Seed priming with melatonin improved salinity tolerance of halophytes during early life-cycle stages

Melatonin (MT) is a tryptophan derivative with multiple functions in both animals and plants. Exogenously-provided MT such as through seed priming has emerged as an effective way to improve stress tolerance of plants. However, little is known about MT priming in improving salinity tolerance of halophytes particularly during their early life-cycle stages. We therefore examined roles of MT priming in enhancing salinity tolerance of seeds and nascent seedlings of five warm subtropical halophytes. Priming with different MT concentrations alleviated primary dormancy of the seeds of annual halophytes Z. simplex and P. oleracea. Seed priming with MT also reduced the inhibitory effects of salinity on germination of halophytes by improving mean final and rate of germination under saline conditions. MT priming also improved germination recovery, when un-germinated seeds were transferred from saline solutions to water. Furthermore, MT priming also improved growth parameters such as total length, leaf area and photosynthetic pigments of the seedlings of test species under both non-saline and saline conditions. In general, low (5 and 100 µM) concentrations of MT were found most effective in improving seed dormancy, germination and early seedling growth of halophytes particularly under saline conditions.