Sucrose Metabolism During Papaya (Carica papaya) Fruit Growth and Ripening

ADDITIONAL INDEX WORDS. sweetness, carbon import rates, fruit growth, seed development, postharvest ABSTRACT. Papaya (Carica papaya L.) fruit flesh and seed growth, fruit respiration, sugar accumulation, and the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) were determined from anthesis for ≈150 days after anthesis (DAA), the full ripe stage. Sugar began to accumulate in the fruit flesh between 100 and 140 DAA, after seed maturation had occurred. SPS activity remained low throughout fruit development. The activity of SS was high 14 DAA and decreased to less than one-fourth within 56 DAA, then remained constant during the remainder of fruit development. AI activity was low in young fruit and began to increase 90 DAA and reached a peak more than 10-fold higher, 125 DAA, as sugar accumulated in the flesh. Results suggest that SS and AI are two major enzymes that may determine papaya fruit sink strength in the early and late fruit development phases, respectively. AI activity paralleled sugar accumulation and may be involved in phloem sugar unloading. and the activities of SPS, SS and AI during papaya fruit development and ripening. In addition, the patterns of these enzymes' activities during late fruit development were compared between a low-sugar accumulating breeding line and commercial cultivars. An under- standing of the biochemistry and key enzymes involved in sucrose accumulation in papaya is a prerequisite to possible genetic im- provement of the sweetness of this fruit.

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