Scanning Electron Microscopic Analysis of Grain Cross-section from Rice with Different Transparency

doi:10.16819/j.1001-7216.2018.7107

Abstract

Abstract:

【Objective】 The objective of this study was to set up an ideal method of observation of a single starch granule cross-section, to clarify the relationship between rice transparency and amylose content and to find the structure foundation that caused the poor rice transparency. 【Method】 The pre-treated rice grain cross-section and isolated starch were observed under a scanning electron microscopy.【Result】The transparency of both indica and japonica soft rice with amylose contentbelow 15%was significantly decreased. By comparingdifferent methods of grain cross-section pre-treatments, we found that the direct mechanical fracture method can’t break a single starch granule and the mechanical fracture with glass scraping method could break down an individual starch granule, however, it will cause rough surface and thus difficult to be analyzed quantitatively. As for the liquid nitrogen fracture method, we found it’s an ideal way to break a single starch granule and the cavity in starch granule can be easily observed. We then further analyzed the starch granule arrangement and the internal structure of an individual starch granule in paddy rice from both indica and japonica rice cultivars. We found that all the starch granules arranged tightly and obvious air containing space was observed in an individual starch granule from grains of all dark endosperm rice. Also, we found that the number and area of starch granule cavity in glutinous rice was significantly higher than those in dark endosperm rice. Furthermore, we proved that the number and area of starch granule cavity increased as the grain moisture content decreased.【Conclusion】The direct liquid nitrogen fracture treatment of rice grain cross-section is an ideal method for the single starch granule cross-section observation. Besides, the rice grain transparency showed a close relationship with the moisture content and also the number and size of cavity in the middle of a starch granule but not the starch granule arrangement. Moreover, the size and number of cavities increased as the amylose content decreased.

Key words: Oryza sativa L., starch, scanning electron microscopy, transparency, cavity

摘要：

摘要：【目的】探索单淀粉粒断面观察方法,并阐明稻米透明度与直链淀粉含量的关系以及造成稻米透明度下降的淀粉结构基础。【方法】采用扫描电镜对经过不同处理的具有不同透明度的籼稻和粳稻胚乳横断面进行淀粉粒结构观察研究。【结果】籼稻和粳稻稻米的透明度在直链淀粉含量低于15%的软米中明显下降。通过比较不同籽粒横断面断开方式,发现直接机械断裂法无法断开单个淀粉粒,机械断裂加玻璃刀刮刻法可以断开单个淀粉粒但断面结构变形且无法定量分析。液氮脆断法可以观察到单个断裂的淀粉粒以及其中的空腔。比较籼稻和粳稻胚乳横断面淀粉粒的排列方式和单个淀粉粒内部结构,表明所有品种稻米胚乳淀粉粒均规则且紧凑排列,但所有暗胚乳稻米籽粒横断面中淀粉粒内部存在明显的空腔且糯稻淀粉粒空腔的数目和大小均明显高于暗胚乳稻米。进一步通过梯度烘干实验,证明稻米淀粉粒中的空腔数目和大小随着水分的降低而增多和变大。【结论】液氮直接脆断法是观察水稻单个淀粉粒断面的有效方法。稻米透明度与胚乳淀粉粒的排列紧密程度无关而与稻米的含水量以及单个淀粉粒中间的气腔数目和大小直接相关。此外,直链淀粉含量越低,淀粉粒中间的空腔数目越多,孔径越大。

关键词: 水稻, 淀粉粒, 扫描电镜, 透明度, 气腔

CLC Number:

Yan LU, Xiaomin ZHANG, Yan QI, Changquan ZHANG, Yuping LING, Qiaoquan LIU. Scanning Electron Microscopic Analysis of Grain Cross-section from Rice with Different Transparency[J]. Chinese Journal OF Rice Science, 2018, 1(1): 189-199.

陆彦, 张晓敏, 祁琰, 张昌泉, 凌裕平, 刘巧泉. 不同透明度水稻籽粒横断面扫描电镜分析[J]. 中国水稻科学, 2018, 1(1): 189-199.

Figures/Tables 8

Fig. 1. Rice grain appearance of different rice cultivars.

Table 1 Basic physicochemical characters of grains from different rice cultivars.

品种及类型 Cultivar and Type	表观直链淀粉含量 Apparent amylose content /%	水分含量 Moisture content /%	蛋白质含量 Crude protein content/%
籼稻indica
清芦占11Qingluzhan 11	24.64±0.40a	12.38±0.23a	8.68±0.31c
9311	15.83±0.28a	12.40±0.34a	8.23±0.10c
滇屯502Diantun 502	13.54±0.07c	12.36±0.15a	8.53±0.19c
鸭血糯Yaxuenuo	3.21±0.45d	12.42±0.52a	11.20±0.21a
苏御糯Suyunuo	2.97±0.35d	12.25±0.27a	10.01±0.19b
粳稻japonica
武育粳3号Wuyujing 3	15.65±0.43a	12.43±0.41a	6.96±0.20c
日本晴Nipponbare	15.61±0.57a	12.97±0.12a	8.82±0.15b
关东194 Kanto 194	10.17±0.16b	12.25±0.26a	8.84±0.13b
广陵香糯Guanglingxiangnuo	3.21±0.26c	12.26±0.16a	9.67±0.05a
太湖糯Taihunuo	2.89±0.52c	12.13±0.13a	8.84±0.19b

Fig. 2. Scanning electron microscopic images ofindicarice cross-section obtained by different methods. A, Qingluzhan 11; B, 9311; C, Diantun 502; D, Yaxuenuo; E, Suyunuo.1, Normal snapping treatment; 2, Liquid nitrogen freezing treatment; 3, Normal breaking after double-sided blade processing. The arrow refers to the starch cavity. Bar=20 μm.

Fig. 3. Scanning electron microscopic images ofjaponicagrain cross-section obtained by differentmethods.A, Wuyujing 3; B, Nipponbare; C, Kanto 194; D, Guanglingxiangjing; E, Taihunuo.1, Normal snapping treatment; 2, Liquid nitrogen freezing treatment; 3, Normal breaking after double-sided blade processing. The arrow refers to the starch cavity. Bar=20 μm.

Fig. 4. Scanning electron microscopic images of rice grain cross-section obtained by the liquid nitrogen freezing treatment. A, Qingluzhan 11; B, 9311; C, Diantun 502; D, Yaxuenuo; E, Suyunuo; F, Wuyujing 3; G, Nipponbare; H, Kanto 194; I, Guanglingxiangjing; J, Taihunuo.The arrow refers to the starch cavity.2 and 3 were magnified pictures in the box in 1 and 2, respectively.

Table 2 Comparison of cavity number and diameter of individual starch granulein different rice cultivars.

类型Type	品种Cultivar	孔个数Number of holes	孔直径Diameter/nm
籼稻indica	清芦占11Qingluzhan 11	—	—
	9311	—	—
	滇屯502Diantun 502	1.17±0.21b	275.88±28.83c
	鸭血糯Yaxuenuo	1.71±0.47a	513.30±46.13b
	苏御糯Suyunuo	1.94±0.73a	627.27±34.50a
粳稻japonica	武育粳3号Wuyujing 3	—	—
	日本晴Nipponbare	—	—
	关东194 Kanto 194	1.13±0.25b	318.44±22.01c
	广陵香糯Guanglingxiangnuo	1.57±0.36a	566.28±34.80b
	太湖糯Taihunuo	1.87±0.40a	660.56±41.04a

Fig. 5. Rice grain appearance and scanning electron microscopic images of grain cross-section. A, Grain appearance with various moisture content(MC).B, Starch cavity number and diameter of rice obtained by different drying treatments.C, Diantun502; D, Suyunuo; E, Kanto 194; F, Guanglingxiangnuo(GLXN).

Fig. 6. Scanning electron microscopic images of isolated starch from different cultivars. A, Qiangluzhan 11; B, 9311; C, Diantun 502; D, Yaxuenuo; E, Suyunuo.F, Wuyujing 3; G, Nipponbare; H, Kanto 194; I, Guanglingxiangjing; J, Taihunuo. K, Size distribution of indica rice starch granule; L, Size distribution of japonica rice starch granule; The small arrow refers to the ostiole on the surface of starch; The big arrow refers to the starch cavity.

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