Antisense inhibition of the photosynthetic antenna proteins CP29 and CP26:Implications for the mechanism of protective energy dissipation

The specific roles of the chlorophyll alb binding proteins CP29 and CP26 in light harvesting and energy dissipation within the photosynthetic apparatu s have been investigated. Arabidopsis was transformed with antisense constr ucts against the genes encoding the CP29 or CP26 apoprotein, which gave ris e to several transgenic lines with remarkably low amounts of the antisense target proteins. The decrease in the level of CP24 protein in the CP29 anti sense lines indicates a physical interaction between these complexes. Analy sis of chlorophyll fluorescence showed that removal of the proteins affecte d photosystem II function, probably as a result of changes in the organizat ion of the light-harvesting antenna. However, whole plant measurements show ed that overall photosynthetic rates were similar to those in the wild type . Both antisense lines were capable of the qE type of nonphotochemical fluo rescence quenching, although there were minor changes in the capacity for q uenching and in its induction kinetics. High-light-induced violaxanthin dee poxidation to zeaxanthin was not affected, although the pool size of these pigments was decreased slightly. We conclude that CP29 and CP26 are unlikel y to be sites for nonphotochemical quenching.