Variabilidade espacial das respostas metabólicas de plantas de arroz sob salinidade

Abstract

Rice is one of the main food sources in the world. However, the productivity of rice plants is substantially affected by salt stress. Thus, it becomes important to understand the responses of rice plants to salinity, to mitigate the losses caused by this stress factor and provides new targets for plant metabolic engineering. Within this perspective, although several studies have uncovered mechanisms of acclimatization of rice plants to excess salt, little is known about how these responses vary spatially in the plant. In this work, we aimed to elucidate how saline stress alters the primary metabolism of different organs of rice plants. Rice plants were grown in hydroponic solution and subjected to excess NaCl (50 mM) at the R3 stage. After 40 days under excess salt, flag leaves, intermediate leaves, senescent leaves, roots and stems were collected separately, with a part used to determine the accumulated dry biomass and another immediately frozen in liquid nitrogen for metabolic profile analysis via gas chromatography coupled to a mass spectrometer. The results demonstrated that the total dry biomass of rice plants decreased after the imposition of excess NaCl, considerably accelerating leaf senescence. In fact, senescent leaf biomass was higher under NaCl when compared to control plants. Metabolic responses to salinity varied strongly among rice plant organs, being more drastic in source organs, especially flag and intermediate leaves, as revealed by principal component analysis (PCA). In this sense, several metabolites belonging to the group of amino acids, sugars and organic acids were altered after salinity. The level of several amino acids increased in the leaves, mainly in flag and senescent leaves. For example, lysine, isoleucine, proline, threonine and valine were identified as biomarkers of salt stress condition in different leaves. However, no metabolite was identified as a common biomarker among all rice plant organs, emphasizing that metabolic responses to saline stress are organ-specific.