Institute for Molecular Plant Physiology and Biophysics, Biocenter, University of Wuerzburg, 97082 Wuerzburg, Germany.
Curr Biol. 2013 Jan 7;23(1):53-7. doi: 10.1016/j.cub.2012.11.022. Epub 2012 Dec 6.
Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO(2) for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.
气孔是叶片表面的孔，由两个保卫细胞围成，控制着光合作用中 CO2 的吸收和伴随的水蒸气的损失。1898 年，弗朗西斯·达尔文（Francis Darwin）表明，气孔会在大气相对湿度（rh）降低时关闭；然而，我们对导致 rh 变化与气孔开度变化相关的信号通路的理解还很零碎。这里呈现的结果强调了脱落酸（ABA）在气孔对干燥空气的反应中的首要地位。我们表明保卫细胞拥有完整的 ABA 生物合成途径，而且它似乎受到 ABA 的正反馈上调。当野生型拟南芥和 ABA 缺陷突变体 aba3-1 暴露于 rh 降低时，aba3-1 突变体萎蔫，而野生型则没有。然而，当 aba3-1 植物，其中 ABA 合成在保卫细胞中被特异性拯救时，受到干燥空气的挑战时，它们并没有萎蔫。这些数据表明，保卫细胞自主的 ABA 合成是气孔对低 rh 关闭反应所必需的，并且足以使气孔关闭。保卫细胞自主的 ABA 合成使植物能够精确地调整叶片气体交换，以适应环境条件。
