Resposta antioxidativa e ajustamento osmótico de helianthus ANNUUS l. Submetido ao déficit hídrico e salinidade

Abstract

Sunflower is moderately tolerant to salinity and drought. Cultivation can be carried out in arid and semi-arid regions where agricultural productivity is affected by drought and by high concentrations of soluble salts in the soil. In addition, sunflower is promising species for biodiesel production. Knowledge of the physiological, biochemical and molecular mechanisms involved in tolerance and / or susceptibility to stress, saline and water deficit are not yet clearly understood for sunflower, this study aimed to evaluate the effects of saline stress and water deficit on growth indicators, water status and membrane integrity, the possible contribution of organic and inorganic solutes involved in the osmotic adjustment and oxidative damage and the enzymatic and non-enzymatic antioxidative defense system in three organs of sunflower genotypes submitted to stressors sodium chloride (NaCl) and polyethylene glycol (PEG 6000) simulating salinity and drought respectively. The experimental design was completely randomized, with a 2x3 factorial, with two sunflower genotypes (Catissol 01 and Helio 253) and three treatments (control, 100 mM NaCl and -0.50 MPa PEG 6000), with 5 replicates for each treatment and each genotype. The results showed that NaCl and PEG 6000 cause negative changes in growth indicators in the water status and in the membrane integrity of the two genotypes, with Catissol 01 being the most sensitive. Considering the inorganic solutes, regardless of genotype and organ analyzed, NaCl caused an increase in Na + and decrease of K +, increasing Na + / K+ ratio above 1 and generating ionic toxicity. Regarding organic solutes, NaCl and PEG 6000 induced alterations in the metabolism of carbohydrates and nitrogen compounds evidencing the participation of amino acids and proline in the osmoregulation of sunflower plants. It was observed that both genotypes, submitted to drought and salinity, presented oxidative damages represented by increased lipid peroxidation and increased carbonylation of proteins, and decreased protein concentration in some organs, especially when submitted to drought. In plants submitted to salinity, the enzymatic antioxidative defense mechanism seems to have been efficient in the removal of H2O2 and contributing to the increase of photosynthetic pigments, being characterized by the increase of the enzymes superoxide dismutase, ascorbate peroxidase and phenol peroxidase. Such responses varied between genotypes, treatments and organs