Investigation of photosystem 2 characteristics in isolated chloroplasts from heterotic wheat hybrids.
Moscow, Lomonosov Moscow State University, Department of Biophysics, Faculty of Biology, Russia, Moscow, Paustovskogo 5-1-38, E-mail: firstname.lastname@example.org pp.
The increase in biological productivity in heterotic wheat hybrids, relative to their parent forms, was previously shown to be not accompanied by changes in the photosynthetic rate per leaf area unit. However, the rate of Hill reaction per Chl unit was shown to be significantly higher in the hybrids. Thus increase may be caused by higher efficiency of the primary reactions of photosynthesis or by a smaller size of the photosynthetic unit, i. e. the number of pigment molecules in the light-harvesting antenna of the photosynthetic reaction center in the hybrids.
The goal of this work was to assess changes in parameters of photosystem 2 (PS2) in the heterotic hybrids by measuring parameters of the induction curve of chlorophyll fluorescence in the presence of diuron, which block electron transfer from the primary to secondary electron acceptor in PS2. The efficiency of the primary reactions of PS2 was estimated as the (Fm-Fo)/Fm ratio, where Fo is the initial fluorescence intensity with oxidized primary electron acceptor in PS2 (in dark-adapted sample), and Fm is the maximum fluorescence intensity after light-induced reduction of the primary acceptor. The relative size of the light-harvesting antenna of PS2 was estimated as fluorescence rise time during transition from the initial, Fo, to the maximum fluorescence level, Fm.
The measurements were carried out on leaves of winter wheat genotypes: Erythrospermum 388, Gostianum 88, Omskaya iso-15, Progress and the second generation of their heterotic hybrids, obtained by diallel crossing.
In parent forms, the size of the light-harvesting antenna of PS2 increased in the series: Omskaya > Erythrospermum > Progress > Hostianum, and the efficiency of the primary reactions in PS2 decreased in the series: Omskaya > Hostianum > Erythrospermum > Progress.
In all hybrid, except the Progress – Omskaya pair, the antenna size of PS2 was less, whereas the efficiency of PS2 was higher, than in any of the parent forms in respective pair. In other words, significant heterosis effect was observed for both parameters in all pairs of parents, except Omskaya-Progress. The mother effect was more pronounced in these pairs.