The metabolic changes observed during the first phase can be caused by change of hormonal and balances that defines synthesis and activation of enzymes, properties of cellular membranes of the tempered fabrics. The abstsizovy acid collecting in fabrics permeability of membranes for water, water return of cages. By the end of the first phase of a hardening all wintering plants in a condition of rest. However processes of training, reorganization of processes of a metabolism proceed.
Ability to a hardening not all plants possess. Of the southern origin frosts are not capable to transfer. Ability to a hardening at the wood and wintering plants of the northern latitudes enduring a considerable of temperature during the winter period in the period of a summer is absent and is shown only during approach of the autumn lowered temperatures (if the plant to it passed a necessary cycle of development). Training process only to certain stages of development of plants. For
temperatures, it is similar to dehydration of cages at a drought. damages of cages by a frost are loss of turgor by them, an infiltration of mezhkletochnik water and an exit of ions from cages. The exit of ions of K+ and Sakharov from cages is apparently connected with damage of membrane systems of their active. The damaged plants at transfer in a warm place have an appearance scalded, lose turgor, leaves quickly and dry up. When thawing frozen tubers of potatoes, root crops of fodder and sugar beet water easily follows from fabrics. It is important to note that a condition of overcooling (without plants transfer without harm; at the same, but with formation of ice in fabrics of a plant perish.
Upon transition to a condition of rest the balance changes fitogormo-is new: the content of auxin and gibberellin decreases and the content of abstsizovy acid which, weakening and inhibiting growth processes, causes approach of a dormant period. Therefore processing of plants of winter wheat, a lucerne and other cultures during this period growth inhibitors (for example, chlorine-holinkhloridom — CCC or triiodbenzoyny acid) increases resistance of plants to low temperatures.
If ice it is formed a little and cages were not mechanically damaged by its crystals, at the subsequent thawing such plants can keep viability. So, in cabbage at a temperature —. — 6 ° C are formed an ice quantity in mezhkletochnik. However at the subsequent slow thawing mezhkletochnik are filled with water, is absorbed by cages, and leaves come back to a state.
Favorable conditions for passing of the first phase of a of winter plants develop at solar and (daytime temperature to 10 °C) the weather promoting accumulation in fabrics of plants of carbohydrates and other protective substances. Under natural conditions the optimum term of the first phase of a hardening of winter cereals about two weeks. During this time the amount of sugars increases in plants to 70% for dry weight or to 22% for crude weight, i.e. is close to the contents Sakharov in root crops of the best grades of sugar beet.
Increase of frost resistance of plants is closely connected with a hardening — gradual preparation of plants to a of low winter temperatures. The hardening — is reversible physiological resistance to adverse effects of the environment.