Effects of low water potentials on some aspects of carbohydrate metabolism in Chlorella pyrenoidosa.

Chlorella pyrenoidosa was subjected to low water potentials and the resulting changes in carbohydrate metabolism were measured.Water deficit reduced the incorporation of (14)C-glucose into methanol insoluble compounds, principally starch and increased that into sucrose. Even moderate water deficit, for example potentials of -2.5 and -5 atm, greatly reduced the incorporation of (14)C-glucose into uridine diphosphate glucose, while (14)C levels of the hexose monophosphates changed little, indicating a direct stimulus of sucrose synthesis. This increased sucrose synthesis was one of the earliest effect of water deficit, because potentials of -2.5 and -5 atm did not reduce respiration and glucose uptake.At lower water potentials (-10 atm or less) there was reduced (14)C incorporation into all sugar phosphates. This resulted from a combination of reduced (14)C-glucose uptake and increased sucrose synthesis.Water potentials as low as -20 atm had little effect on acetate uptake, or on the (14)C levels in the intermediates of the TCA cycle. This confirmed that low water potentials do not directly inhibit respiratory pathways in Chlorella.The results are discussed in relation to the effect of water deficit on levels of various metabolites in vascular plants, which have been reported by other workers.