High Nitrogen Use Efficiency in Rice Genotypes is Associated with Higher Net Photosynthetic Rate at Lower Rubisco Content

Contrasting rice genotypes differing in leaf mass ratio (LMR) and leaf nitrogen content were screened. A strong inverse relationship was observed between ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content and its efficiency estimated as the ratio of net photosynthetic rate (P_N) to Rubisco content. Similarly, an inverse relationship between the specific activity of fully activated Rubisco and its content was observed. This suggests that a down regulation of Rubisco may occur if the efficiency of the enzyme is superior. Genotypes IET 12989 and IET 13567 recorded higher P_N together with lower Rubisco content in comparison with other genotypes measured. These genotypes showed low LMR and low nitrogen content and hence could be considered as efficient nitrogen users. This revised version was published online in July 2006 with corrections to the Cover Date.