OKUDA, Takashi; National Institute of Agrobiological Sciences: Anhydrobiosis in an African chironomid

Life and death are mutually exclusive states. But some organisms showing no sign of living due to complete desiccation are nevertheless able to resume active life after rehydration. Organisms in this peculiar biological state are highly resistant to dehydration in a condition referred to as �cryptobiosis � or �anhydrobiosis� (Keilin, 1959). Larvae of an insect species, the sleeping chironomid Polypedilum vanderplanki, live in temporary rock pools in semi-arid areas on the African continent and is able to achieve anhydrobiosis. When the rock pools dry up, the larvae become dehydrated but can revive within about an hour after water becomes available upon the next rain (Hinton, 1958). This larva seems to be the largest of all animals to achieve anhydrobiosis. Many anhydrobiotic animals accumulate large amounts of the disaccharide trehalose, which serves as a compatible solute thought to protect desiccating tissues by replacing the primary water of hydration and possibly through sugar glass formation. Anhydrobiotic P. vanderplanki larvae accumulate trehalose to levels of about 20% of their dry weight (40 �g/individual). Using a classical insect endocrine technique we also demonstrated that even larvae without a brain and thorasic ganglia could synthesize trehalose and enter anhydrobiosis successfully. Those observations indicated that induction of anhydrobiosis in P. vanderplanki is not under cerebral control, in spite of the fact that the brain has a significant role in regulating both induction and termination of insect diapause, in general. We also found that tehalose synthesis could be induced by exposuring larvae in 1% NaCl solusion for 1 day even without dehydration, which suggests that an increase in internal ion concentrations might be the trigger synthesizing trehalose.