拔节孕穗期小麦干旱胁迫下生长代谢变化规律

Growth metabolism of wheat under drought stress at the jointing-booting stage

采用盆栽试验模拟干旱胁迫(土壤相对含水量40%–45%)在小麦(Triticum aestivum)拔节孕穗期胁迫12天,测定其生长速率、光合特征及关键代谢产物含量,以探讨干旱胁迫对拔节孕穗期小麦叶片初生及次生代谢产物的影响及其涉及的代谢途径,讨论小麦生长代谢变化规律及应答机制。研究表明:干旱胁迫使小麦叶片气孔受限制导致光合速率下降;使叶绿素含量下降直接影响光系统II活性,最终导致生长率降低。检测出的初级代谢产物组包括有机酸、氨基酸、碳水化合物、嘧啶和嘌呤等64个代谢产物,其中29个代谢产物在干旱胁迫下发生明显的变化。主成分分析(PCA)结果显示全部样本均分布在95%的置信区间内,两个主成分得分为64%。单因素方差分析结果表明,干旱胁迫导致苹果酸、柠檬酸、乌头酸等参与三羧酸(TCA)循环的代谢产物消耗明显,且引起大部分氨基酸(如脯氨酸、丝氨酸、缬氨酸)和碳水化合物(肌醇、果糖、葡萄糖)大量积累的同时转氨基代谢(天冬酰胺、谷氨酰胺和γ氨基丁酸)产物消耗,研究证明干旱胁迫明显地促进小麦叶片的糖酵解和氨基酸合成途径,但抑制了TCA循环和转氨基反应,加速氨基酸代谢网络向脯氨酸合成转变过程。这些结果表明干旱胁迫引起了转氨基反应、TCA循环、糖酵解/糖异生、谷氨酸介导的脯氨酸合成,以及嘧啶和嘌呤等代谢网络系统广泛的变化,说明小麦在合成大量的氨基酸和碳水化合物类物质的同时也消耗了大量的能量,暗示了糖异生到脯氨酸合成的转变。

Aims The aim of this study was to investigate the effects of drought stress on primary, secondary metabolites and metabolic pathways in the leaves of wheat, these parameters were evaluated to determine the physiological adaptive mechanisms by which wheat tolerates drought stress at the jointing-booting stage.Methods A pot experiment was carried out in rain-proof shelter. The relative growth rate, photosynthetic char- acteristics and metabolism seedlings exposed to stresses lasting 12 days at jointing-booting stage were measured. Important findings The results displayed that the photosynthesis decreased under drought stress, causing the decreases of relative growth rate and dry matter mass. Profiles of 64 key metabolites produced by wheat including organic acids, amino acids, carbohydrates, purine, etc. were examined, 29 of them were changed significantly un- der drought stress. Principal component analysis （PCA） showed that 64% variations can be explained by the two principal components. One-way ANOVA analysis results revealed that long term drought stress decreased malic acid, citric acid and aconitic acid significantly, indicating inhibited tricarboxylic acid cycle. We further found that prolonged drought stress led to accumulation of progressive amino acids （proline, serine, valine） and carbohy- drates （myo-inositol, fructose, clucose） in wheat leaves and depletion of transamination products （asparagine, glutamine, γ-aminobutyric acid）. These results imply wheat may enhance its drought tolerance mainly by increas- ing amino acid biosynthesis and glycolysis under water-deficit conditions. Our findings suggest that drought con- dition altered metabolic networks including transamination, the tricarboxylic cycle, gluconeogenesis/glycolysis, glutamate-mediated proline biosynthesis, and the metabolisms of choline, pyrimidine and purine. This study provides new insights into the metabolic adaptation of wheat to drought stress and important information for de- veloping drought-tolerant wheat cultivars.