植物体内有机物运输和分配.ppt

1、BOX: transfer cells(转移细胞),The rate at which material can be actively transported depends on the number of molecular pumps present, which in turn depends on the surface area of the plasma membrane: The larger the membrane, the more molecular pumps it can hold. In certain specialized transfer cells, t

2、he walls are smooth on the outer surface but have numerous finger-like and ridge like outgrowths on the inner surface. The plasma membrane is pressed firmly against all the convolutions and thus has a much larger surface area than it would if the wall were flat. Consequently, room is available for m

3、any molecular pumps, and high-volume transport can occur across these transfer walls. Transfer cells are found in areas where rapid short distance transport is expected to occur: in glands that secrete salt, in areas that pass nutrients to embryos, and in regions where sugar is loaded into or out of

4、 phloem.,(a) Once released from a cell, a molecule diffuses in a series of random short paths as it collides with and bounces off other molecules. Probability favors its entering a neighboring cell (molecules 1, 2, and 3), but it can diffuse laterally along the wall as well (molecules 4 and 5). (b)

5、In many glands, the apopIast is large, so movement between cells may be faster and easier than movement within cells. Such glands often have a lining of compact tissue that isolates the gland, preventing the secreted material from permeating the whole region.,6.1.2 long distance transport(长距离运输),6.1

6、.2.1pathway(途径)：phloem(韧皮部)。Girdling experiment(环割试验)、radioactive tracer(同位素示踪技术)及谚语“树怕扒皮”等可以证明，同化物运输的途径是维管组织的韧皮部。,水分和同化物运输的途径比较,Diagram showing basic elements in the circulation of water, inorganic ions, and assimilates in the plant. Water and inorganic ions taken up by the root move upward in the

7、xylem in the transpiration stream. Some move laterally into tissues of the root and stem, while others are transported to growing plant parts and mature leaves. In the leaves, substantial amounts of water and inorganic ions are transferred to the phloem and are exported with sucrose in the assimilat

8、e stream.,As early as the seventeenth century, Marcello Malpighi of Italy noticed that,when a ring of bark was removed from a stem (a), the tissues above the ring became swollen (b). He correctly interpreted this phenomenon as new growth of wood and bark tissues stimulated by an accumulation of food

9、 moving down from the leaves and intercepted at the ring. Malpighi studied the effect of ringing at different times of the year and found that no swelling occurred during the winter months.,Girdling experiment(环割试验),14CO2示踪技术：Two leaflets of a broad bean plant were enclosed in a Plexiglas container

10、and exposed 14CO2 and light for 35 minutes. During that time, 14CO2 was incorporated into sugars, which were then transported to other parts of the plant.,6.1.2.2 韧皮部组成,由筛管(sieve tube)、伴胞(companion cell)和薄壁细胞组成. 筛管分子(sieve element, SE)：除含有质膜、内质网、质体和线粒体，其它细胞器降解消失，具有韧皮蛋白(phloem protein, P-蛋白)。 筛管与伴胞形成

11、筛管分子-伴胞复合体(sieve element-companion cell complex, SE-CC),(a) Longitudinal (radial) view of secondary phloem of yew (Taxus canadensis), showing vertically oriented sieve cells, strands of parenchyma cells, and fibers. Parts of two horizontally oriented rays can be seen traversing the vertical cells. (

12、b) Detail of portion of the secondary phloem of yew, showing sieve areas, with callose (stained blue) on the walls of the sieve cells, and albuminous cells.,6.1.2.3 运输同化物的种类,汁液干物质1025%，多数为糖，其余为氨基酸(谷氨酸和天冬氨酸)、蛋白质、无机离子、有机离子和植物内源激素。利用蚜虫吻针法方法证明。,(a) Aphid (Longistigma caryae) feeding on a basswood (Tilia

13、 americana,椴木) stem. A droplet of honeydew can be seen emerging from the aphid. (b) A photomicrograph showing part of the modified mouth parts (stylets) of the aphid in a sieve tube of the secondary phloem of the basswood stem. An arrow points to the tips of the stylers.,6.2 韧皮部运输机理,6.2.1运输方向：从源(sou

14、rce )到库(sink)。源是指产生或提供同化物的器官或组织，如功能叶、胚乳等；库是指消耗或积累同化物的器官或组织，如根、茎、果实、种子等。 运输过程包括韧皮部装载、运输和韧皮部卸出三个部分 Assimilate movement is said to follow a source-to-sink pattern. The principal sources of assimilate solutes are the photosynthesizing leaves, but storage tissues may also serve as important sources. All

15、plant parts unable to meet their own nutritional needs may act as sinks, that is, importers of assimilates. Thus, storage tissues act as sinks when they are importing assimilates and as sources when they are exporting assimilates.,6.2.2.1Concept(概念)：是指光合产物从叶肉细胞到筛管分子-伴胞复合体(sieve element-companion cel

16、l complex)的整个过程。 第一步：白天，叶肉细胞光合形成的磷酸三碳糖从叶绿体运到胞质溶胶；晚上，可能以葡萄糖状态离开叶绿体，转变为蔗糖(某些植物后来会将蔗糖转变为其他运输糖)。第二步：叶肉细胞的蔗糖运到叶片细脉的筛分子附近。第三步：筛分子装载，即糖分运入筛分子和伴胞。糖分和其他溶质从源运走的过程称为输出。,6.2.2韧皮部装载(phloem loading),质外体(apoplastic)和共质体(symplastic),同化物生产区,同化物积累区,同化物输出区,质外体运输,共质体运输,6.2.2.2装载途径,6.2.2.3装载机理(限质外体),在筛分子或伴胞质膜中的ATP酶，不断地将

17、H+泵到质外体(细胞壁)。质外体的H+浓度比共质体高，形成质子梯度作为推动力。通过ATP酶释放的能量，推动细胞内H+的输出和外界K+的输入，以维持膜内外的质子梯度。蔗糖与质子沿着这个梯度经过蔗糖-质子同向运输器(sucrose-proton symporter)，一起进入筛分子-伴胞复合体。,6.2.3运输机理,压力流动学说(pressure flow hypothesis)：源端(叶肉细胞)将蔗糖装载入SE-CC，接着木质部水分通过渗透作用也进入SE-CC，由此产生高的膨压。而在库端(如贮藏根)，当糖被卸出时，水分也离开韧皮部，于是膨压很低。源端和库端之间就存在膨压差，它推动筛管内容物的集流

18、，穿过筛孔沿着系列筛分子向前运行，最终进入库细胞。,Sugar is actively loaded into the sieve tube at the source. With the increased concentration of sugar, the water potential is decreased, and water from the xylem enters the sieve tube by osmosis. Sugar is removed (unloaded) at the sink, and the sugar concentration falls; as

19、 a result, the water potential is increased, and water leaves the sieve tube. With the movement of water into the sieve tube at the source and out of it at the sink, the sugar molecules are carried passively by the water along the concentration gradient between source and sink.,(a) As sucrose (s) is

20、 actively transported into sieve elements, s and cell become more negative, moving away from equilibrium with companion cells and other neighboring cells. Water moves into the sieve elements, squeezing phloem sap out through the sieve pores. Because the sugary water escapes through sieve pores, high

21、 pressure does not build up, so the pressure potential does not rise and stop the influx of water. The water potentials of sieve elements and surrounding cells never reach equilibrium as long as sucrose is being pumped. The source of the glucose may be photosynthesis or the breakdown of starch. (b) In sinks, sucrose is actively transported out of sieve elements, and all processes work in reverse compared with sources. In some sinks, most of the sucrose is converte