Acid Phosphatase Activities in Developing Seeds of Pisum sativum L

Abstract

The seedcoats contain almost all of the acid phosphatase activity (EC 3.1.3.2) in the pea seed in the earliest stages of expansion. The seedcoat activity is maximal by the end of the period of rapid cell expansion and declines as the embryo matures. The developing cotyledons show a later rise in acid phosphatase activity to a maximum shortly before dehydration. The activity in the embryonic axis shows a marked increase only during dehydration.

The acid phosphatase activity in the seedcoats results almost entirely from an isoenzyme with high electrophoretic mobility in 5.5% polyacrylamide gels (R_F 0.97). This isoenzyme has not been detected in other tissues from the plant. The phosphatase activity in the cotyledons is accounted for by one major isoenzyme at R_F 0.75 and by four minor components. The partially purified enzyme from the seedcoats shows a broad pH optimum from pH 5.0 to pH 6.0. In contrast, the preparation from the cotyledons has an optimum close to pH 5.6 and is slightly more sensitive to inhibition by 0.2 mM P_I.