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Metabolism and Enzymology

Relationship between Fructose 2,6-Bisphosphate and Carbohydrate Metabolism in Darkened Barley Primary Leaves

United States Department of Agriculture, Agricultural Research Service, Beltsville, Maryland 20705, Plant Photobiology Laboratory, Building 046A, Beltsville Agricultural Research Center, Beltsville, Maryland 20705

Initial dark fructose 2,6-bisphosphate levels in 10-day-old barley (Hordeum vulgare L.) leaves increased when the photosynthetic period was lengthened, when the temperature during the prior photosynthetic period was reduced, and following leaf excision. These treatments also increased the leaf sucrose concentration. Conversely, a decrease in dark fructose 2,6,-bisphosphate occurred during extended darkness, with increasing leaf age and when photosynthate in the leaf was reduced by earlier low light treatments. These variations in fructose 2,6-bisphosphate content correlate with known changes in dark respiration. These findings suggest, but do not conclusively prove, a causal relationship between dark fructose 2,6-bisphosphate levels and dark respiration rates.