Indications for chlororespiration in relation to light regime in the marine diatom Thalassiosira weissflogii.

The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun. The light regime caused a daily cycle in non-photochemical quenching. Remarkable were the changes in fluorescence directly after a light-to-dark transition that occurred in addition to the changes induced by non-photochemical quenching. A transient non-photochemical reduction of PQ and of QA was indicated by a transient increase in apparent Fo and by changes in the shape of the fluorescence induction curve. The observed changes developed approximately the first 100¯120 s after a light-to-dark transition and could be reversed by the application of far-red illumination. Chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with QA, also a reduction of QA. The function and ecological relevance of chlororespiration are discussed. [KEYWORDS: Chlororespiration; Dynamic light; Electron transport; Fluorescence; Fluorescence induction; Thalassiosira weissflogii