Sucrose synthase and sucrose phosphate synthase in potato: distribution of activities and variations in leaves

Activities of sucrose synthase (SS, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14) in leaf, stem, stolon, tuber and root of potato plant (Solanum tuberosum L. cv Kufri Sindhuri) were determined in vitro. SS was determined in both sucrose synthesis (SSsyn) and sucrose cleavage (SScle) directions. Both SS and SPS were present in fairly detectable quantities in immature and mature leaves, stem, stolon, developing tubers and root. The ratio of cleavage to synthesis was 2.5-3.0. Both SSsyn and SPS activities and sucrose contents varied diurnally when measured in mature leaves. Maximum SPS was at 16 h and the minimum at 8 h while the maximum SSsyn was at 20 h and the minimum at 12 h. The variation rhythm of leaf sucrose content synchronized with that of SSsyn