Piruvato e superóxido desmutase como atenuadores do estresse hídrico no crescimento inicial do amendoim

Abstract

Water deficit is one of the most limiting factors in plant development. Plant disorders triggered during water stress involve, in particular, reduced growth, due to reduced photosynthesis as a result of water loss in the cell. Others disorders are oxidative damages that result of the excessive production of reactive oxygen species that lead to lipid peroxidation, protein degradation and cell death. SOD is the precursor enzyme of the cell detoxification process, acting in the elimination of reactive oxygen species (ROS) through the dismutation of superoxide radicals, favoring the neutralization of reactive species and reestablishment of cellular balance. In drought-tolerant plants, SOD activity is high in order to favor the action of other enzymes that precede it in the antioxidant complex. However, in sensitive plants, SOD activity is slower and, therefore, cell damage is greater, leading to unpredictable consequences during management. As tolerance to water stress is governed by genetic factors, the adoption of sensitive cultivars is restricted to favorable environments, where production can be guaranteed. It is not known whether exogenous metabolite supplementation can mitigate the effect of water stress on sensitive plants. To certify this hypothesis, the present work was developed to investigate the role of two physiological and biochemical metabolites, pyruvate and SOD, in the attenuation of the effects of water deficit in peanut plants (Arachis hypogaea L.) submitted to eleven days of water stress. BR 1 (subsp. fastigiata) and IAC Caiapó (subsp. hypogaea), tolerant and sensitive to drought, respectively, were used as tester. The exogenous application of these metabolites at different concentrations were tested in young plants (stage V1) and evaluated for growth, gas exchange, osmotic adjustment and antioxidant complex enzymes. In studies with pyruvate, tested at 100 µM and 50 mM, we found that water deficit affected the growth and physiological functions of both cultivars, but mitigating action was expressive in sensitive IAC Caiapó, at 50 mM, especially in recovery of photosynthesis, stomatal conductance and relative water content, where losses were lower, compared to the stressed treatment plants. This situation favored the accumulation of proline, at lower concentration (100 µM), which was benefited by the amount of water available in the cell (RWC), favored by osmotic adjustment. As to antioxidant enzymes, no expressive result was seen with exogenous pyruvate in this cultivar, in order to avoid possible cell damage caused by water stress. Such response must possibly be associated with the reduced level of damage, represented by the inputs of SOD, CAT and APX found in plants stressed in this work. In assays with exogenous SOD, tested at 2.5, 5.0 and 7.5 U, we found that the enzyme contribution promoted benefits in both cultivars, in different ways. In BR 1, the application of SOD (7.5 U) contributed to recovery the photosynthesis rate by more than 9%, as a consequence of increase in internal Carbon, which at the lowest concentration (2.5U) was enough to raise the rate by 13 %, regarding the stressed treatment. The machinery of antioxidative enzymes was more active in concentrations from 5 U, so that at the end of process of neutralizing H2O2 and O2, the status of the plants practically returned to normality of the control plants. At IAC Caiapó, the benefit of exogenous SOD was more expressive, registered in the recovery of gas exchange and RWC in low concentration (2.5 U), which was sufficient to ensure the recovery of plants under stress. IAC Caiapó, however, as is sensitive to drought, demonstrated that the enzymatic activity for recovery of the antioxidative process was slower, even with contribution of SOD at 5 U, based on the means of the stressed treatment. The results presented in these works are relevant because they demonstrate the attenuating potential of exogenous pyruvate and SOD in the physiology and biochemistry of plants under stress, especially those sensitive to water deficit.