Enzymatic and non-enzymatic protective mechanisms in recalcitrant seeds of Araucaria bidwillii subjected to desiccation.

The changes in several antioxidants as well as in the level of C-centered free radicals and thiobarbituric acid reactive substances (TBARS) were studied in seeds of Araucaria bidwillii Hook desiccated to 37%, 28% and 21% moisture content. The lowest-safe moisture content for the seedling establishment was 37%. The embryo, besides double amounts of free radicals, showed higher levels of both enzymatic and non-enzymatic antioxidants than endosperm. Lutein decreased in both organs whereas alpha-tocopherol values were not affected by desiccation. In the embryo at 37% seed moisture content the antioxidant defense system increased giving rise to a decrease in free radicals. Beyond this point, free radicals and TBARS increased in agreement with the umpiring of the ascorbate/glutathione cycle by the decrease in reduced glutathione and glutathione reductase activity (GR, EC 1.6.4.2). At 21% moisture GR decreased. In the endosperm during desiccation, the consumption of ascorbate, total glutathione and lutein prevented the rise in free radicals and TBARS till 28% moisture, at which an increase in oxidized glutathione was also observed.