Role of sucrose-phosphate synthase in partitioning of carbon in leaves

Variations in leaf starch accumulation were observed among four species (wheat Triticum aestivum L.], soybean Glycine max L. Merr.], tobacco Nicotiana tabacum L.], and red beet Beta vulgaris L.]), nine peanut (Arachis hypogea L.) cultivars, and two specific peanut genotypes grown under different nutritional regimes. Among the genotypes tested, the activity of sucrose phosphate synthase was correlated negatively with leaf sucrose content in seven of the nine peanut cultivars as well as the two peanut cultivars grown with different mineral nutrition. The peanut cultivars differed in the effect of 10 millimolar sucrose on sucrose phosphate synthase activity in leaf extracts. Enzyme activity in crude leaf extracts was inhibited by sucrose (10-42%) in four of the cultivars tested whereas five cultivars were not. Overall, the results suggest that a correlation exists between the activity of sucrose phosphate synthase and starch/sucrose levels in leaves.