Atemoya fruit development and cytological aspects of GA₃-induced growth and parthenocarpy

The exogenous application of GA₃ to atemoya tree flowers induces parthenocarpy, and in association with artificial pollination, it increases the fruit size. Morphological, anatomical, ultrastructural, and chemical aspects were evaluated during development of (1) fruit produced by artificial pollination (AP), (2) fruit from AP followed by the application of 250 ppm GA₃, and (3) parthenocarpic fruit induced by the application of 1000 ppm GA₃. Fruit growth showed a sigmoidal pattern, with development occurring in three phases: (I) cell division, (II) cell differentiation, and (III) maturation. Phase I presented cells with large nuclear volumes and a large population of organelles, phase II presented cells with a reduction in cytoplasm and an increase in vacuole volume, and phase III presented cells with an increase in plastids with reserve compounds. The application of GA₃, in association with pollination, precedes cytological events and delays when applied exclusively. GA₃ promotes the growth of pollinated fruits by stimulating cell division and expansion, which occur in association with reduced seed production, and the GA₃ induces parthenocarpy by maintaining division and stimulating cell expansion. The absence of seeds accounts for the smaller size of the parthenocarpic fruits, and the lower accumulation of calcium accounts for less firm fruit.