Germinação, dormência, composição lipídica e alterações bioquímicas de sementes de Urochloa spp. durante o armazenamento em duas condições

Abstract

The evaluation of seed quality is essential, as it allows obtaining information regarding the potential performance of seedlings under different environmental conditions and for the selection of lots destined for sowing or storage. Urochloa species are of great importance as forage crops, with Brazil being one of the main producers and exporters of seeds of these species, but also because they act as cover plants and/or in consortium with cultivated species. Seed germination is a critical process in the life cycle of higher plants and is very susceptible to adverse environmental conditions, which can cause oxidative stress, resulting from an increase in reactive oxygen species (ROS), which can cause damage to proteins and initiate lipid peroxidation in cell membranes, forming fatty acid hydroperoxides. Therefore, the present work aimed to characterize the lipid profile of the seeds of seven Urochloa genetic materials during storage, relating it to the physiological behavior of germination and dormancy. The seed lots were divided into two portions. The portions were placed in paper bags, which were equilibrated over white silica gel (with orange silica used as an indicator), providing 4.5% relative humidity (RH), as well as over a lithium chloride solution (36.4 g of LiCl in 100 mL of H2O), providing 50% RH. The following analyzes were performed: seed viability, germination, quantification of hydrogen peroxide (H2O2), enzymatic extraction, catalase activity (CAT, EC. 1.11.1.6), superoxide dismutase (SOD, EC.1.15.11), peroxidase (PRX, EC. 1.11.1.7), transesterification of fatty acids and gas chromatography (GC), in addition to lipid composition. The storage experiment was conducted according to a completely randomized design, separately for each genotype, considering two storage conditions (4.5 and 50% RH) and 7 evaluation periods (0, 3, 6, 9, 12, 15 and 24 months), in a 2 x 7 factorial scheme. The SISVAR statistical program was used to carry out the analysis of variance and the grouping of means by Scott-Knott, at a 5% level of significance. It is concluded that relative humidity and the storage period imposed on seeds directly influence their physiological responses, due to oxidative damage, which produces ROS and increases the level of H2O2. The main fatty acids detected were linoleic acid (C18:2), oleic acid (C18:1) and palmitic acid (C16:0). The content of unsaturated fatty acids was predominantly higher than the saturated ones, with linoleic acid being the majority in all genotypes in this study.