Are contents of Rubisco, soluble protein and nitrogen in flag leaves of rice controlled by the same genetics?

Genetic relations among the contents of Rubisco, soluble protein and total leaf nitrogen (N) in leaves of rice (Oryza sativa L.) were studied by quant itative trait loci (QTL) analysis with a population of backcross inbred lin es (BILs) of japonica Nipponbare x indica Kasalath. The ratio of Rubisco to total leaf N in leaves is the main target in improving photosynthetic N-us e efficiency in plants. QTLs controlling Rubisco content were not detected near QTLs for total leaf N content. These results indicate that contents of Rubisco and total leaf N are controlled by different genetics. QTLs that c ontrolled the ratio of Rubisco to total leaf N (CORNs) were detected. These results suggest that some mechanism(s) may be involved in determining this ratio, while the contents of Rubisco and total leaf N are controlled in ot her ways. In elite BILs, the ratios of Rubisco to total leaf N were higher than those of both parents. These results suggest a good possibility of imp roving N-use efficiency by CORNs in cultivated rice. A QTL controlling Rubi sco content was mapped near a QTL for soluble protein content on chromosome 8 at 5 d after heading and on chromosome 9 at 25 d. In each chromosome reg ion, the peaks of both QTLs overlapped accurately, giving a high possibilit y of pleiotropic effects by the same genes. Different QTLs controlling solu ble protein or Rubisco were detected from those detected at 5 d or 25 d aft er heading. This suggests that these traits are genetically controlled depe nding on the growth stages of leaves.