The Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
Plant Cell Environ. 2013 Oct;36(10):1850-9. doi: 10.1111/pce.12094. Epub 2013 Apr 18.
The mechanism of age-induced decreased stomatal sensitivity to abscisic acid (ABA) and soil drying has been explored here. Older, fully expanded leaves partly lost their ability to close stomata in response to foliar ABA sprays, and soil drying which stimulated endogenous ABA production, while young fully expanded leaves closed their stomata more fully. However, ABA- or soil drying-induced stomatal closure of older leaves was partly restored by pretreating plants with 1-methylcyclopropene (1-MCP), which can antagonize ethylene receptors, or by inoculating soil around the roots with the rhizobacterium Variovorax paradoxus 5C-2, which contains 1-aminocyclopropane-1-carboxylic acid (ACC)-deaminase. ACC (the immediate biosynthetic precursor of ethylene) sprays revealed higher sensitivity of stomata to ethylene in older leaves than younger leaves, despite no differences in endogenous ACC concentrations or ethylene emission. Taken together, these results indicate that the relative insensitivity of stomatal closure to ABA and soil drying in older leaves is likely due to altered stomatal sensitivity to ethylene, rather than ethylene production. To our knowledge, this is the first study to mechanistically explain diminished stomatal responses to soil moisture deficit in older leaves, and the associated reduction in leaf water-use efficiency.
本文探讨了年龄导致气孔对脱落酸（ABA）和土壤干燥敏感性降低的机制。较老的、完全展开的叶片部分丧失了对叶面 ABA 喷雾的反应能力，不能关闭气孔，而土壤干燥会刺激内源性 ABA 的产生，而年轻的完全展开的叶片则能更完全地关闭气孔。然而，用 1-甲基环丙烯（1-MCP）预处理植物，或用含有 1-氨基环丙烷-1-羧酸（ACC）脱氨酶的根际细菌 Variovorax paradoxus 5C-2 接种根系周围的土壤，可以部分恢复衰老叶片中 ABA 或土壤干燥诱导的气孔关闭。ACC（乙烯的直接生物合成前体）喷雾显示，衰老叶片中气孔对乙烯的敏感性高于年轻叶片，尽管内源 ACC 浓度或乙烯排放没有差异。综上所述，这些结果表明，衰老叶片中气孔对 ABA 和土壤干燥的相对不敏感性可能是由于气孔对乙烯的敏感性发生了变化，而不是由于乙烯的产生。据我们所知，这是首次从机制上解释了衰老叶片对土壤水分亏缺的气孔反应减弱，以及相关的叶片水分利用效率降低的原因。
