The effects of two drying rates on the desiccation tolerance of embryonic axes of recalcitrant jackfruit (Artocarpus heterophyllus Lamk.) seeds

This study compared the survival, electrolyte leakage and ultrastructural characteristics of embryonic axes of recalcitrant jackfruit dried rapidly (<90 min) or slowly (2-3 d). Axes dried slowly showed decreased viability at higher water content than those dried rapidly; this was mirrored by an increase in electrolyte leakage at approx. 0.8 and 0.4 g H2O g(-1) dry mass, respectively. Rapid drying conferred relatively greater tolerance to dehydration, as attested by the 100% survival attained at approx. 0.4 g g(-1) in contrast to the total mortality of axes dried slowly to this water content. Partially hydrated axes were processed for microscopy using freeze-substitution to prevent rehydration artefacts. Radicles of axes dehydrated to 0.7 g g(-1) were examined microscopically to assess their cellular morphology and appearance of membranes following rapid or slow drying. Measurements showed that drying rate affected the distribution of water within axes, which could be relevant to the extent of stress experienced by germinative cells. Membrane breakdown was not observed in cells dehydrated either rapidly or slowly to 0.7 g g(-1). Endoplasmic reticulum profiles were prominent in dehydrated cells. Autophagy was observed in axes of both treatments. The area occupied by vacuoles increased significantly only following rehydration, and was similar in axes dried rapidly or slowly. Desiccation damage became evident on rehydration, and was reversible following rapid drying but was more severe in axes dried slowly. Prolonged exposure to partial hydration may contribute to the greater sensitivity of vacuoles to damage during rehydration. (C) 2001 Annals of Botany Company.