ULTRACYTOCHEMICAL AND BIOCHEMICAL STUDIES OF PLASMA MEMBRANE ATPASE IN THE INDIVIDUAL PARTS OF THE MATURE,DORMANT SEED OF PISUM SATIVUM

The location and activity of a K⁺-ATPase in mature, dormant peas were investigated using two ultracytochemical techniques, as well as biochemical assays of plasma membrane fractions from separate seed parts. Both the Wachstein and Meisel (1957) and the Ernst (1972) cytochemical methods showed plasma membrane-associated reaction product located primarily on the exterior surfaces of the entire pea embryo, except for the stem apex and tip-most cells of the radicle. No plasma membrane-assocated reaction product was found in the seed coat, which typically consists of cells with degenerating protoplasts. Biochemical results showed the highest specific K⁺-ATPase activity in the radicles (775 nmol Pi/mg protein/hr), followed by epicotyls (168 nmol Pi/mg protein/hr) and cotyledons (147 nmol Pi/mg protein/hr). It is proposed that the entire pea embryo may function in the active absorption of nutrients during the initial phases of germination. Additional functions of the enzyme may include cell wall loosening prior to cell elongation, regulation of cytoplasmic pH, and the generation of turgor.