Control of stomatal aperture by calcium in isolated epidermal tissue and whole leaves of Commelina communis L.

Abstract

SUMMARYPlants of Commelina communis L. were grown in media containing different concentrations of calcium from 1 to 8 mol m −3. After 4 weeks' growth stomatal behaviour was studied both on the intact plants and on isolated abaxial epidermis. The effect of Ca nutrition on stomatal opening was apparently different according to these two methods of observation. The apertures measured in light and in absence of CO2 were smaller on abaxial epidermal strips from plants grown at larger Ca concentrations than those grown at smaller concentrations. The inhibition of opening was thought to be due to the presence of free Ca2+ ions because inhibition was not found when EGTA was included in the medium used for incubating the isolated epidermis, and significant quantities of Ca were lost to the medium by epidermal tissue from plants grown on high concentrations of Ca.Studies on the leaves of intact plants were made with a diffusion porometer and by gas exchange techniques using a leaf cuvette in which the environment was closely controlled. A/c1 curves were used to partition non‐stomatal and stomatal limitations to gas exchange. Porometer measurements of stomatal conductance, determined within the growth room, indicated reduced values for plants grown at low Ca compared with those grown at high Ca, i.e. the observations contradicted those obtained with isolated epidermis.Biomass production increased with Ca up to 4 mol m −3. Analysis of A/c1 curves indicated that plants grown at the larger Ca concentration showed significantly greater values for carboxylation efficiency (dA/dc1). Partitioning of stomatal and non‐stomatal limitations to carbon fixation indicated that the gas‐phase limitations of CO2 were similar at different Ca concentrations. Differences in carboxylation efficiency could account for the greater biomass accumulation found at the larger Ca concentration.Calcium analysis indicated that plants grown at high Ca contained greater bulk leaf Ca concentrations, and a difference in Ca concentration was also evident in epidermal tissue, but the relative distribution of fractionated epidermal Ca was similar. Xylem sap Ca analysis also revealed more Ca in the apoplast of high Ca grown plants.The differences in stomatal behaviour in isolated epidermis and in the intact leaves suggest that in Ca‐rich plants, the level of free Ca2+ ions in the vicinity of guard cells is controlled, thus preventing inhibition of stomatal opening and interference with gas exchange. The loss of this control when epidermis is detached implies that the presence of the mesophyll tissue is important.