The Situation in Biological Science, p 128-134 (1948)
Vernalization, Mentors and Vegetative Hybridization
N. M. Sisakian
Corresponding Member of the Academy of Sciences of the Armenian S.S.R.
In his address, Trofim Denisovich Lysenko gave us a profound analysis of the present state of biology. The principles that T. D. Lysenko developed in his address are directly related not only to biology, but to the other branches of natural science. The Michurin ideas that T. D. Lysenko expounded in his address are correct, progressive. They are near and akin to us Soviet biochemists, the pupils of that distinguished representative of Soviet science, Academician A. N. Bach.
Of particular value for us, the representatives of the Soviet biochemical school, are T. D. Lysenko's references to the close connection that exists between variation, heredity and the metabolic processes (the character and type of metabolism in the organism).
The merit of the Bach and Oparin school consists in that enzymes in the works of this school, for the first time became a powerful instrument for the study of metabolism and for directing the enzymatic processes in working on materials of vegetable or animal origin. Before the work of Bach, Oparin, and their pupils, the action of enzymes was studied in their solutions, artificially produced from destroyed plant or animal tissues. The data obtained in this way is, of course, valuable for the purpose of ascertaining the chemical nature of enzymes, of studying the kinetics of enzymatic action, and also of investigating the activity of enzymes in autolytic mixtures.
But these data can give us no idea of the work of enzymes in the living cell, in which the conditions are far more complex than in autolytic mixtures, in destroyed and dead tissues. Enzymes are of great interest for the biologist not only in themselves, but also, as Alexei Nikolayevich Bach expressed it figuratively, as the key to our knowledge of the chemistry of living phenomena.
Referring to the direct causes that give rise to the fluctuations of enzymatic activity in the animal organism, A. N. Bach wrote twenty-five years ago that variations in the action of enzymes can be explained only by the inconstancy in the concentration of enzymes, or by the variation in their activity at certain moments due to the influence of various conditions.
Taking the views of Michurin and Lysenko as our point of departure, and basing our work on the principles of A. N. Bach's school of biochemistry, we in the Bach Institute of Biochemistry of the Academy of Sciences of the U.S.S.R. undertook researches which led to the discovery of a number of new facts that testify to profound changes in the biochemical activity of organisms under the influence of vernalization and vegetative hybridization.
Already in 1936, we were able to establish that in the vernalization of seeds according to T. D. Lysenko's method, fundamental changes of a biochemical character take place in vegetating plants.
The aim we set ourselves in this series of experiments was to trace the changes in the process of enzymatic formation and breakdown of sucrose in the living cell that occur under the influence of vernalization.
Experiments with the winter wheat Ukrainka showed that in non-vernalized plants, the process of enzymatic formation of sucrose predominates over the hydrolysis process, the breakdown of this substance. In vernalized plants, however, we see the very opposite. The process of vernalization conditions the shifting of the enzymatic equilibrium in the living leaves of plants in the direction of hydrolysis.
It must be observed that high productivity in plants is connected with the predominance of hydrolytic reactions in its vegetating organs.
It must be stated that with vernalization, not only does the direction of the enzymatic formation of sucrose change, but so also does the balance of the dissolved sugars. Vernalization leads to an increase in the quantity of monosaccharoids.
To obtain a complete and true judgment of the results arrived at, we conducted experiments similar to those just described on different varieties of cotton, a plant that differs from wheat both in its :nature and in the factors required for its vernalization. The results of our experiments on cotton fully confirmed the data we obtained in our experiments on wheat. In cotton, as in wheat, vernalization conditions a fundamental change in the direction of the processes of enzymatic formation and breakdown of sucrose.
Our investigation of the action of enzymes in the living plant cell under the influence of vernalization led us to the following main conclusions.
The vernalization of seeds fundamentally changes the correlation between the enzymatic synthesis and hydrolysis of the substances in plants. In the leaves of vernalized plants the process of enzymatic breakdown of substances rises sharply.
As a result of this, during vernalization, the relation between the synthesis and hydrolysis of sucrose is reduced. It must be observed that in their natural state the early ripening of these plants is due to the predominance of the hydrolytic properties of the enzyme.
It must be pointed out that the correlation between synthesis and hydrolysis in plant tissues is a rather characteristic species quality, although it changes regularly in the life cycle of a plant. But the changes in the biochemical activity of plants due to vernalization are of a character entirely different from those that we obtain, for example, by the use of ether, or by dehydrating, wetting, etc., the living tissues.
In such cases we obtain a change of a local character. These changes bear a reversible character, and after these influences are removed they disappear without leaving a trace in the subsequent life of the organism. During vernalization, however, the changes that take place in the biochemical activity of a plant are of a non-reversible character and are preserved in the subsequent course of development of the organism.
For the sake of greater clarity I would like to deal here with another important fact. Comparing winter forms with spring forms of wheat, Academician A. I. Oparin was able to show that winter wheat is always characterized by a higher relation between enzymatic synthesis and hydrolysis, i. e., a relative predominance of the synthetic direction of the reaction over the hydrolytic. In the case of spring wheat, the relation is shifted towards hydrolysis. With the vernalization of the seeds of winter plants, the correlation between synthesis and hydrolysis within them changes and approximates to the type that is usual for spring plants, and, as was shown, the change in the enzymatic equilibrium brought about by vernalization is preserved in the plants until vegetation is finished.
Attaching enormous importance to the influence environment exercises upon the course of development of a hybrid seedling and upon the quality, of the strain that is being reared, I. V. Michurin, as is known, regarded the mentor method as the most powerful means of influencing phasically young plants.
The work I conducted in conjunction with B. A. Rubin with the object of ascertaining the biochemical activity of organisms engendered by vegetative hybridization, led to the establishment of certain definite rules.
We endeavoured to ascertain whether the activity of the enzymes of a phasically young scion is affected by its grafting on to the crown of a phasically old tree, i.e., whether this activity is connected with the nature of the mentor. To study this question we, with the kind consent of S. I. Isayev, utilized the results of the experiments that had been conducted by the Plant-Breeding Department of the Michurin Central Research Institute in the town of Michurinsk.
These researches showed that in the majority of cases grafting on to the crown of the mentor causes sharp changes in the activity of the oxidizing enzymes of the grafted phasically young organism, and the direction of these changes are determined by the nature of the mentor. The late varieties of apple trees that were used as mentors, as a rule, caused a higher activity of the peroxidase of the seedling, whereas its grafting on to the crown of an early variety usually led to a lowering of this activity. For example, in the Grushovka/Bellefleur-Kitaika hybrid combination, judging by the peroxidase indices, part of the seedlings turn in the direction of the Bellefleur-Kitaika and part in the direction of the Grushovka. We observed similar changes also in other hybrid combinations.
We saw a similar picture in another series of experiments in which the buds of hybrid seedlings were grafted on to the crowns of mentors. We showed that the late varieties have a more acute peroxidase and a less active invertase. It turned out that the influence of the properties of the mentor causes a reconstruction of the enzymatic system of the buds. The buds of the late varieties show a more active peroxidase and a less active invertase.
Thus, these data fully bear out what I. V. Michurin said about the interrelation between phasically young and phasically old organisms. In causing late-ripening in the seedlings we at the same time increase its enzymatic activity, and vice versa.
Naturally, these interrelations between biochemical characters can exist only if they physiologically condition each other.
That the changes we have revealed are not fortuitous but conform to a regular law and are conditioned by the complex interrelations that arise in hybridization, is proved by the results obtained in the work I conducted in conjunction with I. E. Glushehenko.
We conducted a comparative biochemical investigation of the seed generations of vegetative and sexual hybrids of tomatoes.
Experiments conducted with the seed generation of the vegetative hybrid combinations: Humbert/Golden Queen, Ficarazzi/Golden Queen, Mexican 353/Golden and Planovy/Yellow Pear form, clearly showed that the morphological changes that take place in the seed generation of vegetative hybrids definitely affect the biochemistry of the fruit as well as the biochemical activity of the plant's assimilating apparatus. Often, as a result of vegetative hybridization, new qualities appear that were absent in the initial pair, and useful characters are strengthened. For example, the leaves of F4 of the seed generation of the hybrid combination Humbert/Golden Queen acquire a high capability for the enzymatic synthesis of sucrose, which capability was entirely lacking in the initial forms. In another case, the fruit of the seed generation (F1) of the hybrid combination Humbert/Ficarazzi contain twice the quantity of vitamin C contained in the parental pairs.
Thus, grafting not only mobilizes the potential possibilities of the hybrid pairs, but, and this is particularly important, creates new qualities, it changes the character and type of metabolism.
As a rule, judging by the biochemical activity of the organism, the seed generation of vegetative hybrids displays characters of the component in the direction of which the morphological changes take place.
The F2 and F4 seed generation of the combination Ficarazzi/Golden Queen revealed a resemblance to Golden Queen on the following points: the amount and structure of sugars, the activity of the peroxidase, and the carotinoid content. As regards quantity of ascorbic acid, general acidity and activity of polyphenolase, they reveal the influence of Ficarazzi.
The fruit of the seed generation of the combination Mexican/Golden show two points that are characteristic of the stock: activity of peroxidase and content of ascorbic acid. The other characters, namely, composition of sugars, general acidity, quantity of carotinoids and activity of polyphenoloxidase, reveal the influence of the scion.
Thus, the characters of the generation depend not only on the characters inherent in each of the parents, but also on a definite combination of these characters.
With vegetative hybridization we very often get plants which produce fruits that differ not only in shape, but also in colour. This feature is particularly marked in seed generation. We have investigated the composition of different fruits, the colour of which differed in the same cluster, and we found that the fruits that were varied in colour also differed considerably in chemical composition.
In another series of experiments we examined the biochemical indices of the seed generation of vegetative and sexual hybrids of Golden Queen and Sparks, and Humbert and Ficarazzi.
It was revealed, for example, that in F3 of the vegetative hybrids of Golden Queen/Sparks, activity of peroxidase in the yellow fruit is expressed by the magnitude 16.1, i.e., considerably in excess, of the activity of the enzyme in Golden Queen, and on this point approximate to the Sparks type.
In the yellow fruit of F3 of the sexual hybrid of Golden Queen × Sparks, the activity of peroxidase is equal to 13.6. As you see, the similarity is very close.
The character of the changes in general acidity is approximately the same. Thus, in both vegetative and sexual hybridization the changes in the activity of oxidizing enzymes in yellow fruits shifts sharply in the direction of the Sparks type.
Consequently, in the fruits of the seed generation of both vegetative and sexual hybrids, changes in biochemical characters conform to law and are identical.