Non-photochemical-quenching Mechanisms in the Cyanobacterium Thermosynechococcus elongatus

Abstract

In the cyanobacterium Synechocystis PCC 6803 grown under iron replete or iron deplete conditions, blue light induces a photoprotective Non-Photochemical-Quenching (NPQ) mechanism. This energy dissipation mechanism involves the phycobilisomes and the Orange Carotenoid Protein (OCP) encoded by the slr1963 gene. In the thermophilic cyanobacterium Thermosynechococcus elongatus there are no OCP-like genes, but instead two adjacent genes encode for the N-terminal and C-terminal domains of an OCP-like gene. The goal of our study was to elucidate the possible role of these genes in the blue-light induced NPQ mechanism. Blue light (at any intensity) was not able to induce any quenching of fluorescence in T. elongatus cells grown in the presence or absence of Fe. In contrast, normal state transitions were observed. The blue-light induced NPQ was also absent in Synechococcus elongatus cells in which the OCP gene is lacking, but it was present in Arthrospira maxima and Anabaena variabilis cells possessing the OCP protein.