MEMÓRIA À SECA NO CERRADO: ACLIMATAÇÃO DIFERENCIAL DO BARU (Dipteryx alata Vogel).

Abstract

The industrialization and the anthropogenic actions in natural environments have produced important changes in the global climate, and it is expected that in the coming years extreme weather events such as heat waves, cold, rain and drought will increase. The studies usually test the drought as an isolated event, but the Cerrado plants are frequently exposed to cyclical events of water restriction and tend to be naturally acclimatized to drought cycles. It is not known, therefore, how the climate changes will alter the survival or development of these species. Some plant species have a differential acclimatization mechanism, also known as "drought memory", characterized by the production of positive differential responses to water restriction events; on the other hand, there are also species that show sensitivity and decrease in their ability to produce responses when subjected to repeated cycles of stress, which directly affects their survival capacity. In this context, the present work exposed Baru seedlings (Dipteryx alata Vogel) to repeated cycles of drought, aiming to evaluate the morphological, anatomical, physiological and biochemical responses and thus characterize the existence of sensitivity or differential responses to drought events. There were practically no changes in morphoanatomical parameters in any of the treatments, and the greatest changes were observed in the biochemical and physiological parameters. Indeed it was possible to observe that when the plants were submitted to only one cycle of drought, there was a drop in gas exchange, an increase in respiration, an increase in the generation of reactive oxygen species and damage to cell membranes, changes that, together, culminated with a lower drought tolerance index. The plants exposed to three cycles of drought, on the other hand, presented a higher drought tolerance index than plants submitted to drought only once time, being able to maintain cellular homeostasis, as evidenced by the maintenance of the photosynthetic rate, respiration and of the generation of reactive oxygen species at levels similar to the control. The maintenance of the physiological parameters apparently involved adjustments at several levels, such as increases in antioxidant system activity and the maintenance of leaf hydraulic conductivity. Thus, the results showed that Baru plants are not sensitive to repeated cycles of drought. On the contrary, these plants presented a set of differential responses that allowed the plants exposed to three drought cycles to perform similarly to the control treatment, indicating the existence of a mechanism of memory to drought in a native brazilian savanna (cerrado) species.