CYTOPLASMIC AND CELL WALL-BOUND В -GLUCOSIDASE ACTIVITY DURING ONTHOGENESIS IN PLANTS OF PISUM SATIVUM L
Activity of cytoplasmic and cell wall-bound molecular forms of P-glucosidase (EC 3.2.1.210) which is degrading plant specific isosuccinimide-p-glucoside (IS-glycoside) during germination and growth of Pisum sativum L. was determined. Pea plants (Ramonskiy 77) were grown hydroponically or during small plot experiments until ripening stage. p-glucosidase activity was determined with IS-glucoside used as a substrate by the amount of glucose formed. Adsorbed P-glucosidase was extracted by cell wall residue washing with 1 M of phosphate-citric buffer (pH 6.0) and ion-bound form with 1 M of NaCl. Simultaneously in plants the content of IS-glucoside and soluble sugars were measured by thin layer chromatography method. It was shown that in over ground part of 5-day-old pea seedlings the activity of cell wall-bound P-glucosidase was higher than cytoplasmatic one. It was 1.5-3-fold increasing and for 10-day-old seedlings for ion-bound with cell wall was 18.50±0.14 and for adsorbed 10.6±0.09 EU mg-1. But later it started sharply decreasing. In dry seeds the activity of P-glucosidase was not detected but it was diagnosed in seeds on milky stage (1.89±0.06 EU mg^t of protein). Activity of cytoplasmic P-glucosidase in leaves of 2-week-old seeds was 4.30±0.14 EU mg-1 of protein and remained relatively high till flowering (bud-formation period) though in roots it was substantially lower.IS-glycoside was also not detected in dry seeds. Amount of IS-glycoside in leaves of 10-day-old seedlings was 5.76±0.06 mg g-1 of we weight which was little lower of glucose but exceeded the level of saccharose. In roots the content of IS-glycoside was always lower as cytoplasmic P-glucosidase activity. Our results show that cytoplasmic and cell wall-bound molecular forms of P-glucosidase are responsible for different functions in ontogenesis of pea plants. Relatively high activity of cytoplasmic P-glucosidase in leaves during all growth stages allows to refill a fund of glucose for respiratory cell metabolism in pea plants through specific IS-glycoside hydrolysis and be involved in transglycosidation reaction with formation of other glycosides. Cell wall-bound adsorbed and ion-bound molecular forms of P-glucosidase which activity is significantly decreasing with aging, provide participation of IS-glycoside as a glucose supplier in construction of cell wall substances in young and actively growing pea seedlings.