Cold stress modulates osmolytes and antioxidant system in Calendula officinalis

Abstract

Understanding the mechanism of adaptation to low-temperature stress is very crucial for developing cold-tolerant crop plants. The present study was used to investigate the response of Calendula officinalis (C. officinalis) to cold stress (CS). Seeds of C. officinalis were grown at normal temperature of 25 °C for 14 days and then shifted to a growth chamber set at 4 °C. The response of C. officinalis seedlings to cold stress was evaluated by estimating the relative growth changes, chlorophyll, electrolyte leakage (EL) and the content of malondialdehyde (MDA), proline, glycine betaine (GB), total soluble sugars, trehalose, total protein content and fatty acid profile. Enzymatic activity of antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) was also assessed. Moreover, transcript expression of cold-responsive genes [APX, CAT, dehydration-responsive element-binding protein (DREB1), GR and SOD] was also evaluated on homology basis. We measured and compared these indices of seedlings leaves under low temperature (4 °C) and normal temperature (25 °C) and observed that on exposure to CS, C. officinalis shows higher accumulation of osmoprotectants (proline, soluble sugars, glycine betaine and trehalose), phenolics and proteins, and increased antioxidant enzyme activity (APX, GR and SOD) except CAT activity, which declined in cold-stressed plants. Transcript expression of cold-responsive genes (SOD, CAT, APX, GR and DREB1) was found to be upregulated under cold stress. Overall, our study suggests that cold exposure/CS, besides eliciting various biochemical/physiological responses, triggers various pathways causing differential gene expression, consequently leading to differential protein expression. Further, this is the first report of C. officinalis under cold stress that may help us in exploring the mechanism of cold tolerance in future.