Ciclos de hidratação e desidratação em sementes de Handroanthus heptaphyllus (Vell.) Mattos

Abstract

During the final stage of formation, orthodox seeds acquire tolerance to desiccation, which allows them to withstand drying in the maturation process. Tolerance to desiccation allows the seeds to undergo hydration and dehydration cycles that may or may not reduce their germination capacity. This work aimed to understand the biochemical and physiological mechanisms of the seeds of Handroanthus heptaphyllus (Vell.) Mattos, are involved in desiccation tolerance in response to hydration and dehydration cycles at different imbibition times. For this, the seeds were soaked for 10 hours (time X) and 35 hours (time Y) and subsequently dehydrated for 12 hours (return to initial fresh weight) progressively for four times (constituting the hydration and dehydration cycles, HD). Germinative parameters (percentage of germination, germination speed index) and biochemical parameters (levels of carbohydrates, proteins, amino acids and H2O2) and activity of the enzymatic antioxidant system in the seeds at the end of the last rehydration of each cycle (catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase). The same biochemical parameters, in addition to biomass accumulation parameters (height, root length, number of leaves, dry mass of aerial part and root) and photosynthetic pigments, were evaluated in seedlings at 60 days. It was found that cycles and times influence seed germination and biochemistry. Seeds that passed through time X had their germination reduced until the fourth cycle, damage to the membrane and accumulation of soluble, non-reducing sugars, amino acids and proline mainly after the first HD cycle (1HD). HD cycles applied during time Y standardized and accelerated germination in the first two cycles, showing no damage to the membrane, but accumulating soluble non-reducing sugars, amino acids and proline, however, at lower levels than those observed in the cycles of time X. Seedlings from seeds that have gone through some cycle had a longer root length, with increased levels of chlorophyll a, total and carotenoids. Higher concentrations of soluble non-reducing sugars, with accumulation of proline were observed after 4HD at both times. It is concluded that HD cycles in time X are more harmful to seed germination and become more severe with the progression of the cycles. However, HD cycles during time Y advanced and synchronized seed germination. The passage through the cycles, regardless of time, increased the concentrations of soluble non-reducing sugars and proline, which gave tolerance to desiccation of the seeds. The presence of these metabolites in high concentrations also in the seedlings suggests that a stress response was passed from the seeds that passed through HD cycles to the seedlings.