EXPRESSION OF THIOL PROTEASES DECREASES IN TOMATO OVARIES AFTER FRUIT-SET INDUCED BY POLLINATION OR GIBBERELLIC-ACID

The modulation of the expression of thiol proteases during both senesc ence and development was investigated Proteolytic activity and some th iol proteases were analyzed in unpollinated tomato (Lycopersicon escul entum Mill. cv. Rutgers) ovaries during presenescence and during early fruit development induced by treatment with gibberellic acid (GA) or by natural pollination. Proteolytic activity in extracts was tested on azocasein and by observing degradation of the ribulose-1,5-bisphospha te carboxylase large subunit in western blots. There was no correlatio n between total activity and protein content. Thiol proteases were ana lyzed by western blot with antibodies raised against papain and a reco mbinant tomato C14 thiol protease. A 58-kDa polypeptide was recognized by both antibodies and two more polypeptides of 47 and 36 kDa were de tected with the second one. All these polypeptide levels increased in untreated unpollinated ovaries at the presenescent stage. Natural poll ination or GA treatment of unpollinated ovaries resulted in decreases of these polypeptides at an early developmental stage. The same patter n was observed for the levels of C14 mRNA. Our results suggest that th e expression of C14 thiol protease occurs in unpollinated ovaries at t he presenescent stage and that it can be suppressed by factors that in duce fruit set and development.