Salt Stress Inhibits Photosynthesis and Destroys Chloroplast Structure by Downregulating Chloroplast Development-Related Genes in Robinia pseudoacacia Seedlings

Transcriptional Profiling to Assess the Effects of Biological Stimulant Atlanticell Micomix on Tomato Seedlings Under Salt Stress

Recent environmental changes in the Mediterranean region, attributable to anthropogenic climate change, present a substantial challenge to the adaptive evaluation of crops and the development of novel improvement strategies. In this study, we established a hydroponic tomato cultivation protocol under in vitro conditions to analyze the transcriptomic profile of seedlings exposed to salinity stress. The study also examined the impact of Atlanticell Micomix, a biological stimulant derived from a mixture of mycorrhizal microorganisms and rhizobacteria, on plant growth and development under standard conditions and in response to moderate salinity. Our transcriptomic analysis indicated a differential effect of biostimulant inoculation compared to the effect induced by salinity stress, involving genes such as GOX3 or DIR1, which are associated with the plant's defense response to adverse conditions. In addition, the presence of a cross-regulatory module between jasmonic acid and auxin, involving potential orthologs of IAA29 and JAZ, was proposed. The application of the biostimulant demonstrated a potential priming effect on the tomato seedlings, which might be useful in reversing the transcriptomic effects caused by salt stress. A comprehensive analysis of the pathways differentially affected by the treatments facilitates further investigation into the mechanisms underlying these effects.

Role of calcium acetate in promoting Vibrio campbellii bioluminescence and alleviating salinity stress in Episcia cupreata

This study examines the role of calcium in regulating the bioluminescence of Vibrio campbellii PSU5986 and its potential to alleviate salt stress in plants, which has implications for developing light-emitting plants (LEPs). The effects of organic calcium acetate (C₄H₆CaO₄) were compared to inorganic calcium chloride (CaCl₂) and skim milk regarding their impact on bacterial bioluminescence and plant physiology. While skim milk induced the highest initial luminescence, both C₄H₆CaO₄ and CaCl₂ prolonged light emission for over 16 h. Notably, C₄H₆CaO₄ prevented leaf shrinkage, a condition observed with inorganic salts after 24 h. Periodic supplementation of C₄H₆CaO₄ (every 6 h) improved bacterial immobilization and colonization, extending luminescence over 4 cycles (24 h). Bacterial enumeration revealed colonization densities of approximately 6.82 × 106 CFU cm⁻2 within leaf tissues and 5.22 × 1011 CFU cm⁻2 on the leaf surface. Quantitative PCR analysis indicated that luxG exhibited significantly higher copy numbers than luxA and luxC, highlighting its critical role in bioluminescence through flavin reductase activity. Additionally, C₄H₆CaO₄ reduced salt-induced oxidative stress by increasing chlorophyll levels while decreasing carotenoid (40.00%), anthocyanin (36.94%), proline (14.13%), and malondialdehyde (21.84%) accumulation compared to NaCl-treated plants. These findings emphasize the potential of C₄H₆CaO₄ to sustain bacterial luminescence and enhance plant resilience, contributing to the advancement of LEP technology as a sustainable bioenergy alternative.

Ameliorative effects of SL on tolerance to salt stress on pepper (Capsicum annuum L.) plants

Salinity is one of the most important problems that threaten agricultural production, especially in arid and semiarid areas. Strigolactones (SLs) are important in providing tolerance to various abiotic stresses in plants. The study was carried out in a hydroponic system to determine the effects of external GR24 (were applied as a foliar spray; 0, 10, and 20 μM) applications at different doses on plant growth and some physiological, biochemical, and gene expression in two pepper genotype (Yalova and Maraş) grown under salt stress (0 and 100 mM NaCl). Plants were harvested and measured 10 days after the NaCl treatments. At the end of the research, it was determined that salt stress negatively affected plant growth in both genotype. Still, SL applications positively affected plant development both under normal and salt stress. While salt stress increased the amount of hydrogen peroxide (H2O2) and malondialdehyde (MDA), SL application caused a decrease in these parameters. Salt stress negatively affected the amount of chlorophyll and photosynthetic properties in both genotype, whereas SL applications mitigated this negative effect. SL applications caused a significant increase in antioxidant enzyme activities under both normal and salt stress conditions. SL content, which decreased with salt stress, increased with exogenous SL application. The content of other plant nutrients except sodium (Na) and chloride (Cl) decreased significantly in pepper seedlings grown under salt stress. External SL applications increased the uptake of these nutrients, especially under salt stress. In addition, the expression levels of CIPK3, CBL2, CCD7, DMAX2, PsbA, PsbB, PsbP1, TIP1;2, TIP5;1, SOS1, SOS2 and HKT2;2 genes were investigated in this study. It was observed that the expression levels of CCD7, DMAX2, SOS1, SOS2, and HKT2;2 genes increased with salinity stress, especially in the Maraş genotype, while SL applications decreased these expression levels. In the study, it was determined that especially exogenous 20 μM SL application could significantly reduce the negative effects of salt stress in pepper.

Melatonin Alleviates Photosynthetic Injury in Tomato Seedlings Subjected to Salt Stress via OJIP Chlorophyll Fluorescence Kinetics

The tomato is among the crops with the most extensive cultivated area and greatest consumption in our nation; nonetheless, secondary salinization of facility soil significantly hinders the sustainable growth of facility agriculture. Melatonin (MT), as an innovative plant growth regulator, is essential in stress responses. This research used a hydroponic setup to replicate saline stress conditions. Different endogenous levels of melatonin (MT) were established by foliar spraying of 100 μmol·L-1 MT, the MT synthesis inhibitor p-CPA (100 μmol·L-1), and a combination of p-CPA and MT, to investigate the mechanism by which MT mitigates the effects of salt stress on the photosynthetic efficiency of tomato seedlings. Results indicated that after six days of salt stress, the endogenous MT content in tomato seedlings drastically decreased, with declines in the net photosynthetic rate and photosystem performance indices (PItotal and PIabs). The OJIP fluorescence curve exhibited distortion, characterized by anomalous K-band and L-band manifestations. Exogenous MT dramatically enhanced the gene (TrpDC, T5H, SNAcT, and AcSNMT) expression of critical enzymes in MT synthesis, therefore boosting the level of endogenous MT. The application of MT enhanced the photosynthetic parameters. MT treatment decreased the fluorescence intensities of the J-phase and I-phase in the OJIP curve under salt stress, attenuated the irregularities in the K-band and L-band performance, and concurrently enhanced quantum yield and energy partitioning ratios. It specifically elevated φPo, φEo, and ψo, while decreasing φDo. The therapy enhanced parameters of both the membrane model (ABS/RC, DIo/RC, ETo/RC, and TRo/RC) and leaf model (ABS/CSm, TRo/CSm, ETo/CSm, and DIo/CSm). Conversely, the injection of exogenous p-CPA exacerbated salt stress-related damage to the photosystem of tomato seedlings and diminished the beneficial effects of MT. The findings suggest that exogenous MT mitigates salt stress-induced photoinhibition by (1) modulating endogenous MT concentrations, (2) augmenting PSII reaction center functionality, (3) safeguarding the oxygen-evolving complex (OEC), (4) reinstating PSI redox potential, (5) facilitating photosynthetic electron transport, and (6) optimizing energy absorption and dissipation. As a result, MT markedly enhanced photochemical performance and facilitated development and salt stress resilience in tomato seedlings.

The relationships between photochemical reflectance index (PRI) and photosynthetic status in radish species differing in salinity tolerance

Since photosynthesis is highly sensitive to salinity stress, remote sensing of photosynthetic status is useful for detecting salinity stress during the selection and breeding of salinity-tolerant plants. To do so, photochemical reflectance index (PRI) is a potential measure to detect conversion of the xanthophyll cycle in photosystem II. Raphanus sativus var. raphanistroides is a wild radish species closely related to domesticated radish, and is distributed throughout the coastal regions of Japan, where it is thought to be salt tolerant. In this study, we raised wild and domesticated radishes under various salt conditions and assessed growth, photosynthetic status, and PRI. When grown at mild salt stress (50 mM NaCl), wild radish leaves showed photosynthetic activity levels comparable to control plants, whereas the photosynthetic activity of domesticated radish was suppressed. This result suggests that wild radishes are more salt-tolerant than domesticated radishes. Although photosynthetic rate and the photochemical quantum yield were significantly correlated with PRI in both species, the PRI resolution was insufficient to distinguish differences in salt tolerance between wild and domesticated radish. Wild radish had a lower maximum quantum yield (Fv/Fm) when grown under moderate salt stress (200 mM NaCl), suggesting chronic photoinhibition. The relationship between non-photochemical quenching (NPQ) and PRI was significant when leaves with chronic photoinhibition were eliminated but this relationship was not significant when they were included. In contrast, the relationship between photosynthesis and PRI was significant regardless of whether leaves displayed chronic photoinhibition or not. We conclude that PRI is useful to detect relatively large reductions in photosynthetic rate under salinity stress, and that care should be taken to evaluate NPQ from PRI.

Exogenous 2,4-Epibrassinolide Alleviates Alkaline Stress in Cucumber by Modulating Photosynthetic Performance

Brassinosteroids (BRs) are recognized for their ability to enhance plant salt tolerance. While considerable research has focused on their effects under neutral salt conditions, the mechanisms through which BRs regulate photosynthesis under alkaline salt stress are less well understood. This study investigates these mechanisms, examining plant growth, photosynthetic electron transport, gas exchange parameters, Calvin cycle dynamics, and the expression of key antioxidant and Calvin cycle genes under alkaline stress conditions induced by NaHCO3. The findings indicate that NaHCO3 stress substantially impairs cucumber growth and photosynthesis, significantly reducing chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), antenna conversion efficiency (Fv'/Fm'), and photochemical quenching coefficient (qP). This disruption suggests a severe dysregulation of the photosynthetic electron transport system, impairing electron transfer from photosystem II (PSII) to photosystem I (PSI) and subsequently the Calvin cycle. Application of exogenous 24-epibrassinolide (EBR) alleviated these effects, reducing leaf chlorosis and growth inhibition and significantly enhancing the expression of key genes within the antioxidant system (AsA-GSH cycle) and the Calvin cycle. This intervention also led to a reduction in reactive oxygen species (ROS) accumulation and improved photosynthetic performance, as evidenced by enhancements in Pn, Gs, E, Fv/Fm, ΦPSII, Fv'/Fm', and qP. Moreover, NaHCO3 stress hindered chlorophyll synthesis, primarily by blocking the conversion from porphobilinogen (PBG) to uroporphyrinogen III (UroIII) and by increasing chlorophyllase (Chlase) and decreasing porphobilinogen deaminase (PBGD) activity. Exogenous EBR countered these effects by enhancing PBGD activity and reducing Chlase activity, thereby increasing chlorophyll content under stress conditions. In summary, EBR markedly mitigated the adverse effects of alkaline stress on cucumber leaf photosynthesis by stabilizing the photosynthetic electron transport system, accelerating photosynthetic electron transport, and promoting the Calvin cycle. This study provides valuable insights into the regulatory roles of BRs in enhancing plant resilience to alkaline stress.

Effects of Drought Stress at the Booting Stage on Leaf Physiological Characteristics and Yield of Rice

Drought stress is a major environmental constraint that limits rice (Oryza sativa L.) production worldwide. In this study, we investigated the effects of drought stress at the booting stage on rice leaf physiological characteristics and yield. The results showed that drought stress would lead to a significant decrease in chlorophyll content and photosynthesis in rice leaves, which would affect rice yield. Three different rice varieties were used in this study, namely Hanyou73 (HY73), Huanghuazhan (HHZ), and IRAT109. Under drought stress, the chlorophyll content of all cultivars decreased significantly: 11.1% and 32.2% decreases in chlorophyll a and chlorophyll b in HHZ cultivars, 14.1% and 28.5% decreases in IRAT109 cultivars, and 22.9% and 18.6% decreases in HY73 cultivars, respectively. In addition, drought stress also led to a significant decrease in leaf water potential, a significant increase in antioxidant enzyme activity, and an increase in malondialdehyde (MDA) content, suggesting that rice activated a defense mechanism to cope with drought-induced oxidative stress. This study also found that drought stress significantly reduced the net photosynthetic rate and stomatal conductance of rice, which, in turn, affected the yield of rice. Under drought stress, the yield of the HHZ cultivars decreased most significantly, reaching 30.2%, while the yields of IRAT109 and HY73 cultivars decreased by 13.0% and 18.2%, respectively. The analysis of yield composition showed that the number of grains per panicle, seed-setting rate, and 1000-grain weight were the key factors affecting yield formation. A correlation analysis showed that there was a significant positive correlation between yield and net photosynthetic rate, stomatal conductance, chla/chlb ratio, Rubisco activity, and Fv/Fm, but there was a negative correlation with MDA and non-photochemical quenching (NPQ). In summary, the effects of drought stress on rice yield are multifaceted, involving changes in multiple agronomic traits. The results highlight the importance of selecting and nurturing rice varieties with a high drought tolerance, which should have efficient antioxidant systems and high photosynthetic efficiency. Future research should focus on the genetic mechanisms of these physiological responses in order to develop molecular markers to assist in the breeding of drought-tolerant rice varieties.

How to survive on Mediterranean coastal cliffs: tolerance to seawater in early life-cycle stages in Brassica incana Ten. (Brassicaceae)

Mediterranean coastal cliffs are reservoirs of plant biodiversity, hosting vulnerable plant species particularly exposed to the risk of local extinction due to extreme abiotic conditions and climate changes. Therefore, studies aiming to understand the tolerance of cliff plant species to abiotic stresses are important to predict their long-time persistence or to highlight inherent threats. We used an integrative approach including anatomical, physiological and phenotypic analyses on (a) seeds, (b) cotyledons of seedlings; and (c) young plants to assess whether the cliff species Brassica incana, can tolerate exposure to different seawater (SW: 25%, 50% and 100%) concentrations during the early stages of its life cycle. Seeds could germinate when exposed to up to 50% SW. Seeds did not germinate in 100% SW, but could resume germination after washing with freshwater. Seed germination rate also decreased with increasing SW concentration. Exposure to SW decreased stomatal size and stomatal index of cotyledons and caused long-lasting and severe damage to the photochemical reactions of photosynthesis. Photochemistry was also sensitive to SW in young plants, but the effect was lower than in cotyledons. This may involve a remodulation of chloroplast dimensions and activation of cellular metabolism. However, photochemical reactions limited photosynthesis at100% SW even after recovery from SW exposure. Our data show that B. incana has strong tolerance to seawater and shows clear signs of halophytic adaptation. Whilst seeds and juvenile plants are able to withstand SW, the seedling stage appears to be more sensitive.

Physiological adaptation of Cyperus esculentus L. seedlings to varying concentrations of saline-alkaline stress: Insights from photosynthetic performance

Soil salinization effects plant photosynthesis in a number of global ecosystems. In this study, photosynthetic and physiological parameters were used to elucidate the impacts of saline-alkaline stress on Cyperus esculentus L. (C. esculentus) seedling photosynthesis. The results demonstrate that salt stress, alkali stress and mixed salt and alkali stress treatments all have similar bell-shaped influences on photosynthesis. At low concentrations (0-100 mmol L-1), saline-alkaline stress promoted net photosynthetic rate, transpiration rate and water use efficiency in C. esculentus. However, as the treatments increased in intensity (100-200 mmol L-1), plant photosynthetic parameters began to decline. We interpreted this as the capacity of C. esculentus to improve osmoregulatory capacity in low saline-alkaline stress treatments by accumulating photosynthetic pigment, proline and malondialdehyde to counterbalance the induced stress - an adaptive mechanism that failed once concentrations reached a critical threshold (100 mmol L-1). Stomatal conductance, maximum photosynthetic rate and actual photosynthetic rate all decreased with increasing concentration of the stress treatments, and intercellular carbon dioxide showed a decreasing and then increasing trend. These results indicated that when the saline-alkaline stress concentrations were low, C. esculentus seedlings showed obvious adaptive ability, but when the concentration increased further, the physiological processes of C. esculentus seedlings were significantly affected, with an obvious decrease in photosynthetic efficiency. This study provides a new understanding of the photosynthetic adaptation strategies of C. esculentus seedlings to varying concentrations of saline-alkaline stress.

Comparative Chloroplast Genomes Analysis Provided Adaptive Evolution Insights in Medicago ruthenica

A perennial leguminous forage, Medicago ruthenica has outstanding tolerance to abiotic stresses. The genome of Medicago ruthenica is large and has a complex genetic background, making it challenging to accurately determine genetic information. However, the chloroplast genome is widely used for researching issues related to evolution, genetic diversity, and other studies. To better understand its chloroplast characteristics and adaptive evolution, chloroplast genomes of 61 Medicago ruthenica were assembled (including 16 cultivated Medicago ruthenica germplasm and 45 wild Medicago ruthenica germplasm). These were used to construct the pan-chloroplast genome of Medicago ruthenica, and the chloroplast genomes of cultivated and wild Medicago ruthenica were compared and analyzed. Phylogenetic and haplotype analyses revealed two main clades of 61 Medicago ruthenica germplasm chloroplast genomes, distributed in eastern and western regions. Meanwhile, based on chloroplast variation information, 61 Medicago ruthenica germplasm can be divided into three genetic groups. Unlike the phylogenetic tree constructed from the chloroplast genome, a new intermediate group has been identified, mainly consisting of samples from the eastern region of Inner Mongolia, Shanxi Province, and Hebei Province. Transcriptomic analysis showed that 29 genes were upregulated and three genes were downregulated. The analysis of these genes mainly focuses on enhancing plant resilience and adapting adversity by stabilizing the photosystem structure and promoting protein synthesis. Additionally, in the analysis of adaptive evolution, the accD, clpP and ycf1 genes showed higher average Ka/Ks ratios and exhibited significant nucleotide diversity, indicating that these genes are strongly positively selected. The editing efficiency of the ycf1 and clpP genes significantly increases under abiotic stress, which may positively contribute to plant adaptation to the environment. In conclusion, the construction and comparative analysis of the complete chloroplast genomes of 61 Medicago ruthenica germplasm from different regions not only revealed new insights into the genetic variation and phylogenetic relationships of Medicago ruthenica germplasm, but also highlighted the importance of chloroplast transcriptome analysis in elucidating the model of chloroplast responses to abiotic stress. These provide valuable information for further research on the adaptive evolution of Medicago ruthenica.

Improving the performance of the photosynthetic apparatus of Citrus sinensis with the use of chitosan-selenium nanocomposite (CS + Se NPs) under salinity stress

BACKGROUND

Abiotic stress, such as salinity, affects the photosynthetic apparatus of plants. It is reported that the use of selenium nanoparticles (Se NPs), and biochemical compounds such as chitosan (CS) increase the tolerance of plants to stress conditions. Therefore, this study aimed to elucidate the potential of Se NPs, CS, and their composite (CS + Se NPs) in improving the photosynthetic apparatus of C. sinensis under salt stress in greenhouse conditions. The grafted seedlings of C. sinensis cv. Valencia after adapting to the greenhouse condition, were imposed with 0, 50, and 100 mM NaCl. After two weeks, the plants were foliar sprayed with distilled water (control), CS (0.1% w/v), Se NPs (20 mg L- 1), and CS + Se NPs (10 and 20 mg L- 1). Three months after treatment, the levels of photosynthetic pigments, leaf gas exchange, and chlorophyll fluorescence in the treated plants were evaluated.

RESULTS

Under salinity stress, total chlorophyll, carotenoid, and SPAD values decreased by 31%, 48%, and 28% respectively, and Fv/Fm also decreased compared to the control, while the ratio of absorption flux (ABS), dissipated energy flux (DI0) and maximal trapping rate of PSII (TR0) to RC (a measure of PSII apparent antenna size) were increased. Under moderate (50 mM NaCl) and intense (100 mM NaCl) salinity stress, the application of CS + Se NPs significantly increased the levels of photosynthetic pigments and the Fv/Fm value compared to plants treated with distilled water.

CONCLUSIONS

It may be inferred that foliar treatment with CS + Se NPs can sustain the photosynthetic ability of C. sinensis under salinity stress and minimize its deleterious effects on photosynthesis.

Sensitivity and responses of chloroplasts to salt stress in plants

Chloroplast, the site for photosynthesis and various biochemical reactions, is subject to many environmental stresses including salt stress, which affects chloroplast structure, photosynthetic processes, osmotic balance, ROS homeostasis, and so on. The maintenance of normal chloroplast function is essential for the survival of plants. Plants have developed different mechanisms to cope with salt-induced toxicity on chloroplasts to ensure the normal function of chloroplasts. The salt tolerance mechanism is complex and varies with plant species, so many aspects of these mechanisms are not entirely clear yet. In this review, we explore the effect of salinity on chloroplast structure and function, and discuss the adaptive mechanisms by which chloroplasts respond to salt stress. Understanding the sensitivity and responses of chloroplasts to salt stress will help us understand the important role of chloroplasts in plant salt stress adaptation and lay the foundation for enhancing plant salt tolerance.

Circadian-based approach for improving physiological, phytochemical and chloroplast proteome in Spinacia oleracea under salinity stress and light emitting diodes

Salt stress is a recognized annihilating abiotic stress that has a significant impact on agricultural and horticulture crop productivity. Plant development faces three distinct dangers as a result of salt stress: oxidative stress, osmotic stress, and ionic toxicity. It has been shown that plants can forecast diurnal patterns using the circadian clock; moreover, they can manage their defensive mechanism for the detoxification of reactive oxygen species (ROS). Circadian rhythmicity in gene expression assembles transcription and translation feedback networks to govern plant shape, physiology, cellular and molecular activities. Both external and internal variables influence the systemic rhythm via input routes. The Malav Jyoti (MJ) and Delhi Green (DG) genotypes of spinach (Spinacia oleracea) were grown in the plant growth chamber. The chamber had an optimized temperature of 25 °C and humidity of 65% containing light emitting diode (LED) having Red: Blue: white (one side) and White fluorescent (other side) under salinity stress. The samples were collected on the basis of 4 h intervals of circadian hours (0 h, 4 h, 8 h and 12 h) during Day-10 and Day-20 of salt treatments. Under salt stress, the circadian and light-emitting diode-based strategy had a substantial influence on spinach's anti-oxidative responses, stomatal movement, CO2 assimilation, PS-I and II efficiency, phytochrome pigment efficiency, and photosynthesis. Based on the findings of the free radical scavenging enzyme tests, the photoperiodic hours for the proteome analysis were set to 11 am and 3 pm on Day-20. When compared to white fluorescent, this study found that LED has the capacity to influence the entrainment cues of the circadian clock in the cultivation of salt-sensitive spinach genotypes. According to our findings, changing the cellular scavenging mechanism and chloroplast proteome has increased the survival rate of spinach genotypes under LED when compared to white fluorescent.

Physiological and biochemical effects of biochar nanoparticles on spinach exposed to salinity and drought stresses

The utilization of nanobiochar in agricultural practices has garnered substantial interest owing to its promising potential. Its nano-size particles possess an enhanced ability to infiltrate plant cells, potentially instigating biochemical and physiological responses that augment stress tolerance. In our study, we aimed to assess the impact and extent of exogenously applied nanobiochar on the growth dynamics and antioxidative responses in Spinacia oleracea L. (spinach) plants subjected to salt stress (50 mM NaCl) and drought stress (maintained at 60% field capacity) compared with respective controls (0 mM NaCl and 100% field capacity). Following a 15-day exposure to stress conditions, nanobiochar solution (at concentrations of 0, 1, 3, and 5% w/v) was sprayed on spinach plants at weekly intervals (at 14, 21, and 28 days after sowing). The foliar application of nanobiochar markedly improved biomass, net assimilation rate, leaf area, and various other growth parameters under drought and salinity stress conditions. Notably, the application of 3% nanobiochar caused the most significant enhancement in growth traits, photosynthetic pigments, and nutrient content, indicating its efficiency in directly supplying nutrients to the foliage. Furthermore, under drought stress conditions, the application of 3% nanobiochar elicited a notable 62% increase in catalase activity, a two-fold rise in peroxidase activity, and a 128% increase in superoxide dismutase activity compared to the control (without nanobiochar). Additionally, nanobiochar application enhanced membrane stability, evidenced by reduced lipid peroxidation and electrolyte leakage. The foliar application of 3% nanobiochar was found as a promising strategy to significantly enhance spinach growth parameters, nutrient assimilation, and antioxidative defense mechanisms, particularly under conditions of drought and salinity stress.

Thirteen complete chloroplast genomes of the costaceae family: insights into genome structure, selective pressure and phylogenetic relationships

BACKGROUND

Costaceae, commonly known as the spiral ginger family, consists of approximately 120 species distributed in the tropical regions of South America, Africa, and Southeast Asia, of which some species have important ornamental, medicinal and ecological values. Previous studies on the phylogenetic and taxonomic of Costaceae by using nuclear internal transcribed spacer (ITS) and chloroplast genome fragments data had low resolutions. Additionally, the structures, variations and molecular evolution of complete chloroplast genomes in Costaceae still remain unclear. Herein, a total of 13 complete chloroplast genomes of Costaceae including 8 newly sequenced and 5 from the NCBI GenBank database, representing all three distribution regions of this family, were comprehensively analyzed for comparative genomics and phylogenetic relationships.

RESULT

The 13 complete chloroplast genomes of Costaceae possessed typical quadripartite structures with lengths from 166,360 to 168,966 bp, comprising a large single copy (LSC, 90,802 - 92,189 bp), a small single copy (SSC, 18,363 - 20,124 bp) and a pair of inverted repeats (IRs, 27,982 - 29,203 bp). These genomes coded 111 - 113 different genes, including 79 protein-coding genes, 4 rRNA genes and 28 - 30 tRNAs genes. The gene orders, gene contents, amino acid frequencies and codon usage within Costaceae were highly conservative, but several variations in intron loss, long repeats, simple sequence repeats (SSRs) and gene expansion on the IR/SC boundaries were also found among these 13 genomes. Comparative genomics within Costaceae identified five highly divergent regions including ndhF, ycf1-D2, ccsA-ndhD, rps15-ycf1-D2 and rpl16-exon2-rpl16-exon1. Five combined DNA regions (ycf1-D2 + ndhF, ccsA-ndhD + rps15-ycf1-D2, rps15-ycf1-D2 + rpl16-exon2-rpl16-exon1, ccsA-ndhD + rpl16-exon2-rpl16-exon1, and ccsA-ndhD + rps15-ycf1-D2 + rpl16-exon2-rpl16-exon1) could be used as potential markers for future phylogenetic analyses and species identification in Costaceae. Positive selection was found in eight protein-coding genes, including cemA, clpP, ndhA, ndhF, petB, psbD, rps12 and ycf1. Maximum likelihood and Bayesian phylogenetic trees using chloroplast genome sequences consistently revealed identical tree topologies with high supports between species of Costaceae. Three clades were divided within Costaceae, including the Asian clade, Costus clade and South American clade. Tapeinochilos was a sister of Hellenia, and Parahellenia was a sister to the cluster of Tapeinochilos + Hellenia with strong support in the Asian clade. The results of molecular dating showed that the crown age of Costaceae was about 30.5 Mya (95% HPD: 14.9 - 49.3 Mya), and then started to diverge into the Costus clade and Asian clade around 23.8 Mya (95% HPD: 10.1 - 41.5 Mya). The Asian clade diverged into Hellenia and Parahellenia at approximately 10.7 Mya (95% HPD: 3.5 - 25.1 Mya).

CONCLUSION

The complete chloroplast genomes can resolve the phylogenetic relationships of Costaceae and provide new insights into genome structures, variations and evolution. The identified DNA divergent regions would be useful for species identification and phylogenetic inference in Costaceae.

Transcriptomics and physiology reveal the mechanism of potassium indole-3-butyrate (IBAK) mediating rice resistance to salt stress

BACKGROUND

IBAK, as a plant growth regulator, has broad application prospects in improving crop resistance to abiotic stress.

RESULTS

In this study, the regulation mechanism of IBAK on rice was revealed by physiology and transcriptomics by spraying 80 mg·L-1 IBAK solution on rice leaves at the early jointing stage under salt stress. The results showed that spraying IBAK solution on leaves under salt stress could significantly increase K+ content, decrease Na+ content, increase net photosynthetic rate (Pn), and increase the activity of catalase (CAT) and the contents of glutathione (GSH) and soluble protein in rice leaves. Using IBAK under salt stress increased the expression of plant hormone signal transduction pathway-related genes LOC4332548 and LOC4330957, which may help rice to more effectively sense and respond to plant hormone signals and enhance resistance to salt stress. In addition, the photosynthesis pathway-related genes LOC4339270, LOC4327150, and LOC4346326 were upregulated after using IBAK under salt stress, and the upregulation of these genes may be beneficial to improve the efficiency of photosynthesis and increase the photosynthetic capacity of rice. Regarding starch and sucrose metabolism pathway, spraying IBAK on leaves could promote the expression of sucrose synthesis-related gene LOC4347800 and increase the expression of starch synthesis-related genes LOC4330709 and LOC4343010 under salt stress. Finally, IBAK spraying resulted in the upregulation of multiple 50 S and 30 S ribosomal protein genes in the ribosome pathway, which may increase protein synthesis, help maintain cell function, and promote rice growth and development.

CONCLUSION

The results of this study revealed the mechanism of IBAK mediating resistance to salt stress in rice.

Abiotic Stress Signaling and Responses in Plants

The responses of plants to stress factors are extremely elaborate [...].

How Does Zinc Improve Salinity Tolerance? Mechanisms and Future Prospects

Salinity stress (SS) is a serious abiotic stress and a major constraint to agricultural productivity across the globe. High SS negatively affects plant growth and yield by altering soil physio-chemical properties and plant physiological, biochemical, and molecular processes. The application of micronutrients is considered an important practice to mitigate the adverse effects of SS. Zinc (Zn) is an important nutrient that plays an imperative role in plant growth, and it could also help alleviate the effects of salt stress. Zn application improves seed germination, seedling growth, water uptake, plant water relations, nutrient uptake, and nutrient homeostasis, therefore improving plant performance and saline conditions. Zn application also protects the photosynthetic apparatus from salinity-induced oxidative stress and improves stomata movement, chlorophyll synthesis, carbon fixation, and osmolytes and hormone accumulation. Moreover, Zn application also increases the synthesis of secondary metabolites and the expression of stress responsive genes and stimulates antioxidant activities to counter the toxic effects of salt stress. Therefore, to better understand the role of Zn in plants under SS, we have discussed the various mechanisms by which Zn induces salinity tolerance in plants. We have also identified diverse research gaps that must be filled in future research programs. The present review article will fill the knowledge gaps on the role of Zn in mitigating salinity stress. This review will also help readers to learn more about the role of Zn and will provide new suggestions on how this knowledge can be used to develop salt tolerance in plants by using Zn.