BIOCHEMICAL CONTROL OF STOMATAL OPENING IN LEAVES

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Abstract
The effect of [alpha]-hydroxysulfonates, inhibitors of glycolic oxidase, supplied to detached tobacco leaves in sunlight in markedly reducing the water lost by transpiration by stomatal closure is reported. This study was aided by a new technique for measuring stomatal apertures without altering the leaf environment by means of silicone rubber impressions made of the leaf surface. A standard assay for measuring the extent of stomatal closure by compounds supplied to tobacco leaf disks in the light is described. With this leaf disk assay, a number of metabolic regulators, including [alpha]-hydroxysulfonates, plant growth regulators, and metal-chelating compounds have been found to prevent stomatal opening at concentrations of about 1 X 10-3 M. One of the [alpha]-hydroxysulfonates has also been shown to close already opened stomata. Evidence is presented that by inducing stomatal closure in intact leaves, it is possible to reduce water lost by transpiration at high light intensities without diminishing photosynthetic CO2 assimilation. These studies offer a new approach to the conservation of water through the biochemical control of leaf stomata.