The Influence of Duration of Illumination and Spectral Composition of Light on the Regenerative Activity of the Meristem of the Shoot Growing Point

By E. I. Zaar

This article was originally published in Russian in Botanicheskii Zhurnal in 1961. It is presented here as part of the Dahlia Archive, with images of the original article and figures included for reference.

The English translation was prepared with AI assistance and reviewed against the original Russian text. As with any historical translation, especially from a technical article of this period, some wording reflects editorial judgment rather than a one-to-one rendering of Russian syntax.

This article is believed to be in the public domain. It is reproduced here on The Dahlia Archive for historical and educational purposes.

Russian:
 Заар, Э. И. Влияние продолжительности освещения и спектрального состава света на регенеративную активность меристемы точки роста побега. Ботанический журнал, т. 46, № 4, 1961, с. 557–560.

English:
 Zaar, E. I. “The Influence of Duration of Illumination and Spectral Composition of Light on the Regenerative Activity of the Meristem of the Shoot Growing Point.” Botanicheskii Zhurnal, 46(4), 1961, 557–560.

For studying the influence of one or another environmental factor, it is sometimes necessary to have two hereditarily identical organisms, one of which would serve as the control. This requirement can be met by twin plants grown from a single seed by dividing it into halves.

Successful experiments carried out by M. D. Danilov (1930), A. Sereisky (1933), and M. A. Nikonenko (1940) showed that by cutting one seed along the axis of symmetry, it is possible to obtain two plants possessing identical heredity. M. D. Danilov, A. Sereisky, and M. A. Nikonenko conducted experiments with the seeds of plants having well-differentiated growing points, such as oak, soybean, and honey locust, and after the embryos were divided, one growing point formed on each half of the embryo.

Repeating the experiments of these researchers during 1950–1953 in the Botanical Garden of the Botanical Institute of the Academy of Sciences of the USSR, under the direction of G. I. Rodionenko (Rodionenko and Zaar, 1951; Zaar, 1955), we obtained twin plants in 20 species from different families, and on each half of the embryo from one to three growing points arose. In dahlia (Dahlia pinnata Cav.), we succeeded in obtaining four twin plants from one embryo (Fig. 1), and on each fourth part of the embryo up to five growing points formed. The method of cutting dahlia seeds into parts was described in detail earlier (Zaar, 1955).

Fig. 1 Diagram of the formation of four twin plants in dahlia (Dahlia pinnata Cav.).

One week after the seeds were cut, growing points appeared on the surface of the cotyledons. As a rule, one growing point formed on each half of the seed (Fig. 2). When the experiments were repeated, seed halves were found with two growing points (Figs. 3, 4), and in individual cases even with three growing points.

Fig. 2 Photograph of one growing point on half of a sprout.

The preliminary experiments that were conducted showed that under different illumination conditions, the number of seed halves with two and three growing points is not the same.

Having mastered the method of obtaining twin plants, we decided to test the influence of external conditions on the regenerative activity of the meristem. Dahlia (Dahlia pinnata Cav.) was chosen as the experimental plant because it had shown the greatest regenerative capacity.

Fig. 3 Photograph of two growing points on half of a sprout.

The question was posed: what dependence exists between the appearance of double growing points on seed halves and the duration of their illumination? To clarify this question, the following experiment was carried out in two series in March 1957. Illumination and temperature remained the same as in the experiments of 1950–1953, namely: incandescent lamps with a total power of 250 watts served as the light sources; the distance from the light source was 50–55 cm; under illumination the temperature was maintained at 25–27°C, and without illumination at 17–18°C. The experiment was arranged according to the following scheme:

Variant I: 12 hours of light + 12 hours of darkness
Variant II: 16 hours of light + 8 hours of darkness
Variant III: 20 hours of light + 4 hours of darkness
Variant IV: 24 hours of light + 0 hours of darkness
Variant V: 24 hours of darkness

Fig. 4. Photograph of two growing points on half of a sprout.

The temperature in variants IV and V was always maintained the same, 25–27°C.

Each variant contained 150–200 halves of dahlia sprouts. The duration of the experiment was 14 days. At the end of the period, the growing points that had formed on the seed halves were counted.

The percentage of double growing points in variants I and II was, respectively, 27 and 36%; in variant III, with 20 hours of light + 4 hours of darkness, it was 42%. Under round-the-clock illumination, the number of seed halves with two growing points was only 10, corresponding to 5% of the total number of seed halves taking part in the experiment. In variant V, round-the-clock darkness, about 70% of the halves died or had no growing points.

Thus, as the duration of illumination increased, the number of halves with two growing points increased, and the best conditions for this were created by alternating light and darkness in variant III of the experiment, 20 hours of light + 4 hours of darkness.

We may consider the formation of several growing points on half of a seed as a positive response of the meristem to an external influence, in this case to the duration of illumination. The results of the experiment are given in the table.

For the formation of new cells of the primary meristem, an inflow of organic and mineral substances is needed, as well as substances of high physiological activity, such as vitamins. It is evident that under the conditions of our experiment, light had a favorable influence on the synthesis of organic substances in the cotyledons and the movement of these substances toward the growing point.

In recent years, reports have appeared in the literature of a number of facts indicating that the direct products of photosynthesis may be not only carbohydrates, but also proteins. Thus, over a number of years, N. P. Voskresenskaya (Voskresenskaya, 1950, 1951, 1953, 1956; Voskresenskaya and Grishina, 1956; Voskresenskaya and Zak, 1957) conducted studies on the influence of different regions of the solar spectrum on the formation of photosynthetic products and found that in the red rays of the spectrum the synthesis of carbohydrates predominates, while in the blue rays the synthesis of proteins predominates.

Voskresenskaya based her investigations on the works of V. V. Sapozhnikov, who, as early as the end of the last century (1890, 1894), indicated that in the process of photosynthesis the synthesis of carbohydrates and proteins proceeds simultaneously.

The next experimental series was set up by us with the aim of determining what influence the spectral composition of light has on the regenerative capacity of the meristem. To clarify this process, we used filters that transmitted: 1) only short-wavelength blue rays; 2) only long-wavelength red rays; and 3) did not transmit the infrared rays of the spectrum. This second experimental series was carried out in four variants:

Variant I: a water filter consisting of a 1% ammoniacal solution of copper sulfate, CuSO₄, which transmitted only blue rays with wavelengths from 450 to 480 mµ.

Variant II: a water filter prepared from a 2% solution of K₂Cr₂O₇, which transmitted only the long-wavelength rays of the spectrum from 650 to 700 mµ.

Variant III: a glass filter transmitting the entire visible part of the spectrum but not transmitting infrared rays.

Variant IV: the control, in which the entire visible part of the spectrum plus infrared rays was transmitted.

In all variants, 16 hours of illumination and 8 hours of darkness were given. The temperature in variants I, II, and IV, when illumination was switched on, was 25–27°C; when illumination was switched off, it did not fall below 17–18°C. In variant III, the temperature was constantly maintained at 17–18°C. Each variant contained 100–180 halves.

The experiment was conducted in crystallizing dishes. A second crystallizing dish with a solution that transmitted rays of either the long-wavelength or short-wavelength part of the spectrum was placed above the experimental dish. To protect the experimental halves from stray light, a screen was used consisting of two layers of paper: an outer black layer, photographic paper, and an inner white layer. The halves of sprouts in variants I and II received the same quantity of energy; for this purpose, the energy equalization of the water filters was checked. The thickness of the water filter in variant I was 6 mm, and in variant II, 10 mm.

On the 13th or 14th day, the growing points formed on the halves of dahlia seeds were counted. The results of the experiment are given in the same table.

The experiment shows that in the formation of the growing point, the main role is played by the long-wavelength part of the spectrum, 650–750 mµ, where, according to modern data, the synthesis of carbohydrates predominates over proteins, variant II. The absence of the infrared part of the light spectrum in the experiment led to the dahlia sprout halves not forming double growing points, variant III. Consequently, for the active functioning of meristematic tissues, both the red and infrared parts of the spectrum are necessary.

The short-wavelength part of the spectrum within the range of 450–480 mµ, the blue rays, not only did not activate the activity of the meristem but, on the contrary, led to the death of the halves. Apparently, in this part of the spectrum, metabolism proceeds in such a distinctive way that it does not support the maintenance of normal life processes in the sprouts. Only in the presence of the long-wavelength part of the spectrum can two or three growing points be obtained on the halves of sprouts.

The general conclusion from the results obtained is as follows: the regenerative capacity of the meristem depends both on the duration of illumination and on the spectral composition of light. The greatest number of sprout halves with two growing points is formed under prolonged illumination, on the order of 20 hours.

I express my deep gratitude for consultation during the work to Associate Professor M. S. Miller of the Department of Botany of the Leningrad State Pedagogical Institute named after A. I. Herzen, and to L. B. Krasilnikov, Candidate of Physical and Mathematical Sciences and staff member of the State Geophysical Observatory, for assistance in checking the spectral characteristics and in the energy equalization of the water filters.

Voskresenskaya, N. P. (1950). On the influence of the wavelength of light on the formation of carbohydrates and proteins in the leaf. Doklady Akademii Nauk SSSR, 72(1).

Voskresenskaya, N. P. (1951). On nitrate reduction in leaves under different illumination conditions. Doklady Akademii Nauk SSSR, 79(1).

Voskresenskaya, N. P. (1953). The significance of the spectral composition of light for the photosynthetic formation of substances. Doklady Akademii Nauk SSSR, 93(5).

Voskresenskaya, N. P. (1956). On the formation of organic acids and amino acids during photosynthesis under different illumination conditions. Fiziologiya Rastenii, 3(1).

Voskresenskaya, N. P., & Grishina, G. S. (1956). On the question of the utilization of C¹⁴O₂ by plants under different illumination conditions. Doklady Akademii Nauk SSSR, 106(3).

Voskresenskaya, N. P., & Zak, E. G. (1957). On the absorption of oxygen by plant leaves in different regions of the spectrum. Doklady Akademii Nauk SSSR, 114(2).

Danilov, M. D. (1930). Experiments with the germination of acorns. Izvestiya Kazanskogo Instituta Selskogo Khozyaystva i Lesovodstva, 1.

Zaar, E. I. (1955). Obtaining twin plants from various seeds. Trudy Botanicheskogo Instituta Akademii Nauk SSSR, Series VI, issue IV.

Nikonenko, M. A. (1940). Twin plants. Yarovizatsiya, 6.

Rodionenko, G. I., & Zaar, E. I. (1951). Obtaining twin plants in dahlias. Priroda, 5.

Sapozhnikov, V. V. (1890). Formation of carbohydrates in leaves and their movement through the plant.

Sapozhnikov, V. V. (1894). Proteins and carbohydrates of green leaves as products of assimilation.

Sereisky, A. (1933). Physiological-morphological and ecological observations on germinating soybean seeds. Botanicheskii Zhurnal, 1–2.

In Zaar’s 1961 bibliography (above), his 1955 paper is cited in abbreviated form as “Получение растений-близнецов из различных семян” (“Obtaining twin plants from various seeds”), Trudy Botanicheskogo Instituta AN SSSR, Series VI, issue IV.

A fuller bibliographic entry located in Letopis’ zhurnal’nykh statei gives the title as “Выращивание растений-близнецов из разрезанных семян” (“Growing twin plants from cut seeds”), Trudy Botanicheskogo Instituta im. V. L. Komarova, Series 6, issue 4, 1955, pp. 317–327.

For researchers who later use this bibliography to search for copies of these publications, I would search using the Russian titles, not the English translations. The most useful terms are:

Воскресенская Н. П. длины волны света углеводов белков листе 1950

Воскресенская Н. П. восстановлении нитратов листьях освещения 1951

Воскресенская Н. П. спектрального состава света фотосинтетического образования веществ 1953

Воскресенская Н. П. органических кислот аминокислот фотосинтезе 1956

Воскресенская Гришина C14O2 1956

Воскресенская Зак поглощении кислорода листьями спектра 1957