Estudo da qualidade fisiológica, bioquímica e ultra-estrutural durante o desenvolvimento e a secagem de sementes de soja

Abstract

During the development and drying, several protection mechanisms act on the maintenance of the physiological quality of the seeds. Studies on desiccation tolerance allow the understanding of the events associated with the maturation of orthodox seeds, such as soybean. Among the mechanism involved on desiccation tolerance, the activity of heat-resistant proteins associated with non-reducing sugars and enzymatic systems that neutralize free radicals have received a special attention. Thus, this work studied the physiological, biochemical and ultra-structural changes during soybean seed development and drying. Physiological quality was evaluated by means of germination tests, emergence under controlled conditions, cold test and electrical conductivity. For the biochemical studies the activity of heat-resistant proteins, the enzymes alcohol dehydrogenase (ADH), malate dehydrogenase (MDH), superoxide dismutase (SOD) and catalase (CAT) were evaluated. The ultra structural study was performed by means of scanning electron microscopy (SEM). The results showed that synthesis of heat-resistant proteins was induced by the decreasing water content of the seeds naturally or artificially starting from 60% of moisture content. The heat-resistant protein synthesis was directly related to the physiological quality of soybean seeds. Soybean seeds become tolerant to desiccation when the seeds posses around 30% of moisture content. The results showed that SOD was active during development and drying of soybean seeds. The activity of MDH was constant during seed drying, whereas the activity of ADH was higher. Catalase was only effective after physiological maturity of soybean seeds. Drying of seeds with moisture content above 30%, caused reduction of cellular volume, disorganization of the cell walls and decrease in physiological quality of the seeds. Higher values of germination were observed in seeds with 30% of moisture content in the field, whereas higher values of vigor were observed in seeds with 40% of moisture content in the field.