基于核磁共振技术的合欢种子吸水特性

doi:10.11707/j.1001-7488.20220403

摘要/Abstract

摘要：

目的: 采用核磁共振技术，从时间、空间角度探究热水处理后合欢种子的初始吸水位点及水分的动态移动过程，揭示其内部水分相态的变化，为合欢种子吸水特性研究提供一种全新的技术手段。方法: 对始温80 ℃热水处理后的合欢种子，用称重法确定种子吸水曲线，用核磁共振成像技术(MRI)观察初始吸水位点及水分在种子体内的移动规律，同时结合横向弛豫时间T₂，探究吸水过程中水分相态及其含量、比例的动态变化。结果: 1) 合欢种子吸水曲线呈“S”型变化，吸水前期(0~4 h)种子吸水率缓慢增加；4~12 h进入快速吸水阶段，吸水率增幅较大；吸水12 h后进入缓慢吸水期。核磁共振成像结果表明，水分最初从种孔进入种子，然后通过3条路线移动：沿着种皮两侧的维管束向合点端移动；通过种皮与子叶的缝隙向下(合点端)移动，同时进入子叶的外侧；水分通过胚根进入胚轴，由胚轴进入子叶并向合点端移动，但其移动速度明显慢于第二条。吸水初期(0~6 h)，右侧种皮的吸胀面积明显大于左侧，之后随浸种时间延长，左侧吸水速度较快，吸胀面积与右侧无明显差异。2) 核磁共振波谱图表明，合欢种子水分质量(X)与核磁共振弛豫图谱峰面积(S)呈显著线性关系：S=21 132X+695.05，R²=0.999 6。3) 核磁共振驰豫图谱结果表明，合欢种子内主要存在3种状态的水，分别是结合水、胞内水和胞外自由水。4) 在0 h时，结合水占45.13%，胞外自由水占53.51%，几乎没有胞内水。在吸水过程中，结合水含量明显减少，比例持续降低，在48 h时仅占2.08%；胞内水比例呈先迅速增加后逐渐减小的变化趋势，胞外自由水的比例一直呈上升趋势，在48 h时二者分别为29.12%、68.80%。整个吸水过程中3种状态水分含量的比例始终处于动态变化中，并且胞外自由水的含量远高于其他状态的水。吸水过程中结合水与胞外自由水的峰顶点呈现左移现象(即流动性在减弱)。结论: 种孔是合欢种子的最初吸水位点，水分进入后通过两侧种皮、种皮与子叶缝隙以及胚轴向合点端移动。吸水过程中，合欢种子中始终存在结合水、胞内水、胞外自由水这3种相态的水，且在整个吸胀过程中相互转化，为种子萌发提供前期准备。

关键词: 合欢, 吸水, 核磁共振技术, 水分相态

Abstract:

Objective: Imbibition is the initial and most important stage of seed germination. Nuclear magnetic resonance (NMR) technology was used to explore the initial water absorption site and the spatial and temporal movement of water throughout the seed after hot water treatment from the perspective of time and space, revealing the changes of water phase in seeds. Thisprovides a new method for the study of water absorption in seeds. Method: The seeds of A. julibrissin were treated with hot water at an initial temperature of 80 ℃. The water absorption was calculated by the increase in weight after soaking divided by the initial weight. MRI technology was used to observe the initial water absorption location and the movement of water in the seeds after water absorption, combined with T₂ relaxation detection technology to explore the dynamic changes in phase and state of the water. Result: 1) The water absorption curve of A. julibrissin seeds exhibited an "S" type behavior, where the water absorption of seeds increased slowly in the early stage (0-4 h); the seeds entered the rapid water absorption stage during 4-12 h, where the water absorption increased greatly; finally the seeds entered the slow water absorption stage at 12 h. During the process of water absorption, the MRI result of the seeds showed that the water initially entered the seeds from the micropyle, then migrated inside the seed through three paths, namely: ①The water moved along the vascular bundle at the seed coat toward the chalazal; ② The water moved down towards the chalazal through the gap between the seed coat and cotyledons, entering the lateral side of cotyledons; ③ The water entered the hypocotyl through the radicle, then entered the cotyledons and moved to the chalazal, but its moving speed was noticeably slower than that of the second path. At the initial stage of water absorption (0-6 h), the imbibition area of the right seed coat was significantly larger than that of the left. Later, with the extension of soaking time, the imbibition speed of the left seed coat was faster, and there was no significant difference between the imbibition area of the left seed coat and that of the right seed coat. 2) The NMR spectrum showed that the water content (X) of A. julibrissin and the peak area (S) had a linear relationship, and the linear regression equation was: S=21 132X+695.05, R²=0.999 6. 3) There were three main states of water in A. julibrissin seeds, namely bound water, cytoplasmic bulk water, and extra-cellular free water. 4) At 0 h, bound water accounted for 45.13% of the water in the cell, extracellular free water accounted for 53.51%, and cytoplasmic bulk water was almost absent. During the process of water absorption, the content of bound water decreased significantly, which continued to decrease, accounting for only 2.08% by 48 h; the content of cytoplasmic bulk water increased rapidly at first and then decreased gradually. The content of extra-cellular free water increased continuously. At 48 h, the percentages of cytoplasmic bulk water and extra-cellular free water were 29.12% and 68.80%, respectively. During the whole process of water absorption, the percentages of water phases in three states was always in dynamic change, and the content of extracellular free water was much higher than that in other states. During this water absorption process, the peak of extra-cellular free water and bound water shifted to the left. Conclusion: The micropyle is the initial sites of water absorption in the seeds of A. julibrissin seeds. The water moves through the seed via the seed coat on both sides, the gap between the seed coat and the cotyledon, and the hypocotyl, and moves towards the chalazal. During the process of water absorption, there are three different water phases, namely bound water, cytoplasmic bulk water, and extra-cellular free water in the seeds of A. julibrissin, and they transform into each other during the entire imbibition process, which prepares the seed for germination.

Key words: Albizia julibrissin, water absorption, NMR technology, water phase state

中图分类号:

S718.43

杜恬恬,代松,钱滕,朱铭玮,陈丽,张中会,李淑娴. 基于核磁共振技术的合欢种子吸水特性[J]. 林业科学, 2022, 58(4): 22-31.

Tiantian Du,Song Dai,Teng Qian,Mingwei Zhu,Li Chen,Zhonghui Zhang,Shuxian Li. Water Absorption Characteristics of Albizzia julibrissin Seeds by Nuclear Magnetic Resonance Technique[J]. Scientia Silvae Sinicae, 2022, 58(4): 22-31.

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驰豫时间 Relaxation time	吸胀时间 Imbibition time/h	峰起始时间 Onset time of peak/ms	峰顶点时间 Peak time/ms	峰结束时间 End time of peak/ms
T_2a	0	0.01±0.00a	0.39±0.05ab	1.23±0.03b
	2	0.01±0.00a	0.37±0.02abc	1.49±0.10a
	4	0.01±0.00a	0.35±0.02abc	1.40±0.03ab
	6	0.01±0.00a	0.45±0.04a	0.80±0.06cd
	8	0.01±0.00a	0.35±0.01abc	0.89±0.05c
	10	0.01±0.00a	0.38±0.06abc	0.91±0.04c
	12	0.01±0.00a	0.35±0.02abc	0.89±0.04c
	24	0.01±0.00a	0.31±0.01bc	0.87±0.13cd
	36	0.01±0.00a	0.28±0.03c	0.67±0.07d
	48	0.01±0.00a	0.29±0.02bc	0.71±0.06cd
T_2b	0	—	—	—
	2	1.60±0.11a	4.44±0.44a	12.35±1.45a
	4	1.45±0.03a	5.54±0.00a	13.70±0.55a
	6	0.85±0.06a	5.06±0.24a	11.36±0.27a
	8	0.96±0.06a	4.73±0.28a	11.12±0.45a
	10	0.98±0.04a	5.20±0.37a	11.65±0.55a
	12	1.08±0.11a	5.20±0.37a	12.22±0.76a
	24	1.57±0.15a	5.66±0.77a	13.17±1.27a
	36	1.39±0.09a	4.52±0.30a	12.77±0.51a
	48	1.30±0.09a	4.41±0.27a	12.18±0.29a
T_2c	0	19.06±3.16a	115.15±5.45a	567.54±12.98b
	2	13.24±1.56b	74.30±4.62b	556.37±34.57b
	4	14.67±0.59b	53.65±2.53c	668.06±26.76a
	6	12.18±0.29b	43.56±2.06c	258.40±6.05c
	8	11.91±0.48b	45.70±2.84c	230.90±13.88cd
	10	12.49±0.59b	48.99±3.04c	219.99±8.81cd
	12	13.10±0.81b	51.37±3.68c	205.92±14.76cd
	24	14.11±1.36b	55.06±3.95c	200.66±9.49d
	36	13.69±0.55b	52.51±3.26c	192.11±13.77d
	48	13.06±0.31b	51.17±2.05c	183.21±11.38d

浸种时间 Soaking time/h	T_2a		T_2b		T_2c
浸种时间 Soaking time/h	峰面积 Peak area S_2a	峰面积比例 Peak area ratio(%)	峰面积 Peak area S_2b	峰面积比例 Peak area ratio(%)	峰面积 Peak area S_2c	峰面积比例 Peak area ratio(%)
0	2 751.16±176.35a	45.13±2.17a	—	—	3 261.93±29.07e	53.51±1.28d
2	2 784.57±57.84a	31.66±0.54b	1 502.58±29.53ef	17.09±0.64d	4 507.49±250.39e	51.25±1.19d
4	3 022.60±37.90a	22.21±0.58c	3 624.92±372.20e	26.63±2.11c	6 964.23±153.73e	51.16±1.81d
6	1 537.42±94.49bc	4.80±0.37d	10 879.07±311.20d	33.98±0.48a	19 597.23±885.78d	61.22±0.89c
8	1 920.43±122.08b	4.80±0.39d	12 504.31±356.11cd	31.29±0.61ab	25 544.01±726.37c	63.91±0.77bc
10	1 475.80±162.72bc	3.10±0.23d	14 031.82±831.13bc	29.47±0.41bc	32 103.99±1 499.64b	67.43±0.29a
12	1 568.39±179.29bc	3.08±0.43d	14 447.96±873.73bc	28.33±0.80bc	34 967.26±2 246.10ab	68.59±0.43a
24	1 715.05±214.01b	2.93±0.49d	16 628.91±1 854.13ab	28.43±1.60bc	40 146.74±2 411.20a	68.64±1.19a
36	1 539.90±76.04bc	2.67±0.19d	17 451.65±1 240.98a	30.21±0.65bc	38 775.87±2 662.22a	67.12±0.31a
48	1 210.71±194.09c	2.08±0.45d	16 912.86±1 606.38ab	29.12±1.11bc	39 948.16±2 370.07a	68.80±0.55a

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