Secagem e resfriamento de sementes de Coffea arabica L. visando à criopreservação

Abstract

The cryopreservation of seeds that present intermediate recalcitrance characteristics, like coffee is an alternative to ensure the conservation of genetic resources for indetermined time. Research on the classic and modern methods contribute to the understanding of seeds response to desiccation and freezing. In this context, four studies were carried out aiming to investigate the effects of the steps of cryopreservation on the physiological, biochemical and ultrastructural characteristics of Coffea arabica L. seeds. In addition, the effects of cathodic water to overcome the damage caused by stresses arising from these steps were evaluated. In the first study, we investigated water content and rate and precooling temperature before immersion in liquid nitrogen. The water content of 20% (wb) allowed higher survival of seeds after cryopreservation when they were pre-cooled at -1 ° C min-1 to the temperature of -40 °C. In the second study, we evaluated different drying methods and a treatment with cathodic water. Slower drying causes reduction in physiological performance and provides an increase in the antioxidant enzyme activity. Faster or slower drying of seeds to 17% wb compromises the ultrastructural cells integrity. However, the cathodic treatment after faster drying (17%) maintains the integrity of the cells. In the third study, different pre-cooling procedures and treatment with cathodic water were evaluated. The best results were found in seeds containing the lowest water content (17% wb) regardless of the drying and pre-cooling methods used. The antioxidant action of cathodic water is beneficial in seeds with the highest water content (20% wb). In the driest seeds, immersion in cathodic water activates the antioxidant enzyme system and improves the ultrastructural aspect of the cells. Endosperms has higher sensitivity to freezing than the embryos. In the last study, we investigated different protocols for cryopreservation of seeds and a treatment with cathodic water. Only different methods of drying and pre-cooling affect the physiological quality and modify biochemical and ultrastructural aspects of the seeds. The seeds cryopreserved with 17% water content (wb) have better quality than those with 20% water content (wb). Coffea arabica L. seeds dried to 17% wb (75% or 81% of relative humidity), pre-cooled or directly immersed in liquid nitrogen have their quality preserved.