The ancient cyanobacterium gloeobacter violaceus PCC 7421 is capable of state transitions and blue-light induced fluorescence quenching

Abstract

The atypical unicellular cyanobacterium Gloeobacter violaceus PCC 7421, diverged very early during the evolution of cyanobacteria, can be regarded as a key organism for understanding many structural, functional, regulatory, and evolutionary aspects of oxygenic photosynthesis. In our current study we investigated whether this ancient cyanobacterium lacking thylakoid membranes is capable of two basic phenomena common to all other photoautrophs: State transitions and non-photochemical fluorescence quenching. Our results clearly indicate dynamic changes in light energy distribution between the two photosystems. Similar to “modern” cyanobacteria G. violaceus is in state II in darkness and in state I upon illumination with weak blue-or far red light. Compared to state II, state I is characterized by an increased functional absorption cross-section of PS2. Furthermore, in contrast to weak blue light, strong blue light reversibly quenches chlorophyll fluorescence in G. violaceus, which suggests the existence of regulated heat dissipation triggered by the orange carotenoid protein in this primordial cyanobacterium.