不同透明度水稻籽粒横断面扫描电镜分析

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

【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。

【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 content below 15%was significantly decreased.By comparing different 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.