The Influence of Water Strain on the Minimum Intercellular Space Carbon dioxide Concentration λ and Stomatal Movement in Wheat Leaves

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Abstract
Eight detached wheat leaves were each subjected to varying degrees of controlled water strain, in a specially constructed leaf chamber (which is described in detail) connected to a closed system incorporating an infra-red gas analyser. The water strain was varied by applying successively to their leaf sheaths two concentrations of mannitol solution (0·2 M. and 0·4 M.) each preceded and followed by water. Conditions were maintained constant for light (900 f.c.), leaf temperature (25° C.) and humidity (50 per cent. RH) of the circulating air as it entered the leaf chamber. Steady-state values (gamma) of the carbon dioxide concentration in the closed system were recorded both for the water and mannitol treatments and the data analysed statistically. The two mannitol treatments were found to increase gamma from 80 p.p.m. with water to 94 and 116 p.p.m. respectively, all differences being highly significant. Concomitant measurements were made of stomata1 resistance with a porometer and of transpiration by means of wet and dry thermocouples; the stomata showed marked closure in response to mannitol treatment (complete closure with the higher concentration) and partial reopening with the leaf sheath in water once more, transpiration also falling and rising inversely with water strain. It is concluded that part of the closing response of wheat stomata to water strain under natural conditions must be operated by increase in the intercellular-space carbon dioxide concentration, but a comparison with previous experimental results suggests that this can only be a small part unless sensitivity to carbon dioxide is greatly increased by water loss. The initial response to mannitol treatment was a preliminary opening of the stomata and a fall of about 10 per cent. in carbon dioxide concentration. These results imply that under natural conditions the preliminary opening of wheat stomata with wilting may be partly passive and partly active with a carbon dioxide-operated mechanism. A subsidiary experiment with water strain varied by removing and restoring the water supply to the leaf sheath gave increases and decreases in carbon dioxide similar to those in the main experiment; the results of the latter need not, therefore, be attributed to metabolism of the mannitol. It is suggested that values of gamma give a good measure of the efficiency of the mesophyll for net carbon dioxide absorption, with the stomatal factor eliminated, under the given conditions and with carbon dioxide ‘limiting’ in the sense used by Maskell (1928).

This publication has 1 reference indexed in Scilit:

  • IX. Observations on stomata
    Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character, 1898