Rhythmical redox homeostasis can be restored by exogenous melatonin in hulless barley (Hordeum vulgare L.var. nudum) under cold stress

Melatonin plays an important role in the ability of plants to adjust circadian rhythm and respond to abiotic stresses. Under stress conditions, exogenous melatonin can improve plant stress resistance by regulating the activity of plant antioxidant enzymes. However, little is known about the effects of exogenous melatonin on redox shock in plants. We measured the indexes related to redox maintenance of exogenous melatonin in pretreated hulless barley seedlings at different temperatures. Under cold stress conditions, pretreatment with 1 μM exogenous melatonin restored the rhythmic accumulation of hydrogen peroxide in hulless barley seedlings, as well as the rhythmic accumulation of superoxide dismutase (SOD) and catalase (CAT). In addition, pretreatment with 1 μM exogenous melatonin conferred a certain protective effect on the transcription-independent rhythmic marker PRX-SO2/3. Additionally, key physiological indicators, such as MDA and soluble sugars, also exhibited rhythmic accumulation under the action of exogenous melatonin pretreatment. Collectively, these data show that pretreatment of exogenous melatonin can help plants sustain stable redox homeostasis under cold stress. According to the previous research, exogenous melatonin could recovery the rhythm of core circadian genes TOC1 and CCA1, it also indicated that the close interaction between circadian system and redox homeostasis.