Simultaneous requirement of carbon dioxide and abscisic acid for stomatal closing inXanthium strumariumL.

摘要

Open stomata of detached leaves ofXanthium strumariumL. closed only when carbon dioxide and abscisic acid (ABA) were presented simultaneously. Three parameters of stomatal closing were determined after additions of ABA to the irrigation water of detached leaves, while the leaves were exposed to various CO2concentrations (CO2s) in the air;a) the delay between addition of ABA and a reduction of stomatal conductance by 5,b) the velocity of stomatal closing, andc) the new conductance. Changes in all three parameters showed that stomatal responses to ABA were enhanced by CO2; this effect followed saturation kinetics. Half saturation occurred at an estimated CO2 in the stomatal pore of 200 μl l-1. With respect to ABA, stomata responded in normal air with half their maximal amplitude at ABAs between 10-6and 10-5M(+-)-ABA. The amounts of ABA taken up by the leaves during the delay increased with a power<1 (on the average, 0.67) of the ABA in the transpiration stream. The minimal amount of ABA found to produce a stomatal response was about 1 pmol of (+-)-ABA per cm2leaf area, almost two orders of magnitude smaller than the original content of the leaves in ABA indicating that most of the endogenous ABA was in a compartment isolated from the guard cells