The processes of starch formation were chosen as the biochemical index, since they are most indicative of the specific directiveness of metabolism in the potato plant. The work consisted in studying the temperature curves of the processes of enzymatic formation and decomposition of starch in the leaves and tubers at various stages of the ontogenesis of the potato.
The chief conclusion to be drawn from these studies is that the temperature optima for the action of the enzymes are not constant. As the plant develops, these optima change, and the direction of the changes harmonizes very well with the course of the temperature changes in the plant's surrounding milieu. At first, roughly for two-thirds of the vegetative period, the temperature optimum for the formation' of starch in potato leaves shifts towards higher temperatures, and in the last period towards lower temperatures. In the tubers, the starch-formation optima shift towards lower temperatures, apparently because the development of the tubers takes place in the latter half of the summer.
Consequently, the temperature optima for the action of one and the same enzymes in different organs of the plant are dissimilar, and their changes in the course of the vegetative period are likewise dissimilar.
In spite of the fact that the experiments were conducted in years when the weather conditions varied considerably, the direction of the shifts of the temperature optima for enzyme action as a rule remained the same.
Hence the temperature curves of enzyme action, like the diurnal rhythm, cannot be regarded as a direct reflection of the conditions of existence of the plant organism. This characteristic was elaborated in the course of a long process of evolutionary adaptation, under the influence of that rhythm of temperature changes in which the plant's evolution proceeded.
These facts accord with Academician T. D. Lysenko's theory of phasic development of plants, according to which the demands made by a plant on its environment entirely depend upon its preceding evolutionary history, upon the environment in which the plant was formed.
The data we obtained also helped in the elucidation of the mechanism by which the mutual coordination of the functions of the various organs of the plant is attained. Experiments show that in the process of development of the potato plant there is not only a fluctuation of the temperature optima, but also changes in the temperature zones of starch synthesis and decomposition. Fluctuation of the optima towards higher temperatures is, as a rule, accompanied by a contraction of the zone of starch synthesis and a considerable expansion of the zone of starch decomposition. For example, in the beginning of July starch synthesis in the leaves took place already at a temperature of 15°, whereas at the end of August this process was to be observed only beginning with 28°.
The predominance at fairly high temperatures of the starch decomposition processes over the synthetic processes should assist the release by the leaves of a certain part of the assimilates accumulated in their tissues during the daytime. This would well explain the earlier observations of Chesnokov and Bazyrina, who discovered that in the first half of the vegetative period of the potato the curve of translocation of the assimilates from the leaves has a double peak, and that one of the maxima occurs in the earlier half of the day.
Widening of the zone of starch synthesis in the course of the development of the potato was also observed in experiments on tubers. For instance, in the tissues of young tubers selected at the beginning of August, starch synthesis occurred only in the high temperature interval, outside of which the processes of starch decomposition predominated.
Hence, in the early period of development of the tubers, when the functions of growth predominate and the storage of starch is not the main process, starch formation is timed to occur in a very limited temperature interval, outside of which the processes of starch decomposition predominate. The biological significance of this regularity evidently consists in the fact that when soluble and easily mobilized forms of carbohydrate predominate in the tissues, the growth of these tissues proceeds more effectively. At a later period, when the growth of the tubers is less intense, and the storage of starch predominates, we observe a considerable expansion of the temperature zone of starch synthesis.
Further researches made it possible to establish that the optima for the action of the starch-forming enzymes in one and the same organ of the plant does not remain constant either in the vegetative or in the diurnal period.
It follows from the data we have obtained for tubers that the intensity of starch synthesis in their tissues is greater at nighttime, and, further, that this process coincides in time with lower temperatures, especially in the later stages of the potato's development.
A reverse picture was established in experiments on leaves, in which the processes of starch synthesis coincide with the higher temperatures. Further, both the general intensity of the process and its coincidence with the high temperature intervals leave no doubt that starch formation in the leaves, in contradistinction to the tubers, is a daytime process. It follows from this that the photoperiodic reactions of plants must under no circumstances be considered in divorcement from the thermoperiodic reactions, with which they seem to be most closely connected.
Our data likewise show that temperatures which favour the processes of starch synthesis in the tubers simultaneously stimulate the processes of starch decomposition in the leaves.
It is appropriate to point out that the so-clearly manifested coordination between the functions of the overground and underground organs of the plant is due to the regulating action of the enzymes, which are specifically adapted to a definite state of the temperature factor.
Thus the periodicity observed in the biochemical activity of plants is a result of the development of the heredity of the organism under the influence of definite external conditions.
The data, I have quoted is only part of the material at our disposal. We do not claim that they give an in any way full explanation of the problem under discussion. They only show that the specific peculiarities of metabolism are as closely connected with the conditions of existence of the organism as are the form and structure of the organism.
Academician T. D. Lysenko is constantly emphasizing that the forms of living bodies were created, and are created, solely by their conditions of life. Hence, changes of vegetable and animal forms can be directed only by skilfully directing the conditions of life of the plants and animals. A splendid example of such direction is the summer planting of potatoes suggested by T. D. Lysenko. Our data, in full accord with T. D. Lysenko's conclusions, also show that in this way the fullest correspondence is obtained between the temperature to which the potato is adapted at the various stages of its development and the actual temperature of its environment. The decisive factor in the degeneration of the potato observed in the South is the high temperature of the soil at nighttime, which far exceeds the temperature level to which the tuber-formation processes in the potato are adapted. Here we have manifested the dual nature of the potato, as a plant which, it is true, originated in the South, but in areas of high elevation. As we know, one of the distinguishing features of the latter is the wide amplitude between day and night temperatures, which is particularly characteristic of the last third of the vegetative period, when the tuber-formation process in the potato is most intense.
In full accordance with the theory of phasic development of plants, our data show that plant metabolism is adapted, not to a constant but to a successively changing temperature. The regular changes of temperature must embrace not only the entire life cycle of the plant organism, but also the separate diurnal periods.