Desenvolvimento de frutos com sementes e alterações citológicas em frutos partenocárpicos de atemoia

Abstract

The period of fruit development is marked by changes in the phases of cell division, expansion and cytological aspects. The exogenous application of GA3 in atemoya flowers induces parthenocarpy and, associated with artificial pollination, increases fruit size. The aim of this study was to characterize the development of the atemoya fruit and to contribute to the elucidation of its induction mechanisms and parthenocarpy. Morphological, anatomical, histochemical, ultrastructural and physiological aspects were evaluated during fruit development. Three treatments were applied: (1) control treatment with fruits produced by artificial pollination (AP); (2) fruits from AP followed by application of 250 ppm of GA3; and (3) parthenocarpic fruits induced by the application of 1000 ppm GA3. The growth of atemoya fruit showed a sigmoid pattern, whose development occurred in three phases: I) cell division, II) cell differentiation and III) maturation. Cell division was restricted to phase I, ending at 70 days post anthesis (DPA). Fruit size was defined at the end of phase II at 105 DPA and cell expansion and mass increase occurred until harvest at 120 DPA. The ultrastructural aspects reveal that phase I presented cells with large nuclear volume and a large population of organelles, phase II, reduction of the cytoplasm and increase of the volume of the vacuole and phase III, increase of plastids with reserve compounds. GA3 promotes the growth of pollinated fruits with a stimulus to cell division and expansion, associated with reduced seed production and induces parthenocarpy by maintaining the division and expressive stimulus to cell expansion. The absence of seeds, occasioned by the exclusive application of GA3, determined the smallest size of the parthenocarpic fruits and the lowest firmness, related to the loosening of the cellular wall caused by the lowest accumulation of calcium.