Salinization disturbs metabolic processes of plants and results in reduced growth and productivity. In our study, the Dongnong 8809 variety of triticale (×Triticosecale Wittmack) was evaluated for its physiological responses to salt stress during the seedling stage. We evaluated biomass production, relative chlorophyll content, chlorophyll fluorescence, and leaf gas-exchange parameters. Our results indicated that salt stress greatly reduced matter accumulation, SPAD value, photosynthetic capacity. However, seedlings treated with exogenous sugars showed significantly enhanced matter accumulation, SPAD value, quantum yield of PSII, electron transport rate, net photosynthetic rate, decreased stomatal limitation value, and improved photosynthetic capacity compared to seedlings treated with salt stress alone. Exogenous glucose and sucrose can alleviate the inhibitory effect of salt stress on the growth of triticale, and of the two exogenous sugars, sucrose had a stronger alleviating effect than that of glucose under salt stress. rate; ETR -electron transport rate; F0 -minimal fluorescence yield of the dark-adapted state; F0' -minimal fluorescence yield of the light-adapted state; Fm -maximal fluorescence yield of the dark-adapted state; Fm' -maximal fluorescence yield of the light-adapted state; Fs -steady-state fluorescence yield; Fv/Fm -maximum quantum yield of PSII photochemistry; Fv/F0 -potential photochemical efficiency; gs -stomatal conductance; Ls -stomatal limitation value; NPQ -nonphotochemical quenching; PN -net photosynthetic rate; qP -photochemical quenching coefficient; WUEwater-use efficiency; WUEi -intrinsic water-use efficiency; Y -quantum yield of PSII.
The ABA-stress-ripening (ASR) gene is an abiotic stress-response gene that is widely present in higher plants. The expression of ASR was recently shown to effectively improve plant tolerance to several abiotic stresses. However, the role of ASR during chilling stress in maize (Zea mays L.) is unclear. In this study, we tested two maize varieties under chilling treatment. Our results showed that Jinyu 5 (JY5), a chilling-sensitive variety, had lower maximum PSII efficiency (Fv/Fm) and higher lipid peroxidation levels than Jidan 198 (JD198) under chilling conditions. At the same time, the enzymes superoxide dismutase (SOD) and peroxidase (POD) were more active in JD198 than in JY5 under chilling conditions. In addition, exogenous ABA spray pretreatments enhanced the chilling tolerance of maize, showing results such as increased Fv/Fm ratios, and SOD and POD activity; significantly reduced lipid peroxidation levels and increased expression of ZmASR1 in both JD198 and JY5 under chilling conditions. Moreover, when the ZmASR1 expression levels in the two maize varieties were compared, the chilling-sensitive line JY5 had significantly lower expression in both the leaves and roots than JD198 under chilling stress, indicating that the expression of ZmASR1 is a chilling response option in plants. Furthermore, we overexpressed ZmASR1 in JY5; this resulted in enhanced maize chilling tolerance, which reduced the decreases in Fv/Fm and the malondialdehyde content and enhanced SOD and POD activity. Overall, these results suggest that ZmASR1 expression plays a protective role against chilling stress in plants.
Proline (Pro) is not only an important osmotic adjustment substance, but it also plays an important role in regulating plant abiotic stress resistance. The maize varieties, Xinxin 2 (low temperature insensitive) and Damin 3307 (low temperature sensitive), were chosen as materials, setting a normal temperature for germination (22 °C/10 °C, 9d), low temperature germination (4 °C/4 °C, 5d) and normal temperature recovery (22 °C/10 °C, 4d), combined with a proline (15 mmol·L−1) soaking treatment, to reveal the seed germination and regulation mechanism in maize embryos. The results showed that proline significantly improved the germination potential, germination rate, germination index and vigor index of seeds under low temperature stress, increasing the length of the coleoptile and radicle, increasing the dry and fresh weight of young buds (coleoptile + radicle), and increasing the activity of α-amylase. Proline enhanced the activities of Δ1-pyrroline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) in maize embryos under low temperature stress, enhanced the proline synthesis pathways, and further enhanced proline accumulation. Proline induced the activity of proline dehydrogenase (ProDH) in the early stage of low temperature stress and stress relief. Under low temperature stress, the activities of hexokinase (HXK), phosphofructokinase (PFK), pyruvate kinase (PK), isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) and glucose-6-phosphate dehydrogenase (G-6-PDH and 6-P-GDH) in maize embryos were decreased, resulting in a decrease in the glycolysis (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate pathway (PPP). Proline alleviated the inhibition of key enzyme activities of the EMP pathway, TCA cycle and PPP of maize embryos under low temperature stress, increased the activities of cytochrome oxidase (COX) and alternative oxidase (AOX), increased the ATP content, alleviated the inhibition of low temperature stress on main cytochrome pathway activity (ρVcyt), while further increasing the total respiratory activity (Vt) and the actual operational activity of the alternative pathway (ρValt) during seed germination at the initial stage of low temperature stress, as well as improving the inhibition of the Vt and ρValt in the middle and late stages of low temperature stress. Under low temperature stress, the content of abscisic acid (ABA) increased significantly, while gibberellin (GA), auxin (IAA) and zeatin nucleoside (ZR) decreased significantly. Proline alleviated the decrease in IAA, ZR and GA contents in maize embryos under low temperature stress, reduced the increase in the ABA content, and reduced the inhibition of low temperature on seed germination.
Maize (Zea mays L.) is more sensitive to low-temperature stress in the early growth period. The study was to explore the response mechanism of proline to low-temperature stress during maize seed germination. Maize varieties Xinxin 2 (low-temperature insensitive) and Damin 3307 (low-temperature sensitive) were chosen as the test materials, setting the normal temperature for germination (22 °C/10 °C, 9d), low-temperature germination (4 °C/4 °C, 5d) and normal temperature recovery (22 °C/10 °C, 4d), combined with proline (15 mmol·L−1) soaking treatment, to study its effects on the osmotic regulation system and antioxidant protection system of maize embryos. Metabolomics analysis was carried out to initially reveal the basis of the metabolic regulation mechanism. The results showed that the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbic acid peroxidase (APX) and glutathione reductase (GR) were induced to some extent under low-temperature stress. The activities of SOD, POD, APX and GR were further enhanced in the soaking seeds with proline. Proline treatment improved the activities of catalase (CAT), monodehydrated ascorbic acid reductase (MDHAR) and dehydroascorbic acid (DHAR), increased the contents of ascorbic acid (AsA) and glutathione (GSH) and decreased the contents of oxidized ascorbic acid (DHA) and reduced glutathione (GSSG) under low-temperature stress. The ratio of AsA/DHA and GSH/GSSG increased. The increase in antioxidant enzyme activity and the content of antioxidants can help to maintain the stability of the AsA-GSH cycle, and effectively reduce the production rate of superoxide anion (O2•−), hydrogen peroxide (H2O2) and malondialdehyde (MDA). Based on the UPLC-MS/MS detection platform and self-built database, 589 metabolites were detected in each treated maize embryo; 262 differential metabolites were obtained, including 32 organic acids, 28 amino acids, 20 nucleotides and their derivatives, 26 sugars and alcohols, 46 lipids, 51 alkaloids, 44 phenols and 15 other metabolites. Sixty-eight metabolic pathways involving different metabolites were obtained by KEGG enrichment analysis. The results showed that proline increased the accumulation of sorbitol, planteose, erythritose 4-phosphate, arabinose and other saccharides and alcohols in response to low-temperature stress, increased the content of osmoregulation substances under low-temperature stress. Proline also restored the TCA cycle by increasing the content of α-ketoglutarate and fumaric acid. Proline increased the contents of some amino acids (ornithine, proline, glycine, etc.), alkaloids (cocamidopropyl betaine, vanillylamine, 6-hydroxynicotinic acid, etc.), phenols (phenolic ayapin, chlorogenic acid, etc.) and vitamins (ascorbic acid, etc.) in the embryo under low-temperature stress. Combined with pathway enrichment analysis, proline could enhance the low-temperature stress resistance of germinated maize embryos by enhancing starch and sucrose metabolism, arginine and proline metabolism, biosynthesis of secondary metabolites, flavonoid biosynthesis and pentose phosphate pathway.
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