Understanding oxidative stress and antioxidant functions to enhance photosynthesis

Rapid Communication: oxidative stress induced by mixed exposure to glyphosate and silver nanoparticles

The aim of this study was to examine oxidative stress induced by the binary mixture of silver nanoparticles (AgNP) and glyphosate (Gly) in Daphnia magna by measurement of reactive oxygen species (ROS) production, glutathione (GSH) levels, enzyme activities of catalase (CAT) and superoxide dismutase (SOD) as well as malondialdehyde (MDA) content. Acute exposure of Daphnia magna to binary mixture of AgNP and Gly resulted in significant biochemical responses indicative of oxidative damage. This response seemed to be related to imbalance in enzymatic/non-enzymatic antioxidant enzymes associated with intracellular overproduction of ROS and significant increase in MDA levels, indicating that the integrity and function of the cell membrane was damaged. These changes adversely affected the fitness and survival of Daphnia magna and negatively influenced offspring growth and reproduction.

Physiological aspects of sex differences and Haldane's rule in Rumex hastatulus

Haldane's rule (HR, impairment of fertility and/or viability of interracial hybrids) seems to be one of few generalizations in evolutionary biology. The validity of HR has been confirmed in animals, and more recently in some dioecious plants (Silene and Rumex). Dioecious Rumex hastatulus has two races differing in the sex chromosome system: Texas (T) and North Carolina (NC), and T × NC males showed both reduced pollen fertility and rarity-two classical symptoms of Haldane's rule (HR). The reduced fertility of these plants has a simple mechanistic explanation, but the reason for their rarity was not elucidated. Here, we measured selected physiological parameters related to the antioxidant defense system in parental races and reciprocal hybrids of R. hastatulus. We showed that the X-autosome configurations, as well as asymmetries associated with Y chromosomes and cytoplasm, could modulate this system in hybrids. The levels and quantitative patterns of the measured parameters distinguish the T × NC hybrid from the other analyzed forms. Our observations suggest that the rarity of T × NC males is caused postzygotically and most likely related to the higher level of oxidative stress induced by the chromosomal incompatibilities. It is the first report on the physiological aspects of HR in plants.

How does light facilitate vitamin C biosynthesis in leaves?

Plants store ascorbate in high concentrations, particularly in their leaves. Ascorbate is an excellent antioxidant that acts as an indispensable photoprotectant. The D-mannose/L-galactose pathway is responsible for ascorbate biosynthesis in plants. Light facilitates ascorbate biosynthesis in a light intensity-dependent manner to enhance ascorbate pool size in leaves, and photosynthesis is required for this process. Light- and photosynthesis-dependent activation of the rate-limiting enzyme GDP-L-galactose phosphorylase (GGP) plays a critical role in ascorbate pool size regulation. In addition, the tight regulation of ascorbate biosynthesis by ascorbate itself has been proposed. Ascorbate represses GGP translation in a dose-dependent manner through the upstream open reading frame in the 5'-untranslated regions of the gene, which may compete with the light-dependent activation of ascorbate biosynthesis. This review focuses on ascorbate biosynthesis based on past and latest findings and critically discusses how light activates this process.

Molecular Approaches Reduce Saturates and Eliminate trans Fats in Food Oils

Vegetable oils composed of triacylglycerols (TAG) are a major source of calories in human diets. However, the fatty acid compositions of these oils are not ideal for human nutrition and the needs of the food industry. Saturated fatty acids contribute to health problems, while polyunsaturated fatty acids (PUFA) can become rancid upon storage or processing. In this review, we first summarize the pathways of fatty acid metabolism and TAG synthesis and detail the problems with the oil compositions of major crops. Then we describe how transgenic expression of desaturases and downregulation of the plastid FatB thioesterase have provided the means to lower oil saturates. The traditional solution to PUFA rancidity uses industrial chemistry to reduce PUFA content by partial hydrogenation, but this results in the production of trans fats that are even more unhealthy than saturated fats. We detail the discoveries in the biochemistry and molecular genetics of oil synthesis that provided the knowledge and tools to lower oil PUFA content by blocking their synthesis during seed development. Finally, we describe the successes in breeding and biotechnology that are giving us new, high-oleic, low PUFA varieties of soybean, canola and other oilseed crops.

NBS1 protein from Physcomitrium patens confers protection against oxidative damage by limiting the accumulation of cellular reactive oxygen species

Nijmegen breakage syndrome 1 (NBS1) protein is a core member of the MRE11-RAD50-NBS1 (MRN) complex that plays a crucial role in DNA damage sensing and repair in plants. Here we report that NBS1 from moss Physcomitrium patens reduces oxidative damage by lowering the cellular ROS in addition to its known role in oxidative DNA damage recovery. Real-time transcript analysis showed up-regulation of the PpNBS1 transcript under different stress conditions. Bacterial cells showed better cell survivability upon over-expressing PpNBS1 protein as compared to untransformed cells. Likewise, overexpression of PpNBS1 in tobacco plants provides improved protection against oxidative damage and exhibited a lesser amount of ROS upon exposure to oxidative stress. Moreover, PpNBS1 contributes to the antioxidant defense mechanism by positively regulating the expression of the antioxidant genes under stress conditions in transgenic tobacco plants. PpNBS1 expressing transgenic tobacco plants resulted in lesser membrane damage, lower lipid peroxidation level, and higher chlorophyll content under stress conditions. Taken together, we conclude in addition to its known role as DNA damage sensor, PpNBS1 also plays a definite role in oxidative stress mitigation by minimizing ROS accumulation in the cell.

Can biochemical traits bridge the gap between genomics and plant performance? A study in rice under drought

The possibility of introducing metabolic/biochemical phenotyping to complement genomics-based predictions in breeding pipelines has been considered for years. Here we examine to what extent and under what environmental conditions metabolic/biochemical traits can effectively contribute to understanding and predicting plant performance. In this study, multivariable statistical models based on flag leaf central metabolism and oxidative stress status were used to predict grain yield (GY) performance for 271 indica rice (Oryza sativa) accessions grown in the field under well-watered and reproductive stage drought conditions. The resulting models displayed significantly higher predictability than multivariable models based on genomic data for the prediction of GY under drought (Q2 = 0.54-0.56 versus 0.35) and for stress-induced GY loss (Q2 = 0.59-0.64 versus 0.03-0.06). Models based on the combined datasets showed predictabilities similar to metabolic/biochemical-based models alone. In contrast to genetic markers, models with enzyme activities and metabolite values also quantitatively integrated the effect of physiological differences such as plant height on GY. The models highlighted antioxidant enzymes of the ascorbate-glutathione cycle and a lipid oxidation stress marker as important predictors of rice GY stability under drought at the reproductive stage, and these stress-related variables were more predictive than leaf central metabolites. These findings provide evidence that metabolic/biochemical traits can integrate dynamic cellular and physiological responses to the environment and can help bridge the gap between the genome and the phenome of crops as predictors of GY performance under drought.

Drought Tolerance Strategies and Autophagy in Resilient Wheat Genotypes

Drought resiliency strategies combine developmental, physiological, cellular, and molecular mechanisms. Here, we compare drought responses in two resilient spring wheat (Triticum aestivum) genotypes: a well-studied drought-resilient Drysdale and a resilient genotype from the US Pacific North-West Hollis. While both genotypes utilize higher water use efficiency through the reduction of stomatal conductance, other mechanisms differ. First, Hollis deploys the drought escape mechanism to a greater extent than Drysdale by accelerating the flowering time and reducing root growth. Second, Drysdale uses physiological mechanisms such as non-photochemical quenching (NPQ) to dissipate the excess of harvested light energy and sustain higher Fv/Fm and ϕPSII, whereas Hollis maintains constant NPQ but lower Fv/Fm and ϕPSII values. Furthermore, more electron donors of the electron transport chain are in the oxidized state in Hollis than in Drysdale. Third, many ROS homeostasis parameters, including peroxisome abundance, transcription of peroxisome biogenesis genes PEX11 and CAT, catalase protein level, and enzymatic activity, are higher in Hollis than in Drysdale. Fourth, transcription of autophagy flux marker ATG8.4 is upregulated to a greater degree in Hollis than in Drysdale under drought, whereas relative ATG8 protein abundance under drought stress is lower in Hollis than in Drysdale. These data demonstrate the activation of autophagy in both genotypes and a greater autophagic flux in Hollis. In conclusion, wheat varieties utilize different drought tolerance mechanisms. Combining these mechanisms within one genotype offers a promising strategy to advance crop resiliency.

Screening of Key Indices and the Gene Transcriptional Regulation Analysis Related to Salt Tolerance in Salix matsudana Seedlings

Pot experiments were performed to comparatively study the differences in 16 salt tolerance indices between the seedlings of six Salix matsudana clones under the stress of various concentrations of NaCl (0, 0.1%, 0.3%, 0.5%, and 0.7%), including the salt injury index, shoot fresh weight, root fresh weight, leaf water content, relative conductivity, malondialdehyde content, and antioxidant enzyme activity. The salt-tolerant clones and key indices of salt tolerance were selected. Transcriptome sequencing analysis was performed on the selected salt-tolerant and salt-sensitive clones under salt stress, and the links between the physiological indices of salt tolerance and gene expression were analyzed. Results: (1) Superoxide dismutase (SOD), peroxidase (POD), chlorophyll, and net photosynthetic rate were closely related to the salt tolerance of Salix matsudana at the seedling stage. The regression equation was constructed as follows: salt tolerance index (y) = 0.224x10 + 0.216x11 + 0.127x12 + 0.191x7 − 0.187 (x10 = chlorophyll, x11 = SOD, x12 = POD, x7 = net photosynthetic rate). (2) The number of differentially expressed genes between the seedlings of salt-tolerant and salt-sensitive clones varied with the time of exposure (0 h, 4 h, 12 h, and 24 h) to 200 mmol·L−1 NaCl stress. The most differentially expressed genes in Sm172 were detected upon 24 h vs. 4 h of salt treatment, while the most in Sm6 were in the 24 h vs. 0 h comparison. Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes analysis showed that several differentially expressed genes were involved in carotenoid biosynthesis and plant mitogen-activated protein kinase signaling pathways. The nine highly expressed transcription factor genes (Sm172-f2p30-2392, Sm172-f2p28-2386, Sm6-f8p60-2372, Sm6-f2p39-2263, Sm6-f16p60-2374, Sm6-f3p60-931, Sm6-f2p60-1067, Sm172-f3p54-1980, and Sm172-f3p54-1980) were closely correlated with the four key indices of salt tolerance. These genes could become genetic resources for salt tolerance breeding of Salix matsudana.

Overexpression of MdASMT9, an N-acetylserotonin methyltransferase gene, increases melatonin biosynthesis and improves water-use efficiency in transgenic apple

Improving apple water-use efficiency (WUE) is increasingly desirable in the face of global climate change. Melatonin is a pleiotropic molecule that functions in plant development and stress tolerance. In apple, exogenous application of melatonin has been largely investigated, but melatonin biosynthesis and its physiological roles remain elusive. In the plant biosynthetic pathway of melatonin, the last and key step is that N-acetylserotonin methyltransferase (ASMT) converts N-acetylserotonin into melatonin. Here, we identified an apple ASMT gene, MdASMT9, using homology-based cloning and in vitro enzyme assays. Overexpression of MdASMT9 significantly increased melatonin accumulation in transgenic apple lines. Moreover, an enhanced WUE was observed in the MdASMT9-overexpressing apple lines. Under well-watered conditions, this increase in WUE was attributed to an enhancement of photosynthetic rate and stomatal aperture via a reduction in abscisic acid biosynthesis. By contrast, under long-term moderate water deficit conditions, regulations in photoprotective mechanisms, stomatal behavior, osmotic adjustment and antioxidant activity enhanced the WUE in transgenic apple lines. Taken together, our findings shed light on the positive effect of MdASMT9 on improving WUE of apple by modulating melatonin biosynthesis.

Lipo-Chitooligosaccharides (LCOs) as Elicitors of the Enzymatic Activities Related to ROS Scavenging to Alleviate Oxidative Stress Generated in Tomato Plants under Stress by UV-B Radiation

Exposure to ultraviolet-B (UV-B) radiation can lead to oxidative damage in plants, increasing reactive oxygen species (ROS) production. To overcome ROS burst, plants have antioxidant mechanisms related to ROS scavenging which can be improved by elicitation with biological agents or derived molecules (elicitors), as they can trigger a physiological alert state called “priming”. This work describes the effects of lipo-chitooligosaccharides (LCOs) treatment applied to tomato plants under UV-B stress. The LCOs used in the study are produced by three species of the genus Ensifer (formerly Sinorhizobium) (SinCEU-1, SinCEU-2, and SinCEU-3) were assayed on tomato plants under UV-B stress. LCOs were able to significantly increase most of the enzymatic activities related to ROS scavenging while non-enzymatic antioxidants were not modified. This response was associated with a lower oxidative stress, according to malondialdehyde (MDA) levels and the higher antioxidant capacity of the plants. Furthermore, the photosynthetic efficiency of LCOs-treated plants indicated a better physiological state than the control plants. Therefore, although more studies and deepening of certain aspects are necessary, LCOs have shown great potential to protect plants from high UV-B radiation conditions.

Heat Stress-Mediated Constraints in Maize (Zea mays) Production: Challenges and Solutions

An increase in temperature and extreme heat stress is responsible for the global reduction in maize yield. Heat stress affects the integrity of the plasma membrane functioning of mitochondria and chloroplast, which further results in the over-accumulation of reactive oxygen species. The activation of a signal cascade subsequently induces the transcription of heat shock proteins. The denaturation and accumulation of misfolded or unfolded proteins generate cell toxicity, leading to death. Therefore, developing maize cultivars with significant heat tolerance is urgently required. Despite the explored molecular mechanism underlying heat stress response in some plant species, the precise genetic engineering of maize is required to develop high heat-tolerant varieties. Several agronomic management practices, such as soil and nutrient management, plantation rate, timing, crop rotation, and irrigation, are beneficial along with the advanced molecular strategies to counter the elevated heat stress experienced by maize. This review summarizes heat stress sensing, induction of signaling cascade, symptoms, heat stress-related genes, the molecular feature of maize response, and approaches used in developing heat-tolerant maize varieties.

Inorganic Nitrogen Enhances the Drought Tolerance of Evergreen Broad-Leaved Tree Species in the Short-Term, but May Aggravate Their Water Shortage in the Mid-Term

With global climate change, atmospheric nitrogen (N) deposition and drought have been well documented to cause substantial challenges for tropical and subtropical evergreen broad-leaved forests. Here, we conducted an experiment that measured the physiological responses of the seedlings of three dominant tree species (Tabebuia chrysantha, Elaeocarpus sylvestris, and Bischofia javanica) of the evergreen broad-leaved forests in South China under control (CT), drought stress (D), N addition (N), and drought stress plus N addition (N+D). We found that N addition significantly decreased malondialdehyde (MDA) content, abscisic acid (ABA) content, total antioxidant capacity (T-AOC), but significantly increased the content of proline (PRO), and the activities of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS) in the three species under D. Meanwhile, we also found that under drought conditions, N addition promoted the leaf transpiration rate (E), stomatal conductance (g _s ), and light-saturated net photosynthetic rate (A _max ) of the three species. These results indicate that N addition can enhance the drought tolerance of the three species by osmotic adjustment and protecting the photosystem. However, the enhancement in A _max and E will cause plants to face more severe drought conditions, especially B. javanica (large tree species). This study helps to explain why the evergreen broad-leaved forests in South China are gradually degrading to shrublands in recent decades.

Comparative transcriptomic analyses of citrus cold-resistant vs. sensitive rootstocks might suggest a relevant role of ABA signaling in triggering cold scion adaption

BACKGROUND

The citrus genus comprises a number of sensitive tropical and subtropical species to cold stress, which limits global citrus distribution to certain latitudes and causes major economic loss. We used RNA-Seq technology to analyze changes in the transcriptome of Valencia delta seedless orange in response to long-term cold stress grafted on two frequently used citrus rootstocks: Carrizo citrange (CAR), considered one of the most cold-tolerant accessions; C. macrophylla (MAC), a very sensitive one. Our objectives were to identify the genetic mechanism that produce the tolerant or sensitive phenotypes in citrus, as well as to gain insights of the rootstock-scion interactions that induce the cold tolerance or sensitivity in the scion.

RESULTS

Plants were kept at 1 ºC for 30 days. Samples were taken at 0, 15 and 30 days. The metabolomic analysis showed a significant increase in the concentration of free sugars and proline, which was higher for the CAR plants. Hormone quantification in roots showed a substantially increased ABA concentration during cold exposure in the CAR roots, which was not observed in MAC. Different approaches were followed to analyze gene expression. During the stress treatment, the 0-15-day comparison yielded the most DEGs. The functional characterization of DEGs showed enrichment in GO terms and KEGG pathways related to abiotic stress responses previously described in plant cold adaption. The DEGs analysis revealed that several key genes promoting cold adaption were up-regulated in the CAR plants, and those repressing it had higher expression levels in the MAC samples.

CONCLUSIONS

The metabolomic and transcriptomic study herein performed indicates that the mechanisms activated in plants shortly after cold exposure remain active in the long term. Both the hormone quantification and differential expression analysis suggest that ABA signaling might play a relevant role in promoting the cold hardiness or sensitiveness of Valencia sweet orange grafted onto Carrizo citrange or Macrophylla rootstocks, respectively. Our work provides new insights into the mechanisms by which rootstocks modulate resistance to abiotic stress in the production variety grafted onto them.

Overexpression mutants reveal a role for a chloroplast MPD protein in regulation of reactive oxygen species during chilling in Arabidopsis

Reactive oxygen species (ROS) contribute to cellular damage in several different contexts, but their role during chilling damage is poorly defined. Chilling sensitivity both limits the distribution of plant species and causes devastating crop losses worldwide. Our screen of chilling-tolerant Arabidopsis (Arabidopsis thaliana) for mutants that suffer chilling damage identified a gene (At4g03410) encoding a chloroplast Mpv17_PMP22 protein, MPD1, with no previous connection to chilling. The chilling-sensitive mpd1-1 mutant is an overexpression allele that we successfully phenocopied by creating transgenic lines with a similar level of MPD1 overexpression. In mammals and yeast, MPD1 homologs are associated with ROS management. In chilling conditions, Arabidopsis overexpressing MPD1 accumulated H2O2 to higher levels than wild-type controls and exhibited stronger induction of ROS response genes. Paraquat application exacerbated chilling damage, confirming that the phenotype occurs due to ROS dysregulation. We conclude that at low temperature increased MPD1 expression results in increased ROS production, causing chilling damage. Our discovery of the effect of MPD1 overexpression on ROS production under chilling stress implies that investigation of the nine other members of the Mpv17_PMP22 family in Arabidopsis may lead to new discoveries regarding ROS signaling and management in plants.

Photosynthesis of winter wheat effectively reflected multiple physiological responses under short-term drought-rewatering conditions

BACKGROUND

Based on the interrelationship among photosynthesis (Pn), water consumption and drought resistance physiology under water changes, this study aimed to explore whether easily measured Pn could be used to reflect the physiological state of winter wheat and soil moisture. The study was a greenhouse pot experiment, with three growth periods and four gradients of moisture.

RESULTS

The instantaneous water use efficiency of wheat improved significantly under short-term regulated deficit irrigation conditions. The photosynthetic parameters could effectively reflect the level of soil moisture (receiver operating characteristic curve analysis, area under the curve = 0.683-0.988). There was a significant correlation between Pn and yield under drought and rewatering (P < 0.05). The water consumption of winter wheat was significantly reduced by 15.5% to 47.6% (P < 0.05) during drought owing to the reduction of stomatal conductance and transpiration rate (Tr). There was a significant linear relationship between Tr and daily water consumption (R²  > 0.745, P< 0.05). There was a significant quadratic linear relationship (R²  > 0.600, P < 0.05) between Pn and the drought resistance indicators. The protective effect of drought resistance physiology on Pn was more significant during drought than during rewatering. Among the four physiological indicators of drought resistance, the relationship between peroxidase activity and Pn was relatively close (grey relational analysis, GRO = 1).

CONCLUSIONS

The photosynthetic parameters during conditions of short-term water changes could effectively reflect the status of soil moisture, water consumption, yield and drought resistance. A focus on Pn and the rational use of related relationships are conducive to the selection of drought-resistant varieties and developing refined agricultural management. © 2021 Society of Chemical Industry.

Plastid retrograde regulation of miRNA expression in response to light stress

BACKGROUND

MicroRNAs (miRNAs) are a class of endogenous noncoding RNAs that play a pivotal role in the regulation of plant development and responses to the surrounding environment. Despite the efforts made to elucidate their function in the adaptation of plants to many abiotic and biotic stresses, their role in high light (HL) stress is still vague. HL stress often arises upon plant exposure to full sunlight. Subsequent changes in nuclear gene expression are triggered by chloroplast-derived retrograde signals.

RESULTS

In this study, we show that HL is involved in miRNA-dependent regulation in Arabidopsis thaliana rosettes. Microtranscriptomic screening revealed a limited number of miRNAs reacting to HL. To explain the miRNA regulation mechanisms at the different biogenesis stages, chemical and genetic approaches were applied. First, we tested the possible role of plastoquinone (PQ) redox changes using photosynthetic electron transport chain inhibitors. The results suggest that increased primary transcript abundance (pri-miRNAs) of HL-regulated miRNAs is dependent on signals upstream of PQ. This indicates that such signals may originate from photosystem II, which is the main singlet oxygen (¹O₂) source. Nevertheless, no changes in pri-miRNA expression upon a dark-light shift in the conditional fluorescent (flu) mutant producing ¹O₂ were observed when compared to wild-type plants. Thus, we explored the ¹O₂ signaling pathway, which is initiated independently in HL and is related to β-carotene oxidation and production of volatile derivatives, such as β-cyclocitral (β-CC). Pri-miRNA induction by β-CC, which is a component of this ¹O₂ pathway, as well as an altered response in the methylene blue sensitivity 1 (mbs1) mutant support the role of ¹O₂ signaling in miRNA regulation.

CONCLUSIONS

We show that light stress triggers changes in miRNA expression. This stress response may be regulated by reactive oxygen species (ROS)-related signaling. In conclusion, our results link ROS action to miRNA biogenesis, suggesting its contribution to inconsistent pri- and mature miRNA dynamics.

Comparative study on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells; UVA light-induced stimulation

AIM

This study aims to determine how photosynthetic and antioxidant activities vary in vegetative and dormant cells of Haematococcus pluvialis subjected to stresses in conditions representative of industrial productions of microalgae under solar light.

METHODS AND RESULTS

The effects of short-term oxidative treatments were examined on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells. The vegetative cells have 1.6 times higher levels of phenolic compounds, but 1.7 times less catalase, ascorbate peroxidase, and superoxide dismutase activities than the astaxanthin-enriched resting cells. Mainly, a UVA dose of 4 J cm^-2 induced increases in photosystem II electron transport rates (ETRmax) (+15%), phenolic compounds (+15%), astaxanthin (+ 48%), catalase (+45%), and superoxide dismutase (+30%) activities in vegetative cells.

CONCLUSION

The UVA-dose strongly stimulates the photosynthetic and antioxidant activities of vegetative cells, but only the accumulation of astaxanthin in resting cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

These preliminary results show that oxidative stresses at sub-lethal levels can stimulate the activities of microalgae. Further investigations are needed to estimate the real influence on metabolite productivities in industrial production conditions.

The Reactions of Photosynthetic Capacity and Plant Metabolites of Sedum hybridum L. in Response to Mild and Moderate Abiotic Stresses

In this article, for the first time, an experimental study of the effect of mild and moderate osmotic stress, NaCl content and the effect of low positive temperature on photosynthetic activity and composition of metabolites of immature plants Sedum hybridum L. is reported. In this representative of the genus Sedum adapted to arid conditions and having the properties of a succulent, a change in photosynthetic activity and an increase in the level of protective metabolites in the shoots were revealed when exposed to mild and moderate stress factors. The results of this study can be used in work on the adaptation of succulent plants to arid conditions, environmental monitoring and work on the directed induction of valuable secondary metabolites in succulents to obtain new herbal medicines.

Enhanced Photosynthetic Capacity, Osmotic Adjustment and Antioxidant Defenses Contribute to Improve Tolerance to Moderate Water Deficit and Recovery of Triploid Citrus Genotypes

Currently, drought stress is a major issue for crop productivity, and future climate models predict a rise in frequency and severity of drought episodes. Polyploidy has been related to improved tolerance of plants to environmental stresses. In Citrus breeding programs, the use of triploidy is an effective way to produce seedless fruits, one of the greatest consumer expectations. The current study used physiological and biochemical parameters to assess the differential responses to moderate water deficit of 3x genotypes compared to 2x genotypes belonging to the same hybridization. Both parents, the mandarin Fortune and Ellendale tangor, were also included in the experimental design, while the 2x common clementine tree was used as reference. Water deficit affects leaf water status, as well as physiological and detoxification processes. Triploid genotypes showed a better ability to maintain water status through increased proline content and photosynthetic capacity. Moreover, less oxidative damage was associated with stronger antioxidant defenses in triploid genotypes. We also found that triploidy improved the recovery capacity after a water deficit episode.

Citrus rootstocks modify scion antioxidant system under drought and heat stress combination

The activation of the antioxidant system under stress combination is a transmissible trait from the rootstock to the scion. Therefore, rootstock selection is key to improve crop performance and a sustainable production under changing climate conditions. Climate change is altering weather conditions such as mean temperatures and precipitation patterns. Rising temperatures, especially in certain regions, accelerates soil water depletion and increases drought risk, which affects agriculture yield. Previously, our research demonstrated that the citrus rootstock Carrizo citrange (Citrus sinensis × Poncirus trifoliata) is more tolerant than Cleopatra mandarin (C. reshni) to drought and heat stress combination, in part, due to a higher activation of the antioxidant system that alleviated damage produced by oxidative stress. Here, by using reciprocal grafts of both genotypes, we studied the importance of the rootstock on scion performance and antioxidant response under this stress combination. Carrizo rootstock, under stress combination, positively influenced Cleopatra scion by reducing H₂O₂ accumulation, increasing superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzymatic activities and inducing SOD1, APX2 and catalase (CAT) protein accumulations. On the contrary, Cleopatra rootstock induced decreases in APX2 expression, CAT activity and SOD1, APX2 and CAT contents on Carrizo scion. Taken together, our findings indicate that the activation of the antioxidant system under stress combination is a transmissible trait from the rootstock to the scion and highlight the importance of the rootstock selection to improve crop performance and maintain citrus yield under the current scenario of climate change.

MdGH3.6 is targeted by MdMYB94 and plays a negative role in apple water-deficit stress tolerance

Drought significantly limits apple fruit production and quality. Decoding the key genes involved in drought stress tolerance is important for breeding varieties with improved drought resistance. Here, we identified GRETCHEN HAGEN3.6 (GH3.6), an indole-3-acetic acid (IAA) conjugating enzyme, to be a negative regulator of water-deficit stress tolerance in apple. Overexpressing MdGH3.6 reduced IAA content, adventitious root number, root length and water-deficit stress tolerance, whereas knocking down MdGH3.6 and its close paralogs increased IAA content, adventitious root number, root length and water-deficit stress tolerance. Moreover, MdGH3.6 negatively regulated the expression of wax biosynthetic genes under water-deficit stress and thus negatively regulated cuticular wax content. Additionally, MdGH3.6 negatively regulated reactive oxygen species scavengers, including antioxidant enzymes and metabolites involved in the phenylpropanoid and flavonoid pathway in response to water-deficit stress. Further study revealed that the homolog of transcription factor AtMYB94, rather than AtMYB96, could bind to the MdGH3.6 promoter and negatively regulated its expression under water-deficit stress conditions in apple. Overall, our results identify a candidate gene for the improvement of drought resistance in fruit trees.

Cyclic electron flow (CEF) and ascorbate pathway activity provide constitutive photoprotection for the photopsychrophile, Chlamydomonas sp. UWO 241 (renamed Chlamydomonas priscuii)

Under environmental stress, plants and algae employ a variety of strategies to protect the photosynthetic apparatus and maintain photostasis. To date, most studies on stress acclimation have focused on model organisms which possess limited to no tolerance to stressful extremes. We studied the ability of the Antarctic alga Chlamydomonas sp. UWO 241 (UWO 241) to acclimate to low temperature, high salinity or high light. UWO 241 maintained robust growth and photosynthetic activity at levels of temperature (2 °C) and salinity (700 mM NaCl) which were nonpermissive for a mesophilic sister species, Chlamydomonas raudensis SAG 49.72 (SAG 49.72). Acclimation in the mesophile involved classic mechanisms, including downregulation of light harvesting and shifts in excitation energy between photosystem I and II. In contrast, UWO 241 exhibited high rates of PSI-driven cyclic electron flow (CEF) and a larger capacity for nonphotochemical quenching (NPQ). Furthermore, UWO 241 exhibited constitutively high activity of two key ascorbate cycle enzymes, ascorbate peroxidase and glutathione reductase and maintained a large ascorbate pool. These results matched the ability of the psychrophile to maintain low ROS under short-term photoinhibition conditions. We conclude that tight control over photostasis and ROS levels are essential for photosynthetic life to flourish in a native habitat of permanent photooxidative stress. We propose to rename this organism Chlamydomonas priscuii.

Transcriptome response of maize (Zea mays L.) seedlings to heat stress

Among stresses, heat stress (HS) is a prime factor restricting plant growth and productivity. However, the molecular mechanisms of plants' response to HS need to be further uncovered. Here, the transcriptome response of maize seedlings to HS was dissected using transcriptome data analysis. The data exhibited that a total of 43,221 genes in maize seedlings had been found, 37,534 of which were referred, while 5686 were not. Under HS, comparison with the control without HS, there were 13,607 genes that were differentially expressed (DEGs, 6195 upregulated and 7412 downregulated). In addition, Gene Ontology (GO) enrichment analysis indicated that there were 220, 478, and 1300 terms that were enriched in cellular component, molecular function, and biological process, respectively. Significantly enriched GO terms were involved in 23 cellular components, 27 molecular functions, and 124 biological processes. Also, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that there were 2613 DEGs that were assigned to 131 pathways, 14 of which (enriched 1068 DEGs in total) were significantly upregulated. These pathways were mainly related to protein renaturation, biomembrane repair, osmotic adjustment, and redox balance. Among them, protein processing in endoplasmic reticulum was the most significantly upregulated. The transcriptome data decoded that protein renaturation, biomembrane repair, osmotic adjustment, and redox balance played a key role in the response of maize seedlings to HS.

The Variation of Selected Physiological Parameters in Elm Leaves (Ulmus glabra Huds.) Infested by Gall Inducing Aphids

Three aphid species, Eriosoma ulmi (L.), Colopha compressa (Koch) and Tetraneura ulmi (L.) induce distinct gall morphotypes on Ulmus glabra Huds.; opened and closed galls. Because the trophic relationship of aphids and their galls shows that throughout the gall formation aphids can elicit multiple physiological regulations, we evaluated the changes of hydrogen peroxide content (H₂O₂), cytoplasmic membrane condition, expressed as electrolyte leakage (E_L) and concentration of thiobarbituric acid reactive substances (TBARS), as well as, the activity of catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) in gall tissues, as well as, in damaged and undamaged parts of galled leaves. All aphid species increased E_L from gall tissues and significantly upregulated APX activity in galls and galled leaves. Alterations in H₂O₂ and TBARS concentrations, as well as GPX and CAT activities, were aphid- and tissue-dependent. The development of pseudo- and closed galls on elm leaves did not have a clear effect on the direction and intensity of the host plant’s physiological response. The different modes of changes in H₂O₂, TBARS, CAT and GPX were found in true galls of C. compressa and T. ulmi. Generally, physiological alterations in new plant tissues were quite different compared to other tissues and could be considered beneficial to galling aphids.

Resveratrol exerts beneficial effects on the growth and metabolism of Lactuca sativa L

In order to assist sustainable agriculture, new strategies and methods are being used based on the utilization of new natural molecules. These natural compounds can be used as potential natural crop protectors and growth promoters, and the elucidation of their modes/mechanisms of action can represent a big step towards cleaner agriculture free of agrochemicals. In the present paper, the mechanisms underlying the effects of exogenous resveratrol (R), a natural phytoalexin found in plants, on Lactuca sativa metabolism were investigated through physiological and metabolomic approaches. The results highlighted that R stimulates the growth of lettuce. A reduction of the O2⋅- production in R-treated seedlings and an increase in the photosynthesis efficiency was observed, indicated by a higher Fv/Fm. The metabolomic analysis of lettuce seedlings treated with R identified 116 metabolites related to galactose, amino acids, sugar and nucleotide sugar, and ascorbate and aldarate metabolisms. Increased content of some polyamines and several metabolites was also observed, which may have contributed to scavenging free radicals and activating antioxidant enzymes, thus reducing oxidative damage and improving PSII protection in R-treated seedlings.

Potassium supply modulates Eucalyptus leaf water-status under PEG-induced osmotic stress: integrating leaf gas exchange, carbon and nitrogen isotopic composition and plant growth

The objective of this study was to quantify the effect of potassium (K) supply on osmotic adjustment and drought avoidance mechanisms of Eucalyptus seedlings growing under short-term water stress. The effects of K supply on plant growth, nutritional status, leaf gas exchange parameters, leaf water potential (Ψw), leaf area (LA), stomatal density (SD), leaf carbon (C) and nitrogen (N) isotopic compositions (δ13C and δ15N ‰) and leaf C/N ratio under polyethylene glycol (PEG)-induced water deficit were measured. Under both control (non-PEG) and osmotic stress (+PEG) conditions, K supply increased plant growth, boosting dry matter yield with decreased C/N leaf ratio and δ15N ‰ values. The +PEG significantly reduced LA, plant growth, dry matter yield, Ψw, number of stomata per plant and leaf gas exchange, relative to non-PEG condition. Potassium supply alleviated osmotic-induced alterations in Eucalyptus seedlings by better regulating leaf development as well as SD, thus improving the rate of leaf gas exchange parameters, mesophyll conductance to CO2 (lower δ13C ‰ values) and water use efficiency (WUE). Consequently, K-supplied plants under drought better acclimated to osmotic stress than K-deficient plants, which in turn induced lower CO2 assimilation and dry matter yield, as well as higher leaf δ13C ‰ and δ15N ‰ values. In conclusion, management practices should seek to optimize K-nutrition to improve WUE, photosynthesis-related parameters and plant growth under water deficit conditions.

Salicylic acid mitigates salt induced toxicity through the modifications of biochemical attributes and some key antioxidants in capsicum annuum

Abiotic stress causes extensive loss to agricultural yield production worldwide. Salt stress is one of them crucial factor which leads to decreased the agricultural production through detrimental effect on growth and development of crops. In our study, we examined the effect of a defense growth substance, salicylic acid (SA 1 mM) on mature vegetative (60 Days after sowing) and flowering (80 DAS) stage of Pusa Sadabahar (PS) variety of Capsicum annuum L. plants gown under different concentrations of NaCl (25, 50, 75, 100 and 150 mM) and maintained in identical sets in pots during the whole experiment. Physiological studies indicated that increase in root & shoot length, fresh & dry weight, number of branches per plant, and yield (number of fruits per plant) under salt + SA treatment. Biochemical studies, enzymatic antioxidants like CAT, POX, and non-enzymatic antioxidant such as ascorbic acid (AsA content), carotenoids, phenolics, besides other defense compounds like proline, protein, chlorophyll contents were studied at 10 days after treatment at the mature vegetative and flowering stage. The addition of SA led to lowering of in general, all studied parameters in the mature vegetative stage but increased the same during the flowering stage, especially in the presence of NaCl; although the control I (without SA and NaCl) remained lower in value than control II (with SA, without NaCl). Interestingly, total phenolics were higher in control I (without SA or NaCl) whereas chlorophylls were higher in treatments with SA and NaCl. Thus, physiological concentration of SA (1 mM) appears to be significantly effective against salt stress during the flowering stage. In addition, during the mature vegetative stage, however, proline accumulates in SA treated sets, to help in developing NaCl-induced drought stress tolerance.

Influence of Seed Source and Soil Contamination on Ecophysiological Responses of Lavandula pedunculata in Rehabilitation of Mining Areas

Mining activities have turned many areas of the Iberian Pyrite Belt (IPB) into extreme environments with high concentrations of metal(loid)s. These harsh conditions can inhibit or reduce the colonization and/or development of most vegetation. However, some species or populations have developed ecophysiological responses to tolerate stress factors and contaminated soils. The main objectives of this study are: (i) to assess the differences in germination, growth, development and physiological behaviour against oxidative stress caused by metal(loid)s in Lavandula pedunculata (Mill.) Cav. from two different origins (a contaminated area in São Domingos mine, SE of Portugal and an uncontaminated area from Serra do Caldeirão, S of Portugal) under controlled conditions; and (ii) to assess whether it is possible to use this species for the rehabilitation of mine areas of the IPB. After germination, seedlings from São Domingos (LC) and Caldeirão (L) were planted in pots with a contaminated soil developed on gossan (CS) and in pots with an uncontaminated soil (US) under controlled conditions. Multielemental concentrations were determined in soils (total and available fractions) and plants (shoots and roots). Germination rate, shoot height, dry biomass and leaf area were determined, and pigments, glutathione, ascorbate and H2O2 contents were measured in plant shoots. Total concentrations of As, Cr, Cu, Pb and Sb in CS, and As in US exceed the intervention and maximum limits for ecosystem protection and human health. The main results showed that L. pedunculata, regardless of the seed origin, activated defence mechanisms against oxidative stress caused by high concentrations of metal(loid)s. Plants grown from seeds of both origins increased the production of AsA to preserve its reduction levels and kept the contents of GSH stable to maintain the cell’s redox state. Plants grown from seeds collected in non-contaminated areas showed a high capacity for adaptation to extreme conditions. This species showed a greater growth capacity when seeds from a contaminated area were sown in uncontaminated soils. Thus, L. pedunculata, mainly grown from seeds from contaminated areas, may be used in phytostabilization programmes in areas with soils with high contents of metal(loid)s.

Stress-regulated elements in Lotus spp., as a possible starting point to understand signalling networks and stress adaptation in legumes

Although legumes are of primary economic importance for human and livestock consumption, the information regarding signalling networks during plant stress response in this group is very scarce. Lotus japonicus is a major experimental model within the Leguminosae family, whereas L. corniculatus and L. tenuis are frequent components of natural and agricultural ecosystems worldwide. These species display differences in their perception and response to diverse stresses, even at the genotype level, whereby they have been used in many studies aimed at achieving a better understanding of the plant stress-response mechanisms. However, we are far from the identification of key components of their stress-response signalling network, a previous step for implementing transgenic and editing tools to develop legume stress-resilient genotypes, with higher crop yield and quality. In this review we scope a body of literature, highlighting what is currently known on the stress-regulated signalling elements so far reported in Lotus spp. Our work includes a comprehensive review of transcription factors chaperones, redox signals and proteins of unknown function. In addition, we revised strigolactones and genes regulating phytochelatins and hormone metabolism, due to their involvement as intermediates in several physiological signalling networks. This work was intended for a broad readership in the fields of physiology, metabolism, plant nutrition, genetics and signal transduction. Our results suggest that Lotus species provide a valuable information platform for the study of specific protein-protein (PPI) interactions, as a starting point to unravel signalling networks underlying plant acclimatation to bacterial and abiotic stressors in legumes. Furthermore, some Lotus species may be a source of genes whose regulation improves stress tolerance and growth when introduced ectopically in other plant species.

Is Photoprotection of PSII One of the Key Mechanisms for Drought Tolerance in Maize?

Drought is one of the most important abiotic stress factors limiting maize production worldwide. The objective of this study was to investigate whether photoprotection of PSII was associated with the degree of drought tolerance and yield in three maize hybrids (30Y87, 31R88, P3939). To do this, three maize hybrids were subjected to three cycles of drought, and we measured the activities of photosystem II (PSII) and photosystem I (PSI). In a second field experiment, three maize hybrids were subjected to drought by withholding irrigation, and plant water status, yield and yield attributes were measured. Drought stress decreased leaf water potential (Ψ_L) in three maize hybrids, and this reduction was more pronounced in hybrid P3939 (−40%) compared to that of 30Y87 (−30%). Yield and yield attributes of three maize hybrids were adversely affected by drought. The number of kernels and 100-kernel weight was the highest in maize hybrid 30Y87 (−56%, −6%), whereas these were lowest in hybrid P3939 (−88%, −23%). Drought stress reduced the quantum yield of PSII [Y(II)], photochemical quenching (qP), electron transport rate through PSII [ETR(II)] and NPQ, except in P3939. Among the components of NPQ, drought increased the Y(NPQ) with concomitant decrease in Y(NO) only in P3939, whereas Y(NO) increased in drought-stressed plants of hybrid 30Y87 and 31R88. However, an increase in cyclic electron flow (CEF) around PSI and Y(NPQ) in P3939 might have protected the photosynthetic machinery but it did not translate in yield. However, drought-stressed plants of 30Y87 might have sufficiently downregulated PSII to match the energy consumption in downstream biochemical processes. Thus, changes in PSII and PSI activity and development of NPQ through CEF are physiological mechanisms to protect the photosynthetic apparatus, but an appropriate balance between these physiological processes is required, without which plant productivity may decline.

Phytochemical and physiological changes in Salvia officinalis L. under different irrigation regimes by exogenous applications of putrescine

Water stress is the major factor limiting plant productivity and quality in most regions of the world. In the present study, a two-year field experiment was conducted to determine the influence of putrescine (Put) on phytochemical, physiological, and growth parameters of Salvia officinalis L. under different irrigation regimes. The highest stem dry weight (56.05 and 65.21 g m⁻²) plus leaf dry weight (124.51 g m⁻²) were predicted in irrigation regimes of (20 and 40%) plus 20% available soil water was depleted (ASWD), respectively. Total phenolic content (TPC) was increased significantly under the irrigation regime of 80% with the application of distilled water in spring. TPC showed an increasing trend with increases in Put concentration under all irrigation regimes in both spring and summer. The highest total flavonoids content (TFC) in wavelengths of 415 and 367 nm were predicted in 2.25 mM Put. The highest ascorbate peroxidase (APX) activity (0.13 μmol mg⁻¹ protein) was predicted in the irrigation regime of 20% with the application of distilled water in spring and summer. There was a significantly negative correlation coefficient between APX, TPC, and TFC. Indeed, there was a decreasing trend in APX and an increasing trend in TPC and TFC with increases in Put concentration under the irrigation regime of 20% ASWD. The highest hydroxyl radical scavenging activity (HRSA) values were obtained under irrigation regimes of 49.27% and 20% ASWD in spring and summer, respectively. There was an increasing trend in endogenous Put with increases in the Put concentration. The responses of compatible osmolytes to irrigation regime can be expressed by quadratic model, suggesting maximum proline (0.52 mg g⁻¹), total reducing sugars (TRS) (0.37 mg g⁻¹), xylose (0.68 mg g⁻¹), and mannose (0.37 mg g⁻¹) values would be obtained in irrigation regimes of 68.33%, 48.33%, 53.75%, and 56.25% ASWD, respectively.

The SnRK2.10 kinase mitigates the adverse effects of salinity by protecting photosynthetic machinery

SNF1-Related protein kinases Type 2 (SnRK2) are plant-specific enzymes widely distributed across the plant kingdom. They are key players controlling abscisic acid (ABA)-dependent and ABA-independent signaling pathways in the plant response to osmotic stress. Here we established that SnRK2.4 and SnRK2.10, ABA-nonactivated kinases, are activated in Arabidopsis thaliana rosettes during the early response to salt stress and contribute to leaf growth retardation under prolonged salinity but act by maintaining different salt-triggered mechanisms. Under salinity, snrk2.10 insertion mutants were impaired in the reconstruction and rearrangement of damaged core and antenna protein complexes in photosystem II (PSII), which led to stronger non-photochemical quenching, lower maximal quantum yield of PSII, and lower adaptation of the photosynthetic apparatus to high light intensity. The observed effects were likely caused by disturbed accumulation and phosphorylation status of the main PSII core and antenna proteins. Finally, we found a higher accumulation of reactive oxygen species (ROS) in the snrk2.10 mutant leaves under a few-day-long exposure to salinity which also could contribute to the stronger damage of the photosynthetic apparatus and cause other deleterious effects affecting plant growth. We found that the snrk2.4 mutant plants did not display substantial changes in photosynthesis. Overall, our results indicate that SnRK2.10 is activated in leaves shortly after plant exposure to salinity and contributes to salt stress tolerance by maintaining efficient photosynthesis and preventing oxidative damage.

A rice R2R3-MYB (OsC1) transcriptional regulator improves oxidative stress tolerance by modulating anthocyanin biosynthesis

The R2R3 type MYB transcription factors participate in controlling flavonoid production in plants, including anthocyanin and proanthocyanin. Black rice with high anthocyanin content is an important candidate for understanding R2R3-MYB-based regulation of the anthocyanin biosynthesis pathway (ABP). This study was undertaken to draw the functional relationship of an R2R3-MYB protein with anthocyanin biosynthesis and oxidative stress tolerance in plants. The expression levels of the late ABP genes in the panicle stage of black rice were in good agreement with the accumulation of anthocyanin, especially cyanidin 3-glucoside. Among all MYB genes present in rice, an R2R3 type (C1) regulates anthocyanin biosynthesis and was studied further. The positive correlation between the expression of ABP genes and OsC1 along with the nuclear localization of OsC1 are in line with its possible involvement as a transcriptional regulator of ABP genes. Interestingly, OsC1 overexpressed in white rice plants triggered anthocyanin production through augmentation of the transcript level of late ABP genes. Moreover, OsC1-transformed plants exhibited a lower amount of reactive oxygen species upon exposure to oxidative stress. The increased anthocyanin content in white rice seedlings resulted in higher photosynthetic efficiency, less membrane damage and consequently lower oxidative stress. The OsC1 transcriptional regulator helps to ameliorate oxidative stresses in plants owing to its anthocyanin modulating ability.

Photosystem I Inhibition, Protection and Signalling: Knowns and Unknowns

Photosynthesis is the process that harnesses, converts and stores light energy in the form of chemical energy in bonds of organic compounds. Oxygenic photosynthetic organisms (i.e., plants, algae and cyanobacteria) employ an efficient apparatus to split water and transport electrons to high-energy electron acceptors. The photosynthetic system must be finely balanced between energy harvesting and energy utilisation, in order to limit generation of dangerous compounds that can damage the integrity of cells. Insight into how the photosynthetic components are protected, regulated, damaged, and repaired during changing environmental conditions is crucial for improving photosynthetic efficiency in crop species. Photosystem I (PSI) is an integral component of the photosynthetic system located at the juncture between energy-harnessing and energy consumption through metabolism. Although the main site of photoinhibition is the photosystem II (PSII), PSI is also known to be inactivated by photosynthetic energy imbalance, with slower reactivation compared to PSII; however, several outstanding questions remain about the mechanisms of damage and repair, and about the impact of PSI photoinhibition on signalling and metabolism. In this review, we address the knowns and unknowns about PSI activity, inhibition, protection, and repair in plants. We also discuss the role of PSI in retrograde signalling pathways and highlight putative signals triggered by the functional status of the PSI pool.

Photosynthesis research under climate change

Increasing global population and climate change uncertainties have compelled increased photosynthetic efficiency and yields to ensure food security over the coming decades. Potentially, genetic manipulation and minimization of carbon or energy losses can be ideal to boost photosynthetic efficiency or crop productivity. Despite significant efforts, limited success has been achieved. There is a need for thorough improvement in key photosynthetic limiting factors, such as stomatal conductance, mesophyll conductance, biochemical capacity combined with Rubisco, the Calvin-Benson cycle, thylakoid membrane electron transport, nonphotochemical quenching, and carbon metabolism or fixation pathways. In addition, the mechanistic basis for the enhancement in photosynthetic adaptation to environmental variables such as light intensity, temperature and elevated CO₂ requires further investigation. This review sheds light on strategies to improve plant photosynthesis by targeting these intrinsic photosynthetic limitations and external environmental factors.

Role of Microalgae in Global CO2 Sequestration: Physiological Mechanism, Recent Development, Challenges, and Future Prospective

The rising concentration of global atmospheric carbon dioxide (CO2) has severely affected our planet’s homeostasis. Efforts are being made worldwide to curb carbon dioxide emissions, but there is still no strategy or technology available to date that is widely accepted. Two basic strategies are employed for reducing CO2 emissions, viz. (i) a decrease in fossil fuel use, and increased use of renewable energy sources; and (ii) carbon sequestration by various biological, chemical, or physical methods. This review has explored microalgae’s role in carbon sequestration, the physiological apparatus, with special emphasis on the carbon concentration mechanism (CCM). A CCM is a specialized mechanism of microalgae. In this process, a sub-cellular organelle known as pyrenoid, containing a high concentration of Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), helps in the fixation of CO2. One type of carbon concentration mechanism in Chlamydomonas reinhardtii and the association of pyrenoid tubules with thylakoids membrane is represented through a typical graphical model. Various environmental factors influencing carbon sequestration in microalgae and associated techno-economic challenges are analyzed critically.

Sandbur Drought Tolerance Reflects Phenotypic Plasticity Based on the Accumulation of Sugars, Lipids, and Flavonoid Intermediates and the Scavenging of Reactive Oxygen Species in the Root

The perennial grass Cenchrus spinifex (common sandbur) is an invasive species that grows in arid and semi-arid regions due to its remarkable phenotypic plasticity, which confers the ability to withstand drought and other forms of abiotic stress. Exploring the molecular mechanisms of drought tolerance in common sandbur could lead to the development of new strategies for the protection of natural and agricultural environments from this weed. To determine the molecular basis of drought tolerance in C. spinifex, we used isobaric tags for relative and absolute quantitation (iTRAQ) to identify proteins differing in abundance between roots growing in normal soil and roots subjected to moderate or severe drought stress. The analysis of these proteins revealed that drought tolerance in C. spinifex primarily reflects the modulation of core physiological activities such as protein synthesis, transport and energy utilization as well as the accumulation of flavonoid intermediates and the scavenging of reactive oxygen species. Accordingly, plants subjected to drought stress accumulated sucrose, fatty acids, and ascorbate, shifted their redox potential (as determined by the NADH/NAD ratio), accumulated flavonoid intermediates at the expense of anthocyanins and lignin, and produced less actin, indicating fundamental reorganization of the cytoskeleton. Our results show that C. spinifex responds to drought stress by coordinating multiple metabolic pathways along with other adaptations. It is likely that the underlying metabolic plasticity of this species plays a key role in its invasive success, particularly in semi-arid and arid environments.

Characterization of Nannochloropsis oceanica Rose Bengal Mutants Sheds Light on Acclimation Mechanisms to High Light When Grown in Low Temperature

A barrier to realizing Nannochloropsis oceanica's potential for omega-3 eicosapentaenoic acid (EPA) production is the disparity between conditions that are optimal for growth and those that are optimal for EPA biomass content. A case in point is temperature: higher content of polyunsaturated fatty acid, and especially EPA, is observed in low-temperature (LT) environments, where growth rates are often inhibited. We hypothesized that mutant strains of N. oceanica resistant to the singlet-oxygen photosensitizer Rose Bengal (RB) would withstand the oxidative stress conditions that prevail in the combined stressful environment of high light (HL; 250 μmol photons m-2 s-1) and LT (18°C). This growth environment caused the wild-type (WT) strain to experience a spike in lipid peroxidation and an inability to proliferate, whereas growth and homeostatic reactive oxygen species levels were observed in the mutant strains. We suggest that the mutant strains' success in this environment can be attributed to their truncated photosystem II antennas and their increased ability to diffuse energy in those antennas as heat (non-photosynthetic quenching). As a result, the mutant strains produced upward of four times more EPA than the WT strain in this HL-LT environment. The major plastidial lipid monogalactosyldiacylglycerol was a likely target for oxidative damage, contributing to the photosynthetic inhibition of the WT strain. A mutation in the NO10G01010.1 gene, causing a subunit of the 2-oxoisovalerate dehydrogenase E1 protein to become non-functional, was determined to be the likely source of tolerance in the RB113 mutant strain.

Rosmarinic Acid Delays Tomato Fruit Ripening by Regulating Ripening-Associated Traits

Fruits are excellent sources of essential vitamins and health-boosting minerals. Recently, regulation of fruit ripening by both internal and external cues for the improvement of fruit quality and shelf life has received considerable attention. Rosmarinic acid (RA) is a kind of natural plant-derived polyphenol, widely used in the drug therapy and food industry due to its distinct physiological functions. However, the role of RA in plant growth and development, especially at the postharvest period of fruits, remains largely unknown. Here, we demonstrated that postharvest RA treatment delayed the ripening in tomato fruits. Exogenous application of RA decreased ripening-associated ethylene production and inhibited the fruit color change from green to red based on the decline in lycopene accumulation. We also found that the degradation of sucrose and malic acid during ripening was significantly suppressed in RA-treated tomato fruits. The results of metabolite profiling showed that RA application promoted the accumulation of multiple amino acids in tomato fruits, such as aspartic acid, serine, tyrosine, and proline. Meanwhile, RA application also strengthened the antioxidant system by increasing both the activity of antioxidant enzymes and the contents of reduced forms of antioxidants. These findings not only unveiled a novel function of RA in fruit ripening, but also indicated an attractive strategy to manage and improve shelf life, flavor, and sensory evolution of tomato fruits.

Development of a Strategy for Enhancing the Biomass Growth and Lipid Accumulation of Chlorella sp. UJ-3 Using Magnetic Fe3O4 Nanoparticles

In this study, magnetic Fe₃O₄ nanoparticles (NPs) were used as an effective enhancer to increase the biomass and total lipid production of Chlorella sp. UJ-3. It was found that the biomass of algal cells increased significantly when they were exposed to low concentrations of Fe₃O₄ NPs (20 mg/L), while the best total lipid content of algal cells was achieved when they were exposed to high concentrations of Fe₃O₄ NPs (100 mg/L). Therefore, we established a strategy to promote the growth and lipid accumulation of microalgae by initially exposing the algal cells to low concentrations of Fe₃O₄ NPs and then treating them with an increased concentration of Fe₃O₄ NPs after 12 days of culture. For this strategy, the biomass and total lipid production of algal cells increased by 50% and 108.7%, respectively, compared to the untreated control. The increase in lipid production and change in the fatty acid composition of Chlorella cells were found to help them to cope with the increased number of reactive oxygen species produced due to oxidative stress in alga cells after the addition of Fe₃O₄ NPs. This study provided a highly efficient way to improve the lipid production of microalgae using nanoparticles.

Investigation of the Geographical Environment Impact on the Chemical Components of Peganum harmala L. through a Combined Analytical Method

By implementing NMR, inductively coupled plasma-atomic emission spectrometry (ICP-AES), and the UV-vis spectroscopic techniques, metabolites, mineral elements, and antioxidant activities (DPPH) of Peganum harmala L. samples from Manasi and Fuhai of Xinjiang were studied in this research to investigate the geographical environment impact at the molecular level. First of all, partial least squares discriminant analysis was conducted to explore differential endogenous metabolites. A total of 18 metabolites were identified, and 14 mineral element contents were calculated quantitatively, which displayed diverse changing trends from these two origins. Valine, succinic acid, betaine, sucrose, and vasicine exhibited significant differences between these two groups as well as mineral nutrient profiles (Mg, Cu, N, K, Na, P, Zn, C) and DPPH antioxidant activities (EC₅₀). The obvious different characteristics of chemical components and antioxidant activities in these two groups were further verified by heat map cluster analysis. Pearson correlation analysis also revealed the remarkable relationship of chemical components and antioxidant activities, which are strongly associated with the regional environment. This study showed that the combination of methodologies proposed will be highly useful in evaluating the environmental variation and diversity in terrestrial ecosystems.

Impact of high irradiance and UV-B on the photosynthetic activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under blue light

The impacts of high-intensity light (HIL) (4 h) and UV-B radiation (1 h) on the photosynthetic activity, content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes (ascorbate peroxidase (APX) and guaiacol-dependent peroxidase (GPX)), content of thiobarbituric acid reactive substances (TBARs), expression of some light-regulated genes in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) hy4 mutant of A. thaliana Col-0 plants grown under blue light (BL) were studied. HIL and UV-B treatments led to decreases in the photosynthetic rate (P_n), photochemical activity of PSII (F_V/F_M) and PSII performance index (PI_ABS) of WT and mutant plants grown under high-intensity BL (HBL) and moderate intensity BL (MBL). However, in HBL plants, the decrease in the photosynthetic activity in hy4 plants was significantly greater than that in WT plants. In addition, hy4 HBL plants demonstrated lowered UAP and carotenoid contents as well as lower activity of APX and GPX enzymes. The difference in the decline in the photosynthetic activity of WT and hy4 plants grown at MBL in response to HIL was nonsignificant, while that in response to UV-B was small. We assume that the deficiency in cryptochrome 1 under HIL irradiation disrupts the interaction between HY5 and HFR1 transcription factors and photoreceptors, which affects the transcription of light-induced genes, such as CAB1, PSY and PAL1 linked to carotenoid and flavonoid biosynthesis. It was concluded that PA stress resistance in WT and hy4 plants depends on the light intensity and reduced stress resistance of hy4 at HBL, is likely linked to low UAP and carotenoid contents as well as lowered APX and GPX enzyme activities in hy4 mutants.

Exogenous ethanol treatment alleviates oxidative damage of Arabidopsis thaliana under conditions of high-light stress

Abiotic stresses, such as high light and salinity, are major factors that limit crop productivity and sustainability worldwide. Chemical priming is a promising strategy for improving the abiotic stress tolerance of plants. Recently, we discovered that ethanol enhances high-salinity stress tolerance in Arabidopsis thaliana and rice by detoxifying reactive oxygen species (ROS). However, the effect of ethanol on other abiotic stress responses is unclear. Therefore, we investigated the effect of ethanol on the high-light stress response. Measurement of chlorophyll fluorescence showed that ethanol mitigates photoinhibition under high-light stress. Staining with 3,3'-diaminobenzidine (DAB) showed that the accumulation of hydrogen peroxide (H₂O₂) was inhibited by ethanol under high-light stress conditions in A. thaliana. We found that ethanol increased the gene expressions and enzymatic activities of antioxidative enzymes, including ASCORBATE PEROXIDASE1 (AtAPX1), Catalase (AtCAT1 and AtCAT2). Moreover, the expression of flavonoid biosynthetic genes and anthocyanin contents were upregulated by ethanol treatment during exposure to high-light stress. These results imply that ethanol alleviates oxidative damage from high-light stress in A. thaliana by suppressing ROS accumulation. Our findings support the hypothesis that ethanol improves tolerance to multiple stresses in field-grown crops.

iTRAQ-based proteomic analysis provides insights into the molecular mechanisms of rice formyl tetrahydrofolate deformylase in salt response

A new molecular mechanism of tetrahydrofolate deformylase involved in the salt response presumably affects mitochondrial and chloroplast function by regulating energy metabolism and accumulation of reactive oxygen species. High salinity severely restrains plant growth and development, consequently leading to a reduction in grain yield. It is therefore critical to identify the components involved in plant salt resistance. In our previous study, we identified a rice leaf early-senescence mutant hpa1, which encodes a formyl tetrahydrofolate deformylase (Xiong et al. in Sci China Life Sci 64(5):720-738, 2021). Here, we report that HPA1 also plays a role in the salt response. To explore the molecular mechanism of HPA1 in salt resistance, we attempted to identify the differentially expressed proteins between wild type and hpa1 mutant for salinity treatment using an iTRAQ-based comparative protein quantification approach. A total of 4598 proteins were identified, of which 279 were significantly altered, including 177 up- and 102 down-regulated proteins. A functional analysis suggested that the 279 differentially expressed proteins are involved mainly in the regulation of oxidative phosphorylation, phenylpropanoid biosynthesis, photosynthesis, posttranslational modifications, protein turnover and energy metabolism. Moreover, a deficiency in HPA1 impaired chlorophyll metabolism and photosynthesis in chloroplasts and affected the electron flow of the electron transport chain in mitochondria. These changes led to abnormal energy metabolism and accumulation of reactive oxygen species, which may affect the permeability and integrity of cell membranes, leading to cell death. In addition, the results were verified by transcriptional or physiological experiments. Our results provide an insight into a new molecular mechanism of the tetrahydrofolate cycle protein formyl tetrahydrofolate deformylase, which is involved in the salt response, presumably by affecting mitochondrial and chloroplast function regulating energy metabolism and accumulation of reactive oxygen species under salt stress.

WRKY Transcription Factors in Cassava Contribute to Regulation of Tolerance and Susceptibility to Cassava Mosaic Disease through Stress Responses

Among the numerous biological constraints that hinder cassava (Manihot esculenta Crantz) production, foremost is cassava mosaic disease (CMD) caused by virus members of the family Geminiviridae, genus Begomovirus. The mechanisms of CMD tolerance and susceptibility are not fully understood; however, CMD susceptible T200 and tolerant TME3 cassava landraces have been shown to exhibit different large-scale transcriptional reprogramming in response to South African cassava mosaic virus (SACMV). Recent identification of 85 MeWRKY transcription factors in cassava demonstrated high orthology with those in Arabidopsis, however, little is known about their roles in virus responses in this non-model crop. Significant differences in MeWRKY expression and regulatory networks between the T200 and TME3 landraces were demonstrated. Overall, WRKY expression and associated hormone and enriched biological processes in both landraces reflect oxidative and other biotic stress responses to SACMV. Notably, MeWRKY11 and MeWRKY81 were uniquely up and downregulated at 12 and 67 days post infection (dpi) respectively in TME3, implicating a role in tolerance and symptom recovery. AtWRKY28 and AtWRKY40 homologs of MeWRKY81 and MeWRKY11, respectively, have been shown to be involved in regulation of jasmonic and salicylic acid signaling in Arabidopsis. AtWRKY28 is an interactor in the RPW8-NBS resistance (R) protein network and downregulation of its homolog MeWRKY81 at 67 dpi in TME3 suggests a negative role for this WRKY in SACMV tolerance. In contrast, in T200, nine MeWRKYs were differentially expressed from early (12 dpi), middle (32 dpi) to late (67 dpi) infection. MeWRKY27 (homolog AtWRKY33) and MeWRKY55 (homolog AtWRKY53) were uniquely up-regulated at 12, 32 and 67 dpi in T200. AtWRKY33 and AtWRKY53 are positive regulators of leaf senescence and oxidative stress in Arabidopsis, suggesting MeWRKY55 and 27 contribute to susceptibility in T200.

Cacao (Theobroma cacao L.) Response to Water Stress: Physiological Characterization and Antioxidant Gene Expression Profiling in Commercial Clones

The increase in events associated with drought constraints plant growth and crop performance. Cacao (Theobroma cacao L.) is sensitive to water deficit stress (DS), which limits productivity. The aim of this research was to characterise the response of seven (CCN51, FEAR5, ICS1, ICS60, ICS95, EET8, and TSH565) commercially important cacao clones to severe and temporal water deficit stress. Ten-month-old cacao trees were submitted to two treatments: well-watered and water-stressed until the leaf water potential (Ψ leaf) reached values between -3.0 and -3.5 MPa. The effects of hydric stress on water relations, gas exchange, photochemical activity, membrane integrity and oxidative stress-related gene expression were evaluated. All clones showed decreases in Ψ leaf, but TSH565 had a higher capacity to maintain water homeostasis in leaves. An initial response phase consisted of stomatal closure, a general mechanism to limit water loss: as a consequence, the photosynthetic rate dropped by approximately 98% on average. In some clones, the photosynthetic rate reached negative values at the maximum stress level, evidencing photorespiration and was confirmed by increased intracellular CO2. A second and photosynthetically limited phase was characterized by a drop in PSII quantum efficiency, which affected all clones. On average, all clones were able to recover after 4 days of rewatering. Water deficit triggered oxidative stress at the early phase, as evidenced by the upregulation of oxidative stress markers and genes encoding ROS scavenging enzymes. The effects of water deficit stress on energy metabolism were deduced given the upregulation of fermentative enzyme-coding genes. Altogether, our results suggest that the EET8 clone was the highest performing under water deficit while the ICS-60 clone was more susceptible to water stress. Importantly, the activation of the antioxidant system and PSII repair mechanism seem to play key roles in the observed differences in tolerance to water deficit stress among clones.

Will Casuarina glauca Stress Resilience Be Maintained in the Face of Climate Change?

Actinorhizal plants have been regarded as promising species in the current climate change context due to their high tolerance to a multitude of abiotic stresses. While combined salt-heat stress effects have been studied in crop species, their impact on the model actinorhizal plant, Casuarina glauca, has not yet been fully addressed. The effect of single salt (400 mM NaCl) and heat (control at 26/22 °C, supra optimal temperatures at 35/22 °C and 45/22 °C day/night) conditions on C. glauca branchlets was characterised at the physiological level, and stress-induced metabolite changes were characterised by mass spectrometry-based metabolomics. C. glauca could withstand single salt and heat conditions. However, the harshest stress condition (400 mM NaCl, 45 °C) revealed photosynthetic impairments due to mesophyll and membrane permeability limitations as well as major stress-specific differential responses in C and N metabolism. The increased activity of enzymatic ROS scavengers was, however, revealed to be sufficient to control the plant oxidative status. Although C. glauca could tolerate single salt and heat stresses, their negative interaction enhanced the effects of salt stress. Results demonstrated that C. glauca responses to combined salt-heat stress could be explained as a sum of the responses from each single applied stress.