Ageing of plants, maturing of fruits and subsidence of leaves. Subsidence of leaves

you are: Ageing of plants, maturing of fruits and subsidence of leaves

Subsidence of leaves represents one of the most complicated processes in a green plant. It can gradually occur in process of plant ageing. In this case the oldest falling down leaves are constantly replaced with the new leaves formed on a top of a stalk. On the other hand, there can be a simultaneous subsidence of all leaves that serves as the mechanism helping listopadnym plants to transfer adverse conditions in the winter. Subsidence of leaves is caused by formation of specialised layers of cages in otdelitelnoj to a zone at the basis chereshka or near to it.

Depending on a plant kind this zone can be generated in the beginning of development of sheet or after its end. The parenhimnye cages making otdelitelnyj a layer, it is frequent on the sizes less, than surrounding cages. In otdelitelnoj to a zone even individual vascular elements happen more shortly, and fibres in a bunch can be absent. Thanks to such combination of anatomic signs otdelitelnaja the zone differs weak durability.

Sbrasyvanie of leaves is initiated by their natural ageing or a signal arriving from environment, as at listopadnyh trees. This signal usually is reduction of length of day (gl. 12), causing changes in a sheet plate that leads eventually sbrasyvaniju all sheet. The conclusion about the photoperiodic control of subsidence can be made proceeding from behaviour of trees near to street lanterns. They often keep leaves in the autumn longer, than other trees. Eventually temperature decrease causes, of course, subsidence and these leaves.

Before sbrasyvaniem leaves in otdelitelnoj to a zone there are numerous changes. Owing to frequent cellular divisions in the basis chereshka the layer of the cages reminding under the form bricks is formed. Active metabolic changes in cages otdelitelnoj zones lead to partial dissolution of cellular walls or a median plate. As a result of a cage are divided among themselves. Eventually under weight of sheet vessels are broken off also sheet separates from a tree. The korkovyj layer forms on a place chereshka penek, protecting fabrics of a tree from microbic infection and limiting water losses. Vessels ksilemy are corked vyrostami next parenhimnyh the cages, named tilami that leads to full blocking of vessels.

Both auksin, and etilen participate in regulation of subsidence of leaves. In active, sheet lives new synthesised auksin it is constantly transported from a sheet plate through chereshok in other parts of a plant, but in process of ageing of sheet the educational level and transport auksina decreases. This decrease serves one of the signals causing changes in otdelitelnoj to a zone that leads sbrasyvaniju leaves. Auksin, put on a sheet plate, subsidence by maintenance of normal metabolic activity in cages chereshka brakes. With approach of winter receipt tsitokininov from roots decreases that, possibly, too brings the contribution to decrease in activity of processes of ability to live of sheet, as tsitokininy as it has been established, slow down ageing of leaves (see gl. 9). When the sheet plate starts to grow old, products of its old cages move downwards on chereshku and cause the ageing beginning in fabrics chereshka. Though there is an assumption that these ' ageing factors ' include abstsizovuju acid (it is discussed more low), is now conventional that abstsizovaja acid, despite its name, makes insignificant impact on subsidence.

Ageing of fabrics important not only in the respect that it regulates formation in leaves of factors of ageing, but also from the point of view of reaction of fabrics otdelitelnoj zones on hormones. When ageing of cages chereshka is slowed down under action auksina, is late as well subsidence of leaves. Any processing accelerating ageing (for example, etilenom), stimulates subsidence. However etilen activates subsidence of leaves only in the event that it process old fabrics chereshka. Auksin usually ingibiruet subsidence of leaves, but can render on this process and stimulating action (thanking its abilities to activate formation etilena) if it is brought after ageing in fabrics otdelitelnoj zones has already begun. Thus, the destiny of sheet is defined by age and a fabric condition, and also presence of hormones.

It is established that etilen is the main natural hormone regulating subsidence of leaves. Besides, that etilen accelerates ageing of cages otdelitelnoj zones, it also directly is responsible for dissolution of cellular walls in the specified zone. This results from the fact that etilen stimulates synthesis of enzyme of cellulose destroying a wall and at the same time supervises allocation tselljulazy from a protolayer in a cage wall. These are active processes which demand, like maturing of fruits, an active power exchange and fiber synthesis; they can be suppressed ingibitorami the given processes. Etilen not only promotes dissolution of a cellular wall thanking its influence on synthesis tselljulazy, but also causes swelling of cages on proksimalnoj to the party (the nearest to a stalk) otdelitelnoj zones (fig. 10.8). As a result distalnaja the part chereshka (turned to a sheet plate) is physically pushed out.

The effect Described above arises at artificial processing chereshkov etilenom. However it is clear that etilen is also the natural agent causing subsidence of leaves as its allocation by cages otdelitelnoj zones amplifies even prior to the beginning of subsidence. The otdelitelnaja zone in essence represents group vysokospetsializirovannyh cages, and etilen influences mainly on - these. Cages, it is frequent only on one layer. The specified cages are unique cages in chereshke and, possibly, in the whole plant which naturally develop considerable quantities tselljulazy. The set example besides serves as an illustration of that there are two co-operating systems regulating growth and development of plants; the hormones providing a signal, and a condition of the cages, which response it is defined by background of their development. Though and it is true that hormones play a certain role in definition of a condition of a cage, it is influenced also by any other factors which completely yet have been not solved by biologists.