Localisation des activités de la p-nitrophénylphosphatase et de la phosphatase alcaline dans les cellules de transfert du noeud cotylédonaire du pois nain

Abstract

The ultrastructural localization of the K+-dependent nitrophenylphosphatase (NPPase) and alkaline phosphatase (ALPase) activities were determined in the transfer cells of the pea cotyledonary node. These two types of activities were generally associated and located essentially on the plasma membrane. NPPase and ALPase activities were also detected along the nuclear membrane of the xylem and phloem transfer cells and along the endoplasmic reticulum profiles (internal face) of phloem transfer cells. Mitochondrial NNPase activity was confined to the outer membrane and cristae. The partial inhibition of the NPPase reaction products by L-p-bromotetramisole and cysteine, the weak reaction observed after deletion of K+, and the suppression of the reaction in the presence of L-p-bromotetramisole are best explained by the concomitant activity of a K+-dependent NPPase and of an ALPase partially inhibited by K+. On the basis of sensitivity to inhibitors, two plasma membrane ALPase isoenzymes were detected. One, extramembranous, was bromotetramisole and cysteine insensitive but inhibited by L-phenylalanine; the other, intramembranous, was bromotetramisole and cysteine sensitive, but insensitive to L-phenylalanine. The other sites of ALPase activities were substantially inhibited by all treatments.