为明确碱胁迫对小麦(Triticum aestivum)根系离子组及代谢组的影响, 探讨其响应变化规律及机制, 该研究以小麦为实验材料, 采用两种碱性盐(NaHCO₃和Na₂CO₃)按摩尔比1:1混合模拟不同碱胁迫强度, 利用气相色谱-质谱联用(GC-MS)技术结合多元变量分析方法, 系统分析小麦根系在碱胁迫下的矿质元素、游离阴离子、代谢产物及代谢途径变化。结果显示: 低浓度碱胁迫下小麦根系仍能维持一定的生长, 但在高浓度碱胁迫下根系生长受到了明显抑制。当碱胁迫强度超过小麦根系调节能力时, 根系中Na含量急剧增加的同时K含量明显减少。碱胁迫刺激根中Ca积累, 而Mg、Cu和Fe含量呈现下降趋势。碱胁迫明显减少根中游离阴离子(主要是Cl^-)含量。检测代谢物组包括有机酸、氨基酸、碳水化合物、嘧啶和嘌呤等70个代谢产物, 主成分分析结果表明代谢物均分布在95%的置信区间内。碱胁明显迫促进苹果酸、琥珀酸等代谢物积累, 但造成糖类(果糖、蔗糖)及多元醇(肌醇、山梨糖醇)和氨基酸(γ-氨基丁酸、丙氨酸)含量显著下降。结果表明: 根系中Na⁺含量剧增, 加上高pH值危害, 导致根系生长率降低; 与此同时, 游离阴离子明显减少, 造成根系内负电荷亏缺和pH不稳定, 导致离子平衡遭到破坏, 进而引起一系列代谢途径的协变反应。小麦根系在碱胁迫下糖酵解、细胞膜脂代谢和氨基酸合成受到明显的抑制, 但三羧酸循环显著增强。这些结果表明碱胁迫(高pH值)对碳素合成和储存有明显的负效应, 降低代谢合成碳骨架和能量, 使得清除活性氧能力明显下降。碱胁迫下根外部质子缺乏造成NO₃^-含量降低, 影响氮素吸收利用, 导致氨基酸合成受阻。三羧酸循环增强为生成有机酸类化合物和调控pH平衡提供能量, 这可能是植物适应碱胁迫的一种特殊对应策略。

Aims The aim of this study was to investigate the effects of alkaline stress on primary, secondary metabolites and metabolic pathways in the roots of wheat (Triticum aestivum). The results were used to evaluate the physiological adaptive mechanisms by which wheat tolerated alkali stress.Methods A pot experiment was carried out in the greenhouse. For each plastic pot, five wheat seeds were planted. After germination, seedlings were allowed to grow under controlled water and nutrient conditions for two months, then seedlings were exposed to alkaline stress (NaHCO₃-Na₂CO₃) for 12 days. The relative growth rate (RGR), absolute water content (AWC), metal elements, free cations and metabolites were measured.Important findings The alkaline stress caused the reduction of RGR and AWC. Alkaline stress caused a rapid increase of Na content with the concurrent decrease in K and Cl content, resulting in inhibited metal element accumulation and an ionic imbalance. In the present study, alkaline stress strongly enhanced Ca accumulation in wheat roots, suggesting that an increased Ca concentration can immediately trigger the salt overly sensitive (SOS)-Na exclusion system and reduce Na-associated injuries. Also, 70 metabolites, including organic acids, amino acids, sugars/polyols and others, behaved differently in the alkaline stress treatments according to a GC-MS analysis. The metabolic profiles of wheat were closely associated with alkaline-stress conditions. Alkaline stress caused the accumulation of organic acids, accompanied by the depletion of sugars/polyols and amino acids. Organic acids could play a central role in the regulation of intracellular pH by accumulating vacuoles to neutralize excess cations. Glycolysis and amino acid synthesis in roots were inhibited under salt stress while prolonged alkaline stress led to a progressive tricarboxylic acid (TCA) cycle. The severe negative effects of alkaline stress on sugar synthesis and storage may reflect the toxic levels of Na⁺ accumulating in plant cells in a high-pH environment, implying that the reactive oxygen species detoxification capacity was diminished by the high pH. A lack of NO₃^- in wheat roots can decrease synthase enzyme activities, limiting the synthesis of amino acids. Under salt stress, the TCA cycle and organic acid accumulation increased, but glycolysis and amino acid synthesis were inhibited in roots. Thus, energy levels and high concentrations of organic acids may be the key adaptive mechanisms by which wheat seedlings maintain their intracellular ion balance under alkaline stress.