Eficiência do aparato fotossintético e o metabolismo do nitrogênio em genótipos de girassol com tolerância diferencial à salinidade

Abstract

The search for cultivars/genotypes with high ability to grow in saline soils has been intensified in recent years. In addition to genetic engineering studies, selection of species with higher salt tolerance becomes essential for cultivation of plants in saline environments. In this study, two sunflower genotypes (Helianthus annuus L.) were grown in nutrient solution in the absence (control) and presence of 100 mM NaCl (salt stress), in order to identify possible physiological and biochemical mechanisms that could be correlated with the differential tolerance to salinity. After analysis of the effects of NaCl on growth, it was observed BRS 321 genotype showed increased tolerance to salinity than Catissol genotype. The better performance of BRS 321 genotype plants was directly related to the higher CO2 assimilation rates and photosynthetic pigments. The better efficiency in photosynthetic machinery evidenced by higher effective efficiency of PSII and electron transport rate, also observed in this genotype, when compared with Catissol genotype. Furthermore, the more tolerant genotype showed an effective control of homeostasis in salinity, due to lower accumulation of Na+ in root tissue and higher K+ levels. Also, the best efficiency in transport, via xylem, NH4+ for shoots tissues, associated with massive nitrogen assimilation, probably served as alternate drain on dissipation of excess energy in transport chain electron of chloroplast. The data obtained in this study allow us to conclude that increased tolerance of sunflower plants to salinity is due to the better performance in photosynthetic apparatus coupled to an efficient assimilation of nitrogen.