Alfalfa (Medicago sativa L.) is an important forage crop, and salt stress is a major limiting factor in its yield. Melatonin (MT) is a multi-regulatory molecule in plants. We showed that basal MT content was positively correlated with the salt tolerance degree of different alfalfa varieties. MT and its precursor 5-HT fully recovered seed germination while partially ameliorated seedling growth of salt-stressed alfalfa. The 5-HT showed some divergent effects from MT with regards to growth amelioration under salinity. Salt stress caused stunted plant growth in soil culture, while MT ameliorated it by elevating plant height, fresh weight, branching number, and chlorophyll content. Silencing of a putative MT receptor, MsPMTR1, which was shown to be membrane-localized, abolished the ameliorative effects of MT on salt-stressed alfalfa seedling growth, while overexpression of MsPMTR1 improved plant growth under salt stress. The RNA sequencing analysis showed that nine pathway genes were specifically induced by MT treatment compared with salt stress. These MT-responsive differentially expressed genes include basal metabolic pathway genes, such as “ribosome, elongation factor,” “sugar and lipid metabolism,” and “photosynthesis” and stress-related genes encoding “membrane integrity” related proteins, heat shock protein, peroxidase/oxidoreductase, and protease. Several abiotic stress response-related genes, such as DRE, ARF, HD-ZF, MYB, and REM were repressed by NaCl treatment while induced by MT treatment. In summary, we demonstrated the importance of MsPMTR1 in MT-mediated salt tolerance in alfalfa, and we also analyzed the regulatory mechanism of MT during alfalfa seed germination under salt stress.

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The tensile properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers obtained from mixed solvents are addressed by virtue of improved solubility. In this work, olive oil (OO) was introduced as a poor solvent for the pre‐swelling of UHMWPE in decalin, and its mass percentage was intended to be 10, 20, 30, and 40 wt% of UHMWPE. Then UHMWPE fibers with high molecular weight retention and low entanglement were prepared with paraffin oil as spinning solvent by gel‐spinning and hot‐drawing. Unlike other samples, there is a more significant molecular chain disentanglement and higher molecular weight retention for UHMWPE fibers as OO addition is 20 wt%. Surprisingly, obtained UHMWPE fibers exhibit tensile strength up to 33.85 cN/dtex and tensile modulus of 1673.27 cN/dtex, with an increase of 24.0% and 32.3%, respectively, compared with that of UHMWPE fibers without decalin/OO pre‐swelling. Furthermore, the obtained UHMWPE fibers are accompanied by a marked improvement in melting temperature, crystallization and orientation.

The molecular weight loss of ultra‐high molecular weight polyethylene (UHMWPE) fibers is extremely serious in comparison with raw materials due to the high temperature and strong shearing during dissolving process. In this study, decalin was introduced as preswelling solvent and the dissolving system was regulated to improve the solubility of UHMWPE in paraffin oil without severe degradation so as to prepare UHMWPE fibers with high molecular weight retention and low entanglement. UHMWPE was preswelling in decalin with different content, the mass ratio of decalin to UHMWPE were 1:1, 1.5:1, 2:1, 2.5:1, and 3:1. All UHMWPE fibers were prepared by gel‐spinning and hot‐drawing. UHMWPE fibers possess the highest molecular weight after preswelling of UHMWPE in decalin (with a mass ratio of 3:1 to UHMWPE, namely UPE/dec‐s‐3 sample). What's more, the entanglement of UHMWPE fibers gained from UPE/dec‐s‐3 sample has been observably diluted in comparation to that from UPE‐neat and other swollen samples. More importantly, the tensile strength and modulus of UHMWPE fibers obtained from UPE/dec‐s‐3 sample can reach 31.41 and 1446.26 cN/dtex, increased by 15.1% and 14.3% compared with UPE‐neat fibers, respectively. Besides, the thermal and crystallization behavior of UHMWPE fibers prepared from swollen UHMWPE have also been boosted.

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