Structural adaptations. Physiological adaptations

you are: Structural adaptations

Besides structural protective adaptations of a plant have also various physiological mechanisms which allow them to adapt to a heat, a cold and a drought. For many sukkulentnyh desert plants the unique mechanism of photosynthesis reducing to a minimum of loss of water is characteristic. Thanks to special type of a metabolism (ITSELF; see gl. 4) these plants can close ustitsa at that time for which the maximum losses of water are dated, i.e. They are capable to carry out photosynthesis, without spending simultaneously too much water on transpiratsiju. These plants open the ustitsa and fix СО2 in the dark when transpiratsija it is minimum, and hold their closed on light when superfluous loss of water could lead issusheniju. Effective photosynthesis proceeds at them at closed ustitsah thanks to the shuttle mechanism which is pumping over СО2 from С4, to С3-системе. This unique adaptive mechanism is extremely important for a survival of plants in desert.

Similar physiological adaptations help plants to avoid damages from a frost. If the plant which has been grown up in a hothouse to expose outside at temperature hardly below zero it most likely will strongly suffer or will be lost, even if in the nature the plant of the same kind easily transfers negative temperatures. Cold constancy development, or acclimatisation, is the process beginning with reduction of length of day and decrease of temperature during autumn time. Acclimatisation is accompanied by numerous physiological changes. To us for the present it is not quite clear, which of these changes are responsible for cold constancy development; in total it is more probable that only the certain combination of such changes gives to a plant ability to take out negative temperatures. One of such processes can be compared to replacement of water by antifreeze in a car radiator. Antifreeze use to prevent formation of ice which could break off a radiator. In a plant, as well as in the car, there is a water which can freeze and thus as a result of expansion to break off cages. at the very beginning of acclimatisation in cages the various dissolved substances collect; they reduce osmotic potential of cages and reduce probability of their freezing as the freezing point of cellular juice as a result of it goes down. At freezing of cages the main harm is put to them by crystals of ice formed inside; these crystals grow, break off various cellular membranes and, at last, kill a cage. Increase of concentration of the dissolved substances protects a plant because it reduces probability of formation of large crystals of ice. At acclimatisation in cellular membranes also there are some changes doing these membranes by less fragile at low temperatures. Probably, it grows out of degree increase not a saturation lipidov membranes; It involves decrease in their melting point thanks to what they at lower temperatures remain semi-fluid.

One more way of protection against the damages connected with freezing, is a synthesis of considerable quantities of fibers of the new types possessing especially high ability to hydration. Gidratatsionnaja water practically does not freeze: it is kept near to molecules of fiber by forces which prevent formation of crystals of ice. Needless to say that the more in a cage of such fibers, the ustojchivee this cage to freezing. At many plants the certain cycle regularly repeats: during autumn time such fibers are synthesised, and in the spring the plant uses them in the metabolism. according to some authors, in fibers on whom cold constancy depends, especially it is a lot of sulfgidrilnyh groups (-SH), characteristic for amino acid tsisteina. If it is true to estimate cold constancy it is possible by means of the chemical analysis, under the maintenance albuminous sulfgidrilnyh groups. The common opinion concerning value ' ' for the present is not present some the connected water, but nevertheless, apparently, in water linkage it is necessary to see one of the mechanisms protecting plants from damages by a frost.