Holbrook N Michele, Shashidhar V R, James Richard A, Munns Rana
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
J Exp Bot. 2002 Jun;53(373):1503-14.
The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA-deficient tomato mutants, sitiens and flacca and their near-isogenic wild-type parent. Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens or flacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA. In the second type of experiment, wild-type shoots were grafted onto a split-root system consisting of one wild-type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild-type roots. In the third type of experiment, grafted plants with wild-type shoots and either wild-type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens. These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.
利用由脱落酸缺乏型番茄突变体sitiens和flacca及其近等基因野生型亲本构建的嫁接植株，对根系在干旱土壤中产生的脱落酸导致气孔关闭这一假说进行了验证。进行了三类实验。在第一类实验中，在野生型与sitiens或flacca之间进行了相互嫁接。气孔导度与地上部的基因型一致，而非与根系的基因型一致。所有嫁接植株的气孔在土壤干燥时都会关闭，无论根系基因型如何，即无论根系产生脱落酸的能力如何。在第二类实验中，将野生型地上部嫁接到由一根野生型根嫁接到一根突变体（flacca或sitiens）根组成的分根系统上。对一个根系停止供水，而另一个根系充分浇水，以使地上部的水势不下降，膨压不丧失。当对突变体根系或野生型根系停止供水时，气孔关闭的程度相似。在第三类实验中，将具有野生型地上部和野生型或sitiens根系的嫁接植株种植在可放置于压力室中的花盆中，随着土壤变干压力增加，以使地上部始终保持完全膨压。随着土壤变干，气孔关闭，无论根系是野生型还是sitiens。这些实验表明，在没有叶片水分亏缺的情况下，土壤干燥时气孔也会关闭，且这一过程不需要根系产生脱落酸。根系发出的一种化学信号导致叶片质外体脱落酸水平发生变化，可能是气孔关闭的原因。
