Desiccation-induced loss of seed viability is associated with a 10-fold increase in CO2 evolution in seeds of the rare tropical rainforest tree Idiospermum australiense

• Here the relationship was investigated between metabolic activity, state of hydration and seed viability in the desiccation-intolerant (recalcitrant) seeds of Idiospermum australiense, a rare and primitive angiosperm tree restricted to wet tropical forest. • Seed CO2 evolution rate, R, was monitored in fully hydrated (control) seeds and seeds that were allowed to desiccate under ambient conditions over a period of c. 90 d. • During desiccation R increased dramatically toward a peak at a seed relative water content of 39 ± 3% (relative to maximum water content, which corresponded to 0.45 ± 0.03 g water g-1 d. wt) followed by a decline toward zero with total desiccation. This peak constituted a 10-fold increase in mean R, relative to the control. Exposing seeds to O2-free air at this peak induced a further large, but transient, increase in CO2 evolution, indicating that the peak developed in the presence of oxidative phosphorylation, rather than due to the absence of it. • The magnitude and mode of the observed increase in CO2 evolution in response to desiccation is unlike any reported so far and thus adds new information about metabolic changes that may occur as the water content of desiccation-intolerant seeds declines