Viability loss pattern under rapid dehydration of Antiaris toxicaria axes and its relation to oxidative damage.

The relation between oxidative damage and viability loss of excised embryonic axes of Antiaris toxicaria subjected to rapid drying with silica gel at 15 degrees C was studied. Changes of survival rate, accumulation of thiobarbituric acid-reactive substances (TBARs), activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and the permeability of cell membrane that was determined as relative electrolyte leakage (REL) were measured. The half-life moisture content (MC(L50)) was 0.41 g H2O/g DW (dry weight basis). During drying, the activities of SOD, CAT and APX increased until MC(L50), and declined thereafter. The generation speed of (.)O2(-), and content of H2O2 and TBARs remained steadily or even decreased at MC levels higher than MC(L50), demonstrating a low oxidative level in these axes. There was no significant correlation between viability loss and accumulation of reactive oxygen species or lipid peroxidation within the dehydration process until MC(L50). Whereas the increase in REL from the beginning of the drying process indicated that the cell membrane was damaged. In conclusion, under rapid drying with silica gel the viability loss of excised recalcitrant A. toxicaria axes seemed to be triggered by mechanical or physical damage, rather than metabolic damage.

The response difference of mitochondria in recalcitrant Antiaris toxicaria axes and orthodox Zea mays embryos to dehydration injury.

Long-term preservation of recalcitrant seeds is very difficult because the physiological basis on their desiccation sensitivity is poorly understood. Survival of Antiaris toxicaria axes rapidly decreased and that of immature maize embryos very slowly decreased with dehydration. To understand their different responses to dehydration, we examined the changes in mitochondria activity during dehydration. Although activities of cytochrome (Cyt) c oxidase and malate dehydrogenase of the A. toxicaria axis and maize embryo mitochondria decreased with dehydration, the parameters of maize embryo mitochondria were much higher than those of A. toxicaria, showing that the damage was more severe for the A. toxicaria axis mitochondria than for those of maize embryo. The state I and III respiration of the A. toxicaria axis mitochondria were higher than those of maize embryo, the former rapidly decreased, and the latter slowly decreased with dehydration. The proportion of Cyt c pathway to state III respiration for the A. toxicaria axis mitochondria was low and rapidly decreased with dehydration, and the proportion of alternative oxidase pathway was high and slightly increased with dehydration. In contrast, the proportion of Cyt c pathway for maize embryo mitochondria was high, and that of alternative oxidase pathway was low. Both pathways decreased slowly with dehydration.