Exogenous application of melatonin and chitosan mitigate simulated microgravity stress in the Rocket (Eruca sativa...

Starting life in space and implementing spaceflight missions requires raising of plants in special conditions, where various stresses, including microgravity, are applied to plant. The use of stimulants is known as a promising effective approach that enhances plant resistance encountered a variety of abiotic stresses. In this study, the impact of two stimulants, melatonin and chitosan, in reducing negative effects of clinorotation on Rocket (Eruca sativa L.) seedlings was investigated from a physiological and biochemical point of view. For this purpose, a completely randomized experiment was designed where the treatments included control (without stimulants and normal gravity), melatonin (100 μM), chitosan (230 M), microgravity, microgravity + melatonin, and microgravity + chitosan. The results disclosed that the microgravity significantly impaired the plant growth and morphology, while exogenous application of melatonin and chitosan improved the plant growth parameters under stress conditions. Under microgravity, there was a reduction of 46.15% in shoot length (4.9 mm) and 41.44% in root length (4.7 mm) compared with the control (9.1 mm; 8.03 mm), respectively. Clinorotation led to a marked increment in the enzymes activity, wherein the POD, SOD and CAT activities increased by 75.13%, 72.67%, and 53.42%, respectively, compared with the control seedlings. In addition, supply of these two stimulants strengthened the scavenging of radial oxygen species and helped the plant to tolerate stress conditions, by activated the enzymatic and non-enzymatic systems. These results can pave the road for more studies and broad application of biological stimuli to overcome the space harsh environmental conditions by plants.