Genetically based differences in photochemical activities of isolated maize (Zea mays L.) mesophyll chloroplasts

Photochemical activity of isolated mesophyll chloroplasts was measured as H ill reaction activity (HRA) and photosystem 1 (PS1) activity in three diall el crosses of maize (Zea mays L.) inbred lines and F-1 hybrids. Statistical ly significant differences between genotypes together with positive heterot ic effect in F-1 generation were found for both traits studied. These diffe rences were more pronounced when HRA or PS1 activity was expressed per leaf area unit or dry matter unit compared to the expression per chlorophyll co ntent unit. Analysis of variance showed that both the genetic and non-genet ic components of variation in the photochemical activity of isolated mesoph yll chloroplasts are present in all three diallel crosses examined. The pos itive heterosis in F-1 hybrids probably arises from non-additive genetic ef fects of a positive dominance type. Additive genetic effects were also stat istically highly significant. We found no differences between reciprocal cr osses.