Arginase, arginine decarboxylase, ornithine decarboxylase and polyamines in tomato ovaries - Changes in unpollinated ovaries and parthenocarpic fruits induced by auxin or gibberellin

Arginase (EC 3.5.3.1) activity has been found in the ovaries and young fruits of tomato (Lycopersicon esculentum Mill. cv Rutgers). Changes in arginase, arginine decarboxylase (EC 4.1.1.19), and ornithine decarboxylase activity (EC 4.1.1.17) and levels of free and conjugated putrescine, spermidine, and spermine were determined in unpollinated ovaries and in parthenocarpic fruits during the early stages of development induced by 2,4-dichlorophenoxyacetic acid (2,4-D) or gibberellic acid (GA(3)). Levels of arginase, free spermine, and conjugates of the three polyamines were constant in unpollinated ovaries and characteristic of a presenescent step. A marked decrease in arginase activity, free spermine, and polyamine conjugates was associated with the initiation of fruit growth due to cell division, and when cell expansion was initiated, the absence of arginase indicated a redirection of nitrogen metabolism to the synthesis of arginine. A transient increase in arginine decarboxylase and ornithine decarboxylase was also observed in 2,4-D-induced fruits. In general, 2,4-D treatments produced faster changes than GA(3), and without treatment, unpollinated ovaries developed only slightly and senescence was hardly visible. Sensitivity to 2,4-D and GA(3) treatment remained for at least 2 weeks postanthesis.