synthase). Our results show that warming triggers a strong up-regulated A. pacificum SG C10-3 proteomic response, which, coupled to modified cell sizes and toxin profiles, could help it to withstand stress conditions. This could presage the success of A. pacificum in anthropized ecosystems submitted to global warming in which this dinoflagellate also might be more toxic.

Physiological and ecological responses of flue-cured tobacco to field chilling stress: insights from metabolomics and proteomics

Introduction

Currently, research on tobacco's response to chilling stress is mostly limited to laboratory simulations, where temperature is controlled to study physiological and molecular responses. However, laboratory conditions cannot fully replicate the complex environment of field chilling stress, so conducting research under field conditions is crucial for understanding the multi-level adaptive mechanisms of tobacco to chilling stress in natural environments.

Methods

This study aims to use field trials, starting from physiological responses, combined with proteomics and untargeted metabolomics, to systematically reveal the physiological and biochemical characteristics and key molecular mechanisms of tobacco leaves under chilling stress. It provides new insights into tobacco's adaptation strategies under chilling stress.

Results

The results showed that (1) chilling stress damages the appearance of tobacco leaves, reduces the chlorophyll content, increases H2O2 and malondialdehyde (MDA) levels in cold-injured tobacco leaves, and damages the plasma membrane system. Although catalase (CAT) activity increases to cope with the accumulation of reactive oxygen species (ROS), the activities of key antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD) significantly decrease, indicating that the antioxidant system of tobacco leaves fails in environments with sudden temperature drops. (2) Proteomics analysis indicated that 410 differentially expressed proteins were identified in cold-stressed tobacco leaves, with 176 upregulated and 234 downregulated. Tobacco leaves under chilling stress attempt to maintain energy supply and physiological stability by enhancing glycolysis, starch, and sucrose metabolism pathways. Concurrently, chilling stress triggers the expression of proteins related to cell wall reinforcement and antioxidant defense. However, due to impaired ribosomal function, protein synthesis is significantly inhibited, which aggravates damage to photosynthesis and cellular functions. (3) Metabolomics analysis revealed that the differential metabolites in cold-stressed tobacco leaves were mainly enriched in tyrosine metabolism, isoquinoline alkaloid biosynthesis, and fatty acid degradation pathways. This indicates that under chilling stress, tobacco leaves enhance adaptability by regulating energy metabolism, increasing antioxidant capacity, and stabilizing cell membrane structure.

Conclusions

Therefore, under chilling stress, tobacco leaves exhibit complex physiological adaptability through multiple regulatory mechanisms involving proteins and metabolites. The research results provide important insights into the metabolic regulatory mechanisms of tobacco in response to extreme environments and also enhance the theoretical foundation for addressing low-temperature stress in practical production.

Preliminary Treatment by Exogenous 24-Epibrassinolide Influences Burning-Induced Electrical Signals and Following Photosynthetic Responses in Pea (Pisum sativum L.)

Long-distance electrical signals (ESs) are an important mechanism of induction of systemic adaptive changes in plants under local action of stressors. ES-induced changes in photosynthesis and transpiration play a key role in these responses increasing plant tolerance to action of adverse factors. As a result, investigating ways of regulating electrical signaling and ES-induced physiological responses is a perspective problem of plant electrophysiology. The current work was devoted to the analysis of the influence of preliminary treatment (spraying) by exogenous 24-epibrassinolide (EBL) on burning-induced ESs and following photosynthetic and transpiratory responses in pea (Pisum sativum L.). It was shown that preliminary treatment by 1 µM EBL (1 day before the experiment) increased the amplitude of burning-induced ESs (variation potentials) in leaves and decreased the time of propagation of these signals from the stem to the leaf. The EBL treatment weakly influenced the magnitudes of burning-induced decreasing the photosynthetic linear electron flow and CO2 assimilation, but these changes were accelerated. Burning-induced changes in the cyclic electron flow around photosystem I were also affected by the EBL treatment. The influence of the EBL treatment on burning-induced changes in the stomatal water conductance was not observed. Our results show that preliminary treatment by EBL can be used for the modification of electrical signals and following photosynthetic responses in plants.

Light increases resistance of thylakoid membranes to thermal inactivation

In the region of slightly acidic pH (рН 5.7), the manganese cluster in oxygen-evolving complex of photosystem II (PSII) is more resistant to exogenous reductants. The effect of such pH on the heat inactivation efficiency of the electron transport chain (O2 evolution and 2,6-dichlorophenolindophenol reduction) in PSII membranes and thylakoid membranes was investigated. Under thylakoid membranes illumination accompanied by lumen acidification, their resistance to heat inactivation increases. In the presence of protonophores, the rate of heat inactivation increases, which seems to be associated not with the protonophore mechanism, but with structural and/or functional changes in membranes. In PSII membrane preparations, the efficiency of the oxygen evolution inhibition at pH 5.7 is also lower than at pH 6.5. The role of reactive oxygen species in thermal inactivation of photosynthetic membranes was investigated using a lipophilic cyclic hydroxylamine ESR spin probe.

Heat stress and bleaching in corals: a bioenergetic model

The coral-dinoflagellate endosymbiosis is based on nutrient exchanges that impact holobiont energetics. Of particular concern is the breakdown or dysbiosis of this partnership that is seen in response to elevated temperatures, where loss of symbionts through coral bleaching can lead to starvation and mortality. Here we extend a dynamic bioenergetic model of coral symbioses to explore the mechanisms by which temperature impacts various processes in the symbiosis and to enable simulational analysis of thermal bleaching. Our model tests the effects of two distinct mechanisms for how increased temperature impacts the symbiosis: 1) accelerated metabolic rates due to thermodynamics and 2) damage to the photosynthetic machinery of the symbiont caused by heat stress. Model simulations show that the model can capture key biological responses to different levels of increased temperatures. Moderately increased temperatures increase metabolic rates and slightly decrease photosynthesis. The slightly decreased photosynthesis rates cause the host to receive less carbon and share more nitrogen with the symbiont. This results in temporarily increased symbiont growth and a higher symbiont/host ratio. In contrast, higher temperatures cause a breakdown of the symbiosis due to escalating feedback that involves further reduction in photosynthesis and insufficient energy supply for CO 2 concentration by the host. This leads to the accumulation of excess light energy and the generation of reactive oxygen species, eventually triggering symbiont expulsion and coral bleaching. Importantly, bleaching does not result from accelerated metabolic rates alone; it only occurs as a result of the photodamage mechanism due to its effect on nutrient cycling. Both higher light intensities and higher levels of DIN render corals more susceptible to heat stress. Conversely, heterotrophic feeding can increase the maximal temperature that can be tolerated by the coral. Collectively these results show that a bioenergetics model can capture many observed patterns of heat stress in corals, such as higher metabolic rates and higher symbiont/host ratios at moderately increased temperatures and symbiont expulsion at strongly increased temperatures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00338-024-02561-1.

Effects of Abscisic Acid on the Physiological and Biochemical Responses of Saccharina japonica Under High-Temperature Stress

Saccharina japonica is one of the most productive aquatic plants in the world, widely used in food, feed, medicine, and other industries. Predominantly inhabiting temperate marine environments in mid- to high-latitude regions of the Northern Hemisphere, the growth of S. japonica is significantly limited by high-temperature stress. Abscisic acid (ABA) plays an important role in plant growth and development and stress responses. However, the role of ABA on high-temperature stress tolerance in S. japonica still needs to be further elucidated. Here, we found that exogenous ABA significantly alleviated disease and decay in S. japonica under high-temperature stress while also increasing the relative growth rate, chlorophyll fluorescence parameters, photosynthetic pigment, and osmotic substance content. Meanwhile, exogenous ABA enhanced the activity of protective enzymes and up-regulated the transcript levels of antioxidant-related genes, thereby reducing oxidative damage. Most importantly, we observed a significant increase in ABA content and the transcript levels of key genes involved in ABA synthesis in S. japonica under high-temperature stress, which were further amplified by the addition of exogenous ABA. In conclusion, this study provides evidence that ABA can moderate the detrimental effects of high-temperature stress and provides a theoretical basis for the screening of S. japonica germplasm resources and the cultivation of new stress-resistant varieties.

Prediction of the potential distribution of a raspberry (Rubus idaeus) in China based on MaxEnt model

Rubus idaeus is a pivotal cultivated species of raspberry known for its attractive color, distinct flavor, and numerous health benefits. It can be used in pharmaceutical, cosmetics, agriculture and food industries not only as fresh but also as a processed product. Nowadays due to climatic changes, genetic diversity of cultivars has decreased dramatically. However, until now, the status of wild R. idaeus resources in China have not been exploited. In this study, we investigated the resources of wild R. idaeus in China to secure its future potential and sustainability. The MaxEnt model was used to predict R. idaeus suitable habitats and spatial distribution patterns for current and future climate scenarios, based on wild domestic geographic distribution data, current and future climate variables, and topographic variables. The results showed that, mean temperature of the coldest quarter (bio11), precipitation of the coldest quarter (bio19), precipitation of the warmest quarter (bio18), and temperature seasonality (bio4) were crucial factors affecting the distribution of R. idaeus. Presently, the suitable habitats were mainly distributed in the north of China including Xinjiang, Inner Mongolia, Gansu, Ningxia, Shaanxi, Shanxi, Hebei, Beijing, Liaoning, Jilin, Heilongjiang. According to our results, in 2050s, the total suitable habitat area of R. idaeus will increase under SSP1-2.6 and then will be decreased with climate change, while in the 2090s, the total suitable habitat area will continue to decrease. From the present to the 2090s, the centroid distribution of R. idaeus in China will shift towards the east and the species will always be present in Inner Mongolia. Our results provide wild resource information and theoretical reference for the protection and rational utilization of R. idaeus.

Chlorophyll Fluorescence in Wheat Breeding for Heat and Drought Tolerance

The constantly growing need to increase the production of agricultural products in changing climatic conditions makes it necessary to accelerate the development of new cultivars that meet the modern demands of agronomists. Currently, the breeding process includes the stages of genotyping and phenotyping to optimize the selection of promising genotypes. One of the most popular phenotypic methods is the pulse-amplitude modulated (PAM) fluorometry, due to its non-invasiveness and high information content. In this review, we focused on the opportunities of using chlorophyll fluorescence (ChlF) parameters recorded using PAM fluorometry to assess the state of plants in drought and heat stress conditions and predict the economically significant traits of wheat, as one of the most important agricultural crops, and also analyzed the relationship between the ChlF parameters and genetic markers.

The mechanisms of photoinhibition and repair in plants under high light conditions and interplay with abiotic stressors

This review comprehensively examines the phenomenon of photoinhibition in plants, focusing mainly on the intricate relationship between photodamage and photosystem II (PSII) repair and the role of PSII extrinsic proteins and protein phosphorylation in these processes. In natural environments, photoinhibition occurs together with a suite of concurrent stress factors, including extreme temperatures, drought and salinization. Photoinhibition, primarily caused by high irradiance, results in a critical imbalance between the rate of PSII photodamage and its repair. Central to this process is the generation of reactive oxygen species (ROS), which not only impair the photosynthetic apparatus first PSII but also play a signalling role in chloroplasts and other cellulular structures. ROS generated under stress conditions inhibit the repair of photodamaged PSII by suppressing D1 protein synthesis and affecting PSII protein phosphorylation. Furthermore, this review considers how environmental stressors exacerbate PSII damage by interfering with PSII repair primarily by reducing de novo protein synthesis. In addition to causing direct damage, these stressors also contribute to ROS production by restricting CO2 fixation, which also reduces the intensity of protein synthesis. This knowledge has significant implications for agricultural practices and crop improvement under stressful conditions.

Genome-wide association analysis reveals the genetic basis of thermal tolerance in dwarf surf clam Mulinia lateralis

Recently, elevated seawater temperatures have resulted numerous adverse effects, including significant mortality among bivalves. The dwarf surf clam, Mulinia lateralis, is considered a valuable model species for bivalve research due to its rapid growth and short generation time. The successful cultivation in laboratory setting throughout its entire life cycle makes it an ideal candidate for exploring the potential mechanisms underlying bivalve responses to thermal stress. In this study, a total of 600 clams were subjected to a 17-day thermal stress experiment at a temperature of 30 °C which is the semi-lethal temperature for this species. Ninety individuals who perished initially were classified as heat-sensitive populations (HSP), while 89 individuals who survived the experiment were classified as heat-tolerant populations (HTP). Subsequently, 179 individuals were then sequenced, and 21,292 single nucleotide polymorphisms (SNPs) were genotyped for downstream analysis. The heritability estimate for survival status was found to be 0.375 ± 0.127 suggesting a genetic basis for thermal tolerance trait. Furthermore, a genome-wide association study (GWAS) identified three SNPs and 10 candidate genes associated with thermal tolerance trait in M. lateralis. These candidate genes were involved in the ETHR/EHF signaling pathway and played pivotal role in signal sensory, cell adhesion, oxidative stress, DNA damage repair, etc. Additionally, qPCR results indicated that, excluding MGAT4A, ZAN, and RFC1 genes, all others exhibited significantly higher expression in the HTP (p < 0.05), underscoring the critical involvement of the ETHR/EHF signaling pathway in M. lateralis' thermal tolerance. These results unveil the presence of standing genetic variations associated with thermal tolerance in M. lateralis, highlighting the regulatory role of the ETHR/EHF signaling pathway in the bivalve's response to thermal stress, which contribute to comprehension of the genetic basis of thermal tolerance in bivalves.

Photosynthesis: Genetic Strategies Adopted to Gain Higher Efficiency

The global challenge of feeding an ever-increasing population to maintain food security requires novel approaches to increase crop yields. Photosynthesis, the fundamental energy and material basis for plant life on Earth, is highly responsive to environmental conditions. Evaluating the operational status of the photosynthetic mechanism provides insights into plants' capacity to adapt to their surroundings. Despite immense effort, photosynthesis still falls short of its theoretical maximum efficiency, indicating significant potential for improvement. In this review, we provide background information on the various genetic aspects of photosynthesis, explain its complexity, and survey relevant genetic engineering approaches employed to improve the efficiency of photosynthesis. We discuss the latest success stories of gene-editing tools like CRISPR-Cas9 and synthetic biology in achieving precise refinements in targeted photosynthesis pathways, such as the Calvin-Benson cycle, electron transport chain, and photorespiration. We also discuss the genetic markers crucial for mitigating the impact of rapidly changing environmental conditions, such as extreme temperatures or drought, on photosynthesis and growth. This review aims to pinpoint optimization opportunities for photosynthesis, discuss recent advancements, and address the challenges in improving this critical process, fostering a globally food-secure future through sustainable food crop production.

H3K27me3 and EZH Are Involved in the Control of the Heat-Stress-Elicited Morphological Changes in Diatoms

Marine water temperatures are increasing due to anthropogenic climate change, constituting a major threat to marine ecosystems. Diatoms are major marine primary producers, and as such, they are subjected to marine heat waves and rising ocean temperatures. Additionally, under low tide, diatoms are regularly exposed to high temperatures. However, physiological and epigenetic responses to long-term exposure to heat stress remain largely unknown in the diatom Phaeodactylum tricornutum. In this study, we investigated changes in cell morphology, photosynthesis, and H3K27me3 abundance (an epigenetic mark consisting of the tri-methylation of lysine 27 on histone H3) after moderate and elevated heat stresses. Mutants impaired in PtEZH-the enzyme depositing H3K27me3-presented reduced growth and moderate changes in their PSII quantum capacities. We observed shape changes for the three morphotypes of P. tricornutum (fusiform, oval, and triradiate) in response to heat stress. These changes were found to be under the control of PtEZH. Additionally, both moderate and elevated heat stresses modulated the expression of genes encoding proteins involved in photosynthesis. Finally, heat stress elicited a reduction of genome-wide H3K27me3 levels in the various morphotypes. Hence, we provided direct evidence of epigenetic control of the H3K27me3 mark in the responses of Phaeodactylum tricornutum to heat stress.

Moderately Elevated Temperature Offsets the Adverse Effects of Waterlogging Stress on Tomato

Global warming and waterlogging stress due to climate change are expected to continue influencing agricultural production worldwide. In the field, two or more environmental stresses usually happen simultaneously, inducing more complex responses in plants compared with individual stresses. Our aim was to clarify how the two key factors (temperature and water) interacted and influenced physiological response and plant growth in tomatoes under ambient temperature, moderately elevated temperature, waterlogging stress, and moderately elevated temperature and waterlogging stress. The results showed that leaf photosynthesis was inhibited by waterlogging stress but enhanced by elevated temperature, as shown by both the light- and temperature-response curves. The elevated temperature decreased leaf water-use efficiency, but enhanced plant growth and fresh and dry weights of plants under both normal water supply and waterlogging stress conditions. Elevated temperature generally decreased the anthocyanin and flavonol index in tomato leaves compared with the control temperature, regardless of water status. The increase in the optimal temperature was more pronounced in plants under normal irrigation than under waterlogging stress. Waterlogging stress significantly inhibited the root length, and leaf number and area, while the moderately elevated temperature significantly enhanced the leaf number and area. Overall, the moderately elevated temperature offset the effects of waterlogging stress on tomato plants, as shown by leaf gas exchange, plant size, and dry matter accumulation. Our study will improve the understanding of how tomatoes respond to increasing temperature and excess water.

Comparative proteomics in tall fescue to reveal underlying mechanisms for improving Photosystem II thermotolerance during heat stress memory

BACKGROUND

The escalating impacts of global warming intensify the detrimental effects of heat stress on crop growth and yield. Among the earliest and most vulnerable sites of damage is Photosystem II (PSII). Plants exposed to recurring high temperatures develop heat stress memory, a phenomenon that enables them to retain information from previous stress events to better cope with subsequent one. Understanding the components and regulatory networks associated with heat stress memory is crucial for the development of heat-resistant crops.

RESULTS

Physiological assays revealed that heat priming (HP) enabled tall fescue to possess higher Photosystem II photochemical activity when subjected to trigger stress. To investigate the underlying mechanisms of heat stress memory, we performed comparative proteomic analyses on tall fescue leaves at S0 (control), R4 (primed), and S5 (triggering), using an integrated approach of Tandem Mass Tag (TMT) labeling and Liquid Chromatography-Mass Spectrometry. A total of 3,851 proteins were detected, with quantitative information available for 3,835 proteins. Among these, we identified 1,423 differentially abundant proteins (DAPs), including 526 proteins that were classified as Heat Stress Memory Proteins (HSMPs). GO and KEGG enrichment analyses revealed that the HSMPs were primarily associated with the "autophagy" in R4 and with "PSII repair", "HSP binding", and "peptidase activity" in S5. Notably, we identified 7 chloroplast-localized HSMPs (HSP21, DJC77, EGY3, LHCA4, LQY1, PSBR and DEGP8, R4/S0 > 1.2, S5/S0 > 1.2), which were considered to be effectors linked to PSII heat stress memory, predominantly in cluster 4. Protein-protein interaction (PPI) analysis indicated that the ubiquitin-proteasome system, with key nodes at UPL3, RAD23b, and UCH3, might play a role in the selective retention of memory effectors in the R4 stage. Furthermore, we conducted RT-qPCR validation on 12 genes, and the results showed that in comparison to the S5 stage, the R4 stage exhibited reduced consistency between transcript and protein levels, providing additional evidence for post-transcriptional regulation in R4.

CONCLUSIONS

These findings provide valuable insights into the establishment of heat stress memory under recurring high-temperature episodes and offer a conceptual framework for breeding thermotolerant crops with improved PSII functionality.

Aster × chusanensis Growth and Phenolic Acid Composition under Different Cultivation Temperatures

Plants of the Asteraceae family have been cultivated worldwide for economic, medicinal, and ornamental purposes, including genera such as Aster, Helianthus, and Cosmos. Numerous studies examined their secondary metabolites; however, those of Aster × chusanensis, which is a natural hybrid species in South Korea, are unclear, and optimized propagation methods should be identified. We analyzed phenolic acid concentrations in each part of Aster × chusanensis through HPLC. Further, we investigated the growth characteristics and secondary metabolite concentrations under various growth temperatures using division propagation, followed by growing at 20, 25, and 30 °C in a growth chamber. Chlorogenic acid was the primary compound, which was particularly high in the leaves. The growth characteristics did not differ significantly between temperatures, and 30 °C was most efficient for phenolic acid biosynthesis. Our results provide valuable information on optimized propagation and secondary metabolite concentrations under different temperatures of Aster × chusanensis.

Multi-scale analysis of heat stress acclimation in Arabidopsis seedlings highlights the primordial contribution of energy-transducing organelles

Much progress has been made in understanding the molecular mechanisms of plant adaptation to heat stress. However, the great diversity of models and stress conditions, and the fact that analyses are often limited to a small number of approaches, complicate the picture. We took advantage of a liquid culture system in which Arabidopsis seedlings are arrested in their development, thus avoiding interference with development and drought stress responses, to investigate through an integrative approach seedlings' global response to heat stress and acclimation. Seedlings perfectly tolerate a noxious heat shock (43°C) when subjected to a heat priming treatment at a lower temperature (38°C) the day before, displaying a thermotolerance comparable to that previously observed for Arabidopsis. A major effect of the pre-treatment was to partially protect energy metabolism under heat shock and favor its subsequent rapid recovery, which was correlated with the survival of seedlings. Rapid recovery of actin cytoskeleton and mitochondrial dynamics were another landmark of heat shock tolerance. The omics confirmed the role of the ubiquitous heat shock response actors but also revealed specific or overlapping responses to priming, heat shock, and their combination. Since only a few components or functions of chloroplast and mitochondria were highlighted in these analyses, the preservation and rapid recovery of their bioenergetic roles upon acute heat stress do not require extensive remodeling of the organelles. Protection of these organelles is rather integrated into the overall heat shock response, thus allowing them to provide the energy required to elaborate other cellular responses toward acclimation.

Elevated [CO2] and temperature augment gas exchange and shift the fitness landscape in a montane forb

Climate change is simultaneously increasing carbon dioxide concentrations ([CO2]) and temperature. These factors could interact to influence plant physiology and performance. Alternatively, increased [CO2] may offset costs associated with elevated temperatures. Furthermore, the interaction between elevated temperature and [CO2] may differentially affect populations from along an elevational gradient and disrupt local adaptation. We conducted a multifactorial growth chamber experiment to examine the interactive effects of temperature and [CO2] on fitness and ecophysiology of diverse accessions of Boechera stricta (Brassicaceae) sourced from a broad elevational gradient in Colorado. We tested whether increased [CO2] would enhance photosynthesis across accessions, and whether warmer conditions would depress the fitness of high-elevation accessions owing to steep reductions in temperature with increasing elevation in this system. Elevational clines in [CO2] are not as evident, making it challenging to predict how locally adapted ecotypes will respond to elevated [CO2]. This experiment revealed that elevated [CO2] increased photosynthesis and intrinsic water use efficiency across all accessions. However, these instantaneous responses to treatments did not translate to changes in fitness. Instead, increased temperatures reduced the probability of reproduction for all accessions. Elevated [CO2] and increased temperatures interacted to shift the adaptive landscape, favoring lower elevation accessions for the probability of survival and fecundity. Our results suggest that elevated temperatures and [CO2] associated with climate change could have severe negative consequences, especially for high-elevation populations.

Hydrogen peroxide sulfenylates and inhibits the photorespiratory enzyme PGLP1 to modulate plant thermotolerance

Climate change is resulting in more frequent and rapidly changing temperatures at both extremes that severely affect the growth and production of plants, particularly crops. Oxidative stress caused by high temperatures is one of the most damaging factors for plants. However, the role of hydrogen peroxide (H2O2) in modulating plant thermotolerance is largely unknown, and the regulation of photorespiration essential for C3 species remains to be fully clarified. Here, we report that heat stress promotes H2O2 accumulation in chloroplasts and that H2O2 stimulates sulfenylation of the chloroplast-localized photorespiratory enzyme 2-phosphoglycolate phosphatase 1 (PGLP1) at cysteine 86, inhibiting its activity and promoting the accumulation of the toxic metabolite 2-phosphoglycolate. We also demonstrate that PGLP1 has a positive function in plant thermotolerance, as PGLP1 antisense lines have greater heat sensitivity and PGLP1-overexpressing plants have higher heat-stress tolerance than the wild type. Together, our results demonstrate that heat-induced H2O2 in chloroplasts sulfenylates and inhibits PGLP1 to modulate plant thermotolerance. Furthermore, targeting CATALASE2 to chloroplasts can largely prevent the heat-induced overaccumulation of H2O2 and the sulfenylation of PGLP1, thus conferring thermotolerance without a plant growth penalty. These findings reveal that heat-induced H2O2 in chloroplasts is important for heat-caused plant damage.

What if the upwelling weakens? Effects of rising temperature and nutrient depletion on coastal assemblages

Surface temperature of the oceans has increased globally over the past decades. In coastal areas influenced by eastern boundary upwelling systems (EBUS), winds push seawater offshore and deep, cold and nutrient-rich seawater rise towards the surface, partially buffering global warming. On the North coast of Portugal, the NW Iberian upwelling system allows extensive kelp forests to thrive in these "boreal-like" conditions, fostering highly diverse and productive communities. However, the warming of the upper layer of the ocean may weaken this upwelling, leading to higher sea surface temperature and lower nutrient input in the coastal areas. The effects of these changes on the structure and function of coastal ecosystems remain unexplored. The present study aimed to examine the combined effects of elevated temperature and nutrient depletion on semi-naturally structured assemblages. The eco-physiological responses investigated included growth, chlorophyll fluorescence and metabolic rates at the levels of individual species and whole assemblages. Our findings showed interactive effects of the combination of elevated temperature with nutrient depletion on the large canopy-forming species (i.e., kelp). As main contributor to community response, those effects drove the whole assemblage responses to significant losses in productivity levels. We also found an additive effect of elevated temperature and reduced nutrients on sub-canopy species (i.e., Chondrus crispus), while turfs were only affected by temperature. Our results suggest that under weakening upwelling scenarios, the ability of the macroalgal assemblages to maintain high productivity rates could be seriously affected and predict a shift in community composition with the loss of marine forests.

Plastid-expressed AdDjSKI enhances photosystem II stability, delays leaf senescence, and increases fruit yield in tomato plants under heat stress

Heat stress substantially reduces tomato (Solanum lycopersicum) growth and yield globally, thereby jeopardizing food security. DnaJ proteins, constituents of the heat shock protein system, protect cells from diverse environmental stresses as HSP-70 molecular co-chaperones. In this study, we demonstrated that AdDjSKI, a serine-rich DnaJ III protein induced by pathogens, plays an important role in stabilizing photosystem II (PSII) in response to heat stress. Our results revealed that transplastomic tomato plants expressing the AdDjSKI gene exhibited increased levels of total soluble proteins, improved growth and chlorophyll content, reduced malondialdehyde (MDA) accumulation, and diminished PSII photoinhibition under elevated temperatures when compared with wild-type (WT) plants. Intriguingly, these transplastomic plants maintained higher levels of D1 protein under elevated temperatures compared with the WT plants, suggesting that overexpression of AdDjSKI in plastids is crucial for PSII protection, likely due to its chaperone activity. Furthermore, the transplastomic plants displayed lower accumulation of superoxide radical (O2 •─) and H2O2, in comparison with the WT plants, plausibly attributed to higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. This also coincides with an enhanced expression of corresponding genes, including SlCuZnSOD, SlFeSOD, SlAPX2, and SltAPX, under heat stress. Taken together, our findings reveal that chloroplastic expression of AdDjSKI in tomatoes plays a critical role in fruit yield, primarily through a combination of delayed senescence and stabilizing PSII under heat stress.

Carotenoid Accumulation in the Rhododendron chrysanthum Is Mediated by Abscisic Acid Production Driven by UV-B Stress

Rhododendron chrysanthum (R. chrysanthum) development is hampered by UV-B sunlight because it damages the photosynthetic system and encourages the buildup of carotenoids. Nevertheless, it is still unclear how R. chrysanthum repairs the photosynthetic system to encourage the formation of carotenoid pigments. The carotenoid and abscisic acid (ABA) concentrations of the R. chrysanthum were ascertained in this investigation. Following UV-B stress, the level of carotenoids was markedly increased, and there was a strong correlation between carotenoids and ABA. The modifications of R. chrysanthum's OJIP transient curves were examined in order to verify the regulatory effect of ABA on carotenoid accumulation. It was discovered that external application of ABA lessened the degree of damage on the donor side and lessened the damage caused by UV-B stress on R. chrysanthum. Additionally, integrated metabolomics and transcriptomics were used to examine the changes in differentially expressed genes (DEGs) and differential metabolites (DMs) in R. chrysanthum in order to have a better understanding of the role that ABA plays in carotenoid accumulation. The findings indicated that the majority of DEGs were connected to carotenoid accumulation and ABA signaling sensing. To sum up, we proposed a method for R. chrysanthum carotenoid accumulation. UV-B stress activates ABA production, which then interacts with transcription factors to limit photosynthesis and accumulate carotenoids, such as MYB-enhanced carotenoid biosynthesis. This study showed that R. chrysanthum's damage from UV-B exposure was lessened by carotenoid accumulation, and it also offered helpful suggestions for raising the carotenoid content of plants.

GOES-R land surface products at Western Hemisphere eddy covariance tower locations

The terrestrial carbon cycle varies dynamically on hourly to weekly scales, making it difficult to observe. Geostationary ("weather") satellites like the Geostationary Environmental Operational Satellite - R Series (GOES-R) deliver near-hemispheric imagery at a ten-minute cadence. The Advanced Baseline Imager (ABI) aboard GOES-R measures visible and near-infrared spectral bands that can be used to estimate land surface properties and carbon dioxide flux. However, GOES-R data are designed for real-time dissemination and are difficult to link with eddy covariance time series of land-atmosphere carbon dioxide exchange. We compiled three-year time series of GOES-R land surface attributes including visible and near-infrared reflectances, land surface temperature (LST), and downwelling shortwave radiation (DSR) at 314 ABI fixed grid pixels containing eddy covariance towers. We demonstrate how to best combine satellite and in-situ datasets and show how ABI attributes useful for ecosystem monitoring vary across space and time. By connecting observation networks that infer rapid changes to the carbon cycle, we can gain a richer understanding of the processes that control it.

Three-state mathematical model for the assessment of DCMU-treated photosystem II heterogeneity

Photosystem II (PSII) is one of the main pigment-protein complexes of photosynthesis which is highly sensitive to unfavorable environmental factors. The heterogeneity of PSII properties is essential for the resistance of autotrophic organisms to stress factors. Assessment of the PSII heterogeneity may be used in environmental monitoring for on-line detection of contamination of the environment. We propose an approach to assess PSII oxygen-evolving complex and light-harvesting antenna heterogeneity that is based on mathematical modeling of the shape of chlorophyll a fluorescence rise of 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated samples. The hierarchy of characteristic times of the processes considered in the model makes it possible to reduce the model to a system of three ordinary differential equations. The analytic solution of the reduced three-state model is expressed as a sum of two exponential functions, and it exactly reproduces the solution of the complete system within the time range from microseconds to hundreds of milliseconds. The combination of several such models for reaction centers with different properties made it possible to use it as an instrument to study PSII heterogeneity. PSII heterogeneity was studied for Chlamydomonas at different intensities of actinic light, for Scenedesmus under short-term heating, and for Chlorella grown in nitrate-enriched and nitrate-depleted media.

Differential heat-response characteristics of two plastid isoforms of triose phosphate isomerase in tomato

Heat stress causes dysfunction of the carbon-assimilation metabolism. As a member of Calvin-Benson-Bassham (CBB) cycle, the chloroplast triose phosphate isomerases (TPI) catalyse the interconversion of glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP). The tomato (Solanum lycopersicum) genome contains two individual SlTPI genes, Solyc10g054870 and Solyc01g111120, which encode the chloroplast-located proteins SlTPI1 and SlTPI2, respectively. The tpi1 and tpi2 single mutants had no visible phenotypes, but the leaves of their double mutant lines tpi1tpi2 had obviously reduced TPI activity and displayed chlorotic variegation, dysplasic chloroplasts and lower carbon-assimilation efficiency. In addition to altering carbon metabolism, proteomic data showed that the loss of both SlTPI1 and SlTPI2 severely affected photosystem proteins, reducing photosynthetic capacity. None of these phenotypes was evident in the tpi1 or tpi2 single mutants, suggesting that SlTPI1 and SlTPI2 are functionally redundant. However, the two proteins differed in their responses to heat stress; the protein encoded by the heat-induced SlTPI2 showed a higher level of thermotolerance than that encoded by the heat-suppressed SlTPI1. Notably, heat-induced transcription factors, SlWRKY21 and SlHSFA2/7, which negatively regulated SlTPI1 expression and positively regulated SlTPI2 expression, respectively. Our findings thus reveal that SlTPI1 and SlTPI2 have different thermostabilities and expression patterns in response to heat stress, which have the potential to be applied in thermotolerance strategies in crops.

Mesophyll conductance limits photosynthesis in fluctuating light under combined drought and heat stresses

Drought and heat stresses usually occur concomitantly in nature, with increasing frequency and intensity of both stresses expected due to climate change. The synergistic agricultural impacts of these compound climate extremes are much greater than those of the individual stresses. However, the mechanisms by which drought and heat stresses separately and concomitantly affect dynamic photosynthesis have not been thoroughly assessed. To elucidate this, we used tomato (Solanum lycopersicum) seedlings to measure dynamic photosynthesis under individual and compound stresses of drought and heat. Individual drought and heat stresses limited dynamic photosynthesis at the stages of diffusional conductance to CO2 and biochemistry, respectively. However, the primary limiting factor for photosynthesis shifted to mesophyll conductance under the compound stresses. Compared with the control, photosynthetic carbon gain in fluctuating light decreased by 38%, 73%, and 114% under the individual drought, heat, and compound stresses, respectively. Therefore, compound stresses caused a greater reduction in photosynthetic carbon gain in fluctuating light conditions than individual stress. These findings highlight the importance of mitigating the effects of compound climate extremes on crop productivity by targeting mesophyll conductance and improving dynamic photosynthesis.

Transcriptome and photosynthetic analyses provide new insight into the molecular mechanisms underlying heat stress tolerance in Rhododendron × pulchrum Sweet

Rhododendron species provide excellent ornamental use worldwide, yet heat stress (HS) is one of the major threats to their cultivation. However, the intricate mechanisms underlying the photochemical and transcriptional regulations associated with the heat stress response in Rhododendron remain relatively unexplored. In this study, the analyses of morphological characteristics and chlorophyll fluorescence (ChlF) kinetics showed that HS (40 °C/35 °C) had a notable impact on both the donor's and acceptor's sides of photosystem II (PSII), resulting in reduced PSII activity and electron transfer capacity. The gradual recovery of plants observed following a 5-day period of culture under normal conditions indicates the reversible nature of the HS impact on Rhododendron × pulchrum. Analysis of transcriptome data unveiled noteworthy trends: four genes associated with photosynthesis-antenna protein synthesis (LHCb1, LHCb2 and LHCb3) and the antioxidant system (glutamate-cysteine ligase) experienced significant down-regulation in the leaves of R. × pulchrum during HS. Conversely, aseorbate peroxidase and glutathione S-transferase TAU 8 demonstrated an up-regulated pattern. Furthermore, six down-regulated genes (phos-phoenolpyruvate carboxylase 4, sedoheptulose-bisphosphatase, ribose-5-phosphate isomerase 2, high cyclic electron flow 1, beta glucosidase 32 and starch synthase 2) and two up-regulated genes (beta glucosidase 2 and UDP-glucose pyrophosphorylase 2) implicated in photosynthetic carbon fixation and starch/sucrose metabolism were identified during the recovery process. To augment these insights, a weighted gene co-expression network analysis yielded a co-expression network, pinpointing the hub genes correlated with ChlF dynamics' variation trends. The cumulative results showed that HS inhibited the synthesis of photosynthesis-antenna proteins in R. × pulchrum leaves. This disruption subsequently led to diminished photochemical activities in both PSII and PSI, albeit with PSI exhibiting heightened thermostability. Depending on the regulation of the reactive oxygen species scavenging system and heat dissipation, photoprotection sustained the recoverability of R. × pulchrum to HS.

Photosynthetic responses of heat-stressed apple leaves to foliar application of salicylic and ascorbic acid

High temperatures have significant impacts on fruit tree production. Foliar spraying application of promoting agents can be a sustainable approach to managing high-temperature stress in orchards. The mechanism of certain improving agents on photosynthesis is not yet well understood, particularly in fruit trees. Photosynthesis, as a vital and very sensitive process in plants, is a pivotal component in fruit production. Therefore, in this study, we explored the potential of two different promoting agents, salicylic acid (SA) and ascorbic acid (AsA), to alleviate oxidative stress caused by high temperature in controlled conditions (37°C for 1 h) at the photosynthetic level. For studying photosynthetic responses, we used chlorophyll fluorescence measurements. According to our findings, foliar application of promoting agents effectively increased the high-temperature tolerance of apple leaves, when compared to sole heat stress treatment. Both promoting agents significantly increased photosynthetic efficiency under stress, while the maximum was observed with AsA. In general, AsA and SA applications had a positive effect on the photosynthesis of apple leaves at high temperatures.

A review of changes at the phenotypic, physiological, biochemical, and molecular levels of plants due to high temperatures

MAIN CONCLUSION

This review summarizes the physiological, biochemical, and molecular regulatory network changes in plants in response to high temperature. With the continuous rise in temperature, high temperature has become an important issue limiting global plant growth and development, affecting the phenotype and physiological and biochemical processes of plants and seriously restricting crop yield and tree growth speed. As sessile organisms, plants inevitably encounter high temperatures and improve their heat tolerance by activating molecular networks related to heat stress, such as signal transduction, synthesis of metabolites, and gene expression. Heat tolerance is a polygenic trait regulated by a variety of genes, transcription factors, proteins, and metabolites. Therefore, this review summarizes the changes in physiological, biochemical and molecular regulatory networks in plants under high-temperature conditions to lay a foundation for an in-depth understanding of the mechanisms involved in plant heat tolerance responses.

Prediction of biomass accumulation and tolerance of wheat seedlings to drought and elevated temperatures using hyperspectral imaging

Early prediction of important agricultural traits in wheat opens up broad prospects for the development of approaches to accelerate the selection of genotypes for further breeding trials. This study is devoted to the search for predictors of biomass accumulation and tolerance of wheat to abiotic stressors. Hyperspectral (HS) and chlorophyll fluorescence (ChlF) parameters were analyzed as predictors under laboratory conditions. The predictive ability of reflectance and normalized difference indices (NDIs), as well as their relationship with parameters of photosynthetic activity, which is a key process influencing organic matter production and crop yields, were analyzed. HS parameters calculated using the wavelengths in Red (R) band and the spectral range next to the red edge (FR-NIR) were found to be correlated with biomass accumulation. The same ranges showed potential for predicting wheat tolerance to elevated temperatures. The relationship of HS predictors with biomass accumulation and heat tolerance were of opposite sign. A number of ChlF parameters also showed statistically significant correlation with biomass accumulation and heat tolerance. A correlation between HS and ChlF parameters, that demonstrated potential for predicting biomass accumulation and tolerance, has been shown. No predictors of drought tolerance were found among the HS and ChlF parameters analyzed.

Responses of photosynthesis-related genes in Sargassum horneri to high temperature stress

Golden tide outbreak threatened the marine ecological environment. Sargassum horneri is a single dominant species of the Yellow Sea golden tide, which growth and development are affected by changes in sea water temperature. This study investigated the photosynthetic physiology of copper algae and found that the growth rate, chlorophyll a content, carotenoid content, Fv/Fm, and maximum electron transfer efficiency were significantly reduced, indicating that Sargassum horneri was under stress under high temperature. In this study, high-throughput sequencing was used to analyze the response mechanisms of photosynthesis-related genes in S. horneri under high temperature stress. The results showed that most of the photosynthesis-related genes in S. horneri were downregulated and photosynthesis was inhibited under high temperature stress. However, the expression levels of ferredoxin, ferredoxin-NADP reductase, light-harvesting protein complexes, and oxygen-evolving complex genes were significantly upregulated (P ≤ 0.05) after five days of high temperature treatment. This study found that photosynthesis related genes play a crucial role in regulating the photosynthetic response of S. horneri to high temperature stress.

Regulation of chloroplast biogenesis, development, and signaling by endogenous and exogenous cues

Chloroplasts are one of the defining features in most plants, primarily known for their unique property to carry out photosynthesis. Besides this, chloroplasts are also associated with hormone and metabolite productions. For this, biogenesis and development of chloroplast are required to be synchronized with the seedling growth to corroborate the maximum rate of photosynthesis following the emergence of seedlings. Chloroplast biogenesis and development are dependent on the signaling to and from the chloroplast, which are in turn regulated by several endogenous and exogenous cues. Light and hormones play a crucial role in chloroplast maturation and development. Chloroplast signaling involves a coordinated two-way connection between the chloroplast and nucleus, termed retrograde and anterograde signaling, respectively. Anterograde and retrograde signaling are involved in regulation at the transcriptional level and downstream modifications and are modulated by several metabolic and external cues. The communication between chloroplast and nucleus is essential for plants to develop strategies to cope with various stresses including high light or high heat. In this review, we have summarized several aspects of chloroplast development and its regulation through the interplay of various external and internal factors. We have also discussed the involvement of chloroplasts as sensors of various external environment stress factors including high light and temperature, and communicate via a series of retrograde signals to the nucleus, thus playing an essential role in plants' abiotic stress response.