Fast movements of plants. Fast movements of leaves at a sensitive plant mimosa pudica

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Leaves at Mimosa pudica, as well as at Samanea, make tsirkadnye niktinasticheskie movements. But they can move extremely quickly also in reply to mechanical, temperature, chemical and electric razdrazhiteli. In some seconds after a touch to sheet chereshki leaflets fall also develop. such fast reaction demanding high degree of coordination, is caused by transformation of the mechanical stimulus perceived by touch cages chereshka, to an electric signal. This signal - possibly, depoljarizatsija membranes - quickly extends on a fabric, will not reach yet motor cages of a sheet small pillow which immediately change the volume, and it leads to movement of leaves or leaflets.

It is possible to measure Extending electric signal by means of two glass electrodes filled with a solution of salt one of which place on chereshok, and another - in the soil surrounding roots, or on a wall of a pot with a plant. The signal represents short-term shift of a potential difference between electrodes (fig. 13.2). It is transferred on a shank at a mimosa with a speed about 2 sm/with and approximately in 5 times faster on sheet of insectivorous plant Dionaea (a Venus flycatcher). Speed of transfer increases in 3 times at rise in temperature on everyone 10 ° that specifies in participation of chemical reactions. At removal floemy distribution of signals is slowed down; means, they are transferred on cages floemy. The signal cannot break a barrier from dead cages; it means that it, possibly, is not connected with diffusion of water-soluble hormones.

Though external electrodes also allow to establish that in plants for communication between cages electric signals are used, they do not give any instructions concerning mechanisms of transfer or cages participating in it. By means of endocellular microelectrodes (fig. 7.8 see) it was possible to show that certain cages in floeme and protoksileme mimosas are ' excitable ' (fig. 13.3). Their potential of rest, i.e. transmembrannyj the potential before excitation, is much more negative, than at surrounding cages. When as a result of electric or chemical stimulation this potential (i.e. Electronegativity of an inside of a membrane) decreases to defined ' threshold ' level, a cage gives ' the category '.

All stimulus which are stronger threshold, cause identical reaction (' all or anything '), consisting in depoljarizatsii to zero or even to positive level with the subsequent fast return to rest potential. Excitable cages in a vegetative fabric are always connected plazmodesmami on which, probably, and electric signals are transmitted. The extending signal named in potential of action, is similar to action potentials in a nervous fabric, with that only a difference that in plants has not been found any chemical transmitter. Atsetilholin which transmits a signal from one cage to another in a nervous fabric, is and in plants, but there is no convincing data in favour of that he here again participates in transfer of intercellular signals.

The Irritation chereshka at a mimosa a light touch or a water drop raises the potential of the action limited to limits of given sheet. But if to stimulate sheet with a burn or damage, other leaves are involved also; such stimulus cause not only action potential, but also so-called changing potential. This potential, apparently, is transferred by chemical substance which extends on ksileme, passes through a sheet small pillow and initiates new potential of action on its distant party. Last is transferred on excitable cages floemy and protoksi-lemy, will not reach yet other sheet small pillow in which then there are characteristic changes tourist's mountain, leaders to sheet folding. Depending on force of initial irritation changing (gradualnyj) the potential can pass again through a sheet small pillow and stimulates one more potential of action on its distant party. Thus, the changing potential co-ordinates movement of various leaves of a plant, raising the potentials of action transferred on certain zones of a fabric.

Apparently, at a mimosa movement of bodies is entirely defined by changes tourist's mountain. Reduction of volume of those or other motor cages is accompanied by allocation from them ions To + and tanninopodobnyh substances in extracellular space. Such change caused as believe, fast increase in permeability of membranes, is accompanied by electric signals which can be revealed by means of microelectrodes. External similarity between this process and reduction of muscles at animals allows to assume and presence of the general internal features, such, as participation sokratitelnyh type fibers aktomiozina; however while there is no weighty data which would confirm a hypothesis about the similar mechanism or contradicted it.

Some researchers underlined value tanninov for mimosa movements. This heterogeneous group of the condensed phenolic connections can form complexes as with fibers, and inorganic ions. Tanniny denaturirujut fibers also could damage a cage, but do not cause harmful effects while they are isolated in membrannyh sacks vakuolej. Probably, them especially it is a lot of in vakuoljah the plants capable to tigmonasticheskim to movements (fig. 13.4). During such movements tanninovye units in vakuoljah dissociate, and some tanniny, probably, are allocated through membranes of motor cages. Then they diffundirujut in gidatody (time) in epidermise a sheet small pillow. As tanniny possess knitting taste and operate as natural repellents, allocation tanninov at sheet movement can promote protection of a plant against insects.