Castor bean is a crop of social and economic importance in Brazil and worldwide. The oil produced from its seeds, comprised mainly of ricinoleic acid, is strategic for the manufacture of lubricants, cosmetics, polymers, among others. Although castor bean is considered drought tolerant, the lack of rain during flowering can reduce plant yield. Differential responses to drought in the species have been observed in the genebank accessions and between cultivars. In order to better understand the physiological mechanisms of response to water deficit and direct breeding programs, the objective was to analyze the differential expression of genes potentially related to tolerance to water deficit in castor bean and the behavior of enzymes of the antioxidant defense system. The study was conducted with three accessions (China Careca, IAC 2028 and PB 07) subjected to a test solution with polyethylene glycol (PEG 6.000) for a period of 24 hours for induction of drought. CAT, APX, SOD-Cu/Zn, Fe-SOD and Mn-SOD genes had higher differential expression in China Careca accession. The SOD-Cu/Zn gene was the most differentially expressed in China Careca access when compared to control (3.57 times). Analysis of the activity of enzymes related to oxidative stress (catalase - CAT, ascorbate peroxidase - APX, Guaiacol Peroxidase and Superoxide Dismutase-GPOX activity-SOD) revealed that the accessions have different mechanisms of response to water deficit. The results indicate that China Careca accession can be considered of great importance for breeding programs by presenting precocity characteristic, more efficient antioxidant defense system and resistance to drought.
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