Ação da prolina exógena no cultivo in vitro de genótipos de cana-de-açúcar submetidos ao estrese salino

Abstract

Sugarcane is one of the main agricultural products in the economic and social scenario Brazilian and maintenance, as well as increased production and productivity is linked to genetic improvement with selection of new genotypes that have the characteristics of agronomic interest. The techniques of tissue culture can be used in studies of selection or evaluation of the tolerance of plants contributing to clarify the changes from the conditions of stress. The productivity of sugarcane is influenced by several environmental factors such as salinity that limits production due to osmotic effects and ion toxicity by absorption of Na+ and Cl-. Salt stress increase the concentration of reactive oxygen species (ROS), may promote oxidative stress and cause injury to lipids, proteins, carbohydrates and DNA. To minimize the damage caused by the accumulation of ROS, plants possess the antioxidant defense system involving substances of nature enzyme (catalase-CAT, peroxidase-POD, ascorbate peroxidase-APX and polyphenoloxidase, PPO) and not enzyme as the proline. The objectives of this study were to evaluate the effects of exogenous proline in cultivation in vitro of sugarcane submitted to salt stress and analyze the biochemical changes that occur in these conditions. Plants were micropropagated genotypes RB931011 and RB872552. Plants were grown, for 20 days, in the absence or presence of 20 mM proline with or without 100 mM NaCl, totaling five treatments. We used a completely randomized design with 2x5 factorial (genotype x treatment). Leaf samples were collected proceeding to analysis of endogenous levels of proline and total soluble proteins, percentage of electrolyte leakage, concentration of Na+ and K+ and activity of enzymes CAT, POD, APX and PPO. The data were analyzed using ANOVA and means compared by Tukey test at 5% probability. In the saline treatments, both genotypes showed an increase in electrolyte leakage, caused possibly, by lipid peroxidation. Plants grown under salt stress showed a reduced content of total soluble protein and in parallel maintenance or increase in the endogenous proline content. The salt also promoted the increase in the concentration of Na+ and decreased K+ generating thus a high ratio Na+/K+. The activity of CAT, POD, APX and PPO, responsible for the elimination of ROS, increased with increasing salinity in both genotypes. The RB931011 genotype had a greater acclimation compared to genotype RB872552 due to the largest increase in endogenous proline content and increased activity of antioxidant enzymes resulting in minor membrane damage.