Estresse por baixa temperatura em arroz: aspectos moleculares, bioquímicos e fisiológicos

Abstract

Due to its tropical origin, rice (Oryza sativa) is very impacted by cold stress and consequently presents great losses of growth and yield. It is the second most consumed cereal in the world and the decrease in production caused by extreme temperature events can have significant impacts in the world economy. Sensitivity and symptoms of plant responses to stress due to low temperatures vary with the stage of developmental. It is observed that in the first developmental stage there is a delay and decrease of seed germination and on vegetative stage, foliar chlorosis, short stature and decrease of the profile. It is observed that in the first development stage there is a delay and decrease of the germination of the seeds and in the vegetative stage, leaf chlorosis, short stature and reduction of tillering. At reproductive stage, the abortion and sterility of the spikelets, incomplete panicle excretion, abnormalities in the development of the anthers, grain spots and late and incomplete maturation of the grain. The purposed of this study was to evaluate the adaptive mechanisms of response to stress induced by low temperatures at the molecular, biochemical and physiological levels at the vegetative and reproductive stages. Twenty-two rice genotypes from the USDA mini-core collection for cold tolerance, in vitro, were analyzed through morphological parameters. Of these 22, four genotypes (two tolerant and two sensitive) were selected for vegetative stage evaluation of photosynthetic parameters, biochemical and gene and protein expression. Analysis of photosynthetic parameters and gene expression were repeated during the reproductive stage. The first effects of low temperature stress were identified in photosynthesis in all genotypes and in both stages. Biochemical profile and genes of lipid transfer proteins (LTPs), OsGH3-2, OsSRO1a, OsZFP245, OsTPP1 and the LRR-RLKs, BHLH, GLYI and LTP1 proteins at the vegetative stage have demonstrated that, despite impacts of low temperature in the tolerant genotypes, had a fast adjustment for cellular homeostasis to be maintained, showing a clear difference in gene expression between the genotypes. It was also visualized that the expression of OsLTP7, OsLTP10, transcription factors and low temperature genes were higher in the tolerant genotypes in both tissues. Low temperature stress severely affected production parameters, with a yield loss of 40 and 90% in tolerant and sensitive genotypes, respectively. Therefore, this study identified the genotype Nipponbare as possible tolerant to low temperatures in both stages. LTP genes, OsGH3-2, OsSRO1a, OsZFP245 and OsTPP1, and the porteins LRR-RLKs, bHLH, GLYI and LTP1 are good candidates at the screening for cold tolerance at the vegetative stage, whereas OsLTP7, OsLTP10, OsNAC9, OsNAC10 and OsNAP can be used, for the same purpose, at reproductive stage.