Abstract:

The photosynthetic rate, oxygen evolution activity of the PSⅡ center, and chloroplast ultrastructure of three hybrid poplar clones under light stress were investigated using an oxygen electrode, IRGA (infra-red CO2 gas analyzer), chlorophyll fluorometer and transmission electron microscopy. The photosynthetic rate and PSⅡ oxygen evolution varied negatively with the pretreatment-PFD (Photon Flux Density), whereas the chlorophyll a/b varied positively with the pretreatment-PFD for two triploid clones. Both the maximal and effective PSⅡ efficiencies of the diploid clone B11 were much higher than those of the two triploid clones B346 and B342. The non-photochemical quenching of triploid B346 was higher than in the B342 and B11 clones. The photosynthetic capacity and resistance to light stress for the diploid clone was higher than in triploid clones. There was no close relationship between chlorophyll content and photosynthetic rate, there was seasonal variation in CHL content and CHLa/b, and the ratio of CHLa to CHLb decreased with enhancing pretreatment-PFDs. The chloroplast protein inhibitor streptomycin (SM) blocked the re-synthesis process of D1 protein. Transmission electron micrographs showed that 1h strong irradiance exposure could result in the decomposition of the lamellar structure of grana. Clones B11 and B342 were more resistant to light stress than clone B346.