The Effect of Chilling on the Photosynthetic Apparatus of Microalga Lobosphaera incisa IPPAS C-2047

Abstract

Photosynthetic organisms have developed a set of mechanisms aimed at preventing photo oxidative reactions in the photosynthetic apparatus (PSA) initiated by excessively absorbed light energy. Along with high irradiance, other stres sors, e.g., chilling temperatures, can lead to the absorption of the excess of light energy and hence to photo oxidative stress. Here, we studied induction of photoprotective mechanisms in response to chilling (0°C) at a low irradiance (50 μmol PAR photons m -2 •s -1 ) in the cells of microalga Lobosphaera incisa IPPAS C 2047. After 4 days of incubation at a low tempera ture, L. incisa IPPAS C 2047 cells showed a notable decrease in the photochemical activity of photosystem II (PSII) and in the efficiency of photosynthetic electron transport, as well as a significant increase in the thermal dissipation of the absorbed light energy in the light harvesting antenna. In contrast, most conventional markers of PSA acclimation to excess light ener gy [total chlorophyll and carotenoid content; violaxanthin cycle pigment content and de epoxidation state; photosynthetic antenna, PSII, and photosystem I (PSI) ratio] remained virtually unchanged. The content of major unsaturated fatty acids also remained almost unaffected, except for arachidonic acid (increased by 40%) recently assumed to activate violaxanthin de epoxidase by adjusting its lipid microenvironment. Significant changes (4 7 fold increase) were observed in the expres sion of the gene encoding protective protein LhcSR. Pre conditioning at 5°C prior to the acclimation to 0°C augmented the PSA photochemical activity. Our data show that the mid term (4 d) acclimation of L. incisa IPPAS C 2047 to a chilling temperature at a low irradiance triggers the PSA response resembling, in part, the response to high light but relying mostly on the LhcSR protein dependent quenching of excitation in the photosynthetic antenna.

The Photoprotective Protein PsbS from Green Microalga Lobosphaera incisa: The Amino Acid Sequence, 3D Structure and Probable pH-Sensitive Residues

“…Soil microalga Lobosphaera incisa IPPAS C-2047 (Trebouxiophyceae, Chlorophyta) was cultivated as described earlier [42]. Preliminary low-coverage genome sequencing data revealed fragments of L. incisa DNA homologous to the psbS gene of vascular plants (the contig containing these fragments is deposited to GenBank, accession number OR604506; the sequence is also presented in Supplementary Materials Table S2).…”