Conteúdo de Tococromanóis em espécies arbóreas de várzea da Amazônia Central sob condições controladas

Abstract

With more than 1,000 registered tree species, Amazonian white-water (várzea) forests are the most species-rich floodplain forests worldwide. The floodplain vegetation colonizing such environments is subjected to a gradient of different levels of inundation, which define habitats from permanently aquatic, at the lowest positions, to almost terrestrial at higher positions. Annual flooding in these forests may reach the height of 15 m, although its mean amplitude is of 10 m, which corresponds to an inundation period of trees of up to 270 days per year. The present study investigated the content of E Vitamins in leaves of 19 common tree species of Amazonian várzea in order to test for the relation between the antioxidant properties of E Vitamins and the occurrence of tree species along the flooding gradient. Three evergreen species were selected to perform experiments in climatic chambers, Garcinia brasiliensis, Laetia corymbulosa and Pouteria glomerata, under the following experimental conditions: 1) gradual artificial inundation associated with light suppression, 2) darkness, and 3) drought (relative humidity = 45% ± 5%); all of them over a 120 days period. Investigated parameters were: the content of tococromanols, chlorophyll fluorescence, leaf anatomy, and flushing and shedding of leaves. The results show that the α-tocoferol concentration relates primarily to the growth rate of the species rather than their position at the flooding gradient in the natural environment. The latex of G. brasiliensis presented 7 of the 8 existing forms of E vitamins. Plants subjected to drought and plants that were located in the greenhouse showed the highest concentrations of α-tocoferol. G. brasiliensis was characterized through very high δ-tocotrienol concentrations, constituting the second record ever described in literature pointing out the occurrence of this E-vitamin in plant leaves. The Fv/Fm ratio of chlorophyll fluorescence never declined below the threshold of 0,5. When the Fv/Fm ratio of the species subjected to drought approached to values slightly below 0,6, the species shed their leaves. After 120 days of flooding, leaf anatomy of individuals of all the investigated species was different from that of individuals located in the greenhouse. From all potencially stressful conditions, drought demonstrated the highest impact, while under artificial inundation plants were highly tolerant, keeping their leaves all over the experimental period. Although using different strategies, the three tested species survived the potentially stressful conditions without major problems, recovering themselves efficiently after suppressing the experimental conditions.