Fruit Development and ABA Biosynthesis During Caryocar brasiliense (Caryocaraceae) Seed Maturation

Little is currently known about the interactions between structural and physiological factors in Neotropical fruit development. We sought to characterize fruit development and the dynamics of ABA biosynthesis during seed maturation in Caryocar brasiliense, a tree species endemic to the Cerrado biome of Brazil. Biometric evaluations were made of both the pericarp and seed during fruit development. ABA1, NCED4, and NCED9 expression were evaluated in embryonic tissues during seed maturation, as well as anatomical, histochemical, and ultrastructural evaluations, in vitro and ex vitro embryo cultures, and ABA quantifications. Fruit development demonstrated three stages: histodifferentiation (0–40 days after anthesis—DAA); endocarp maturation (40–60 DAA); and the conclusion of mesocarp and seed maturation (60–90 DAA). The embryos showed early degrees of differentiation: hypocotyl expansion, development of the leaf primordia, and vascularization. Seed maturation occurred (from 40 DAA) concomitantly with the development of endocarp aculei in four phases influenced by ABA dynamics. The beginning of reserve deposition and the acquisition of dehydration tolerance were related to increases in extra-embryonic ABA. ABA biosynthesis at the radicular pole was related to increased reserve deposition and dehydration tolerance (which was not associated with the occurrence of a desiccation phase). The maturation of C. brasiliense seeds is influenced by embryonic and extra-embryonic ABA, and the dormancy of the pyrenes results from the interaction of the effects of that hormone and pericarp tissue.