银杏种子萌发过程低场核磁T2反演谱解译初探

Preliminary study on interpretation of LF-NMR T2 inversion spectrum of ginkgo biloba seed during germination process

随着科学技术的发展,低场核磁共振(Low Field Nuclear Magnetic Resonance, LF-NMR)横向弛豫时间(Transverse Relaxation Time, T_2)反演谱检测技术越来越多的被应用于农业,但当前对T_2反演谱的解译尚停留在水分相态分布层面。为探索从物质成分角度对种子T_2反演谱进行解译的新方法,该研究以银杏种子为对象,利用低场核磁共振技术检测并对比银杏鲜种、种子粉末及其主要成分试样的T_2反演谱,分析各信号峰的形成机理,并以此为依据对其在种子萌发过程中的变化进行解译。研究结果表明:淀粉与蛋白质混合试样T_2反演谱的峰T_(21)、T_(22)、T_(23)以及淀粉与油脂混合试样的峰T_(24)在峰顶时间上和种子粉末试样相对应信号峰完全一致;在物质成分及配比完全相同的情况下,种子粉末试样T_2反演谱的峰T_(21)~T24的峰顶时间较鲜种分别相差12.98%、32.21%、13.02%、0%,T_(21)、T_(22)峰比例较鲜种分别偏少41.72%、29.33%,T_(23)峰比例偏多92.26%,T_(24)峰比例偏少91.71%,说明种子组织结构会对其内部水分的弛豫时间和相态分布比例造成一定影响。仅从物质成分角度考虑,种子内水分的弛豫时间主要在淀粉、蛋白质的影响下表现为T_(21)、T_(22)、T_(23),在淀粉和油脂的影响下表现为T_(24)。由此认为峰T_(21)、T_(22)主要为吸附在淀粉和蛋白质上相态不同的结合水的信号,峰T_(23)为主要被淀粉和蛋白质束缚后产生的半结合水的信号,峰T_(24)主要为种子中自由水的信号(少量源自油脂)。此外,种子即将裂壳时将形成T_(2a)(峰顶时间在10 ms左右)、T_(2b)(峰顶时间>1 000 ms)2个新信号峰,可作为预示种子萌发状态即将发生重要变化的"预兆峰"。提出的从化学组分及核磁检测原理角度对银杏种子萌发过程T_2反演谱进行解译的新途径,可为基于LF-NMR方法对种子萌发过程中化学组分变化进行活体分析提供参考。

With the development of science and technology,low field nuclear magnetic resonance(LF-NMR)is increasingly used in agriculture.At present,the interpretation of the transverse relaxation time(T2)inversion spectrum stays at the level of the water phase state distribution in the measured sample.It is beneficial to connect the T2 inversion spectrum to the chemical composition of test subject.In order to find such a connection as the substance-oriented interpretation of the T2 inversion spectrum,LF-NMR was applied for 20 ginkgo biloba(Ginkgo Biloba L.)seeds during germination that divided into 10 groups.Temporal observation of ginkgo biloba seeds over the germination process were carried out in vivo using LF-NMR.Their T2 inversion spectra were collected and compared with those from the reference samples that made from seed powder or different mixtures of the main ingredients of ginkgo biloba seeds to explore the forming mechanism of the signal peaks of T2 inversion spectra for a viable interpretation from the perspective of substances.Analysis of the T2 inversion spectra of ginkgo biloba seeds indicated that water in live ginkgo biloba seed could be divided into 4 phase states according to T2,including 2 distinctive bound water of different kinetic activity with transverse relaxation times spiking at T21 and T22,semi-bound water spiking at T23,and free water at T24.The peak T21,T22,T23 of the T2 inversion spectrum of the starch and protein mixed sample and the peak T24 of the starch and oil mixed sample were exactly the same as the corresponding signal peaks of the seed powder sample in terms of peak time.When the material composition and the ratio were completely the same,the peak times of the peak T21-T24 of the T2 inversion spectrum of the seed powder sample were 12.98%,32.21%,13.02%and 0%different from those of the fresh seed,respectively.The proportions of peak T21 and T22 are 41.72%and 29.33%less than those of fresh species,respectively,the proportion of peak T23 is 92.26%higher,and the proportion of peak T24 is 91.71%lower.This showed that the seed tissue structure would affect the relaxation time and phase distribution ratio of its internal water to a certain extent.Only from the perspective of material composition,the water in seed was mainly expressed as relaxation time T21,T22,T23 under the influence of starch and protein,and T24 under the influence of starch and lipid.Therefore,it was believed that peak T21 and T22 was the signal of bound water(their phases are different)that mainly adsorbed on starch and protein,peak T23 is the signal of semi-bound water that mainly fettered by starch and protein,and peak T24 is mainly the signal of free water in seed(a small amount derived from lipid).Results of the temporal observation over the germination process found an interesting pattern of change regarding the water phase states in live seeds.While the unit mass signal amplitude of semi-bound water on a monotonous rise and the rest phase states fluctuate over time,the relaxation time of all signal peaks showed an increasing trend on the whole,and there was no significant fluctuation except T21.What’s more,2 new signal peaks that spiking at T2a(around 10 ms)and T2b(over 1000 ms)developed when a seed approaches the stage of seed-split and the spikes continued to grow ever since.We called them the“prophet spikes”for they foretell an important change in the seed and was about to split.The approach supply a new angle to interpret T2 inversion spectra with chemical and NMR detection principle insights and a new reference for in vivo analysis of chemical composition changes during seed germination based on LF-NMR method.