Hormonal control of seed development in GA- and ABA-deficient tomato (Lycopersicon esculentum Mill. cv. Moneymaker) mutants

Developing seeds of tomato gibberellin (GA)-deficient gib1 and abscisic acid (ABA)-deficient sitw mutants enabled us to analyze the role of GA in the regulation of embryo histo-differentiation, and the role of ABA in the regulation of maturation and quiescence. Our data show that DNA synthesis and mitotic microtubule arrays are markers for cell division activity and histo-differentiation during early embryogenesis. Cortical microtubular cytoskeleton alone is a marker for expansion growth during maturation, as seed and embryo gain dry weight and attain their final size. During this phase germinability, desiccation tolerance and dormancy are acquired, and a transient increase in ABA occurs, preceding the achievement of physiological maturity and subsequent quiescence. In the gib1 mutant embryo development was retarded in all parameters studied, except for a transient rise in ABA content. In the sitw mutant embryonic DNA synthesis activity was resumed upon completion of histo-differentiation, the microtubular cytoskeleton network was re-established during maturation and followed by viviparous germination. This suggests that ABA controls the suppression of these events during maturation and quiescence. Induction of full seed germinability, desiccation tolerance and dormancy was related to the completion of embryo histo-differentiation but was independent of the state of the microtubular cytoskeleton during maturation.