Deshayes A
Laboratoire de Mutagenese, B. V. 1540, 21034 Dijon, France.
Mutat Res. 1976 Jun;35(2):221-45. doi: 10.1016/0027-5107(76)90188-3.
A homozygous tl/tl chlorophyll mutant of Nicotiana tabacum var. Samsun shows spontaneous somatic variations on its leaves. These variations are either single (dark or light) or twinned (dark and light). In vitro culture of variation-free leaf fragments, on a particular medium, directly yields neoformed buds. These buds are placed on a medium for root formation, so that neoformed plants are obtained from which a new cycle of bud neoformation can be started. In this way, one obtains several sets of plants of the same somatic origin but which differ from each other by one or more neoformation cycles. At each cycle, the somatic variation ability is characterized on the basis of four criteria: (1) numbers and proportions of dark, light and twinned variations, (2) distribution of dark variations according to their sizes, (3) distribution of variations according to the foliar level, and (4) sexual transmission of each character. As early as at the second neoformation cycle, one observes a significant increase of variability among the numbers of variations and shifts in size distributions. The increase of variability is more striking after the third cycle; particularly, plants obtained in this manner have acquired, on the average, the ability to vary earlier in the development of the foliar initium. This property is expressed through the enlargement of the mean size of the variations. In each case, the observed variability is somatically maintained through cuttings. This, together with the fact that the observed shifts in frequency distributions as well as the changes in numbers of variations are sexually transmitted after the third neoformation cycle, definitely means that genetic changes have occurred. Consequently, it seems that from one neoformation cycle to another, in vitro culture of leaf fragments has cumulative effects which, beyond a particular threshold, are sexually transmitted. The only character, among four, not to be affected by in vitro culture is the distribution of somatic variations according to the foliar level. Thus, it seems that this character is strictly controlled by changes in physiological conditions which occur during the plant growth; in particular, the transition of the shoot apex from vegetative to flowering state. The effects of in vitro culture on the ability to somatically vary are discussed on the basis of four hypotheses: (1) modification in number of chromosomes (polyploidy, aneuploidy); (2) modification in chromosome structure (translocation); (3) selection of a particular kind of cells and (4) cumulative alteration of genetic information either by mutation or by disturbance in cell regulation process.
烟草品种萨姆斯un的纯合tl/tl叶绿素突变体在其叶片上表现出自发的体细胞变异。这些变异要么是单一的（深色或浅色），要么是成对的（深色和浅色）。在特定培养基上对无变异的叶片片段进行离体培养，可直接产生新形成的芽。将这些芽置于生根培养基上，从而获得新形成的植株，从中可以开始新的芽形成周期。通过这种方式，可以获得几组具有相同体细胞起源但因一个或多个新形成周期而彼此不同的植株。在每个周期，根据四个标准对体细胞变异能力进行表征：（1）深色、浅色和成对变异的数量和比例；（2）深色变异按其大小的分布；（3）变异按叶水平的分布；（4）每个性状的有性传递。早在第二个新形成周期，就观察到变异数量的变异性显著增加以及大小分布的变化。第三个周期后变异性的增加更为显著；特别是，以这种方式获得的植株平均在叶原基发育早期就获得了变异的能力。这种特性通过变异平均大小的增大来体现。在每种情况下，观察到的变异性通过扦插在体细胞中得以维持。这一点，再加上在第三个新形成周期后观察到的频率分布变化以及变异数量的变化是有性传递的这一事实，明确意味着发生了遗传变化。因此，似乎从一个新形成周期到另一个周期，叶片片段的离体培养具有累积效应，超过特定阈值后会进行有性传递。在四个表征标准中，唯一不受离体培养影响的性状是体细胞变异按叶水平的分布。因此，似乎这个性状受到植物生长过程中发生的生理条件变化的严格控制；特别是，茎尖从营养状态向开花状态的转变。基于四个假设讨论了离体培养对体细胞变异能力的影响：（1）染色体数量的改变（多倍体、非整倍体）；（2）染色体结构的改变（易位）；（3）特定类型细胞的选择；（4）遗传信息通过突变或细胞调节过程的干扰而发生的累积改变。
