Ion Binding by Surfaces of Isolated Cuticular Membranes

Abstract

A markedly greater binding of Ca++ from Ca45Cl2 and SO-- 4 from K2S35O4 occurred on the inner compared to the outer surfaces of enzymically isolated cuticular membranes of astomatous, ripe tomato fruit cuticles and stomatous green onion leaf cuticles. This was related to morphological differences in the cuticular surfaces. The outer surfaces were smooth, while the inner surfaces showed protrusions and cuticular fragments outlining the epidermal cell walls, including the guard cells in the onion. Retention of ions, on comparable cuticular surfaces, against blotting, washing, and exchange was greater for Ca++ than SO4, and for onion leaf than tomato fruit. Total removal for SO4 but not for Ca++ was accomplished by exchange. Maximum fixation of Ca++ on surfaces of tomato fruit cuticle occurred within 3 minutes from a concentration of 1 m[image] CaCl2-Saturation with SO-- 4 was not achieved even after 200 minutes. lon binding on fresh but not on boiled cuticular surfaces of tomato fruit, or a dialyzing membrane was enhanced by KCN and kinetin, but greatly reduced by DNP.