糯小麦的遗传、选育和应用前景

Genetics,Selection and Prospects of Waxy Wheat

小麦籽粒胚乳通常含有直链和支链两种淀粉。糯性小麦或部分糯性小麦的胚乳淀粉 ,全部或大部分是支链淀粉。颗粒凝结型淀粉合成酶 (GBSS) ,亦称作蜡质蛋白 ,是合成禾谷类作物胚乳直链淀粉的关键酶 ,由蜡质基因编码。六倍体面包小麦有 3个蜡质基因位点 :位于 7AS的 WX- A1、4AL 的 WX- B1和 7DS的 WX- D1。这些蜡质基因位点的突变或缺失 ,可使小麦不产生颗粒凝结型淀粉合成酶 ,导致胚乳中无直链淀粉或仅含有少量直链淀粉。对3个由蜡质基因编码的颗粒凝结型淀粉合成酶 ,蛋白所作的分析表明 ,在某些小麦品种中出现了蜡质基因位点的缺失。已发现许多小麦品种携有 WX- A1或 WX- B1蜡质基因的缺失位点 ,有些品种中甚至同时携有这两个蜡质基因的缺失位点。但是 ,仅有 1个中国地方品种“白火麦”携有 WX- D1缺失位点。这 3个蜡质基因的缺失位点存在着剂量效应 ,把它们同时组合到 1个小麦品系中 ,就能产生直链淀粉含量非常低甚至不含直链淀粉的胚乳。由直链淀粉含量变化引起的糯性或部分糯性小麦淀粉 ,与通常的小麦淀粉相比 ,其特性有很大差异。文章对糯性小麦的应用潜力 ,包括其工业利用、亚洲面条制作、专用食品的生产以及延长烘烤食品的货架寿命等作了综述。

Wheat grain endosperm contents normally two kinds of starch,amylose and amylopectin.Waxy wheat or partial waxy wheat represents the wheat,whose grain endosperm consists of completely or predominantly amylopectin respectively.Granulebound starch synthase(GBSS),also called waxy protein,is the key enzyme for amylose synthesis in the endosperm of cereals and is encoded by the waxy genes.In hexaploid bread wheat,there are three waxy loci:WX-A1 on chromosome arm 7AS,WX-B1 on chromosome arm 4AL,and WX-D1 on chromosome arm 7DS respectively.Mutations of these waxy loci,also called the null alleles of these loci may eliminate the production of GBSS,which is normally the major protein within the endosperm starch granules,result in amylose-free or low amylose content starch.Separation of the GBSS proteins encoded by the three waxy loci reveal the presentation of the null alleles of the waxy loci in different wheat lines.Lots of common wheat varieties were discovered that they carry null allele of WX-A1 or WX-B1 and even some carry both these two null alleles.However,only one Chinese landrace‘Baihuo’ has been found that it is the carrier of null allele of WX-D1.Different researchers also reported the dosage effects of the three null alleles of waxy loci.Combining the three null alleles of three waxy loci within a same line has produced wheat lines with much lower amylose content and even amylose-free starch.Numerous efforts to develop waxy wheats are underway in Europe,North America,Japan and Australia.Waxy and partial waxy wheat starch have quite different quality characteristics caused by the change of amylose content compared to the normal starch.The potential applications of the waxy wheat including the industrial uses,Asian noodle making,specific food production and extending the shelf-life of baked products were also reviewed.