NEW INSIGHTS INTO THE ANHYDROBIOTIC PHENOMENON - THE EFFECTS OF TREHALOSE CONTENT AND DIFFERENTIAL RATES OF EVAPORATIVE WATER-LOSS ON THE SURVIVAL OF APHELENCHUS-AVENAE

The effects of differential rates of evaporative water loss on the survival capabilities of small aggregates (ca. 10 mg wet wt) of Aphelenchus avenae were assessed. This was achieved using a comparative approach between rapid (direct transfer of preconditioned nematodes to low relative humidities) and gradual (sequential transfer of preconditioned nematodes to successively lower relative humidities) dehydration regimes. Alterations in the levels and types of polyhydroxy compounds accumulated were also assessed during the induction process. Glycerol and glucose levels remained low (< 1% dry wt) while trehalose levels increased dramatically during preconditioning (8-10% dry wt), but the elevated levels were unable to support survival during periods of rapid water loss. Survival was directly related to the rate of evaporative water loss, with the highest level of survival being afforded by the most gradual dehydration regime. In addition, the water loss curves identified a critical period where hydration levels ranged from 40% to 12% H2O. During this time, slow drying was essential if the nematodes were to successfully survive the dehydration process. Survival curves also revealed the existence of a transition phase in the dehydration process, where nematodes required further dehydration before revival could occur. These results are discussed in relation to the adaptive significance of polyhydroxy compound accumulation and the probable role that specific hydration levels play in the implementation of other adaptations at the cellular and subcellular levels. (C) 1993 Wiley-Liss, Inc.