- UID
- 699520
- 在线时间
- 小时
- 注册时间
- 2011-12-7
- 最后登录
- 1970-1-1
- 主题
- 帖子
- 性别
- 保密
|
All the cells in a particular plant start out with the same complement of genes. How then can these cells differentiate and form structures as different as roots, stems, leaves, and fruits? The answer is that only a small subset of the genes in a particular kind of cell are expressed, or turned on, at a given time. This is accomplished by a complex system of chemical messengers that in plants include hormones and other regulatory molecules. Five major hormones have been identified: auxin, abscisic acid, cytokinin, ethylene, and gibberellin, studies of planrts have now identified a new class of regulatory molecules called oligosaccharins.
Unlike the oligosaccharins, the five well-known plant hormones are pleiotropic rather than specific; that is, each has more than one effect on the growth and development of plants. The five have so many simultaneous effects that they are not very useful in artificially controlling the growth of crops. Auxin, for instance, stimulates the rate of cell elongation, causes the plant to develop a vascular system, to form lateral roots, and to produce ethylene.
The pleiotropy of the five well-studied plant hormones is somewhat analogous to that of certain hormones in animals. For example, hormones from the hypothalamus in the brain stimulate the anterior lobe of the pituitary gland to synthesize and release many different hormones, one of which stimulates the release of hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle cells, and so forth. In other words, there is a hierarchy of hormones.
Such a hierarchy may also exist in plants. Oligosaccharins are fragments of the cell wall released by enzymes release different oligosaccharins. There are indications that pleiotropic plant hormones may actually function by activating the enzymes that release these other, more specific chemical messengers from the cell wall.
130. The passage suggests that which of the following is a
function likely to be performed by an oligosaccharin?
(A) To stimulate a particular plant cell to become part of a plant's root system
(B) To stimulate the walls of a particular cell to produce other oligosaccharins
(C) To activate enzymes that release specific chemical messengers from plant cell walls
(D) To duplicate the gene complement in a particular plant cell
(E) To produce multiple effects on a particular subsystem of plant cells
132. According to the passage, which of the following best
describes a function performed by oligosaccharins?
(A) Regulating the daily functioning of a .plant's cells
(B) Interacting with one another to produce different chemicals
(C) Releasing specific chemical messengers from a plant's cell walls
(D) Producing the hormones that cause plant cells to differentiate to perform different functions
(E) Influencing the development of a plant's cells by controlling the expression of the cells' genes
各位前辈NN,这篇文章中 oligosaccharins 的作用到底是啥 130和132都涉及到了 没搞清楚 跪求各位NN赏脸看看
|
|
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2013-11-3 08:58:56
收藏
收藏
楼主
