Effects of Leaf Age and Position on the Shoot Axis on Potassium Absorption by Tomato Leaf Slices

The effect of leaf age on K (⁸⁶Rb) influx into tomato (Lycopersiconesculentum Mill.) leaf lamina slices was determined for leaves5, 9 and 13 counting acropetally. Potassium influx rates expressedon a leaf fresh weight basis declined rapidly during leaf elongationat external KCI concentrations between 0.5 and 20.0 mM. In fullyexpanded leaves, K influx rates declined more slowly with age.The onset of senescence in mature leaves did not result in alarge loss in K uptake capability. Leaf position on the shootaxis and the stage of whole plant development had little influenceon K influx into leaf cells. It is suggested that the rapiddecrease in K influx in growing leaves is related to a dilutionin the concentration of K transporter sites resulting from anincrease in cell volume and weight. Lycopersicon esculentum Mill, tomato, free space, potassium, influx rate, ion uptake, leaf slices, leaf age leaf ontogeny     

Effect of Leaf Age on Potassium Efflux and Net Flux in Tomato Leaf Slices

The effects on leaf age on K (⁸⁶Rb) efflux, influx and net fluxinto lamina slices from leaf 7 on a tomato plant (Lycopersiconesculentum Mill.) were determined. The ontogenetic trend inK efflux was dependent on the external K concentration. At externalKCI concentrations between 0.5 and 10.0 mM, K efflux rates increasedduring leaf elongation. Only a small increase in efflux occurredin mature leaves with increasing age. It is suggested that thetonoplast retains its structural integrity through the initialstages of leaf senescence. In fully expanded leaves, a zeronet K flux (a balance between influx and efflux) was achievedat external KCI concentrations between 1.0 and 3.5 mM. The Kcontent of lamina slices from leaves 5 and 13 remained constantwhen bathed in a solution containing 2 to 3 mM K. It is suggestedthat the decline in K concentration in mature tomato leaf tissueis due to a decline in leaf free space K concentrations below1 to 3 mM which would result in a net efflux out of leaf cells. Lycopersicon esculentum Mill., tor ato, free space, ion fluxes, leaf age, leaf ontogeny, potassium