Effects of melatonin on germination and amino acid content in different wheat varieties seeds under polyethylene glycol stress

In this research, the effects of melatonin on germination and amino acid content in wheat (Triticum aestivum L.) seeds under polyethylene glycol (PEG-6000) stress were investigated. The results revealed that 10 μM melatonin could aggravate the adverse effects of drought stress on germination percentage, germination index, and germination potential of two wheat varieties (JM22 and HG35). However, 300 μM melatonin could obviously alleviate the negative effect of water stress on germination and increase radicle length, radicle number and plumule length of germinated seeds. Principal component analysis showed that amino acid content apparently changed in germination and the variation amplitude was different due to melatonin concentrations and wheat varieties. Lys content in wheat seed under 300 μM melatonin plus PEG treatment increased compared with that under PEG. Meanwhile, Lys content was significantly and positively correlated with germination percentage, germination index, germination potential, radicle length, and plumule length, respectively. Our results suggested Lys play an important role in the regulation of melatonin on drought resistance of wheat seed during germination. This may be of value for saving water resources in North China Plain.


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Drought is a major abiotic stress that lead to great loss in agriculture worldwide. 30 In North China Plain, wheat production has been enduring severely constraint such as 31 yield increasing, quality improving, and groundwater exploitation decreasing. 32 Meanwhile, effective rainfall is scarce for meeting needs of plants during wheat 33 growth stage [1]. As food crop, it is urgent to ensure wheat supply safety for the 34 rapidly increasing world population. Melatonin, a derivative of the essential amino  Previous studies had pointed out that melatonin applied to cucumber seeds could 40 improve their germination rate during chilling stress and water-stress with respect to 41 untreated seeds [4,9]. The pretreatment of seeds with melatonin reduced copper 42 toxicity in red cabbage seedlings (Brassica oleracea rubrum) [10]. As is well-known, 43 amino acid metabolism was related and provided nutrient during seed germination  The main aims of this article were: (1) to investigate the germination 60 characteristics of two wheat varieties at different levels of melatonin over drought 61 conditions; (2) and to evaluate changes in amino acid content during germination of 62 wheat seed. This would help to obtain exact data for further use in wheat yield 63 protection during drought resistance.

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Tested materials and reagents 66 The experiment was carried out in a key laboratory of crop growth regulation, Firstly, distilled water was used as the basic medium to prepare a 20% PEG solution.

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Secondly, melatonin was firstly diluted by 1mL 95% ethyl alcohol and then was 79 added to 20% PEG solution to prepare 0, 1, 10, 100 and 300 μmol/L melatonin  The germination percentage was a proportion of emerged-germinating seed in total 96 cultivated seed on 7 days after placement in the incubator.

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The germination potential was the germination percentage on 3 days after 98 placement in the incubator.

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Root length, sprout length, and radical length of germinated seed were measured 100 5 repeats with ruler began from 72 hours after placement in the incubator.

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Vigor index was measured according to Lu et al. [17].    In this study, radicle length and radicle number of two wheat cultivars were both 168 increased gradually from 72 hours to 144 hours after germination (Fig 1) significant difference on radicle number between control and 300μM+PEG treatment.

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The changing trend of plumule length was similar to that of JM22. Additionally, as a 186 drought-resistant variety, radicle length and radicle number of HG35 were both higher 187 than that of JM22 under PEG treatment. The results showed the variations among all different treatments (Fig 2). Principal

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Germination represent dry seeds germinated by distilled water; PEG represent dry seeds 206 germinated by 20% PEG; Seed represent dry seeds.

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Glu content was the highest in wheat seed of both cultivars, followed by Pro  contents increased (Fig 3 and Table 1S). Cys and Lys content in HG35 seed under 231 300μM melatonin plus PEG treatment was higher than that of PEG treatment, 232 whereas other components was lower. shows different treatments (seed represent no-germinated seeds; CK represent seeds 236 germinated by distilled water; PEG represent seeds germinated by 20%PEG; 1μM, 10μM, 237 100μM, and 300μM, represent seeds germinated by 1μM, 10μM, 100μM, and 300μM 238 melatonin plus 20%PEG, respectively), and the vertical axis shows different amino acid. 239 Color gradients represent the differences value of amino acid contents under other treatments 240 compared with that of CK. Correlation between amino acid content and morphological indexes correlated with germination index, radical length, and radical number (Table 3) (Table S1 and Fig 3). This indicated that Glu and Pro possibly provided