RELATION OF RUBISCO TO MAIZE GRAIN-YIELD IMPROVEMENT - EFFECT OF WATER RESTRICTION

Yield improvement in maize (Zea mays L.) can be obtained by repeated cycles of mass stratified selection, but the biochemical mechanisms behind this method are not understood. This research focuses on testing the possible role of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) in this process, and how water deficiency affects the enzyme during the grain-filling period. Rubisco activity and Rubisco protein were measured in the leaf above the ear of maize plants from the original and improved population throughout the grain filling, under irrigated and water-deficient conditions imposed during the linear part of the filling period. In fully irrigated plants, rubisco activity was higher in the selected population, but rubisco protein content was not. In water-deficient plants, rubisco activity srongly decreased in both maize populations, but rubisco protein was less affected. Grain yeild was higher in the improved Population in irrigated plants, but the advantage was lost during water deficiency. The above data suggest the the mass stratified method for grain yield improvement is selecting for plants with higher catalytic activity of rubisco, rather than greater contents of rubisco protein.