ABAXIAL AND ADAXIAL STOMATAL BEHAVIOUR AND RESPONSES TO FUSICOCCIN ON ISOLATED EPIDERMIS OFCOMMELINA COMMUNISL.

Abstract

Summary A comparative study was made of the behaviour of abaxial and adaxial stomata on isolated epidermis of Commelina communis incubated under controlled conditions. The degree of opening and of K+ accumulation, and the responsiveness to light, carbon dioxide, abscisic acid and KC1 concentration were substantially higher in abaxial than in adaxial stomata; thus their differential behaviour is mainly a result of inherent, rather than of environmental, differences between the two epidermes. The isolation of guard cells, by killing other epidermal cells, failed to annul the disparity, suggesting that any difference in subsidary cell resistance between the two epidermes is not responsible for this phenomenon. Fusicoccin was able to overcome the smaller opening of adaxial stomata, indicating that there is no fundamental difference in the potential opening ability between abaxial and adaxial stomata. Even in a medium free of KC1, fusicoccin stimulated exceptionally high K+ accumulation in adaxial guard cells, demonstrating that endogenous K+available in the adaxial epidermis is sufficient for wide opening. Accordingly, an inherent metabolic condition of adaxial stomatal cells appears to prevent them opening as wide as abaxial stomata. The effectiveness of fusicoccin to produce exceptionally wide adaxial apertures suggests that, when necessary, the proton pump can operate as efficiently in adaxial as in abaxial guard cells.

Effects of Phenylacetic Acid on Abaxial and Adaxial Stomatal Movements and Its Interaction With Abscisic Acid

“…Thus, its effects on abaxial and adaxial stomata suggest a hormonal basis for their differential behaviour. In fact, our experimental results that indole-3-acetic acid (Pemadasa, 1982b), like fusicoccin (Pemadasa, 1981), is highly effective in producing exceptionally wide adaxial apertures and, therefore, eliminating the normal disparity in abaxial and adaxial opening also substantiate this supposition.…”

“…The observed reduction of the PAA-effect with increasing external KCl concentration substantiates this view, for the effect of decreasing concentration gradient would be to reduce the net K+ efflux in spite of the high membrane permeability. On the other hand, even if incubated in 200 mol na^^ KCl under illumination in COj-free air, the K"*" content is much less in adaxial than in abaxial guard cells (Pemadasa, 1981), a clear evidence of an inherent restriction to K' *' fluxes. This could well be a result of restricted membrane permeability, which PAA is postulated to alleviate progressively with increasing concentration.…”

“…The absolute stomatal responses, i.e. the difference in aperture between a particular PAA treatment and the relevant control (Travis and Mansfield, 1979a;Pemadasa, 1981), show clearly the dependence of the PAA-effect not only on its own concentration, but also on the external KCl regime (Fig. 2).…”

“…This suggested that, in addition to its inhibition of blue light reception, PAA also has other effects on guard cell functioning. The experiments described here examine this possibility, and the results show contrasting responses of adaxial and abaxial stomata to variations of PAA concentration, and, therefore, reveal further complications in the unknown mechanism of differential abaxial and adaxial stomatal behaviour (Turner, 1970(Turner, , 1979Pemadasa, 1979aPemadasa, , 1981. …”

DIFFERENTIAL ABAXIAL AND ADAXIAL STOMATAL RESPONSES TO INDOLE‐3‐ACETIC ACID INCOMMELINA COMMUNISL.

“…An earlier study using isolated epidermes (Pemadasa, 1981) demonstrated that the well known disparity in abaxial and adaxial stomatal opening (Turner, 1970(Turner, , 1979Pemadasa, 1979a) is chiefly a refiection of inherent, rather than of environmental, differences between the two epidermes. Although the reaction to external stimuli is basically similar, the degree of responsiveness is markedly higher in abaxial than in adaxial stomata; isolation of guard cells by killing subsidiary and other epidermal cells (Squire and Mansfield, 1972) cannot eliminate this difference (Pemadasa, 1981).…”