Abstract
Melatonin (N-acetyl-5-methoxytryptamine) plays important role in multiple plant developmental processes and stress responses. We investigated the possible mediatory role of melatonin in growth, photosynthesis, and the response to cold stress in rice by using three different experiments: soaking seed; immersing roots, and spraying to leaves with 0, 20, or 100 μM melatonin. After 6 days of cold stress, the growth of rice seedlings was significantly inhibited, but this inhibition was alleviated by exogenous melatonin. Furthermore, exogenous melatonin pretreatment alleviated the accumulation of reactive oxygen species, malondialdehyde and cell death induced by cold stress. Melatonin pretreatment also relieved the stress-induced inhibitions to photosynthesis and photosystem II activities. Further investigations showed that, antioxidant enzyme activities and non-enzymatic antioxidant levels were increased by melatonin pretreatments. The treatment methods of seed soaking and root immersion were more effective in improving cold stress resistance than the spraying method. The results also indicated the dose-dependent response of melatonin on rice physiological, biochemical, and photosynthetic parameters.
Highlights
Low temperature is one of the major abiotic stresses that limits crop growth, productivity, survival and geographical distribution of plants (Mishra et al, 2011; Hu et al, 2016), especially in temperate zones and high-elevation environments (Andaya and Mackill, 2003)
The low temperature stress inhibited the growth of rice seedlings, while melatonin pretreatment alleviated this inhibition to a certain extent (Figure 1A)
These results indicate that exogenous melatonin application improved cold stress resistance in rice seedlings
Summary
Low temperature is one of the major abiotic stresses that limits crop growth, productivity, survival and geographical distribution of plants (Mishra et al, 2011; Hu et al, 2016), especially in temperate zones and high-elevation environments (Andaya and Mackill, 2003). Plants growth at low temperature lead to oxidative stress through increasing reactive oxygen species (ROS), such as hydrogen peroxide, superoxide anion, and hydroxyl radicals (Tasgın et al, 2006; Hu et al, 2016). To prevent the oxidative injury induced by ROS, plants have evolved an complex antioxidant system including enzymatic antioxidants such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and non-enzymatic antioxidants such as glutathione and proline (Erdal, 2012; Erdal et al, 2015; Ghaderian et al, 2015; Chen et al, 2016).
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