SUCROSE-PHOSPHATE SYNTHASE - AN ENZYME WITH HETEROTIC ACTIVITY CORRELATED WITH MAIZE GROWTH

Identification of biochemical determinants linked to growth that can be quantitated early in seedling development may be important for breeding purposes. Carbohydrate metabolism is a good candidate for such an approach. The genetic variation and inheritance of the activity of two key enzymes of carbohydrate metabolism, sucrose phosphate synthase (SPS) and ADP glucose pyrophosphorylase (ADPGppase), were studied in maize (Zea mays L.) third and fourth leaves in a half 5 x 5 diallel design. Early greenhouse growth traits (estimated in two trials) and held performances (2 locations x 2 years) were also measured. Genetic variation was observed in greenhouse-grown leaf tissues for SPS activities under limiting and nonlimiting substrate concentrations, representing the phosphorylated and unphosphorylated state of the enzyme, respectively. Heterosis for SPS was significant in both conditions. In hybrids, SPS activity in the fourth leaf was significantly correlated with the forage dry matter yield measured In the field in 1991 (r = 0.89***, 0.87***, 0.71*, and 0.42 ns, depending on the location), suggesting that SPS activity could be a limiting factor of maize development; but no significant correlations were detected between SPS activities and forage yield measured the next year in two locations. The ADPGppase activity of hybrids was not significantly different from that of parental lines.