Ascorbate deficiency does not limit non-photochemical quenching in Chlamydomonas reinhardtii

Vidal-Meireles, Andre and Tóth, Dávid and Kovács, László and Neupert, Juliane and Tóth, Szilvia Zita (2019) Ascorbate deficiency does not limit non-photochemical quenching in Chlamydomonas reinhardtii. PLANT PHYSIOLOGY. ISSN 0032-0889 (In Press)

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Abstract

Ascorbate (Asc, vitamin C) plays essential roles in development, signaling, hormone biosynthesis, regulation of gene expression, stress resistance and photoprotection. In vascular plants, violaxanthin de-epoxidase (VDE) requires Asc as reductant, thereby it is required for the energy-dependent component of non-photochemical quenching (NPQ). To assess the role of Asc in NPQ in green algae, which are known to contain low amounts of Asc, we searched for an insertional Chlamydomonas reinhardtii mutant affected in the VTC2 gene encoding GDP-L-galactose phosphorylase, which catalyzes the first committed step in the biosynthesis of Asc.. The Crvtc2-1 knockout mutant was viable and, depending on the growth conditions, contained 10 to 20% Asc relative to its wild type. When C. reinhardtii was grown photomixotrophically at moderate light, the zeaxanthin-dependent component of NPQ emerged upon strong red illumination both in the Crvtc2-1 mutant and in its wild type. Deepoxidation was unaffected by Asc deficiency, demonstrating the Chlorophycean VDE found in C. reinhardtii does not require Asc as a reductant. The rapidly induced, energy-dependent NPQ component characteristic of photoautotrophic C. reinhardtiicultures grown at high light was not limited by Asc deficiency either. On the other hand, a reactive oxygen species-induced photoinhibitory NPQ component was greatly enhanced upon Asc deficiency, both under photomixotrophic and photoautotrophic conditions. These results demonstrate Asc has distinct roles in NPQ formation in C. reinhardtiithan in vascular plants.

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