Aspectos ecofisiológicos e bioquímicos de plantas de cambuí (Myrciaria floribunda (H. West ex Willd.) O. Berg) (Myrtaceae) submetidas à condição de deficiência hídrica

Abstract

The Brazilian northeast has native fruit trees that are little-known, however, they have a great potential to become commercially important. Among these species, we can name Myrciaria floribunda (H. West ex Willd.) O. Berg (Myrtaceae), popularly known as cambuí. Despite of the potential this plant has, currently, there is not enough data in the literature about the species responses to environmental stresses such as water deficit. Thus, considering a low rainfall scenario and agriculture expansion to arid and semi-arid regions, the objective of this study was to characterize the ecophysiological and biochemical mechanisms of drought tolerance in cambuí plants. The study was carried out with plants that were approximately 2.5 years old in a greenhouse at the Campus of Engineering and Agricultural Sciences from the Federal University of Alagoas. The experimental design was completely randomized, with two treatments: control (irrigation according to plant needs) and water deficit (total suspension of irrigation), with 10 replications of one plant for each treatment. The effective quantum efficiency of PSII (ΦPSII), potential quantum efficiency of PSII (Fv/Fm), soil moisture at 20 cm depth and visual analysis for wilt symptoms were monitored up to 30 days of stress imposition. Plants under stress showed reductions in ΦPSII and Fv/Fm greater than 25%, soil moisture was close to 0% and wilting characteristics were very pronounced, being considered the maximum stress. In the period of maximum stress, the number of leaves, relative water content, electrolyte extravasation, SPAD index, chlorophylls a and b, total chlorophylls, chlorophylls a/b ratio, proteins, amino acids and total soluble sugars, foliar free proline, lipid peroxidation (Malondialdehyde - MDA content) and antioxidant capacity of the enzymes Superoxide Dismutase (SOD), Ascorbate Peroxidase (APX) and Catalase (CAT) were quantified. The data obtained was submitted to variance analysis by the F test (p<0.05) in the SISVAR software. The plants under imposition of water deficit decreased ΦPSII from the 21st day, and the Fv/Fm, from the 24th day. In addition, water deficit promoted a decrease in the relative content of water, total soluble proteins, and antioxidant activity of the SOD enzyme. On the other hand, water deficit induced an increase in total soluble amino acids, foliar free proline, and antioxidant activity of CAT and APX enzymes. The increase in proline was 1,226.66%, the most pronounced. Cambuí has high tolerance to stress caused by water deficiency, because even with some potentially deleterious changes, such as the decrease in ΦPSII, Fv/Fm and SOD enzymatic activity, there were important responses associated with stress tolerance, such as the increase in proline and enzymatic activity of CAT and APX, being the possible reason for the maintenance of photosynthetic pigments and lipid peroxidation contents.

Keywords: Antioxidant Metabolism; Osmoregulators; Physiological Parameters.