Clinorotation Affects Induction of the Heat Shock Response in Arabidopsis thaliana Seedlings

Clinorotation used to simulate microgravity effects in ground-based experiments is considered as a mild stress factor for plants. We have assumed that it might influence the plant tolerance to other stressful factors. To test this, Arabidopsis thaliana seedlings were grown on a horizontal clinostat (2 rpm) or under stationary conditions (control), and then were subjected to heat treatment. The kinetics of gene expression of cytosolic HSP70s and HSP90s during exposure to 37°C for 0.5-2 h was examined by RT-qPCR to estimate level of the heat shock reaction. It was shown that clinorotation caused the minor increase in transcript abundance of five AtHSP70s and AtHSP90-1 under normal temperature, as well as a faster onset and enhancement of their induction during heat shock. The heat tolerance was evaluated as a function of seedling survival after exposure to 45°C for 45 min. Seedlings grown under clinorotation were determined to withstand heat treatment better than seedlings grown under stationary conditions. The obtained data support the assumption that clinorotation may provide cross-protection of plants against fluctuations in environmental conditions.