Exogenous melatonin improves growth in hulless barley seedlings under cold stress by influencing the expression rhythms of circadian clock genes

Abstract

Background Melatonin is a hormone substance that exists in various living organisms. Since it was discovered in the pineal gland of cattle in 1956, the function of melatonin in animals has been roughly clarified. Nevertheless, in plants, the research on melatonin is still insufficient. Hulless barley (Hordeum vulgare L. var. nudum hook. f.) is a crop that originates from cultivated barley in the east, usually grown on the Qinghai-Tibet Plateau, becoming the most important food crop in this area. Although the genome and transcriptome research of highland barley has gradually increased recently years, there are still many problems about how hulless barley adapts to the cold climate of the Qinghai-Tibet Plateau. Methods In this study, we set three temperature conditions 25°C, 15°C, 5°C hulless barley seedlings, and at the same time soaked the hulless barley seeds with a 1 µM melatonin solution for 12 hours before the hulless barley seeds germinated. Afterwards, the growth and physiological indicators of hulless barley seedlings under different treatment conditions were determined. Meanwhile, the qRT-PCR method was used to determine the transcription level of the hulless barley circadian clock genes under different treatment conditions under continuous light conditions. Results The results showed the possible mechanism by which melatonin pretreatment can promote the growth of hulless barley under cold stress conditions by studying the effect of melatonin on the rhythm of the circadian clock system and some physiological indicators. The results revealed that the application of 1 µM melatonin could alleviate the growth inhibition of hulless barley seedlings caused by cold stress. In addition, exogenous melatonin could also restore the circadian rhythmic oscillation of circadian clock genes, such as HvCCA1 and HvTOC1, whose circadian rhythmic phenotypes were lost due to environmental cold stress. Additionally, the results confirmed that exogenous melatonin even reduced the accumulation of key physiological indicators under cold stress, including malondialdehyde and soluble sugars. Discussion Overall, these findings revealed an important mechanism that exogenous melatonin alleviated the inhibition of plant vegetative growths either by restoring the disrupted circadian rhythmic expression oscillations of clock genes, or by regulating the accumulation profiles of pivotal physiological indicators under cold stress.

Melatonin-Mediated Abiotic Stress Tolerance in Plants

“…Under cold stress, melatonin upregulates genes related to stress responsive pathways such as C-repeat binding factor/dehydration-responsive element-binding protein (CBF/DREB), cold regulated 15a ( COR15a ), calmodulin binding transcription activator 1 ( CAMTA1 ), and zinc finger transcription factors 10 and 12 (ZAT 10 and ZAT 12; Zhao et al, 2017 ; Guo et al, 2018 ; Wang et al, 2018 ). The rhythmic expression patterns of circadian clock genes are also altered by melatonin supplementation in hulless barley seedlings, regulating their growth and enhancing cold resistance ( Chang et al, 2021 ).…”

“…For example, the expression levels of a key gene ( ClAOC1 ) in JA biosynthesis, and a key gene ( ClAMI1 ) in IAA biosynthesis are upregulated in watermelon leaves after melatonin application under cold stress ( Chang et al, 2020 ; Li H. et al, 2021 ). Consequently, the JA and IAA contents increase, thus improving photosynthesis and redox homeostasis ( Chang et al, 2021 ).…”

Melatonin Induced Cold Tolerance in Plants: Physiological and Molecular Responses

“…Moreover, MT also modulates the expression of ABA synthesis genes (CsNCED1 and CsNCED2) and ABA catabolism genes (CsCYP707A1 and CsCYP707A2) to confer cold tolerance in plants ( Zhao et al, 2017 ). The application of MT also induces the RBOHD-dependent H 2 O 2 generation in cold stress and increase in H 2 O 2 promotes Ca 2+ accumulation that sends signals for anti-oxidant activities and improve the cold tolerance ( Chang T. et al, 2021 ). MT application also upregulate the expression of anti-oxidant genes (CsSOD, CsPOD, CsCAT, and CsAPX) that increases the anti-oxidant activities of and resultantly increased the ROS scavenging ( Li et al, 2019 ).…”

Melatonin in Plant Defense against Abiotic Stress

“…There was alteration in the 46 metabolites studied such as arabinose, glucopyranose, mannose, maltose, and turanose which were greatly enhanced in Cynodon dactylon [96]. Supplementation of 1 µM melatonin improves growth in Hordeum vulgare under cold stress [139]. In a study performed on Pistacia vera (L.) grown under cold stress, application of melatonin caused a significant decrease in the expression of oxidative stress biomarkers, with a subsequent decrease in sugar, proline, and GABA content [140].…”