A modified assay method shows leaf sucrose-phosphate synthase activity is correlated with leaf sucrose content across a range of sugarcane varieties

Abstract

Eight different commercial and breeding varieties of sugarcane (Saccharum spp.) grown in controlled conditions were assayed for leaf sucrose-phosphate synthase (SPS) (EC 2.1.4.14) activity and leaf sucrose content. Leaf SPS activity measured at 25˚C ranged between 0.06 and 0.14 nmol sucrose formed mg protein ^-1 min^-1. The cross-varietal average for leaf SPS activity was 0.10 nmol µg protein^-1 min^-1 (equivalent to 63.4 µmol h^-1 g FW^-1 or 17.6 nkat g FW^-1) which is consistent with previously published leaf SPS activities for sugarcane; however, previous studies have assayed leaf SPS activity at either 30 or 37˚C. The range of leaf sucrose content across varieties (5.5–18.0 mg sucrose g FW^-1, average 11.3 mg g FW^-1) was consistent with all but one of four previously published reports. Leaf SPS activity and leaf sucrose content were significantly correlated across the eight varieties examined (r² =0.877, d.f. =7,P<0.001). Whilst previous reports have indicated a co-relationship between leaf SPS activity and leaf sucrose content in single sugarcane varieties both diurnally and with different nutrient regimes, this study shows, for the first time, that this co-relationship also holds true across a range of sugarcane varieties.