DISCRETE SUBCELLULAR-LOCALIZATION OF MEMBRANE-BOUND ATPASE ACTIVITY IN MARINE ANGIOSPERMS AND MARINE-ALGAE

The subcellular distribution of membrane-bound ATPases was compared am ong terrestrial plants, seagrasses and marine algae by cytochemical te chniques. High ATPase activity was detected in the copiously invaginat ed plasma membrane that was characteristic of transfer cells but not i n the tonoplast of epidermal cells in mature leaves of seagrasses. Mag nesium- or Ca2+-dependent ATPase activity was induced together with th e characteristics of transfer cells during the development of leaf tis sues able to resist seawater. Northern hybridization revealed the effe ctive induction of the synthesis of mRNA for plasma-membrane H+-ATPase during the development of leaves. Such high ATPase activity was not d etected in the smooth plasma membranes of marine macro-algae but was f ound in the membranes of some cytoplasmic vesicles or microvacuoles, p roviding evidence of the excretion of salts by exocytosis. It appears, therefore, that two essentially different methods for excreting exces s salts have developed separately in these two classes of marine plant s. The evolution of mechanisms of salt tolerance in the plant kingdom is discussed in terms of the differential subcellular distribution of ATPase activity.