Johnson K A, Sussex I M
Department of Biology, Yale University, New Haven, CT 06511.
Chromosoma. 1990 Jul;99(3):223-30. doi: 10.1007/BF01731133.
The cotyledon parenchyma cells of common bean (Phaseolus vulgaris L.) produce large quantities of storage proteins during embryo maturation; throughout this period, these cells also accumulate nuclear DNA (nDNA). To investigate the basis of this nDNA accumulation, we have measured storage protein mRNA pools, nDNA mass, and gene copy number at specific stages of cotyledon development. RNA blotting and hybridization show that transcripts encoding the major embryo-specific storage proteins are present very early in cotyledon development, accumulate in coordinate fashion to peak during mid-maturation, and fall in abundance prior to the onset of dormancy. During this same period, nDNA mass per parenchyma cell nucleus, as measured by Feulgen microspectrophotometry, increases from 2C-4C to about 64C (C being the haploid germ cell genomic complement). The nDNA values do not cluster around integral multiples of the diploid 2C amount. DNA blotting and hybridization are used to evaluate the relative representations of different classes of the bean genome in DNA samples isolated from vegetative tissues, from cotyledons beginning to accumulate storage proteins, and from cotyledons of late maturation embryos entering dormancy. The results demonstrate that the observed DNA accumulation in the cotyledon parenchyma is due to overlapping rounds of replication of the complete genome and not to disproportionate amplification of specific sequences nor to random DNA synthesis.
菜豆（Phaseolus vulgaris L.）子叶薄壁细胞在胚胎成熟过程中产生大量贮藏蛋白；在此期间，这些细胞也积累核DNA（nDNA）。为了研究这种nDNA积累的基础，我们在子叶发育的特定阶段测量了贮藏蛋白mRNA库、nDNA质量和基因拷贝数。RNA印迹和杂交分析表明，编码主要胚胎特异性贮藏蛋白的转录本在子叶发育早期就已存在，在成熟中期以协同方式积累至峰值，并在休眠开始前丰度下降。在同一时期，通过孚尔根显微分光光度法测量，每个薄壁细胞核的nDNA质量从2C - 4C增加到约64C（C为单倍体生殖细胞基因组含量）。nDNA值并不聚集在二倍体2C量的整数倍附近。DNA印迹和杂交用于评估从营养组织、开始积累贮藏蛋白的子叶以及进入休眠的晚期成熟胚胎的子叶中分离的DNA样品中菜豆基因组不同类别的相对含量。结果表明，在子叶薄壁细胞中观察到的DNA积累是由于整个基因组的多轮重叠复制，而不是特定序列的不成比例扩增或随机DNA合成。
