Sucrose Phosphate Synthase , Sucrose Synthase , and Invertase Activities in Developing Fruit of Lycopersicon esculentum Mill . and the Sucrose Accumulating Lycopersicon hirsutum Humb . and Bonpl . 1 Daphne Miron and Arthur

The green-fruited Lycopersicon hirsutum Humb. and Bonpi. accumulated sucrose to concentrations of about 118 micromoles per gram fresh weight during the final stages of development. In comparison, Lycopersicon esculentum Mill. cultivars contained less than 15 micromoles per gram fresh weight of sucrose at the ripe stage. Glucose and fructose levels remained relatively constant throughout development in L. hirsutum at 22 to 50 micromoles per gram fresh weight each. Starch content was low even at early stages of development, and declined further with development. Soluble acid invertase (EC 3.2.1.26) activity declined concomitant with the rise in sucrose content. Acid invertase activity, which was solubilized in 1 molar NaCI (presumably cellwall bound), remained constant throughout development (about 3 micromoles of reducing sugars (per gram fresh weight) per hour. Sucrose phosphate synthase (EC 2.4.1.14) activity was present at about 5 micromoles of sucrose (per gram fresh weight) per hour even at eariy stages of development, and increased sharply to about 40 micromoles of sucrose (per gram fresh weight) per hour at the final stages of development studied, parallel to the rise in sucrose content. In comparison, sucrose phosphate synthase activity in L. esculentum remained low throughout development. The possible roles of the sucrose metabolizing enzymes in determining sucrose accumulation are discussed. The green fruited, wild Lycopersicon species (subspecies Eriolycopersicon) has been reported to contain high levels of sucrose, as compared with the red-fruited (Eulycopersicon) species, which contains primarily glucose and fructose in the mature fruit, with only trace amounts of sucrose (4). The species that accumulate sucrose are characterized by high TSS2 content ('Brix) and are of potential importance in improving fruit quality of cultivated Lycopersicon esculentum ' Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel, No. 2982-E, 1990 series. This research was supported by grant US 1321-87 from The United States-Israel Binational Agricultural Research and Development Fund. D. M. received support from the Israel Ministry of Science and Technology, the National Council for Research and Development. This work forms a part of a Ph.D. thesis of D. M. 2 Abbreviations: TSS, total soluble solids; SPS, sucrose phosphate synthase; daa, days after anthesis. 623 Mill. (20). Sucrose-accumulating storage tissues are characterized by a metabolic transition during development. During the initial growth phase, soluble acid invertase activity was relatively high, declining concomitantly with sucrose accumulation. Such a transition has been reported, for example, in sugar beet (7), sugar cane (8), sweet melon (12, 16, 18, 21), carrot (19), and citrus (14). In Solanaceae other than Lycopersicon, we have observed such a transition in Solanum muricatum Ait. (pepino) fruit (22). Among the Lycopersicon spp., Manning and Maw (17) reported that the sucrose-accumulating Lycopersicon peruvianum Mill. and Lycopersicon hirsutum had low soluble invertase activity, as compared with L. esculentum. Recently Yelle et al. (26) reported a loss of acid invertase activity during the development of the sucroseaccumulating Lycopersicon chmielewskii. In some of the above storage organs, sucrose accumulation is accompanied by an increase in sucrose synthase activity (6, 16, 18, 21, 22), suggesting that this enzyme may play a physiologically significant role. However, such a rise in activity has not been reported consistently ( 12). A rise in SPS activity parallels the rise in sucrose during the development of sweet melon (12, 16). Recently Hubbard et al. (12), following a procedure that minimized loss of labile SPS activity during tissue preparation and extraction, reported a sharp increase in SPS activity in sweet melons, reaching an activity of 32 ,umol of sucrose (g fresh weight)-' h-'. They suggested that sucrose accumulation is determined by the balance between sucrose synthesis (SPS activity) and degradation (invertase and sucrose synthase activities). Recently Fieuw and Willenbrink (6) also reported SPS activity, previously undetected in sugar beet root, using refined assay conditions. In this paper, we report a sharp rise in SPS activity, together with the loss ofsoluble acid invertase, during the development of L. hirsutum, a green-fruited, sucrose-accumulating species. The roles of sucrose-metabolizing enzymes in determining sink strength and sucrose accumulation are discussed. MATERIALS AND METHODS