A Specific Feature of Nitrogen Utilization Efficiency in Leaf Photosynthesis in Oryza glaberrima Steud

Specific characteristics in the photosynthetic response to nitrogen application were compare between Oryza glaberrima Stend. strains introduced from West Africa and O. sativa L. strains including japonica, javanica, indica and japonica-indica types. These plants were grown in solution culture with different nitrogen concentrations. Chlorophyll content in leaf, the maximum quantum yield (Fv / Fm) in photosystem II and total Rubisco activity showed no significant inter-specific difference. However, O. glaberrima strains represented significantly high nitrogen utilization efficiency (CO2 exchange rate / nitrogen content in unit leaf area), high stomatal and mesophyll conductances in leaves with low nitrogen content, and high photosynthetic efficiency per unit Rubisco activity (CO2 exchange rate / total Rubisco activity). These findings suggest that the in vivo activation level of Rubisco is higher in O. glaberrima strains than in O. sativa strains. The high nitrogen utilization efficiency detected here is unique to O. glaberrima, and is considered to be an advantageous genetic character in photosynthesis. The introduction of such a character into O. sativa is regarded as a step toward the genetic improvement of leaf phtosynthetic ability of this species grown in a nitrogen-input saved condition.