Estresse hídrico e ácido abscísico em mudas de Ormosia arborea (Vell.) Harms: ecofisiologia e anatomia foliar

Abstract

Many physiological, morphological and anatomical parameters can indicate whether particular species is tolerant to a condition of water deficit. Furthermore, during the water deficit is the increase in concentration of abscisic acid (ABA), which triggers different responses in the plant in dry condition. Thus, the objective was to evaluate the effect of water stress and ABA application in gas exchange, antioxidant enzymes, initial growth and leaf Anatomy in seedling of Ormosia arborea. The experiment was conducted in fully randomized design and consisted of six treatments: 1) daily irrigation without ABA. 2) daily irrigation + 10 μM ABA; 3) daily irrigation + 100 μM ABA; 4) suspension of daily irrigation; 5) suspension of daily irrigation + 10 μM ABA and 6) suspension of daily irrigation + 100 μM ABA, 24 seedlings per treatment. The first application of ABA occurred at the beginning of the experiment, and the second application took place 25 days after the second water suspension, based on the photosynthetic rate close to one; the leaves were sprayed with ABA solutions until the point of dripping. We evaluated the gas exchange, water potential, the chlorophyll a fluorescence, antioxidant enzymes, initial growth and foliar anatomy of the seedlings. The seedlings under water deficit showed a significant reduction in gas exchange, however, the suspension of daily irrigation + 10 μM ABA provided greater tolerance to water deficit, since they did not reach null values of photosynthetic rate. The variable fluorescence, maximum, effective efficiency of photosystem in the conversion of absorbed energy (Fv/F0), quantum efficiency of photosystem II (Fv/Fm) showed a reduction in seedlings of water deficit, and increase in basal quantum production of non-photochemical processes of photosystem II (F0/Fm). The seedlings under water deficit showed an increase in the activity of enzymes catalase, peroxidase and superoxide dismutase during photosynthesis. In relation to the growth parameters, the seedlings of the water deficit presented lower values than the irrigated seedlings for the growth characteristics during the photosynthesis (fresh and dried mass of the root, fresh and dry mass of the aerial part, the length of leaves, number of leaves, chlorophyll index, stem diameter and IQD). In the non-irrigated seedlings treated with ABA, this hormone may have stimulated the growth of the roots. In relation to leaf anatomy, the main changes were the increase in cuticle thickness, epidermis and palisade parenchyma of the seedlings under water deficit.