1939: Biology

Chemicals and Hormones in Plant-Growth.

In the field of plant biology, just as in the field of animal biology, the chemical messengers or hormones have caused new and stimulated interest the past year. Pollen grains were made to germinate faster and larger if they were treated with a growth hormone. Dr. P. F. Smith of the University of Oklahoma has treated these pollen grains with indole-3-acetic acid and has not only cut the germinating time 50 per cent in some three or four species, but has also succeeded in increasing the percentage of germination in at least one species. These results may have their practical value in plant breeding and greenhouse horticulture.

Iodine has long been known to be essential for the normal health and growth of animals, including humans. Now, Dr. W. L. Powers of Oregon State College reports that iodine may prove as essential for plant life. In his carefully controlled experiments he has shown that the amount of iodine needed is only about one part to two to four million parts of water. He suggests that iodine may be necessary for chlorophyll formation. However, he finds that lower forms without chlorophyll, such as the yeasts and also the nitrogen-fixing bacteria of the root nodule, also seem to thrive better with the addition of iodine to the media.

Dr. R. W. Oliver of the Ottawa Central Experimental Farm has carried on some interesting experiments to show that honey is a better growth hormone than some of the commercial phytohormone preparations. The most extensive tests were made on varieties of the chrysanthemum. In addition, he found that evergreen cuttings would also respond to the solution of one part honey and three parts water. It is suggested that some chemical in the honey is responsible for this growth stimulus.

Dr. E. D. McAlister, a biophysicist at the Smithsonian Institution has discovered a chemical which acts as an intermediary for carbon dioxide and chlorophyll. While Dr. McAlister was testing the carbon dioxide utilization of plant seedlings, he found the plants to be using carbon dioxide for a short time after they had been placed in complete darkness. This seemed to be contrary to the established idea of photosynthesis. Hence, Dr. McAlister began a search and demonstrated a chemical which acts as the intermediate substance and seizes the carbon dioxide molecule and delivers it to the green coloring matter or chlorophyll of the plant.

A Chinese biologist, Mr. Cheong-yin Wong, while working at Michigan State College, has shown that by the treatment of the ovaries of unpollinated flowers of some plants with the growth hormone, naphthalene acetic acid, seedless fruits could be produced. Seedless watermelons, cucumbers and green peppers were produced by the above method. Mr. Wong reports that these fruits appeared to be normal in respect to flavor and texture when compared to the seeded varieties.

Dr. F. E. Meier of the Smithsonian Institution has shown that ultra-violet radiation, which is known to be deadly to some cells, is also a stimulant to growth in the same type of cells if the radiation is administered in doses of less than the lethal magnitude. Dr. Meier used cultures of the species of unicellular algae or water plant. The interesting phase of this experiment seemed to be that stimulative influence of radiation was not only present in the treated generation but that the accelerated proliferation was carried over into succeeding generations without the successive generations having been so treated directly.

Experiments in Genetics.

Interesting studies on chromosomes and other structures of importance in the field of genetics have continued. Dr. J. O. Beasley, of the Bureau of Plant Industry, has shown that the drug colchicine when applied to young plants, brings about a doubling of chromosomes in the cells and hence the new plant which is created will breed true and not be sterile as most hybrids are. Dr. Beasley's experiments were carried out with hybrids of several varieties of the cotton plant. Other workers are carrying on similar experiments with this drug on other plants such as tobacco and also with berries and fruit trees.

Another series of experiments, somewhat related to the above have been carried on by Dr. D. Kostoff of the Institute of Genetics in Moscow. Dr. Kostoff has used a fungicide, distributed under the trade name 'Granosan' for doubling the chromosome number in plant cells. He states that this substance has the advantage over colchicine in that seeds treated with it are not subject to fungi infections, whereas the colchicine treated ones may be thus attacked.

Parasites as Purveyors of Nitrogen.

Rust jungi, probably the worst parasitic enemies of wheat and other grains, may possibly be shown to be also beneficial to their host plants. Dr. Branquinho d'Oliveira, of the National Agronomic Station at Lisbon, grew seedlings of wheat on media from which all nitrogen had been eliminated. He then inoculated a portion of this series with spores of various species of rust fungi. An analysis of the plants at a later time showed that those receiving the inoculation had a higher nitrogen content than the control series. These experiments suggest that rust fungi may be able to take nitrogen from the air and fix it just as do some root nodule bacteria in the pea and clover plant family.

Cellular Differentiation.

In the field of embryology an interesting series of experiments on plant tissue have been carried out during 1939. Dr. P. H. White, of the Rockefeller Institute for Medical Research, Princeton, N. J., has developed a technique whereby he can grow plant cells in culture media, and while growth of these cells will continue indefinitely, no apparent differentiation occurs unless the growth conditions are altered. In his experiments, Dr. White has removed unspecialized cells from a wound area of plants such as the tobacco and tomato. He places these unspecialized cells on a culture medium having the necessary mineral salts, carbohydrates, vitamins and hormones, and allows them to grow. Dr. White has been able to keep these cells growing continuously as undifferentiated cells for several years on the culture media used. However, when the unspecialized cells are placed in a nutrient solution instead of a more viscid medium they sink to the bottom and then they differentiate into stems, leaves, roots and so forth. Just why cellular differentiation can be induced by this method is still unanswered.

Vitamins and Other Chemicals in Plant Growth.

In the field of vitamin research, investigations are being continued and new vitamins are being added to the present alphabet. At the same time the chemical structures and the synthesis of old vitamins are being completed. A school of investigators at Harvard University and St. Louis University Medical School, working independently, have recently arrived at the same structural formula for vitamin K. This vitamin has been shown to play an essential rôle in the coagulation of blood. While the investigations leading to the discovery of a blood coagulating substance such as vitamin K have been of extreme importance, the discovery of a chemical in the human body which prevents the coagulation of blood may some day be of equal importance. This new chemical known as aspartic acid has been described by Doctors I. J. Greenblott and M. X. Sullivan of Georgetown University. It is an amino-acid found in both plant and animal tissues. This chemical which is present normally in food and liberated therefrom by the process of digestion may be the anti-coagulant of blood which acts as the weapon against thrombosis. While work on this chemical is only in its initial stages, it is possible to visualize the use of the chemical, after its chemical structure becomes known, as a substitute for sodium citrate and other chemicals now used as anti-coagulants in blood collections outside of the body.

Important investigations on vitamin B have been reported by Dr. R. J. Williams of the University of Oregon. He found that this vitamin stimulated the growth of yeast. Since its discovery this vitamin has been shown to function as a stimulating substance important in the growth of a number of living things from bacteria, fungi, plants and lower and higher animal life. For this reason it is called the universal vitamin or pantothenic acid.

Another substance, given the name coenzyme R has recently been discovered by Doctors F. E. Allison and F. W. Minor of the U. S. Department of Agriculture. This substance is thought to be indispensable for the growth of nitrogen-fixing bacteria which inhabit the roots of clover and related plants. Another nitrogen-fixing bacterium which lives free in the soil instead of the roots proper, has been found to require small traces of a metal called molybdenum. This metal has long been found to be useful in the steel and metal industries but Doctors D. Burk and K. Horner were the first investigators to find it to be necessary for the growth of plants.

From this brief résumé on recent researches on biology it can be seen that the smallest plants, just as the largest animals, require vitamins, hormones and other substances for their successful development, growth and reproduction. Furthermore, it has been shown in a number of instances that the nature of these essential substances are identical in plant and animals. See also HORTICULTURE; ROCKEFELLER FOUNDATION; ZOOLOGY.