Cellular levels of ribulose 1,5 Bisphosphate carboxylase and chloroplast compartment size in wheat mesophyll cells

Abstract

Pyke, K. A. and Leech, R. M. 1987. Cellular levels of ribulose 1,5 bisphosphate carboxylase and chloroplast compartment size in wheat mesophyll cells.-J. exp. Bot. 38: 1949-1956.The amount of the photosynthetic enzyme ribulose 1,5 bisphosphate carboxylase (RUBISCO),as determined in mesophyll cells in primary wheat leaves was related to the size of the chloroplast compartment within the cell for wheat species of three ploidy levels. A similar comparison was made for several genotypes of the hexaploid breadwheat Triticum aestivum. Estimation of total chloroplast volume per mesophyll cell was made assuming chloroplasts to be oblate spheroid in shape.A significant correlation was found between the amount of RUBISCO per cell and the total chloroplast volume per cell for diploid, tetraploid and hexaploid wheat species. A significant correlation between cellular RUBISCO level and total chloroplast volume per cell was also observed for a range of genotypes of the hexaploid T. aestivum but these genotypes of T. aestivutn accumulate a greater amount of RUBISCO per unit chloroplast volume than do any other wheat species. For these genotypes of T. aestivum the stromal concentration of RUBISCO was estimated at 0·5 mol m-3 with a ribulose Msphosphate binding site concentration of 4·0 mol m-3.These results are discussed with respect to a gene dosage hypothesis to explain the accumulation of RUBISCO in leaf mesophyll cells. Oxford University Press 1987.