Sussmilch Frances C, Brodribb Timothy J, McAdam Scott A M
School of Biological Sciences, University of Tasmania, Hobart, TAS, Australia.
J Exp Bot. 2017 May 17;68(11):2913-2918. doi: 10.1093/jxb/erx124.
A major environmental signal influencing day-time stomatal aperture is the vapour pressure deficit between the leaf and atmosphere (VPD). In angiosperms, increased VPD triggers biosynthesis of abscisic acid (ABA), prompting rapid stomatal closure. Altered cell turgor has been proposed as the trigger for ABA biosynthesis, but the timing and nature of the genetic signals linking these processes have remained uncertain. We investigated this in Arabidopsis by examining changes induced by a decrease in leaf turgor, simulating a natural increase in VPD. We found that the rate-limiting gene within the de novo ABA biosynthesis pathway, 9-cis-epoxycarotenoid dioxygenase 3 (NCED3), was induced and ABA levels increased within just 5 min of decreased leaf turgor. This rapid induction matches the time-frame for initiation of stomatal closure in response to a doubling in VPD. We further examined Arabidopsis histidine kinase1 (AHK1) as the most likely candidate for the turgor-sensing receptor involved, but found no significant difference between wild-type and an ahk1 null mutant in the induction of ABA-biosynthetic genes, ABA production, or stomatal behaviour. We show that decreased leaf turgor triggers de novo ABA biosynthesis within the time-frame of the stomatal response to VPD, but that AHK1 does not fulfil a critical role as a turgor-sensing receptor within this pathway.
影响白天气孔孔径的一个主要环境信号是叶片与大气之间的蒸汽压亏缺（VPD）。在被子植物中，VPD升高会触发脱落酸（ABA）的生物合成，促使气孔迅速关闭。细胞膨压的改变被认为是ABA生物合成的触发因素，但连接这些过程的遗传信号的时间和性质仍不确定。我们通过研究叶片膨压降低所诱导的变化来在拟南芥中对此进行研究，模拟VPD的自然升高。我们发现，从头ABA生物合成途径中的限速基因9-顺式环氧类胡萝卜素双加氧酶3（NCED3）在叶片膨压降低仅5分钟内就被诱导，且ABA水平升高。这种快速诱导与气孔对VPD加倍做出响应而开始关闭的时间框架相匹配。我们进一步研究了拟南芥组氨酸激酶1（AHK1）作为最有可能参与膨压感应受体的候选基因，但发现在ABA生物合成基因的诱导、ABA产生或气孔行为方面，野生型和ahk1缺失突变体之间没有显著差异。我们表明，叶片膨压降低在气孔对VPD响应的时间框架内触发了从头ABA生物合成，但AHK1在该途径中并未作为膨压感应受体发挥关键作用。
