Suppression of the phytoene desaturase gene influence on the organization and function of photosystem II (PSII) and antioxidant enzyme activities in tobacco

Carotenoid compounds play a key role in plant photosynthesis. Some are integrated within the photosynthetic system, where they serve as regulators of light harvesting. In this study, we found pigment alterations in transgenic tobacco leaves following RNAi mediated suppression of pds (phytoene desaturase). Native green gel analysis and pigment determinations showed that the ratios of Chl a/b in PSI and PSII cores and in LHCII were unaffected by gene silencing. SDS-PAGE indicated that the Chl-binding complexes of PSI and PSII cores were unchanged in the transgenic plants, but the LHCII levels were changed. A new band around 50 kDa was found, with a protein density around 18 kDa increased. Chl fluorescence kinetics showed that energy transfer and photosynthesis in the pds-silenced plants were inhibited under both high and moderate light, and that both Fv′/Fm′ and qP were decreased when qN was increased. The number of Chl molecules in every LHCII protein complex was decreased, resulting in less efficient energy transfer and a severe decline in PSII activity. Antioxidant enzymes no longer worked in concert, which could explain the appearance of the leaf albinism.