Seedling Cold Tolerance Research Articles

Genetic variation in the aquaporin TONOPLAST INTRINSIC PROTEIN 4;3 modulates maize cold tolerance.

Cold stress is a major abiotic stress that threatens maize (Zea mays L.) production worldwide. Understanding the molecular mechanisms underlying cold tolerance is crucial for breeding resilient maize varieties. Tonoplast intrinsic proteins (TIPs) are a subfamily of aquaporins in plants. Here, we report that TIP family proteins are involved in maize cold tolerance. The expression of most TIP genes was responsive to cold stress. Overexpressing TIP2;1, TIP3;2 or TIP4;3 reduced the cold tolerance of maize seedlings, while loss-of-function mutants of TIP4;3 exhibited enhanced cold tolerance. Candidate gene-based association analysis revealed that a 328-bp transposon insertion in the promoter region of TIP4;3 was strongly associated with maize cold tolerance. This transposon insertion conferred cold tolerance by repressing TIP4;3 expression through increased methylation of its promoter region. Moreover, TIP4;3 was found to suppress stomatal closure and facilitate reactive oxygen species (ROS) accumulation under cold stress, thereby inhibiting the expression of cold-responsive genes, including DEHYDRATION-RESPONSIVE ELEMENT BINDING FACTOR 1 (DREB1) genes and a subset of peroxidase genes, ultimately attenuating maize cold tolerance. This study thus elucidates the mechanism underlying TIP-mediated cold tolerance and identifies a favourable TIP4;3 allele as a potential genetic resource for breeding cold-tolerant maize varieties.

Further enhancement of cold tolerance in rice seedlings by Piriformospora indica collaborating with plant growth-promoting bacteria: Evidence from the antioxidant defense, osmoregulation, photosynthesis, and related genes

As the global population continues to grow, so does the demand for food. However, cold stress due to global climate change greatly threatens the safe production of rice. Piriformospora indica plays a pivotal role as a functional microbiota in improving cold tolerance in rice. However, the addition of P. indica alone has a limited effect. In this study, an attempt was made to select plant growth-promoting bacteria (Agrobacterium rhizogenes and Bacillus subtilis) as helper bacteria to help P. indica function better and further enhance rice cold tolerance. Under cold stress, the co-addition of the three beneficial microorganisms significantly increased the biomass, photosynthetic performance indicators, osmoregulatory substance contents, and antioxidant enzyme activities of rice. P. indica and helper bacteria significantly reduced the cold stress-induced increases in malondialdehyde content and electrolyte leakage rate in rice leaves and triggered a substantial upregulation of cold-tolerant genes in rice. This suggests that P. indica and helper bacteria can synergistically improve the cold resistance of rice. The findings of the research offer a conceptual foundation and practical assistance for enhancing rice's resilience to cold temperatures.

Exogenous glucose irrigation alleviates cold stress by regulating soluble sugars, ABA and photosynthesis in melon seedlings

Melon (Cucumis melo L.) is an important economic crop and widely planted around the world. Cold stress severely limits its development and yield. Carbohydrates play multiple roles in plant cold tolerance. However, little is known in melon. Based on the metabolome analysis, a total of 635 metabolites were identified upon cold stress in melon seedlings. KEGG analysis shows that differential metabolites were mainly enriched in the glycolysis/gluconeogenesis pathway and pentose phosphate pathway, with glucose being one of the most prominent metabolites. To further investigate the role of glucose in cold tolerance of melon seedlings. We found that root irrigation was more effective than foliar spraying for exogenous glucose application, with optimal concentrations of 0.5% and 1% for cold-tolerant and cold-sensitive genotypes, respectively. Glucose irrigation mainly promoted soluble sugar accumulation to reduce cold damage in melon seedlings. For cold-sensitive genotype, only the sucrose content could be increased, while for cold-tolerant genotype, sucrose, fructose and glucose content could be simultaneously increased. Meanwhile, glucose irrigation recruited ABA not antioxidant enzyme system to cope with cold stress. Hence, glucose watering could improve the maximum photochemical efficiency of seedling photosystem II (Fv/Fm), alleviate physiological drought, reduce the accumulation of malondialdehyde, and accelerated the photosynthetic efficiency of melon seedlings. Based on coefficient of variation and principal component analysis, it was confirmed again that glucose irrigation did alter the strategies for withstanding cold stress and enhance the cold tolerance of melon seedlings. Thus, the results would provide a theoretical basis and feasible measures to protect melon seedings from cold damage.

Genome-wide association study and candidate gene identification for the cold tolerance at the seedling stage of rapeseed (Brassica napus L.)

Rapeseed (Brassica napus L.) is an important overwintering oilseed crop and suffers from severe cold stress during the seedling stage due to the increasingly delayed sowing in the Yangtze River Basin. However, the genetic basis underlying cold tolerance in rapeseed seedlings is not well understood. In this study, we observed the cold tolerance of 217 rapeseed accessions in the field and found a significant negative correlation between cold tolerance grades and malondialdehyde (MDA) contents. A genome-wide association study (GWAS) of cold tolerance grades Identified four significant loci in the genomic region of one MYB transcription factor BnaA8.MYB60. Furthermore, field accessions with BnaA8.MYB60Hap1 exhibited significantly higher cold tolerance and lower expression of BnaA8.MYB60 compared to the majority of accessions with BnaA8.MYB60Hap2. These results suggested that variations in the genomic sequences of BnaA8.MYB60 caused the divergence of gene expression levels and functions on cold tolerance in rapeseed seedlings. This study could provide the theoretical guidance for the breeding of cold-tolerant rapeseed varieties.

Aquaporin CmPIP2; 3 links H2O2 signal and antioxidation to modulate trehalose-induced cold tolerance in melon seedlings.

Cold stress severely restricts the growth and development of cold-sensitive crops. Trehalose (Tre), known as the 'sugar of life', plays key roles in regulating plant cold tolerance by triggering antioxidation. However, the relevant regulatory mechanism remains unclear. Here, we confirmed that Tre triggers apoplastic hydrogen peroxide (H2O2) production and thus plays key roles in improving the cold tolerance of melon (Cucumis melo var. makuwa Makino) seedlings. Moreover, Tre treatment can promote the transport of apoplastic H2O2 to the cytoplasm. This physiological process may depend on aquaporins. Further studies showed that a Tre-responsive plasma membrane intrinsic protein 2; 3 (CmPIP2; 3) had strong H2O2 transport function and that silencing CmPIP2; 3 significantly weakened apoplastic H2O2 transport and reduced the cold tolerance of melon seedlings. Yeast library and protein-DNA interaction technology were then used to screen two Tre-responsive transcription factors, abscisic acid responsive element (ABRE)-binding factor 2 (CmABF2) and abscisic acid responsive element (ABRE)-binding factor 3 (CmABF3), which can bind to the ABRE motif of the CmPIP2; 3 promoter and activate its expression. Silencing of CmABF2 and CmABF3 further dramatically increased the ratio of apoplastic H2O2/cytoplasm H2O2 and reduced the cold tolerance of melon seedlings. This study uncovered that Tre treatment induces CmABF2/3 to positively regulate CmPIP2; 3 expression. CmPIP2; 3 subsequently enhances the cold tolerance of melon seedlings by promoting the transport of apoplastic H2O2 into the cytoplasm for conducting redox signals and stimulating downstream antioxidation.

PHD17 acts as a target of miR1320 to negatively control cold tolerance via JA-activated signaling in rice

Plant Homeo Domain (PHD) proteins are involved in diverse biological processes during plant growth. However, the regulation of PHD genes on rice cold stress response remains largely unknown. Here, we reported that PHD17 negatively regulated cold tolerance in rice seedlings as a cleavage target of miR1320. PHD17 expression was greatly induced by cold stress, and was down-regulated by miR1320 overexpression and up-regulated by miR1320 knockdown. Through 5′RACE and dual luciferase assays, we found that miR1320 targeted and cleaved the 3′UTR region of PHD17. PHD17 was a nuclear-localized protein and acted as a transcriptional activator in yeast. PHD17 overexpression reduced cold tolerance of rice seedlings, while knockout of PHD17 increased cold tolerance, partially via the CBF cold signaling. By combining transcriptomic and physiological analyses, we demonstrated that PHD17 modulated ROS homeostasis and flavonoid accumulation under cold stress. K-means clustering analysis revealed that differentially expressed genes in PHD17 transgenic lines were significantly enriched in the jasmonic acid (JA) biosynthesis pathway, and expression of JA biosynthesis and signaling genes was verified to be affected by PHD17. Cold stress tests applied with MeJA or IBU (JA synthesis inhibitor) further suggested the involvement of PHD17 in JA-mediated cold signaling. Taken together, our results suggest that PHD17 acts downstream of miR1320 and negatively regulates cold tolerance of rice seedlings through JA-mediated signaling pathway.

Carbon nanoparticle exposure strengthens water-relation parameters by stimulating abscisic acid pathway and aquaporins genes in rice

Mechanism of action and molecular basis of positive growth effects including yield increase due to carbon nanoparticle (CNP) treatment in rice plants is dissected here. CNP at 500 -750 µg/mL were found to be the optimum dosages showing best seedling growth. CNP treatment resulted increase in stomata size, stomatal conductance and water use efficiency along with low relative humidity, decrease in stomata frequency and internal CO2 concentration. CNP-coupled with water uptake was found to be endocytosis mediated, although CNP uptake was not affected by endocytosis inhibitor application in roots. Genomic analysis resulted major involvement of ABA pathway and stomata size and frequency genes in Arabidopsis and rice. Elevated endogenous ABA in rice seedlings and flag leaves along with increased expression of ABA biosynthetic genes in Arabidopsis and rice AtNCED3, AtNCED6, OsNCED1 confirmed increased ABA synthesis. Negative regulators of ABA pathway, OsSNRK2 down-regulation and up-regulation of stomagen (OsEPFL9) reconfirmed ABA's involvement. CNP treatment exerted cold tolerance in seedlings and water stress tolerance in reproductive stage. CNP treatment under water withheld condition resulted water stress tolerance by maintaining lower stomatal conductance, transpiration rate and higher relative water content. Increased ABA (OsSNRK1, OsSNRK2) and aquaporin (OsPIP2–5 and OsPIP1–3) genes’ expressions could explain the better water stress tolerance in rice plants treated with CNP. Altogether, due to thermomorphogenesis, down-regulation of Phytochrome B transcript resulted altered the ABA pathway and stomatal distribution with size (Graphical Abstract). These changes resulted improved water relation parameters and water use efficiency (WUE) showing improvement in yield. Detailed mechanism of action of CNP in abiotic stress tolerance can be exploited using nano-agriculture at field level.

Shallow water seeding cultivation enhances cold tolerance in tobacco seedlings

Cold stress can impact plant biology at both the molecular and morphological levels. We cultivated two different types of tobacco seedlings using distinct seeding methods, observing significant differences in their cold tolerance at 4 °C. After 12 h cold stress, shallow water seeding cultivation treatment demonstrates a relatively good growth state with slight wilting of the leaves. Tobacco grown using the float system exhibited short, thick roots, while those cultivated through shallow water seeding had elongated roots with more tips and forks. After cold stress, the shallow water seeding cultivation treatment demonstrated higher antioxidant enzyme activity, and lower malondialdehyde (MDA) content.Transcriptome analysis was performed on the leaves of these tobacco seedlings at three stages of cold treatment (before cold stress, after cold stress, and after 3 days of recovery). Upon analyzing the raw data, we found that the shallow water seeding cultivation treatment was associated with significant functional enrichment of nicotinamide adenine dinucleotide (NAD) biosynthesis and NAD metabolism before cold stress, enrichment of functions related to the maintenance of cellular structure after cold stress, and substantial functional enrichment related to photosynthesis during the recovery period. Weighted gene co-expression network analysis (WGCNA) was conducted, identifying several hub genes that may contribute to the differences in cold tolerance between the two tobacco seedlings. Hub genes related to energy conversion were predominantly identified in shallow water seeding cultivation treatment during our analysis, surpassing findings in other areas. These include the AS gene, which controls the synthesis of NAD precursors, the PED1 gene, closely associated with fatty acid β-oxidation, and the RROP1 gene, related to ATP production.Overall, our study provides a valuable theoretical basis for exploring improved methods of cultivating tobacco seedlings. Through transcriptome sequencing technology, we have elucidated the differences in gene expression in different tobacco seedlings at three time points, identifying key genes affecting cold tolerance in tobacco and providing possibilities for future gene editing.

Coronatine-treated seedlings increase the tolerance of cotton to low-temperature stress

Coronatine, an analog of Jasmonic acid (JA), has been shown to enhance crop tolerance to abiotic stresses, including chilling stress. However, the underlying molecular mechanism remains largely unknown. In this study, we investigated the effect of Coronatine on cotton seedlings under low temperature using transcriptomic and metabolomics analysis. Twelve cDNA libraries from cotton seedlings were constructed, and pairwise comparisons revealed a total of 48,322 differentially expressed genes (DEGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified the involvement of these unigenes in various metabolic pathways, including Starch and sucrose metabolism, Sesquiterpenoid and triterpenoid biosynthesis, Phenylpropanoid biosynthesis, alpha-Linolenic acid metabolism, ABC transporters, and Plant hormone signal transduction. Additionally, substantial accumulations of jasmonates (JAs), abscisic acid and major cell wall metabolites were observed. Transcriptome analysis revealed differential expression of regulatory genes, and qRT-PCR analysis confirmed the expression patterns of 9 selected genes. Co-expression analysis showed that the JA-responsive genes might form a network module with ABA biosynthesis genes or cell wall biosynthesis genes, suggesting the existence of a COR-JA-cellulose and COR-JA-ABA-cellulose regulatory pathway in cotton seedlings. Collectively, our findings uncover new insights into the molecular basis of coronatine--associated cold tolerance in cotton seedlings.

Glutathione is required for nitric oxide-induced chilling tolerance by synergistically regulating antioxidant system, polyamine synthesis, and mitochondrial function in cucumber (Cucumis sativus L.)

In this paper, we discussed the physiological mechanism of enhanced chilling tolerance with combined treatment of nitric oxide (NO) and reduced glutathione (GSH) in cucumber seedlings. With prolonged low temperature (10 °C/6 °C), oxidative stress improved, which was manifested as an increase the hydrogen peroxide (H2O2) and malondialdehyde (MDA), causing cell membrane damage, particularly after 48 h of chilling stress. Exogenous sodium nitroprusside (SNP, NO donor) enhanced the activity of nitric oxide synthase NOS-like, the contents of GSH and polyamines (PAs), and the cellular redox state, thus regulating the activities of mitochondrial oxidative phosphorylation components (CI, CII, CIV, CV). However, buthionine sulfoximine (BSO, a GSH synthase inhibitor) treatment drastically reversed or attenuated the effects of NO. Importantly, the combination of SNP and GSH treatment had the best effect in alleviating chilling-induced oxidative stress by upregulating the activities of antioxidant enzyme, including superoxidase dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) and improved the PAs content, thereby increased activities of CI, CII, CIII, CIV, and CV. This potentially contributes to the maintenance of oxidative phosphorylation originating from mitochondria. In addition, the high activity of S-nitrosoglutathione reductase (GSNOR) in the combined treatment of SNP and GSH possibly mediates the conversion of NO and GSH to S-nitrosoglutathione. Our study revealed that the combined treatment with NO and GSH to synergistically improve the cold tolerance of cucumber seedlings under prolonged low-temperature stress.

Overexpression of VaBAM3 from Vitis amurensis enhances seedling cold tolerance by promoting soluble sugar accumulation and reactive oxygen scavenging.

The VaBAM3 cloned from Vitis amurensis can enhance the cold tolerance of overexpressed plants, but VaBAM3 knock out by CRISPR/Cas9 system weakened grape callus cold tolerance. In grape production, extreme cold conditions can seriously threaten plant survival and fruit quality. Regulation of starch content by β-amylase (BAM, EC: 3.2.1.2) contributes to cold tolerance in plants. In this study, we cloned the VaBAM3 gene from an extremely cold-tolerant grape, Vitis amurensis, and overexpressed it in tomato and Arabidopsis plants, as well as in grape callus for functional characterization. After exposure to cold stress, leaf wilting in the VaBAM3-overexpressing tomato plants was slightly less pronounced than that in wild-type tomato plants, and these plants were characterized by a significant accumulation of autophagosomes. Additionally, the VaBAM3-overexpressing Arabidopsis plants had a higher freezing tolerance than the wild-type counterparts. Under cold stress conditions, the activities of total amylase, BAM, peroxidase, superoxide dismutase, and catalase in VaBAM3-overexpressing plants were significantly higher than those in the corresponding wild-type plants. Furthermore, sucrose, glucose, and fructose contents in these lines were similarly significantly higher, whereas starch contents were reduced in comparison to the levels in the wild-type plants. Furthermore, we detected high CBF and COR gene expression levels in cold-stressed VaBAM3-overexpressing plants. Compared with those in VaBAM3-overexpressing grape callus, the aforementioned indicators tended to change in the opposite direction in grape callus with silenced VaBAM3. Collectively, our findings indicate that heterologous overexpression of VaBAM3 enhanced cold tolerance of plants by promoting the accumulation of soluble sugars and scavenging of excessive reactive oxygen species. These findings provide a theoretical basis for the cultivation of cold-resistant grape and support creation of germplasm resources for this purpose.

Genome-wide characterization of cytochrome P450 genes reveals the potential roles in fruit ripening and response to cold stress in tomato.

Plant cytochrome P450 (CYP) superfamily, the largest enzyme metabolism family, has been identified in many species and plays a vital role in plant development and stress response via secondary metabolite biosynthesis. A comprehensive identification and functional investigation of CYPs in tomato plants would contribute to deeper understanding of their biological significance. In this study, 268 tomato CYP genes were identified and found to be unevenly located on 12 chromosomes. Based on the phylogenetic analysis, these 268 SlCYPs were classed into two distinct clades (A-type and non-A-type) and nine clans, including 48 families. Moreover, 67 tandem and 22 WGD (whole genome duplication)/segmental duplication events were detected, of which 12 SlCYP genes experienced both WGD/segmental and tandem duplication events, indicating that tandem duplication plays a major role in the expansion of the SlCYP family. Besides, 48 pairs containing 41 SlCYP and 44 AtCYP genes were orthologous, while 216 orthologous pairs were obtained between tomato and potato. The expression level of all SlCYP genes in tomato tissues at different development stages was analyzed, and most expressed SlCYPs showed a tissue-specific pattern. Meanwhile, 143 differentially expressed SlCYPs were identified under cold stress. Furthermore, the RT-qPCR results indicated that SlCYPs may be involved in fruit ripening and cold tolerance in tomato seedlings. These findings provide valuable insights into the evolutionary relationships and functional characteristics of SlCYPs, which can be utilized for further investigation of fruit metabolic pathways and cold tolerance in tomato.

Transcriptome and Metabolome Analyses Reveal Ascorbic Acid Ameliorates Cold Tolerance in Rice Seedling Plants

Ascorbic acid (AsA) plays a crucial role in the physiological processes of rice plants when they encounter various biotic and abiotic stresses. However, the specific mechanism by which AsA affects cold tolerance in rice seedlings remains unclear. Two rice genotypes, Zhongzao39 (ZZ39) and its recombinant inbred line RIL82, were exposed to cold stress, resulting in more damage observed in RIL82 compared to ZZ39. This damage included higher levels of relative electrolytic leakage (REC), malondialdehyde (MDA), H2O2, a lower Fv/Fm, and a lower survival rate. A comprehensive analysis of transcriptome and metabolome data indicated that AsA was involved in regulating cold tolerance in ZZ39 and RIL82 seedling plants. AsA content increased in ZZ39 while it decreased in RIL82 under cold stress. Additionally, analysis of carbohydrate contents highlighted their important role in the responses to cold stress of these two genotypes. Importantly, exogenous AsA and sucrose, either alone or in combination, enhanced the values of maximum fluorescence quantum yield (Fv/Fm) and effective quantum yield (YII) as well as decreased H2O2 and MDA levels to improve cold tolerance in both genotypes compared with plants treated with H2O. These findings highlight the potential significance of AsA in mitigating the effects of cold stress on rice seedling plants.

Effects of exogenous glycine betaine on growth and development of tomato seedlings under cold stress.

Low temperature is a type of abiotic stress affecting the tomato (Solanum lycopersicum) growth. Understanding the mechanisms and utilization of exogenous substances underlying plant tolerance to cold stress would lay the foundation for improving temperature resilience in this important crop. Our study is aiming to investigate the effect of exogenous glycine betaine (GB) on tomato seedlings to increase tolerance to low temperatures. By treating tomato seedlings with exogenous GB under low temperature stress, we found that 30 mmol/L exogenous GB can significantly improve the cold tolerance of tomato seedlings. Exogenous GB can influence the enzyme activity of antioxidant defense system and ROS levels in tomato leaves. The seedlings with GB treatment presented higher Fv/Fm value and photochemical activity under cold stress compared with the control. Moreover, analysis of high-throughput plant phenotyping of tomato seedlings also supported that exogenous GB can protect the photosynthetic system of tomato seedlings under cold stress. In addition, we proved that exogenous GB significantly increased the content of endogenous abscisic acid (ABA) and decreased endogenous gibberellin (GA) levels, which protected tomatoes from low temperatures. Meanwhile, transcriptional analysis showed that GB regulated the expression of genes involved in antioxidant capacity, calcium signaling, photosynthesis activity, energy metabolism-related and low temperature pathway-related genes in tomato plants. In conclusion, our findings indicated that exogenous GB, as a cryoprotectant, can enhance plant tolerance to low temperature by improving the antioxidant system, photosynthetic system, hormone signaling, and cold response pathway and so on.

Construction and Identification of Cold Tolerance in Different Broccoli Cultivars at the Seedling Stage

This study aimed to develop a systematic method for assessing the cold tolerance of broccoli seedlings, which is helpful to evaluating the cold tolerance of broccoli cultivars. We selected 14 classical broccoli cultivars and evaluated their cold tolerance by examining physiological indicators including the levels of cold resistance, electrical conductivity, malondialdehyde (MDA), soluble sugar, and hydrogen peroxide (H2O2). The results showed that there were significant differences in detected characteristics in all cultivars after cold stress during the seedling stage (p < 0.05). Among them, Meiqing had the strongest cold tolerance, followed by King 11, Zhongqing 15, Meiao 7172, Zhongqing 318, Zheqing 80, Zhongqing 16, Zhongqing 319, and Lvxiong 90. However, Zhongqing 11, Yanxiu, Qianghan, and Feicui 5, showed the worst cold tolerance (all died). Pearson correlation analysis indicated that there was a significantly negative correlation between the cold tolerance and the electrical conductivity during broccoli seedling stage, with a correlation coefficient of −0.586 (p < 0.05). At the same time, we found that the electrical conductivity of all broccoli cultivars showed a positive correlation with the MDA and soluble sugar levels, with the correlation coefficients 0.650 and 0.573, respectively (p < 0.05). This study not only firstly provides a fundamental method for evaluating the cold tolerance in different broccoli genotypes and the other cruciferous vegetables, but also offers a scientific evidence explaining the cold tolerance of the Meiqing, King 11, and Zhongqing 15 cultivars widely cultivated in China.

Suitable water management improving cold tolerance of rice seedlings

Suitable water management improving cold tolerance of rice seedlings

Identification of candidate genes that regulate the trade-off between seedling cold tolerance and fruit quality in melon (Cucumis melo L.).

Trade-offs between survival and growth are widely observed in plants. Melon is an annual, trailing herb that produces economically valuable fruits that are traditionally cultivated in early spring in China. Melon seedlings are sensitive to low temperatures, and thus usually suffer from cold stress during the early growth period. However, little is known about the mechanism behind the trade-offs between seedling cold tolerance and fruit quality in melon. In this study, a total of 31 primary metabolites were detected from the mature fruits of eight melon lines that differ with respect to seedling cold tolerance; these included 12 amino acids, 10 organic acids, and 9 soluble sugars. Our results showed that concentrations of most of the primary metabolites in the cold-resistant melons were generally lower than in the cold-sensitive melons; the greatest difference in metabolite levels was observed between the cold-resistant line H581 and the moderately cold-resistant line HH09. The metabolite and transcriptome data for these two lines were then subjected to weighted correlation network analysis, resulting in the identification of five key candidate genes underlying the balancing between seedling cold tolerance and fruit quality. Among these genes, CmEAF7 might play multiple roles in regulating chloroplast development, photosynthesis, and the ABA pathway. Furthermore, multi-method functional analysis showed that CmEAF7 can certainly improve both seedling cold tolerance and fruit quality in melon. Our study identified an agriculturally important gene, CmEAF7, and provides a new insight into breeding methods to develop melon cultivars with seedling cold tolerance and high fruit quality.

Stress memory in seedlings of primed seed chickpea (Cicer arietinum L.) using sodium nitroprusside under cold stress

Pea cultivation has been developed as a rich source of protein in many countries. The spring cultivation of chickpeas has low performance and efficiency due to the short length of the growth period and the confrontation of the reproductive period with drought and high temperature stress. Autumn cultivation of chickpeas is introduced as an important solution in reducing the yield caused by high temperature and drought stress during the flowering time of spring cultivation. However, in autumn cultivation, sensitivity to cold is the main limitation. So, the present study was performed to investigate the effect of nitric oxide on stress memory due to seed priming with sodium nitroprusside for cold tolerance of chickpea seedlings under simulated autumn temperatures. This experiment was conducted as a factorial in a completely randomized design with nine replicates at the Research Center for Plant Sciences of Ferdowsi University, Mashhad Iran, in 2020. Experimental factors included seed priming at two levels (control and sodium nitroprusside) and chickpea cultivars, including a susceptible genotype (MCC505) and a cold-tolerant cultivar (Saral). This experiment evaluated the gene expression of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase) in the seedling stage. The results revealed that superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase genes were expressed in sodium nitroprusside and control treatments. In the Saral cultivar, sodium nitroprusside increased the gene expression of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase enzymes by 29, 88, 54, and 63%, respectively. On the other hand, the gene expression of these enzymes in the control treatment may be due to the effect of temperature on them. There was a significant increase in the expression of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase genes in the Saral cultivar compared to the MCC505 genotype. In general, sodium nitroprusside increased the activity of antioxidant enzymes in the Saral cultivar through the expression of antioxidant enzyme genes.

OsLUX Confers Rice Cold Tolerance as a Positive Regulatory Factor.

During the early seedling stage, rice (Oryza sativa L.) must overcome low-temperature stress. While a few cold-tolerance genes have been characterized, further excavation of cold-resistance genes is still needed. In this study, we identified a cold-induced transcription factor-LUX ARRHYTHMO (LUX)-in rice. OsLUX was found to be specifically expressed in leaf blades and upregulated by both cold stress and circadian rhythm. The full-length OsLUX showed autoactivation activity, and the OsLUX protein localized throughout the entire onion cell. Overexpressing OsLUX resulted in increased cold tolerance and reduced ion leakage under cold-stress conditions during the seedling stage. In contrast, the knockout of OsLUX decreased seedling cold tolerance and showed higher ion leakage compared to the wild type. Furthermore, overexpressing OsLUX upregulated the expression levels of oxidative stress-responsive genes, which improved reactive oxygen species (ROS) scavenging ability and enhanced tolerance to chilling stress. Promoter analysis showed that the OsLUX promoter contains two dehydration-responsive element binding (DREB) motifs at positions -510/-505 (GTCGGa) and -162/-170 (cCACCGccc), which indicated that OsDREB1s and OsDREB2s probably regulate OsLUX expression by binding to the motif to respond to cold stress. Thus, OsLUX may act as a downstream gene of the DREB pathway. These results demonstrate that OsLUX serves as a positive regulatory factor of cold stress and that overexpressing OsLUX could be used in rice breeding programs to enhance abiotic stress tolerance.

IMPROVING COLD STRESS TOLERANCE IN RICE SEEDLINGS

Cold stress has become problematic for rice seedling production in many sub-tropical areas, including in Bangladesh. Cold stress causes poor germination, stunted seedlings, chlorosis or withering, and limited tillering. Application of various exogenous stimulants metabolically prepares plants to fight against cold stress. This review summarized the role of different exogenous stimulants in mediating cold tolerance in rice seedlings. Seed priming or seedling treatment with exogenous stimulants can be promising approach to improve cold stress tolerance. However, additional research should be conducted to reveal the molecular mechanisms, as well as field level trials should be conducted to determine field level applicability.