Caracterização fisiológica, bioquímica e molecular da germinação de sementes de mamona (Ricinus communis L.) sob estresses salino e osmótico

Abstract

Ricinus communis L. (Euphorbiaceae), known as castor, is a species that stands out in the national and international scenario for the oil extracted from its seeds which is widely demanded by by the global bioindustries. In addition to its multiple commercial and bioindustrial uses, it has socioeconomic importance in the semiarid regions of Brazil and global wide. However, semiarid regions have adverse environmental conditions such as short periods of rain and soils with saline levels. Conditions that limit water absorption and promote greater generation of reactive oxygen species (ROS), such as superoxide anion-O2, hydroperoxyl-HO2 radical, hydroxyl-OH radical, hydrogen peroxide-H2O2 and singlet oxygen, 1O2, compromising the germinative processes, growth, and development of seedlings, reduce productivity and can lead to plant death. During the germination process, the activity of ROS removing enzymes has been reported, such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), among others, which constitute efficient detoxification mechanisms during imbibition, these enzymes can be used as molecular markers to elucidate the events that occur during the germination process. Therefore, this proposal provides a better understanding of the mechanisms involved in the response of castor beans to abiotic stresses by water restriction and saline conditions at the physiological level, related to antioxidant enzymes by means of biochemical and molecular studies. A REVIEW was developed where studies were identified on advances in research related to the cultivation of castor under abiotic stresses due to water restriction and salt stress, germination, and early stages of development of seedlings and antioxidant enzymes, shighlighting the enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). In CHAPTER 1, we performed the biometric characterization of two R. communis cultivars (BRS Nordestina and BRS Paraguaçu), we noticed that the seeds of Cultivar BRS Paraguaçu are larger than those of BRS Nordestina, which may be related to the higher water absorption observed for the seeds of that cultivar. Through the imbibition studies in osmotic water restriction (PEG) and salinity (NaCl), we observed that there is a difference in the water restriction capacity for these two solutions at the same osmotic potential, where for the imbibition by PEG at -0.23 MPa there was a drastic decrease in water absorption, inhibiting the cell cycle and the germination process while in the same osmoticum by NaCl imbibition there was only a slight delay in water absorption compared to the control. The imbibition in light potentials of NaCl (-0.23 MPa) stimulated a greater activity of the antioxidant enzyme SOD, while for the imbibition in PEG due to severe water restriction, the activity of the SOD enzyme was lower than the control. In CHAPTER 2, we performed the characterization of the family of 6 putative RcAPX genes that code for the enzyme Ascorbate peroxidase (APX) in castor beans, , through phylogenetic analysis we identified the orthologous genes in other angiosperms where we classified the APX genes according to location intracellular (citosol, plastid and peroxisomes). We observed that the RcAPX genes have a large number of exons/introns in addition to sharing conserved motifs. An increase in the total activity of the APX enzyme was observed after 48 h of imbibition (post-germinative) in the imbibition of water (control) and in NaCl -0.23 MPa (saline restriction) in both cultivars evaluated, while that imbibition in a -0.23 MPa PEG repressed the activity of APX. In CHAPTER 3, we identified and characterized 2 putative RcCAT genes representing the Catalase (CAT) gene family in Castor beans, predicted for peroxisome intracellular localization, from phylogenetic comparison we found orthologous genes in other angiosperms where we observed the classification into three groups. We found differences in gene structure and motif order for the RcCAT2 gene compared to the angiosperm CAT genes. Through the analysis of regulatory elements in the promoter region of these genes, we identified possible forms of regulation related to biotic and abiotic stresses, as well as plant hormones such as ABA. Finally, the enzymatic activity of catalase was shown to be modulated according to development time, stress during germination and respective genotype. The results herein contribute to a better understanding of the effects of water and saline restriction stresses in castor beans, in addition to the characterization of a family of genes that code for important antioxidant enzymes in seed responses to abiotic stress conditions.