Effect of light on growth and endogenous hormones in Chlorella minutissima (Trebouxiophyceae)

Stirk W.A., Bálint P., Tarkowská D., Novák O., Ljung K., Turečková V., Strnad M., Ördög V., van Staden J.

Keywords: Abscisic acid · Auxins · Brassinosteroids · Cytokinins · Gibberellins · Microalgae
Abstract: Plant growth regulators (PGRs) play an important role in mediating growth and stress responses in plants. Light influences PGRs concentrations in vascular plants. The effect of light on growth and endogenous PGR concentrations in microalgae was investigated in the present study. Chlorella minutissima MACC 360 was grown in 14:10 h light:dark (L:D), continuous dark (CD) and continuous dark with the addition of 5 g L-1 glucose (CD+G) for 48 h. Cultures were synchronized in the L:D cultures, increasing in size during the light period and dividing during the dark period. C. minutissima cells did not increase in size or undergo cell division in CD cultures. In CD+G conditions, the cultures were no longer synchronized but did continue to increase in cell size and constantly underwent cell division although fewer cells divided than in the L:D cultures. Endogenous auxin and cytokinin concentrations increased over time in the actively growing cultures (L:D and CD+G) but did not increase in the CD cultures. The largest increase in auxin content was in the CD+G cultures while the L:D cultures had the largest cytokinin increase. Gibberellin and brassinosteroid concentrations decreased over time in all the cultures with the most rapid decrease occurring in the actively growing cultures (L:D and CD+G). Abscisic acid (ABA) concentrations were low and only increased in the CD cultures. These results show that light does influence endogenous PGR concentrations in C. minutissima with auxins, cytokinins, gibberellins and brassinosteroids playing a role in cell growth while ABA responded to stress.
DOI: IEB authors: Ondřej Novák, Miroslav Strnad, Danuše Tarkowská