Movement and redistribution of nutrients. Characteristics floemnogo transport

you are: Movement and redistribution of nutrients

Sahara dvizhutsja on floeme in the form of the concentrated solution in which the maintenance of sugars makes usually 7-25%, (0,2-0,7. Disputes on were originally conducted, whether the water which is carrying out functions of solvent, with same CKOростью, as sugar moves. Movement mechennyh 14С sugars was rather fast, but did not coincide with speed of movement of water, mechennoj tritiem (3Н). Now clearly that movement of sugars occurs only on sitovidnym to tubes, whereas molecules mechenoj waters freely diffundirujut through plazmalemmu. Therefore random motion of very small number of molecules mechenoj waters led to their diffusion from sitovidnyh tubes and as a result there was an impression that water does not move together with sugars. That all solution really moves as a unit, has been shown in graceful experience in which bunches sitovidnyh the tubes, taken of chereshka Heracleum, remained the connected ends with a plant and continued to function. By means of a narrow ray of light naprevali a small site on a surface of bunches, and then, using the thermocouple, carefully measured speed of movement nagretogo a solution on a bunch course. This method has shown that nagretyj the solution moved on a bunch with a speed about 35 sm/ch that coincides with observable speeds of transport of sucrose.

Sahara often move on floeme on distance of several metres with a speed to 100 Such distances and speeds see/ch are too great to consider diffusion by the main transport mechanism. For effective floemnogo transport are required live sitovidnye the tubes capable to an active metabolism. That is why floemnyj transport is braked at ' koltsevanii ' a stalk which is leading to death of all live cages in a small zone round a stalk. Thus water can reach leaves through intact ksilemnye a tube, but sugar do not pass through floemu okoltsovannoj a zone. Similarly ingibitory breath can prevent transport formed at photosynthesis assimiljatov.

It has appeared that floemnyj transport is difficult for studying, as the experiences breaking in one way or another thin balance of pressure in a complex sitovidnyh of tubes, lead to erroneous results. One of few methods with which help contents and properties floemy were successfully investigated, is based on use of plant louses. These insects possess unique ability to define a site any one sitovidnoj tubes and to pierce its stiletom during feeding on a plant (fig. 8.4). Having pierced once sitovidnuju a tube, they should not spend more than any efforts as under the influence of pressure in sitovidnyh tubes there is their compulsory feeding.

Hence, the contents nature sitovidnyh tubes and process floemnogo transport can be studied, using a plant louse in quality.svoeobraznyh cranes. A body of an insect delete, and stilet remains thrust in sitovidnuju a tube in a kind mikro-kanjuli through which floemnyj juice flows under the influence of pressure in sitovidnoj to a tube. By means of this method it is possible to show that in floeme there are concentration and pressure gradients, and higher concentration of sucrose and higher hydrostatic pressure are observed near to the donor, and lower concentration and pressure - about an acceptor.

Despite the fact that what sitovidnye tubes floemy, being under pressure, adjoin to vessels ksilemy, testing a tension, both these systems are in a condition of water balance, i.e. They have identical water potential. high negative water potential concentrated floemnogo juice will neutralise influence of positive hydrostatic pressure in sitovidnyh tubes. Therefore sitovidnye tubes have negative water net-potential, about equal to water potential ksilemnyh the vessels containing very diluted solution (with small negative water potential) and testing a tension (fig. 8.5.