The rice cultivar (Oryza sativa L.) BRS AG, developed by Embrapa Clima Temperado, is the first cultivar designed for purposes other than human consumption. It may be used in ethanol production and animal feed. Different abiotic stresses negatively affect plant growth. Soil salinity is responsible for a serious reduction in productivity. Therefore, the objective of this study was to evaluate the gene expression and the activity of antioxidant enzymes (SOD, CAT, APX and GR) and identify their functions in controlling ROS levels in rice plants, cultivar BRS AG, after a saline stress period. The plants were grown in vitro with two NaCl concentrations (0 and 136 mM), collected at 10, 15 and 20 days of cultivation. The results indicated that the activity of the enzymes evaluated promotes protection against oxidative stress. Although, there was an increase of reactive oxygen species, there was no increase in MDA levels. Regarding genes encoding isoforms of antioxidant enzymes, it was observed that OsSOD3-CU/Zn, OsSOD2-Cu/Zn, OsSOD-Cu/Zn, OsSOD4-Cu/Zn, OsSODCc1-Cu/Zn, OsSOD-Fe, OsAPX1, OsCATB and OsGR2 were the most responsive. The increase in the transcription of all genes among evaluated isoforms, except for OsAPX6, which remained stable, contributed to the increase or the maintenance of enzyme activity. Thus, it is possible to infer that the cv. BRS AG has defense mechanisms against salt stress.

The objective of this study was to relate the activation of enzymatic antioxidant system to the production of reactive oxygen species induced by salt stress. Rice (Oryza sativa L.) genotypes BRS Bojuru and BRS Pampa, tolerant and sensitive to salinity, respectively, were subjected to 150 mM NaCl for 0, 6, 24, 48, and 72 h. A significant increase of superoxide anion and H₂O₂ and a decrease in malondialdehyde (MDA) content were observed in the tolerant genotype, whereas in the sensitive genotype, there was no change in superoxide anion content, reduced H₂O₂ content, and increased MDA content. The superoxide dismutase (SOD) activity increased significantly in both genotypes, and increases in amounts of transcript were observed for OsSOD3Cu/Zn and OsSODA1-Mn in the tolerant genotype and for OsSOD4-Cu/Zn, OsSOD3-Cu/Zn, OsSODCc1-Cu/Zn, OsSOD-Fe, and OsSODA1-Mn in the sensitive genotype. The activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were not significantly and consistently changed, but OsCATA, OsAPX2 and OsGR1 were induced in both genotypes. OsCATB transcription was increased in the tolerant genotype and OsCATC and OsAPX3 in the sensitive genotype under salinity. It is concluded that OsAPX3, OsGR2, OsGR3, and OsSOD3-Cu/Zn genes are the most suitable to distinguish tolerant from sensitive genotypes under salt stress.

Due to its tropical origin and adaptation, rice is significantly impacted by cold stress, and consequently sustains large losses in growth and productivity. Currently, rice is the second most consumed cereal in the world and production losses caused by extreme temperature events in the context of "major climatic changes" can have major impacts on the world economy. We report here an analysis of rice genotypes in response to low-temperature stress, studied through physiological gas-exchange parameters, biochemical changes in photosynthetic pigments and antioxidants, and at the level of gene and protein expression, towards an understanding and identification of multiple low-temperature tolerance mechanisms. The first effects of cold stress were observed on photosynthesis among all genotypes. However, the tropical japonica genotypes Secano do Brazil and Cypress had a greater reduction in gas exchange parameters like photosynthesis and water use efficiency in comparison to the temperate japonica Nipponbare and M202 genotypes. The analysis of biochemical profiles showed that despite the impacts of low temperature on tolerant plants, they quickly adjusted to maintain their cellular homeostasis by an accumulation of antioxidants and osmolytes like phenolic compounds and proline. The cold tolerant and sensitive genotypes showed a clear difference in gene expression at the transcript level for OsGH3-2, OsSRO1a, OsZFP245, and OsTPP1, as well as for expression at the protein level for LRR-RLKs, bHLH, GLYI, and LTP1 proteins. This study exemplifies the cold tolerant features of the temperate japonica Nipponbare and M202 genotypes, as observed through the analysis of physiological and biochemical responses and the associated changes in gene and protein expression patterns. The genes and proteins showing differential expression response are notable candidates towards understanding the biological pathways affected in rice and for engineering cold tolerance, to generate cultivars capable of maintaining growth, development, and reproduction under cold stress. We also propose that the mechanisms of action of the genes analyzed are associated with the tolerance response.