SUCROSE METABOLISM AND ACCUMULATION IN DEVELOPING FRUIT OF CUCUMIS

Sucrose, reducing sugars and starch content were measured in developing cucumber (C. sativus cv Delilah), sweet melon (C. melo cv Galia and cv Noy Yizre''el) and non-sweet melon (C. melo cv Bird''s Nest) fruit. Sweet melon were characterized by accumulation of sucrose in the maturing fruit, while cucumber and non-sweet melon had a low sucrose content at all stages studied. Soluble acid invertase activity (EC 3.2.1.26) dramatically decreased in sweet melon, concomitant with the onset of sucrose accumulation. Significant activity of soluble acid invertase was retained in mature cuncumber and non-sweet melon. Insoluble acid invertase, determined not to be an artifact of extraction, constituted a significant portion of total invertase activity (ca 25% in young sweet melon and ca 50% in young cucumber). In sweet melon sucrose synthase activity (EC 2.4.1.13), measured in both the cleavage and synthesis direction, increased during the sucrose accumulation period. The results are discussed in terms of the roles of invertase and sucrose synthase in sucrose accumulation in Cucumis.