H fluxes in excised samanea motor tissue : I. Promotion by light

Abstract

Previous investigators revealed that white light-promoted leaflet opening in Samanea saman (Jacq) Merrill depends upon K(+) uptake by extensor cells and efflux from flexor cells of the pulvinus, while dark-promoted closure depends upon K(+) fluxes in the opposite directions. We now monitored H(+) fluxes during pulvinar movement to test a model proposing coupled H(+)/K(+) fluxes. H(+) fluxes were monitored by measuring changes in the pH of a weakly buffered solution (initial pH = 5.5) bathing excised strips of extensor or flexor tissue. White light at hour 3 of the usual dark period promoted pulvinar opening, H(+) efflux from extensor cells and uptake by flexor cells, while darkness at hours 2 to 4 of the usual light period promoted pulvinar closure, H(+) uptake by extensor cells and efflux from flexor cells. The following conditions altered H(+) fluxes during dark-promoted closure. (a) Light reversed the directions of the fluxes in both extensor and flexor cells. (b) Anoxia increased the rate of H(+) uptake by extensor cells and promoted H(+) uptake (rather than efflux) by flexor cells, consistent with an outwardly directed H(+) pump. KCN showed similar effects initially, but they were transient. (c) Increase in external pH from 5.5 to 6.7 promoted H(+) efflux (rather than uptake) by extensor cells and increased the rate of H(+) efflux from flexor cells, presumably by decreasing the rate of inward diffusion. (d) Change in external K(+) did not alter H(+) fluxes by extensor cells, but removal of external K(+) decreased the rate of H(+) efflux from flexor cells by 70%. These observations support a model for coupled H(+)/K(+) fluxes in pulvinar cells during light-and dark-promoted leaflet movements.