[The responses of the CO2-control system in the stomates of Zea mays to white light]

Abstract

Stomatal movements were recorded in isolated leaf sections of Zea mays. Through continuous operation of the porometers it was possible to follow the reactions of the stomatal feedback system.White light was provided by a high-pressure xenon arc. Radiation intensity was varied in steps. The experiments were performed in air, in air free of CO2, and in nitrogen.The equilibrium width of the stomata and the speed of the opening movement were measured and evaluated.The experimental analysis of the stomatal reactions confirmed that the CO2-feedback system is clearly responsible for the stomatal responses to light. Light interferes at three stages of the servo-system: 1. Light starts and maintains assimilation. Through the agency of this process the CO2 concentration within the leaf is lowered. Light may be regarded as an ingoing or disturbing signal. The dependence of this reaction on radiation intensity is described by a saturation curve. 2. Light supplies energy to the opening mechanism of the stomata. This process is independent of the assimilation of carbon dioxide. Light is a source of auxiliary energy for the controlled system. Most probably energy is derived from an intermediary step of photosynthetic phosphorylation. This reaction shows a linear dependence on light intensity, at least up to 60 mW cm(-2), and occurs to the same extent in air, in air minus CO2, and in nitrogen. 3. Light induces reversible effects of fatigue and recovery. It adjusts the level at which the stomata are in equilibrium as well as the speed of the subsequent opening movements. Light influences the command signal of the controlling system and the efficiency of utilisation of auxiliary energy. These reactions occur equally in air, in CO2-free air, and in nitrogen. They cannot be described quantitatively as yet and appear to be located in the cytoplasm, probably at the interfaces. An hypothesis is suggested according to which stomatal movement results from an interaction of an osmotic regulatory system with a system of turgor control, the former providing energy for the latter. Osmoregulation is achieved by energy-dependent ion translocations in mitochondria and chloroplasts; turgor adjustments are made through changes in the permeabilities for water and solutes, brought about by CO2 and light.