Adenosine Triphosphatase Activities in Leaves of the Mangrove Avicennia nitida Jacq: Influence of Sodium to Potassium Ratios and Salt Concentrations

Homogenates from the salt-excreting leaves of the mangrove Avicennia nitida were subjected to differential centrifugation and investigated for adenosine triphosphatase activities. At pH 6.75 a salt stimulation with peaks at three different sodium to potassium ratios could be demonstrated above the activity due to Mg²⁺ ions. The stimulation by sodium and potassium depends on the ionic strength of the test medium, higher salt concentrations being inhibitory. The plant system seems thus more complicated than the animal activities. Technically, this means that a search for (Na⁺ + K⁺)-activated ATPases in plants should be performed with a close spacing of Na:K ratios at several constant levels of salt. Literature data on the transport of Na⁺ and K⁺ indicate that the physiological situation is rather complex in plants.