Papel do oxigênio dissolvido em torno das raízes na tolerância de arroz à salinidade

Abstract

Salinity causes damage to plants by limiting the absorption of water and nutrients by reducing the soil water potential, being a source of ions that intoxicate the vegetable by its excess, and by inducing other stresses. Rice can be considered a very important agricultural product for human food security, since 85% of the total rice production is destined for human consumption. Conferencing tolerance to salinity does not only mean an economic gain, but a social gain for the facilitation of its cultivation in marginal areas of cultivation, where the producers do not have soils or water sources with great quality and not even capacity of great investments, as well as in the northeast Brazilian. The objective of this research was to evaluate the influence of oxygenation around rice roots on physiological and biochemical mechanisms capable of conferring acclimation to salinity. For that, an experiment was developed in a factorial scheme with three levels of oxygenation around the roots of rice plants cv. SCSBRS 113 and three levels of salinity during the tillering period to evaluate through the physiological and biochemical responses the oxygenation action around the roots of rice, as well as their interaction with the salinity. A second experiment was carried out in a factorial scheme with three levels of oxygenation around the roots and two levels of salinity before the tillering period to evaluate the sensitivity to the stresses and the formation of the ROL barriers. The growth and development of rice plants under low oxygenation were much more impaired than under salinity, but the combination of these stresses brought even greater losses. In addition, the high oxygenation of the nutrient solution only contributed to a longitudinal growth of 25% of the roots, independently of the salinity. No participation of salinity or oxygenation in inducing catabolic processes of chlorophyll a, b and carotenoids was observed in this study. On the other hand, low oxygenation contributed to a restriction of hexoses. In general, it was concluded that tolerance to salinity is closely linked to the conservation of stomatal conductance, reduction of the high flux of Na+ and Cl- into the roots and a better efficiency in the fight against ROS mainly in leaves, while tolerance to a higher hypoxia may be related to the conservation of stomatal conductance, with its positive impact on the energy and structural resources, besides the adaptations of the rice plants to this type of environment. The interaction of oxygenation and salinity treatments indicated that low oxygenation aggravated the physiological stress already imposed by salinity and that an increase in oxygenation had little effect on repairing or alleviating saline stress.