| 英文摘要 |
Drought stress seriously affects plant growth, which is one of the major abiotic stresses leading to a decline in yield, and researchs on improving drought resistance of crops has aroused wide concern. Maize (Zea mays L.), one of the most widely cultivated crops in the world, is an extremely important food, feed and economic crop in China. Previous reports have indicated that 2-(3,4-dichlorophenoxy)-triethylamine (DCPTA) can promote the growth and photosynthetic capacity of plants. However, only a small number of these studies have focused on crops, and few reports have focused on whether DCPTA affects stress tolerance. In the present study, the effects of DCPTA on the plant growth, photosynthesis indexes, antioxidant defence mechanisms, nitrogen metabolism of the maize seedlings (maize inbred line, Chang 7-2) under PEG-6000 simulated drought stress; yeild and nitrogen metabolism of the maize (maize variety, Zhengdan 958) were investigated to explore the physiological functions of DCPTA pretreatment on improving drought resistance of maize. The main results are as follows: (1)The DCPTA treatment partly counteracted the observed decreases in biomass, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), effective photochemical efficiency of photosystem II (ΦPSII), maximum photochemical efficiency of PSII (Fv/Fm), non-photochemical quenching (NPQ), and photosynthetic pigment content and increased the minimal fluorescence (Fo) induced by drought stress. The DCPTA treatment also alleviated the damage induced by drought stress in the photosynthetic apparatus. In addition, DCPTA pretreatment simultaneously increased the root size (e.g., the length, surface area, and volume) and root hydraulic conductivity, which promoted the maintenance of higher relative leaf water contents (RLWC) under stress conditions. These results indicate that exogenous DCPTA ameliorates simulated drought conditions by improving the growth and photosynthetic capacity of maize seedlings. (2)The activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) were enhanced by drought stress and further enhanced by the DCPTA application. The activities of catalase (CAT), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) declined continuously under drought stress; Up-regulation of activities and the transcript levels of the AsA-GSH cycle enzymes in DCPTA-treated seedlings contributed to the increase in the contents of AsA and GSH and inhibited the increased generation rate of superoxide anion radicals (O₂˙⁻), the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and electrolyte leakage (EL) induced by drought stress. These results demonstrate that the enhanced antioxidant capacity of the AsA-GSH cycle induced by DCPTA application may represent an efficient mechanism for increasing the drought stress tolerance of maize seedlings. (3)In this study, transcriptome analysis, quantitative real-time polymerase chain reaction (qRT-PCR) analysis and western-blot of DCPTA-treated maize seedlings exposed to 15% polyethylene glycol (PEG)-simulated drought stress were investigated to explore the possible mechanism of exogenous DCPTA-improved plant growth and drought tolerance. Among the differentially expressed genes (DEG), the nitrogen (N) metabolism-related genes encoding nicotinamide adenine dinucleotide-nitrate reductase (NADH-NR), ferredoxin-nitrite reductase (Fd-NiR), reduced ferredoxin-glutamate synthase (Fd-GOGAT), and chloroplastic glutamine synthetase (GS2) were enriched in responses to PEG-simulated drought stress and/or DCPTA treatment. Moreover, under simulated drought stress, DCPTA treatment maintained the relative expression levels of NADH-NR, Fd-NiR, GS2 and Fd-GOGAT and the stability of enzyme protein content. Simultaneously, exogenous DCPTA partially mitigated PEG-simulated drought-induced reductions in the enzymatic activities of NR, NiR, GOGAT, GS, glutamic-pyruvic transaminase (GPT) and glutamic-oxaloacetic transaminase (GOT) and the contents of nitrate (NO₃⁻), nitrite (NO₂⁻)) and soluble protein; increases in proteolytic activity and the contents of ammonium (NH₄⁺) and free amino acids. Taken together, the results indicate that exogenous DCPTA improved plant growth and drought tolerance through regulating N-mechanism enzymatic activities involved in transcription and enzymatic protein synthesis. (4)The results demonstrated that the foliar application of DCPTA (25 ㎎/L) significantly alleviated drought-induced decreases in maize yield, shoot and root relative growth rate (RGR), leaf relative water content (RLWC), net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), nitrate (No₃⁻), nitrite (NO₂⁻), and soluble protein contents, and nitrate reductase (NR), nitrite reductase (NiR), isocitrate dehydrogenase (ICDH), alanine aminotransferase (AlaAT) and aspartate aminotransferase (AspAT) activities. In addition, the foliar application of DCPTA increased the intercellular CO₂ concentration (Ci), the ammonium (NH₄⁺) and free amino acid contents, and the glutamate dehydrogenase (GDH) and protease activities of the maize. Simultaneously, under drought conditions, the DCPTA application improved the spatial and temporal distribution of roots and increased the root hydraulic conductivity (Lp), flow rate of root-bleeding sap and NO₃⁻ delivery rates of the maize. Taken together, our results suggest that exogenous DCPTA mitigates the repressive effects of drought on N metabolism and subsequently enhances drought tolerance during the pre-female inflorescence emergence stage of maize. Key words: maize; drought stress; DCPTA; photosynthesis indexes; antioxidant defence mechanisms; nitrogen metabolism; RNA-seq
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