| Waxy wheat shows special starch quality due to the high amylopectin content. Waxy wheat foods have unique flavor and great potential values in research and development. Therefore, the study of waxy wheat starch has become the focus of hot spots increasingly. Waxy wheat (Triticum aestivum L.) cultivar, Yangnuo 1, and non-waxy wheat cultivar, Yangmai 13, were used as materials in this paper. Morphologic changes and differences of endosperm amyloplast in the process of caryopsis development and germination were investigated by using resin semi-thin section technology, histochemical staining technology, frozen section technique and scanning electron microscope observation. Differences of starch structural features and physicochemical properties of two wheat cultivars were studied by using Rapid Visco Analyser (RVA), X-ray power diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). Main results as follows.(1) Changes of morphology, grain weight, the soluble sugar content and total starch content in the process of caryopsis development of two wheat cultivars were basically the same. Endosperm amyloplast of both wheat cultivars appeared firstly at 6 days after flowering (DAF), extended and multiplied along with the development of caryopsis. The accumulation speed of endosperm amyloplast became faster at 12～24 DAF, and the endosperm cells were highly enriched at 28 DAF. Overall, endosperm amyloplast of Yangnuo 1 had better development status and higher proportion of small amyloplast.(2) The endosperm and pericarp of two wheat cultivars showed difference in response to I2-KI. The developing endosperm of Yangmai 13 was stained blue black by I2-KI, while those of Yangnuo 1 were stained reddish-brown. The pericarp could be stained blue black in early stage of two wheat cultivars, while it could not be stained in late stage as the degradation of amyloplast.(3) The degradation of endosperm in different parts showed different time sequences. Consumption of endosperm started from the region adjacent to the embryo, and expanded to the dorsal side away from the embryo along the ventral groove in two germinating wheat cultivars. At the same time, many small dissolution pores appeared on the surface of endosperm amyloplast and the pores became bigger and deeper until amyloplast disintegrated and be consumed. In Yangnuo 1, the rate of degradation of endosperm amyloplast was faster than in Yangmai 13.(4) A-type large amyloplast (granule size≥10 μm) and B-type small amyloplast (granule size<10 μm) exist in both two wheat cultivars. The large amyloplast was ellipsoidal-shaped with smooth surface, and most small amyloplasts were more spherical-or irregular polyhedral-shaped with rough surface. The polarization cross was in the central of amyloplast, and brightness of Yangnuo 1 was higher than Yangmai 13. The proportion of small amyloplast of Yangnuo 1 was higher than Yangmai 13 by granule size distribution determination.(5) According to the analysis of starch gelatinization characteristics, the peak viscosity, peak time, breakdown viscosity, final viscosity, setback and peak time of Yangnuo 1 were obviously lower than Yangmai 13, while the pasting temperature was higher than Yangmai 13.(6) FTIR spectra analysis showed that the two wheat cultivars had different maximum absorbance values at 1047,1022, and 995 cm-1, and the (1045/1022) cm-1 ratio existed significant difference. In Yangnuo 1, the starch had higher surface structure order degree than Yangmai 13. Similar XRD patterns of two wheat cultivars were found, but with different intensities. Significant difference was found at 20 of 20°. The relative degree of crystallinity of Yangnuo 1 was 30.95%, which was higher than that of Yangmai 13 (24.22%).Based on the results above, it was concluded that the processes of development and degradation of endosperm amyloplast in waxy and non-waxy wheat was similar. Nevertheless, the amyloplast morphologic structure, dyeing properties, granule size distribution characteristic and some physicochemical properties were obviously different. These results not only further deepen the research of waxy wheat amyloplast, but also provide a theoretical basis for quality improvement, food processing, resource development and application of waxy wheat. |
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