Agrobiology p. 314-317
NEW ACHIEVEMENTS IN CONTROLLING THE NATURE OF PLANTS (1940)
T. D. Lysenko
But what would happen if the plant were not provided with the conditions it requires and given other conditions? What would be the result of this? You could reply: "The plant will not accept conditions that do not suit it, will not assimilate them, and as a result will perish." That is true. However, it is not always so.
If one approaches the plant from the standpoint of the Michurin theory, if one treats the plant organism properly, it is possible not only to increase the yield by humouring the nature of the organism but also to remould its very nature, its very heredity, in accordance with the conditions prevailing in the particular bed, field or garden. In other words, the heredity may be changed deliberately in the direction we desire. This can be done by means of skilful training of the plant.
What, then, does this skillful training of plant organisms consist in?
It consists not only in humouring the plant's nature but also in opposing it with a view to inducing new demands in the given plant.
Winter habit is one of the stable hereditary properties of cereals. In farming it is absolutely necessary to cater to the requirements of winter plants with the help of agrotechnique and to furnish them with cold, otherwise there will be no harvest. But what would be the result if we "mistreated" winter wheat Novokrymka 0204 and did not provide it with the conditions essential for vernalization? The result would be no crop. A study of the biology of winter wheat has shown that the different varieties require different periods of chilling for vernalization. Novokrymka 0204 requires a temperature of approximately 0° C. for a period of 35 days in order to go through the entire process of vernalization. If the temperature is 3°‑5° C. the process of vernalization will require 40 days. If the temperature is 15°‑20° C., the process of vernalization will not take place altogether, or, if it does, will take a considerably longer period of time.
But what will be the result if we chill soaked seeds of this same Novokrymka 0204 for only 25‑30 days? Vernalization will proceed normally. After 30 days we cut the cold treatment off. Thus, the seeds will still be 5 days short of the normal period for completing the process of vernalization. From numerous experiments we know that if the period this variety normally requires for vernalization is artificially shortened by even one or two days, the other processes, which follow vernalization, cannot take place. In every phase of the development of the plant organism, including the phase of vernalization, a qualitative change takes place in its demands on environmental conditions. But for this change to take place certain definite external conditions quantitative in character must be available. After the organism has been provided with these conditions and has assimilated them, it suffers a qualitative change, development enters a new phase and the demands of the organism on its environment also change. For example, the demand of winter plants for the cold which they need in order to pass through the process of vernalization is replaced by a demand for warmth. For the phases following vernalization, for the subsequent processes, warmth is now indispensable.
Thus, the soaked Novokrymka 0204 seeds which we chilled for 30 days (we vernalize them that long) are then sown in the field in the spring. It is not very warm in the spring, but neither is it cold. And now, instead of completing the process of vernalization in 5 days, which this sort of winter wheat would do at a temperature of about 0° C., the plant begins to experience distress, figuratively speaking. It "languishes" in this way for 15‑20 days, but in the end it completes its vernalization. But once vernalization has actually taken place, despite the abnormality, despite the "distress," further development proceeds at a very rapid pace. The field conditions for this are good: the days are long, there is plenty of light, it is warm and there is sufficient nutriment.
In the summer the seeds of the plants ripen. The question arises: will these seeds be normal, common seeds possessing the normal heredity of the winter variety? It turns out that they will not. In these seeds the old, long‑established, conservative heredity of the winter habit has been broken down. In this generation the heredity has not been reproduced as it was in the numerous preceding generations. Cold was not given the plant at a particular, critical moment, towards the end of vernalization.
In our experiment the vernalization was completed in warmth and not in cold. What does this mean with regard to the plant? It is impossible to conceive that one and the same process can take place in a living organism both in cold and in warmth in absolutely the same way. If we take seeds of any variety of winter wheat, divide them into two lots and let the vernalization of one lot be completed in cold, and of the other lot in warmth, then, of course, the processes of vernalization in these two lots of seeds will differ qualitatively. The heredity as regards the phase of vernalization will also be different in the organisms grown from these seeds.
Suppose we sow the seeds of the plants that completed vernalization in warmth. The new organisms, as experiments have shown, no longer stand in particular need of vernalization chilling. They no longer have that urgent need of cold which exists in ordinary winter plants. The old, conservative hereditary property of winter habit has been destroyed by us in 10‑15 days, i.e., during the time when the plants of the preceding generation completed the process of vernalization in conditions of spring temperature.
I must state that this is not only easily said but easily done. All that is needed to destroy any conservative hereditary trait prejudicial to the definite end we pursue is a knowledge of the conditions with which the organism should be provided, and when. It is necessary to know when to stop humouring the old, strong heredity, when to remove the conditions which the old heredity requires and to substitute for them conditions for which we wish to create a demand in the organism. I must stress that in this interesting task everything depends on the skill and knowledge of the experimenter.
We tried giving the winter plant warmth at the beginning of the vernalization process instead of at the end. In this experiment, after very prolonged treatment, the heredity changed, but we obtained deformed organisms.
In order to change the nature of the vernalization phase, it is necessary to modify the conditions under which vernalization takes place at the end of the process.
How did we arrive at this conclusion?
Here it would be in place to mention the absolute necessity of coordination between the experimental work of scientists and practical life. Whatever the experiment we undertake, we must always keep an eye on what is happening around us in life. We must examine life closely and try to understand the facts we observe in it and to link them up with the experiment we are working on.
In practical farming, people have been sowing winter wheat for thousands of years in the early autumn, in August, when it is warm (cold sets in much later), and the winter habit of this variety of grain has never changed because of this. Why then provide warmth at the beginning of vernalization? The process of vernalization simply will not take place in this case; the organism will wait for the onset of cold. In order to convert winter wheat hereditarily into spring wheat, warmth must be supplied only at a strictly definite time, namely, before the end of the process of vernalization.
Several researchers attempted giving the plant warmth after earing, when not a breath, so to speak, of the process of vernalization was left; vernalization had long been completed in the given plant. In such experiments these researchers wanted to change a property which the organism had possessed in the past, but which it had already outlived, a property which could reappear only in the succeeding generation. Thus, these people tried to change something in the organism which it no longer possessed at the time of the experiment. They explain this mode of experimentation by asserting that an organism possesses a specific hereditary substancegeneswhich in its normal state is not subject to the processes of either oxidation or reduction. As they conceive it, the genes of winter habit are always present in the form of particles in the cells of the winter varieties of plants. Therefore, according to their view, the time of treatment and the state of the organism at that time are of no importance. And despite their obviously incompetent experiments these scientists say that it is impossible to change winter varieties into spring varieties by bringing external conditions to bear upon them.
When we provided warmth for winter plants at the beginning of vernalization, no good results by way of transforming the nature of the plant were obtained. But when we began to provide warmth at the end of the process of vernalization, the results were considerably better—the old heredity was often broken down immediately. On the basis of these experiments we arrived at the following conclusion: the conditions in accordance with which we wish to create a new heredity must be furnished at the end of the process whose nature we are changing.
Today there is not a single hereditary winter variety of wheat that cannot be converted into hereditary spring wheat in two or three generations. From wheats preferring cold at the vernalization stage it is possible, by a proper growth of wheat varieties, to obtain spring forms which do not require cold.
So much nonsense has been written to condemn these simple results. If actual experiments conflict with theory, we should pay more heed to the experimental results than to the theory that they falsify.
To understand the process of transforming winter wheat into spring forms, we should compare the procedure discussed above with Waddington's experiments with fruitflies. In both cases the transformation was induced by heat applied during a definite developmental "window". In both cases the transformation was not immediate, but took multiple generations before the acquired (i.e., "learned") behavior became fully hereditary.
It did take several generations longer for Waddington's fruitflies to become inherently crossveinless, but this is not too surprising. It is doubtful that any fruitfly had ever previously gained an advantage by lacking crossveins. But it is highly likely that annual grains had previously shifted from winter to spring forms, and vice versa, many times over the course of their evolution.
In principle, transforming winter annuals into spring formsand spring into winteris no more remarkable than converting biennials into annuals, and the reverse. Annual Queen Anne's Lace is readily transformed into biennial carrots; and carrots are notorious for giving rise to annual forms. The same is true of beets and radishes. Prof. Devries preferred to work with annual forms of Evening Primroses, but they continually gave rise to some biennial specimens.
Modern research has shown that numerous genes are altered in expression by cold. Ciannamea, et al. (2006) identified 70 genes in Lolium perenne "that are either up- or down-regulated with a minimal 2-fold difference compared with the common reference." Most were affected early in the chilling process, while a few were altered towards the end of the period. If the chilling ended before the last genes were altered in expression, they would behave like mutant genes with double or half the normal expression, while other genes would behave normally. The result would be a "genomic shock" like that which frequently accompanies true gene mutations or hybridization. These genes would not be permanently altered, of course, but the rest of the genome could accomodate their temporarily "mutated" degree of expression, allowing the plants to struggle towards complete vernalization. When this process is repeated for 2 or 3 more generations, the altered expression of accessory genes (those that accomodate the over- or under-expression of the few genes) may become canalized in their ability to finish the vernalization process without assistance from the genes that require chilling to function normally.