Summary: A comparison was made of the xerotolerant yeast and its non-tolerant counterpart when fully adapted to growth media of high and low water activity ( ), and during the period of adaptation from a high aw to a medium containing NaCl (10%, w/v). Comparisons of the fully adapted yeasts were confined to levels of activity of phosphofructo-kinase and -glycerol-3-phosphate dehydrogenase. The results confirmed our previous findings obtained with different assay procedures that growth at diminished dramatically increased the level of glycerol phosphate dehydrogenase in but had little or no effect in that respect on Simultaneously phosphofructokinase activity was about doubled in and about halved in Differences between the two yeasts were even more conspicuous during the period of response to salt stress. apparently adapted fully to the salt broth within 6 h (at 30 °C) inasmuch as viability was unaffected by the transfer and glycerol content reached its maximum by then. On the other hand, took about 140 h to adapt by a process that could be resolved into two stages. Stage 1 was marked by a catastrophic drop in apparent viability and widely different counts on three plating media. Stage 2 was identified by similar counts on all three plating media and a progressive increase in viability up to the level of the original inoculum. Glycerol phosphate dehydrogenase activity increased during this stage but glycerol accumulation began in both species immediately after transfer. Throughout the entire adaptation period, consumed glucose much more slowly than did The complexity of the response of to salt stress has focused attention on this species as a reference for studying yeast water relations in general.


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