Exogenous Hemin alleviates NaCl stress by promoting photosynthesis and carbon metabolism in rice seedlings

Effects of exogenous Uniconazole (S3307) on oxidative damage and carbon metabolism of rice under salt stress

BACKGROUND

Salt stress significantly suppresses rice growth. Uniconazole (S3307) is recognized for its potential to enhance plant stress tolerance. Nevertheless, the mechanisms through which S3307 induces salt tolerance in rice by modulating the carbon metabolism pathway are not fully understood. In this study, at the one-leaf-one-heart stage, the foliage of rice HD961 and 9311 was treated with 10 mg·L- 1 S3307, followed by a 0.6% (102.56 mmol·L- 1) NaCl treatment 24 h later.

RESULTS

The results demonstrated that salt stress markedly suppressed the growth of rice aboveground and underground, reduced the net photosynthetic rate (Pn), and ultimately led to a decline in yield. However, salt stress increased the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) and enhanced sucrose metabolism simultaneously of rice leaves. However, compared to salt stress, foliar spraying of S3307 under salt stress increased rice biomass accumulation, enhanced photosynthetic efficiency, reduced malondialdehyde (MDA) content, and further enhanced the activities of superoxide dismutase (SOD), POD, CAT, and APX. Meanwhile, the application of S3307 effectively further promoted the accumulation of sucrose, glucose, and soluble sugar (SS) in rice leaves under salt stress. It also enhanced the activities of key enzymes in glycolysis, namely hexokinase (HK) and pyruvate kinase (PK), and facilitated the accumulation of α-ketoglutaric acid (α-KG), citric acid (CA), and pyruvate (PA). Meanwhile, it increased the effective panicle number (EPN), grains per panicle, yield per panicle and theoretical yield of rice.

CONCLUSION

Therefore, S3307 can mitigate the damage caused by salt stress and enhance yield and rice resistance by improving photosynthetic characteristics, strengthening the antioxidant system, and promoting physiological activities in carbon metabolism pathways such as Carbohydrate, glycolysis (EMP) and the tricarboxylic acid (TCA) cycle.

Prohexadione Calcium Improves Rice Yield Under Salt Stress by Regulating Source-Sink Relationships During the Filling Period

Salt stress is an important factor affecting the growth and development of rice, and prohexadione calcium (Pro-Ca) plays an important role in alleviating rice salt stress and improving rice yield. However, there are few studies on how Pro-Ca improves rice yield under salt stress by regulating the source-sink metabolism. In this study, we used Guanghong 3 (salt-tolerant variety) and Huanghuazhan (salt-sensitive variety) as experimental materials to investigate the dynamic changes in the synthesis and partitioning of nonstructural carbohydrates among source-sink, the dynamic changes in related enzyme activities, the effects of the source-sink metabolism on yield in rice under salt stress and the effect of Pro-Ca during the filling period. The results of this study showed that Pro-Ca improved photosynthetic efficiency by increasing leaf photosynthetic gas exchange parameters and other stomatal factors on the one hand and, on the other hand, promoted sugar catabolism and reduced sugar synthesis by increasing leaf sucrose synthase activity and decreasing sucrose phosphate synthase activity, alleviating the inhibitory effect of high concentrations of sugars in the leaves on photosynthesis. Meanwhile, Pro-Ca promotes the transport of sugars from source (leaves) to sink (seeds), increases the sugar content in the seeds, and promotes starch synthesis in the seeds by increasing starch phosphorylase, which promotes seed filling, thus increasing the number of solid grains on the primary and secondary branches of the panicle in rice, increasing the 1000-grain weight, and ultimately increasing the seed setting rate and yield. These results indicated that Pro-Ca alleviated the inhibitory effect of salt stress on rice leaf photosynthesis through stomatal and non-stomatal factors. Meanwhile, Pro-Ca promotes the transport of rice sugars from source to sink under salt stress, regulates the source-sink relationship during the filling period of rice, promotes starch synthesis, and ultimately improves rice yield.

RNA-seq analysis and lipid profiling reveal the competitive regulation of starch and triacylglycerol synthesis during grain-filling stage in tetraploid rice

Autotetraploid rice is a useful germplasm for polyploid rice breeding in improving nutritional values. Nevertheless, underlying mechanism of starch and lipid accumulation in tetraploid rice caryopsis remains largely unknown. Here, regulatory mode of starch and triacylglycerol (TAG) synthesis during grain-filling stage in diploid and tetraploid indica rice varieties 9311 was investigated. As a result, tetraploid rice exhibited the reduced starch (-13.22 %) and apparent amylose (-24.76 %) contents, increased the in vitro starch digestion percentage. Meanwhile, lipid detection and thin layer chromatography revealed an increase in fatty acids (+15.26 %) and TAG (+28.82 %) contents characterized by a significant increase in the mole ratio of C18:1 and the decrease of C16:0 and C18:2. Moreover, RNA-seq and functional analyses identified that OsAGPL1, encoding a rate-limiting enzyme involved in starch synthesis, was consistently down-regulated. Additionally, two TAG synthesis-associated genes OsSAD1 and OsFATB2 were up-regulated and down-regulated, respectively, which contributed to higher mole ratio of C18:1 and lower ratio of C16:0 in tetraploid rice caryopses. This study proposes a regulatory model of increased lipid and reduced starch synthesis during grain-filling stage and provides three candidate genes for genetic engineering in nutritional quality improvement of autotetraploid rice.

Effects of Exogenous Spermidine on Seed Germination and Physiological Metabolism of Rice Under NaCl Stress

Salt stress is one of the principal abiotic stresses limiting agricultural production and seriously inhibiting seed germination rates. This study selected the salt-tolerant rice variety HD961 and the salt-sensitive rice variety 9311 as experimental materials to investigate the physiological and metabolic effects of exogenous Spd seed priming on rice seeds and seedlings under NaCl stress. The experiment involved treating rice seeds with 0.1 mmol·L-1 Spd and then subjecting them to 100 mmol·L-1 NaCl stress for 24 h, with sampling for analysis at the 24 h and the four-leaf-one-heart stage. The results indicated that under NaCl stress, the rice's germination and vigor indices significantly decreased. However, exogenous Spd seed priming reduced the accumulation of malondialdehyde, enhanced the capacity for osmotic adjustment, and increased the amylase and antioxidant activity by 50.07% and 26.26%, respectively. Under NaCl stress, the morphological development of rice seedlings was markedly inhibited, whereas exogenous Spd seed priming improved the aboveground and belowground biomass of the rice under stress conditions, as well as the content of photosynthetic pigments. It also reduced the damage to seedlings from electrical conductivity, helped maintain ionic balance, and promoted the excretion of Na+ and Cl- and the absorption of K+ and Ca2+. In the salt-sensitive rice variety 9311, the soluble protein content increased by 15.12% compared to the salt-tolerant rice variety HD961, especially under 100 mmol·L-1 NaCl stress, when the effect of exogenous Spd seed priming was more pronounced. In summary, these findings might provide new research perspectives and strategies for improving the salt tolerance of rice under NaCl stress.

The varying responses of leaves and roots and the link between sugar metabolic genes and the SWEET family in Dendrobium officinale under salt stress

BACKGROUND

Dendrobium officinale Kimura et Migo is a perennial epiphytic herb in traditional Chinese medicine, showing remarkable resistance to salt stress. Water-soluble sugars serve as important osmoprotectants and play crucial roles in plant stress responses. Previous studies have primarily focused on sugar metabolism in individual tissues under stress, resulting in a limited understanding of the regulatory differences between tissues and the relationship between sugar metabolism and transport.

RESULTS

A variety of salt-responsive genes were identified through transcriptome analysis of D. officinale. GO and KEGG enrichment analyses revealed functional differences among the differentially expressed genes (DEGs) between leaves and roots. Expression analysis indicated that sugar metabolic genes and D. officinale Sugars Will Eventually be Exported Transporters (DoSWEETs) displayed distinct expression patterns in leaves and roots under salt stress. Most sugar metabolic genes were up-regulated in the leaves and down-regulated in the roots in response to salt, while DoSWEETs predominantly responded in the roots. Specifically, DoSWEET2a, 6a, 12a, 14, and 16 were confirmed via RT-qPCR. Additionally, positive correlations were observed between certain genes (scrK, INV, SUS) and DoSWEETs, with INV (LOC110096666) showing a strong positive correlation with all detected DoSWEETs in both leaves and roots.

CONCLUSIONS

Our findings not only illustrated the distinct responses of leaves and roots to salt stress, but also highlighted the relationship between sugar metabolic genes and DoSWEETs in adapting to such stress. This enhances our understanding of the differential responses of plant tissues to salt stress and identified candidate genes for salt-resistance breeding in D. officinale.

Potassium indole-3-butyric acid affects rice's adaptability to salt stress by regulating carbon metabolism, transcription factor genes expression, and biosynthesis of secondary metabolites

Soil salinity pollution is increasing worldwide, seriously affecting plant growth and crop production. Existing reports on how potassium indole-3-butyric acid (IBAK) regulates rice salt stress adaptation by affecting rice carbon metabolism, transcription factor (TF) genes expression, and biosynthesis of secondary metabolites still have limitations. In this study, an IBAK solution at 40 mg L-1 was sprayed on rice leaves at the seedling stage. The results showed that the IBAK application could promote shoot and root growth, decrease sucrose and fructose content, increase starch content, and enhance acid invertase (AI) and neutral invertase (NI) activity under salt stress, indicating altered carbon allocation. Furthermore, the expression of TF genes belonging to the ethylene responsive factor (ERF), WRKY, and basic helix-loop-helix (bHLH) families was influenced by IBAK. Many key genes (OsSSIIc, OsSHM1, and OsPPDKB) and metabolites (2-oxoglutaric acid, fumaric acid, and succinic acid) were upregulated in the carbon metabolism pathway. In addition, this study highlighted the role of IBAK in regulating the biosynthesis of secondary metabolites pathway, potentially contributing to rice stress adaptability. The results of this study can provide new sustainable development solutions for agricultural production.

Comparative transcriptome and coexpression network analysis revealed the regulatory mechanism of Astragalus cicer L. in response to salt stress

BACKGROUND

Astragalus cicer L. is a perennial rhizomatous legume forage known for its quality, high biomass yield, and strong tolerance to saline-alkaline soils. Soil salinization is a widespread environmental pressure. To use A. cicer L. more scientifically and environmentally in agriculture and ecosystems, it is highly important to study the molecular response mechanism of A. cicer L. to salt stress.

RESULTS

In this study, we used RNA-seq technology and weighted gene coexpression network analysis (WGCNA) were performed. The results showed 4 key modules were closely related to the physiological response of A. cicer. L. to salt stress. The differentially expressed genes (DEGs) of key modules were mapped into the KEGG database, and found that the most abundant pathways were the plant hormone signal transduction pathway and carbon metabolism pathway. The potential regulatory networks of the cytokinin signal transduction pathway, the ethylene signal transduction pathway, and carbon metabolism related pathways were constructed according to the expression pathways of the DEGs. Seven hub genes in the key modules were selected and distributed among these pathways. They may involved in the positive regulation of cytokinin signaling and carbon metabolism in plant leaves, but limited the positive expression of ethylene signaling. Thus endowing the plant with salt tolerance in the early stage of salt stress.

CONCLUSIONS

Based on the phenotypic and physiological responses of A. cicer L. to salt stress, this study constructed the gene coexpression network of potential regulation to salt stress in key modules, which provided a new reference for exploring the response mechanism of legumes to abiotic stress.

Integrative Analyses Reveal the Physiological and Molecular Role of Prohexadione Calcium in Regulating Salt Tolerance in Rice

Salinity stress severely restricts rice growth. Prohexadione calcium (Pro-Ca) modulation can effectively alleviate salt stress in rice. In this study, we explored the effects of Pro-Ca on enhancing salt tolerance in two rice varieties, IR29 and HD96-1. The results revealed that Pro-Ca markedly enhanced root and shoot morphological traits and improved plant biomass under salt stress. Chlorophyll a and b content were significantly increased, which improved photosynthetic capacity. Transcriptomic and metabolomic data showed that Pro-Ca significantly up-regulated the expression of genes involved in E3 ubiquitin ligases in IR29 and HD96-1 by 2.5-fold and 3-fold, respectively, thereby maintaining Na+ and K+ homeostasis by reducing Na+. Moreover, Pro-Ca treatment significantly down-regulated the expression of Lhcb1, Lhcb2, Lhcb3, Lhcb5, and Lhcb6 in IR29 under salt stress, which led to an increase in photosynthetic efficiency. Furthermore, salt stress + Pro-Ca significantly increased the A-AAR of IR29 and HD96-1 by 2.9-fold and 2.5-fold, respectively, and inhibited endogenous cytokinin synthesis and signal transduction, which promoted root growth. The current findings suggested that Pro-Ca effectively alleviated the harmful effects of salt stress on rice by maintaining abscisic acid content and by promoting oxylipin synthesis. This study provides a molecular basis for Pro-Ca to alleviate salt stress in rice.

An integration of physiology, transcriptomics, and proteomics reveals carbon and nitrogen metabolism responses in alfalfa (Medicago sativa L.) exposed to titanium dioxide nanoparticles

Nanoparticle (NP) pollution has negative impacts and is a major global environmental problem. However, the molecular response of alfalfa (Medicago sativa L.) to titanium dioxide nanoparticles (TiO2 NPs) is limited. Herein, the dual effects of TiO2 NPs (0-1000 mg L-1) on carbon (C) and nitrogen (N) metabolisms in alfalfa were investigated. The results showed that 500 mg L-1 TiO2 NPs (Ti-500) had the highest phytotoxicity in the C/N metabolizing enzymes; and it significantly increased total soluble sugar, starch, sucrose, and sucrose-phosphate synthase. Furthermore, obvious photosynthesis responses were found in alfalfa exposed to Ti-500. By contrast, 100 mg L-1 TiO2 NPs (Ti-100) enhanced N metabolizing enzymes. RNA-seq analyses showed 4265 and 2121 differentially expressed genes (DEGs) in Ti-100 and Ti-500, respectively. A total of 904 and 844 differentially expressed proteins (DEPs) were identified in Ti-100 and Ti-500, respectively. Through the physiological, transcriptional, and proteomic analyses, the DEGs and DEPs related to C/N metabolism, photosynthesis, chlorophyll synthesis, starch and sucrose metabolism, and C fixation in photosynthetic organisms were observed. Overall, TiO2 NPs at low doses improve photosynthesis and C/N regulation, but high doses can cause toxicity. It is valuable for the safe application of NPs in agriculture.

Integrated transcriptome and metabolome analysis of salinity tolerance in response to foliar application of choline chloride in rice (Oryza sativa L.)

Introduction

Salt stress is a major abiotic stress that affects crop growth and productivity. Choline Chloride (CC) has been shown to enhance salt tolerance in various crops, but the underlying molecular mechanisms in rice remain unclear.

Methods

To investigate the regulatory mechanism of CC-mediated salt tolerance in rice, we conducted morpho-physiological, metabolomic, and transcriptomic analyses on two rice varieties (WSY, salt-tolerant, and HHZ, salt-sensitive) treated with 500 mg·L-1 CC under 0.3% NaCl stress.

Results

Our results showed that foliar application of CC improved morpho-physiological parameters such as root traits, seedling height, seedling strength index, seedling fullness, leaf area, photosynthetic parameters, photosynthetic pigments, starch, and fructose content under salt stress, while decreasing soluble sugar, sucrose, and sucrose phosphate synthase levels. Transcriptomic analysis revealed that CC regulation combined with salt treatment induced changes in the expression of genes related to starch and sucrose metabolism, the citric acid cycle, carbon sequestration in photosynthetic organs, carbon metabolism, and photosynthetic antenna proteins in both rice varieties. Metabolomic analysis further supported these findings, indicating that photosynthesis, carbon metabolism, and carbon fixation pathways were crucial in CC-mediated salt tolerance.

Discussion

The combined transcriptomic and metabolomic data suggest that CC treatment enhances rice salt tolerance by activating distinct transcriptional cascades and phytohormone signaling, along with multiple antioxidants and unique metabolic pathways. These findings provide a basis for further understanding the mechanisms of metabolite synthesis and gene regulation induced by CC in rice in response to salt stress, and may inform strategies for improving crop resilience to salt stress.

Calcium signal regulated carbohydrate metabolism in wheat seedlings under salinity stress

This study aimed to explore the mechanism by which calcium (Ca) signal regulated carbohydrate metabolism and exogenous Ca alleviated salinity toxicity. Wheat seedlings were treated with sodium chloride (NaCl, 150 mM) alone or combined with 500 μM calcium chloride (CaCl2), lanthanum chloride (LaCl3) and/or ethylene glycol tetraacetic acid (EGTA) to primarily analyse carbohydrate starch and sucrose metabolism, as well as Ca signaling components. Treatment with NaCl, EGTA, or LaCl3 alone retarded wheat-seedling growth and decreased starch content accompanied by weakened ribulose-1,5-bisphosphate carboxylation/oxygenase (Rubisco) and Rubisco activase activities, as well as enhanced glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, alpha-amylase, and beta-amylase activities. However, it increased the sucrose level, up-regulated the sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities and TaSPS and TaSuSy expression together, but down-regulated the acid invertase (SA-Inv) and alkaline/neutral invertase (A/N-Inv) activities and TaSA-Inv and TaA/N-Inv expression. Except for unchanged A/N-Inv activities and TaA/N-Inv expression, adding CaCl2 effectively blocked the sodium salt-induced changes of these parameters, which was partially eliminated by EGTA or LaCl3 presence. Furthermore, NaCl treatment also significantly inhibited Ca-dependent protein kinases and Ca2+-ATPase activities and their gene expression in wheat leaves, which was effectively relieved by adding CaCl2. Taken together, CaCl2 application effectively alleviated the sodium salt-induced retardation of wheat-seedling growth by enhancing starch anabolism and sucrose catabolism, and intracellular Ca signal regulated the enzyme activities and gene expression of starch and sucrose metabolism in the leaves of sodium salt-stressed wheat seedlings.

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.

Regulatory effects of Hemin on prevention and rescue of salt stress in rapeseed (Brassica napus L.) seedlings

BACKGROUND

Salt stress severely restricts rapeseed growth and productivity. Hemin can effectively alleviate salt stress in plants. However, the regulatory effect of Hemin on rapeseed in salt stress is unclear. Here, we analyzed the response and remediation mechanism of Hemin application to rapeseed before and after 0.6% (m salt: m soil) NaCl stress. Experiment using two Brassica napus (AACC, 2n = 38) rapeseed varieties Huayouza 158R (moderately salt-tolerant) and Huayouza 62 (strongly salt-tolerant). To explore the best optional ways to improve salt stress resistance in rapeseed.

RESULTS

Our findings revealed that exogenous application of Hemin enhanced morph-physiological traits of rapeseed and significantly attenuate the inhibition of NaCl stress. Compared to Hemin (SH) treatment, Hemin (HS) significantly improved seedlings root length, seedlings height, stem diameter and accumulated more dry matter biomass under NaCl stress. Moreover, Hemin (HS) significantly improved photosynthetic efficiency, activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and decreased electrolyte leakage (EL) and malondialdehyde (MDA) content, thus resulting in the alleviation of oxidative membrane damage. Hemin (HS) showed better performance than Hemin (SH) under NaCl stress.

CONCLUSION

Hemin could effectively mitigate the adverse impacts of salt stress by regulating the morph-physiological, photosynthetic and antioxidants traits of rapeseed. This study may provide a basis for Hemin to regulate cultivated rapeseed salt tolerance and explore a better way to alleviate salt stress.

Carbon monoxide/heme oxygenase system in plant: Roles in abiotic stress response and crosstalk with other signals molecules

Carbon monoxide (CO) has been recognized as a crucial gasotransmitter mainly produced by heme oxygenase (HO)-catalyzed heme degradation in plant. Recent studies have shown that CO plays an important role in regulating growth and development of plant, as well as and responding to a variety of abiotic stresses. Meanwhile, many studies have reported on CO working in combination with other signal molecules to mitigate abiotic stress. Here, we presented a comprehensive overview of recent developments in which CO reduces plant damage caused by abiotic stresses. The regulation of antioxidant system, photosynthetic system, ion balance and transport are the main mechanisms of CO-alleviated abiotic stress. We also proposed and discussed the relationship between CO and other signal molecules, including nitric oxide (NO), hydrogen sulfide (H2S), hydrogen gas (H2), abscisic acid (ABA), indole 3-acetic acid (IAA), gibberellin (GA), cytokine (CTK), salicylic acid (SA), jasmonic acid (JA), hydrogen peroxide (H2O2) and calcium ion (Ca2+). Furthermore, the important role of HO genes in alleviating abiotic stress was also discussed. We proposed promising and new research directions for the study of plant CO, which can provide further insights on the role of CO in plant growth and development under abiotic stress.