Abstract
BackgroundSoil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy. The indoleamine melatonin (N-acetyl-5-methoxytryptamine) has a wide array of biological roles in plants, including acting as an auxin analog and an antioxidant. Previous studies have shown that exogenous melatonin application alleviates the salt-induced growth inhibition in non-halophyte plants; however, to our knowledge, melatonin effects have not been examined on halophytes, and it is unclear whether melatonin provides similar protection to salt-exposed halophytic plants.ResultsWe exposed the halophyte Limonium bicolor to salt stress (300 mM) and concomitantly treated the plants with 5 μM melatonin to examine the effect of melatonin on salt tolerance. Exogenous melatonin treatment promoted the growth of L. bicolor under salt stress, as reflected by increasing its fresh weight and leaf area. This increased growth was caused by an increase in net photosynthetic rate and water use efficiency. Treatment of salt-stressed L. bicolor seedlings with 5 μM melatonin also enhanced the activities of antioxidants (superoxide dismutase [SOD], peroxidase [POD], catalase [CAT], and ascorbate peroxidase [APX]), while significantly decreasing the contents of hydrogen peroxide (H2O2), superoxide anion (O2•−), and malondialdehyde (MDA). To screen for L. bicolor genes involved in the above physiological processes, high-throughput RNA sequencing was conducted. A gene ontology enrichment analysis indicated that genes related to photosynthesis, reactive oxygen species scavenging, the auxin-dependent signaling pathway and mitogen-activated protein kinase (MAPK) were highly expressed under melatonin treatment. These data indicated that melatonin improved photosynthesis, decreased reactive oxygen species (ROS) and activated MAPK-mediated antioxidant responses, triggering a downstream MAPK cascade that upregulated the expression of antioxidant-related genes. Thus, melatonin improves the salt tolerance of L. bicolor by increasing photosynthesis and improving cellular redox homeostasis under salt stress.ConclusionsOur results showed that melatonin can upregulate the expression of genes related to photosynthesis, reactive oxygen species scavenging and mitogen-activated protein kinase (MAPK) of L. bicolor under salt stress, which can improve photosynthesis and antioxidant enzyme activities. Thus melatonin can promote the growth of the species and maintain the homeostasis of reactive oxygen species to alleviate salt stress.
Highlights
Soil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy
Melatonin can promote the growth of the species and maintain the homeostasis of reactive oxygen species to alleviate salt stress
After 15 days of treatment, seedlings treated with exogenous melatonin and 0 mM NaCl had a fresh weight that was 49.1% greater than that of untreated control seedlings, whereas those treated with both melatonin and 300 mM NaCl had a fresh weigh that was 64.5% greater than that of seedlings treated with 300 mM NaCl only
Summary
Soil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy. Biotic and abiotic stresses severely inhibit plant growth and development [38, 52] Among these stressors, soil salinization is becoming an increasingly serious problem worldwide, causing cultivated land loss and desertification and seriously impacting agriculture and the economy [10, 17, 18, 36]. Soil salinization is becoming an increasingly serious problem worldwide, causing cultivated land loss and desertification and seriously impacting agriculture and the economy [10, 17, 18, 36] Some plants such as halophytes with high salt tolerance can survive in saline soils being higher or equal to 200 mM NaCl, which can increase the use of saline land and even improve it [7, 11, 31, 32, 41]. The activation of a plant’s antioxidant system under adverse conditions helps the plant maintain its normal life activities and increases its tolerance to stress
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