Adenosine triphosphatase in epidermal tissue of Commelina benghalensis: possible involvement of isozymes in stomatal movement

Abstract

Lower epidermal extracts of Commelina benghalensis possessed high ATPase activity. The presence of two isoenzymes of ATPase was indicated by their pH response and their preferential activation by K⁺ or Ca²⁺. One of the two isozymes of ATPase was with an optimal pH of 5.5 (ATPase 5.5), activated by Ca²⁺ and the other with an optimal pH of 7.5 (ATPase 7.5) was stimulated by K⁺. The response of these two isozymes to various inhibitors was in close agreement with their effect on stomatal movement. Activity of ATPase 5.5 was maximal in night and minimal during the day. On the other hand ATPase 7.5 was active during the day and was at a low level at night. Thus the optimal pH, inhibitor response and their diurnal rhythm suggested the existence of two isozymes of ATPase in the lower epidermis: ATPase 7.5 associated with stomatal opening and ATPase 5.5 with stomatal closure.