植物体内有机物运输和分配.pptx

《植物体内有机物运输和分配.pptx》由会员分享，可在线阅读，更多相关《植物体内有机物运输和分配.pptx（22页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、(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)In many glands,the

2、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.第1页/共22页6.1.2 long distance transport(长距离运输)6.1.2.1pathway(途径)：p

3、hloem(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。第2页/共22页水分和同化物运输的途径比较第3页/共22页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 xylem

4、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 assimilate stream.第

5、4页/共22页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 moving

6、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)第5页/共22页14CO2示踪技术：Two leaflets of a broad bean plant were enclosed in a Plexiglas container and

7、 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.第6页/共22页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)。筛管与伴胞形成筛管分子

8、-伴胞复合体(sieve element-companion cell complex,SE-CC)第7页/共22页(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.(b)Detai

9、l 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.第8页/共22页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。第9页/共22页(a)Aphid(Longistigma caryae)feeding on a basswood(Tilia am

10、ericana,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.第10页/共22页6.2 韧皮部运输机理6.2.1运输方向：从源(source

11、)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 plant par

12、ts 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.第11页/共22页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 cell com

13、plex)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)第12页/共22页质外体(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装载途径第13页/共22页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

14、地将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。第14页/共22页第15页/共22页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

15、就存在膨压差，它推动筛管内容物的集流，穿过筛孔沿着系列筛分子向前运行，最终进入库细胞。第16页/共22页第17页/共22页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 s

16、ugar concentration falls;as 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

17、.第18页/共22页(a)As sucrose(s)is 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 th

18、rough sieve pores,high 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 breakd

19、own 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 converted to glucose and then polymerized to starch(storage organs),is respired(most tissues),or is used to construct new compo

20、unds(growing tissues).第19页/共22页BOX:P-protein hypothesisP-protein,found as a fine network adjacent to the plasma membrane inner surface of uninjured sieve elements.When phloem is ruptured,the phloem sap initially surges toward the break;this rapid movement sweeps the P-protein into the cell center,wh

21、ere it becomes a tangled mass.When it is carried to a sieve area or sieve plate,the P-protein mass is too large to pass through and forms a P-protein plug.第20页/共22页6.2.4 韧皮部卸出(phloem unloading)6.2.4.1Concept(概念)：是指装载在韧皮部的同化产物输出到库的接受细胞(receiver cell)的过程。步骤：首先是蔗糖从筛分子卸出，然后以短距离运输途径运到接受细胞，最后在接受细胞贮藏或代谢。第21页/共22页感谢您的观看！第22页/共22页