Singletary G. W., Banisadr R., Keeling P. L.
ICI Seeds, P.O. Box 500, Slater, Iowa 50244.
Plant Physiol. 1997 Jan;113(1):293-304. doi: 10.1104/pp.113.1.293.
In cereals, starch is synthesized in endosperm cells, which have a ploidy level of three. By studying the allelic dosage of mutants affecting starch formation in maize (Zea mays L.) kernels, we determined the effect of down-regulated enzyme activity on starch accumulation and the activity of associated enzymes of carbohydrate metabolism. We found a direct relationship between the amount of starch produced in the endosperm and the gene dosage of amylose extender-1, brittle-2, shrunken1, and sugary-1 mutant alleles. Changes in starch content were found to be caused by changes in the duration as well as the rate of starch synthesis, depending on the mutant. Branching enzyme, ADP-glucose pyrophosphorylase, and sucrose synthase activities were linearly reduced in endosperm containing increasing dosages of amylose extender-1, brittle-2, and shrunken-1 alleles, respectively. De-branching enzyme activity declined only in the presence of two or three copies of sugary-1. No enzyme-dosage relationship occurred with the dull1 mutant allele. All mutants except sugary-1 displayed large increases (approximately 2- to 5-fold) in activity among various enzymes unrelated to the structural gene. This occurred in homozygous recessive genotypes, as did elevated concentrations of soluble sugars, and differed in magnitude and distribution among enzymes according to the particular mutation.
在谷物中，淀粉在胚乳细胞中合成，胚乳细胞的倍性水平为三倍体。通过研究影响玉米（Zea mays L.）籽粒淀粉形成的突变体的等位基因剂量，我们确定了酶活性下调对淀粉积累以及碳水化合物代谢相关酶活性的影响。我们发现胚乳中产生的淀粉量与直链淀粉延伸因子-1、脆性-2、皱缩1和含糖-1突变等位基因的基因剂量之间存在直接关系。根据突变体的不同，淀粉含量的变化是由淀粉合成持续时间以及合成速率的变化引起的。在分别含有增加剂量的直链淀粉延伸因子-1、脆性-2和皱缩-1等位基因的胚乳中，分支酶、ADP-葡萄糖焦磷酸化酶和蔗糖合酶的活性呈线性降低。只有在存在两个或三个拷贝的含糖-1时，去分支酶活性才会下降。与迟钝1突变等位基因不存在酶剂量关系。除含糖-1外，所有突变体在与结构基因无关的各种酶中活性都大幅增加（约2至5倍）。这种情况发生在纯合隐性基因型中，可溶性糖浓度也会升高，并且根据特定突变，酶之间的活性增加幅度和分布有所不同。
