A enzima superóxido dismutase atenua o estresse hídrico em genótipos de algodoeiro?

Abstract

Cotton is one of the main crops commercially exploited in the semi-arid region of Brazil, where rainfall is irregular in quantity, spatial and temporal distribution. Under such conditions, water stress can be avoided or minimized by the plants' enzymatic and nonenzymatic defense systems. Based on the importance of Superoxide Dismutase (SOD), due to its performance in various enzymatic processes in the plant, the objective was to evaluate its exogenous application, as a mitigation of the deleterious effects of water stress on growth and physiology of cotton in the vegetative phase. The research was carried out in a protected environment (greenhouse), at Embrapa Algodão, in the city of Campina Grande, PB, in plastic pot with a capacity of 0.6 dm3 of soil. Four cotton genotypes (BRS Seridó, FM 966, FMT 705 and CNPA 7MH), two water availability (stress and full irrigation) and four concentrations of superoxide dismutase (0, 50, 100 and 150 U g-1 MF min-1 of SOD) were tested, in a 4 x 2 x 4 factorial scheme, distributed in randomized blocks, with four replications and one plant per plot, resulting in 32 treatments, and 128 experimental units. Growth, mass accumulation, gas exchange and chlorophyll a fluorescence analyzes were performed. In cotton plants under water deficit, but without SOD application, there was a reduction in stem diameter, plant height, transpiration, CO2 assimilation rate and shoot mass, but increased root dry mass and root to shoot ratio. With SOD application, the R/PA ratio decreased. In all studied cotton genotypes, the quantum efficiency of photosystem II and plant tolerance to water deficit increase with the application of 150 U g-1 MF min-1 of Superoxide Dismutase (SOD). The enzyme also contributes to increase shoot dry mass in genotypes considered less tolerant to drought, in a similar proportion to tolerant genotypes.