Interação entre a deficiência de ferro e toxidez por alumínio em Oryza rufipogon e Oryza sativa

Abstract

Rice is one of the most widely grown and consumed cereals in the world and is the staple food for more than half of the world's population. Due to its wide distribution of cultivation, rice cultivation is exposed to the most diverse climatic and environmental conditions and, consequently, to various abiotic stresses. Among the stresses to which rice is exposed is iron deficiency (Fe) and aluminum toxicity (Al), two major problems in world agriculture. In this context, the objective of the present work was to evaluate the response of wild rice species Oryza rufipogon and cultivated species Oryza sativa cultivar IRGA 429 submitted to Fe deficiency and Al toxicity regarding physiological and biochemical variables, and gene expression under Fe deficiency and Al toxicity. The experiments were carried out at the Plant Physiology Laboratory of Agrobiological Interest of the Federal University of Santa Maria (UFSM), in Santa Maria (RS). Rice plants were grown under hydroponic system in growth room with controlled temperature and photoperiod and submitted to nutrient solution containing the treatments: control solution, Al toxicity (150μM and 300μM Al), Fe deficiency (absence of Fe) and Al toxicity allied to Fe deficiency. After exposure to the different treatments, physiological (fresh and dry biomass, plant height, root system morphological parameters, leaf area and leaf number) biochemical (antioxidants enzymes, hydrogen peroxide content and photosynthetic pigments) and molecular variables (expression of OsIRT1, OsYSL15, OsIRO2 genes by RT-qPCR) were collected and analyzed. Expected changes were observed in plants of the two species submitted to Al. Plants under Fe deficiency showed younger leaf chlorosis, as expected. However, chlorosis was reverted to levels similar to plants grown under control conditions for both O. rufipogon and O. sativa when they were grown under combined Fe deficiency and Al excess. It was also observed that Fe deficiency-induced transporters, OsIRT1 and OsYSL15, had their root expression suppressed by the presence of Al. The transcription factor that regulates Fe deficiency responses, OsIRO2, however, was induced by Fe deficiency alone in both species, and was not suppressed in the combined treatment, indicating that the reversal effect of Al-dependent Fe deficiency symptom acts at a later stage than OsIRO2 induction. It is speculated, therefore, that some Al-induced factor inhibits carriers below the Fe deficiency response cascade. The results obtained here suggest for the first time a mechanism for beneficial effects of Al on rice plants.