Importance of Rubisco activase in maize productivity based on mass selection procedure

The original maize (Zea mays L.) var. Zacatecas 58(Z0) and five composites of cycles 5, 10, 15, 20, and 23 of stratified massselection (Z5, Z10, Z15, Z20, and Z23) for improved productivity applied tothe original variety were used as the model system.Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (Rubisco)activity and the rates of net photosynthesis in the leaves above the earwere compared in all the composites during the grain filling period. Leaveswere sampled weekly from anthesis to physiological maturity. Results showeda significant and gradual increase in Rubisco activity for the improvedpopulations. In vivo photosynthesis measured by IRGAduring the same period also showed increased levels associated withincreases of grain yield. The highest Rubisco activity, photosynthetic rateand grain yield were found in the Z23 population. Western blot analysis forRubisco protein did not show significant differences either during thefilling period or between populations. The same analysis, however, forRubisco activase protein showed increasing contents in the improvedpopulations. These data confirm and complement previous findings,indicating that the stratified visual mass selection procedure applied tomaize plants is associated with leaf content of Rubisco activase protein.The possible regulatory role of Rubisco activase during grain filling isdiscussed.