褪黑素壳聚糖微粒防止褪黑素降解并有效提高其抗旱功能

Melatonin chitosan microparticles decrease degradation and increase drought resistance properties of melatonin

【目的】褪黑素可提高作物抗旱性,但容易降解。本研究试图开发具有缓释和抵御光降解能力的褪黑素壳聚糖微粒,并对其抗旱性进行评价。【方法】利用壳聚糖与三聚磷酸钠和果胶所产生的静电引力,使三者之间产生交联形成包裹褪黑素的杂化微粒,从而实现褪黑素的缓释和保活。确定投入褪黑素质量为5 mg时制备的褪黑素壳聚糖微粒作为试验材料(MP-MT)。利用扫描电子显微镜(SEM)和傅立叶变换红外光谱(FTIR),对褪黑素壳聚糖微粒(MP-MT)表面形貌及官能团特性进行表征。采用超高效液相色谱技术,探究MP-MT对褪黑素的缓释性能和抵抗光降解的性能。以两叶一心的小麦幼苗为试材,进行灌根试验。将基质最大持水量的80%设为正常对照(CK1),基质最大持水量的40%设为干旱对照(CK2);在干旱胁迫下,设施用1.0 g/L褪黑素(MT1.0)、壳聚糖微粒(MP)和含褪黑素0.5、1.0、1.5 g/L的褪黑素壳聚糖微粒(MP-MT0.5、MP-MT1.0、MPMT1.5),共7个处理。在处理后第8天,取样分析小麦幼苗株高、干重、鲜重、叶片SPAD值、根系生长、抗氧化酶活性及丙二醛含量。【结果】当褪黑素投入量为5 mg时MP-MT对褪黑素的包封率最稳定,为52.14%,之后的相关试验均以该比例制备的褪黑素壳聚糖微粒(MP-MT)作为试验材料。通过SEM照片发现,MP-MT微粒粒径相较于壳聚糖微粒增加且表面变粗糙。MP-MT微粒FTIR结果同时检测出现了壳聚糖、褪黑素等组分的特征峰,表明褪黑素在微粒中存在。模拟释放试验结果表明,MP-MT在pH 5.0和pH 7.0磷酸缓冲溶液下36 h的释放率分别为65.43%、50.13%。模拟光降解试验表明,可见光照射4 h时MP-MT中褪黑素的光降解率较普通MT降低了143.37%。小麦幼苗干旱胁迫试验结果表明,与MT1.0处理相比,3个MP-MT处理的小麦幼苗干重增加4.50%~22.73%,根系长度增加15.92%~32.56%,过氧化酶活性提高19.56%~20.34%,丙二醛含量降低9.77%~12.30%(P<0.05)。【结论】壳聚糖/三聚磷酸钠/果胶的褪黑素封装体系可以实现褪黑素的缓释和保活,显著提高干旱胁迫下小麦幼苗SPAD值,促进根系发育,提高抗氧化酶活性,从而提高小麦幼苗抗旱性。

【Objectives】Melatonin is capable of increasing drought tolerance of crops but it is easily degraded when exposed to environment.We tried to protect melatonin from degradation by coating it with chitosan,and tested the drought resistance property of the prepared melatonin chitosan particles(MP-MT).【Methods】The MP-MTs were prepared by cross-linking chitosan,sodium tripolyphosphate,and pectin through electrostatic gravitational force to form hybridized particles first,then melatonin was encapsulated into the particles in a certain mass ratio.The optimum addition rate of melatonin was 5 mg of MP-MTs.The surface morphology and functional groups of MP-MT were characterized by scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR).The release rate of melatonin was tested by dissolving MT-MPs in pH 5.0 and pH 7.0 phosphate buffer solutions.The photodegradation of melatonin was tested by exposing MP-MT to sunlight.A drought resistance pot experiment was conducted using wheat seedlings with two leaves and one shoot as test materials.The drought stress was kept at 40%of maximum substrate water holding capacity,and 1.0 g/L melatonin solution(MT1.0),chitosan(MP),and 0.5,1.0,and 1.5 g/L of MT-MP were used as treatments.The growth of plants and roots,leaf SPAD value,antioxidant enzyme activity,and malondialdehyde content of wheat seedlings were investigated on the 8th day after treatment.【Results】The SEMs showed that the MP-MT particles had a rougher surface than melatonin.FTIR results revealed the presence of characteristic peaks of chitosan and melatonin in MP-MT.The release rate of MP-MT was 65.43%and 50.13%at pH 5.0 and pH 7.0 in phosphate buffer solution for 36 h,respectively.The photodegradation rate of melatonin in MP-MTs was 143.37%lower than normal melatonin after 4 h of light exposure.Chitosan did not show any effect on wheat seedlings growth.Further,compared with MT1.0 treatment,the dry weight of wheat seedlings treated with three MP-MT treatments increased by 4.50%-22.73%,the root length increased by 15.92%-32.56%,the activity of peroxidase increased by 19.56%-20.34%,and the content of malondialdehyde decreased by 9.77%-12.30%(P<0.05).【Conclusions】The encapsulation of melatonin with chitosan/sodium tripolyphosphate/pectin particles decreases the degradation of melatonin through slow release and retention of melatonin,and thus significantly increases the drought resistance effect of melatonin.Encapsulation also elicited the same drought resistance property with melatonin at lower application rate,making it suitable for practical application in agriculture.