Major Element Composition of Epidermal and Mesophyll Tissues2Commelina CommunisL. andVicia FabaL.: Some Further Considerations of the Role of Ions in Stomatal Functioning

Abstract

Epidermal and mesophyll tissues of Commelina communis L. and Vicia Jaba L. were analysed by atomic absorption spectrometry for the major plant inorganic cations and anions (K, Na, Ca, Mg, P, NO3-N, CI) when stomata of the leaf were open and closed. Water-soluble and residual levels of the elements were estimated and a charge balance of the soluble fraction made. The major portion of K, Na, CI, and P was extracted in the water-soluble fraction of the epidermal and mesophyll tissues of both species. In both species the bulk of Ca remained in the insoluble residue of the epidermis whereas in mesophyll tissue it was equally distributed be between the two fractions in C. communis but mainly in the insoluble residue in V. faba. Magnesium was predominantly found in the water-soluble fraction of V. faba mesophyll tissue and distributed approximately equally between the two fractions in the epidermal tissue. In O. communis Mg was slightly more abundant in the water-soluble fraction of both mesophyll and epidermis. In both species no statistically significant differences in the levels of the elements could be detected between epidermal and mesophyll tissues from leaves with open stomata and the same tissues from leaves with closed stomata, suggesting that there was no major flux of ions between mesophyll and epidermis during stomatal movements. Regardless of whether the stomata were open or closed, there were considerably more water soluble inorganic cations than anions present in all tissues of both species with K being the major cation and CI being the major anion. In V.faba and C. communis epidermis there was 49-53 per cent and 56-68 per cent excess cation respectively. In the mesophyll tissue the excess cation was 63-75 per cent and 75-78 per cent in V.faba and C. communis respectively. When the partitioning of the levels of the elements between epidermis and mesophyll of a leaf is considered, except for NO3-N in both species and Na in V. faba, 20 per cent or less of each element was present in the epidermis. 1 Much of this work was completed while the first author was a Research Associate at the Southern Piedmont Conservation Research Centre, Watkinsville, Georgia 30677, U.S.A. This content downloaded from 40.77.167.19 on Mon, 04 Jul 2016 04:23:57 UTC All use subject to http://about.jstor.org/terms 974 Willmer, Pallas, and Jackson—Epidermal and Mesophyll Tissues