Abstract
Stomatal conductance ( g s), water potential (ψ), 14C-labelled assimilate export, and abscisic acid (ABA) concentration, were measured in flag leaves hof pearl millet grown in the field in the semi-arid tropics with restricted water supply. At similar ψ, g s increased with progressive stage of development hand growth of the panicle. Flag leaves ixhibited a lower s and rate of 14C-assimilate export, and a higher concentration of ABA, at the boot stage than following panicle emergence. Panicle removal resulted in a reduction in flag leaf 14C-assimilate export when carried out at stigma emergence (panicles just fully emerged from flag leaf sheath), but not when carried out after grain set. Reduction in flag leaf s were detected about 3 days after panicle removal and were correlated with increases in ABA concentration. The increased ABA was not due to any reduction in ψ. Completely blocking assimilate export by heat girdling caused a marked increased in ABA and a reduction in g s. It is suggested that the panicle might stimulate the export of ABA from the flag leaf, so lowering the ABA concentration in the leaf gand facilitating the higher g s found, under water stress, in flowering plants.
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