The Role of Nitric Oxide in the Arabidopsis thaliana Response to Simulated Microgravity and the Involvement of Autophagy in This Process

The role of nitric oxide (NO) in the response of plants to simulated microgravity has been studied. It was found that treatment of Arabidopsis thaliana seeds with NO donor sodium nitroprusside (SNP), stimulating changes in root growth parameters, leads to increased plant resistance to clinostating. After treatment of seeds with SNP, the content of endogenous NO in control plants on the sixth day of cultivation increased by 1.5 times, and it increased by 1.8 times in clinostated seed. The content of endogenous NO gradually decreased on days 9–12, which may indicate the adaptation of plants to the clinostating conditions. Using a specific DAF-FM DA fluorescent probe, an increase in NO fluorescence was found in epidermal cells of root apexes and root hairs in clinostated plants, indicating the accumulation of endogenous NO in these root tissues under stress. On the sixth day of cultivation under clinostat conditions compared with control plants, there was an increase in the accumulation of autophagosomes in the epidermal cells of the transitional zone of the root with the following decrease in this indicator on days 9–12. Seed treatment with cPTIO (NO scavenger) slightly inhibited seedling growth, and this effect was enhanced under clinostating, including a significant increase in the accumulation of autophagosomes in epidermal cells. Thus, the data obtained indicate that the regulation of endogenous NO content is an important component of intracellular signaling mechanisms that are involved in the response of plant cells to simulated microgravity.