The purpose in writing on this subject is twofold. First, it is intended to bring to the attention of the scientific community the very real possibility of the stimulating effect of Stearic Acid on plants.
Secondly, publication of these results should make them available hibiscus powderfor further evaluation of the potential benefit of using this material in plant growth stimulation.
Stearic Acid is one of a group of long-chain fatty acids occurring in the cells of plants and animals. It occurs very extensively in nature, most often being incorporated into triglycerides.
It is a solid, a white amorphous powder. Other physical properties include a molecular weight of 248.47; density 0.747 gms./ml.; melting point 393 degrees Centigrade, and solubility 0.034 gms. in 100 ml. of water.
It is known to have surfactant properties, being only slightly soluble in polar and non-polar solvents. Because of its' surfactant properties, it has been used extensively in the manufacture of soaps and detergents. It is also known to promote the growth of some soil organisms, such as bacteria.
This report describes the results obtained on five different varieties of vegetable plants and one flowering plant, to illustrate the possible general effectiveness of plant growth stimulation.
Other types of plants affected have also been observed to grow at a faster rate after treatment with Stearic Acid.
These affected plants include the following: a Pereskia cactus ("lemon vine") had grown very slowly for three months. After treatment, it grew to over fifteen feet in length, over a five-month period. A Swedish Ivy plant, two years old, had leaves on new growth twice as large as older leaves, starting two months after beginning treatment.
Finally, six months after treatment, a Hibiscus plant, which was a cutting from another plant, had grown larger than its' untreated parent.
Tomatoes and other vegetables (radish, broccoli, cabbage), and cactus plants were also observed to be stimulated to an increased rate of growth by using Stearic Acid alone, leading to this claim of it being a general plant stimulating agent.
Test results on beans, squash, carrots, red beets, corn and marigold are reported here. Only Stearic Acid powder was used to treat plants. Control plants were untreated. No additional watering was used in an outdoor garden. Only the normal amount of rainfall reached the plants.
The method used was to place about two grams of Stearic Acid powder under the soil, close to the plant, when the plants were from two to three weeks old, and had developed true leaves. It has been found that this is a necessary procedure, because when seeds were planted in soil that had already been treated with Stearic Acid, a reduction in the number of seeds germinating was observed.
In a separate experiment, when pea seeds were placed in water containing some Stearic Acid, the seeds swelled and burst within three or four days; resulting in a white, gelatinous mass. Treating seeds with Stearic Acid, then, seems to adversely affect the rate of germination of seeds.
The somewhat reduced amount of germination that has been observed, plus the definite slower growth rate of most treated seedlings, confirm the necessity of adding Stearic Acid after the plants have advanced past the seedling stage, in order to obtain the maximum benefit from this method of treatment.
SUMMARY OF RESULTS
The yield of bean plants treated with Stearic Acid was nearly twice the amount in terms of the number and weight of pods per plant, when compared to untreated plants. Fifteen plants both control and treated were tested. Average number of pods/plant was 14, for control plants and 25 pods/plant for treated plants.
For carrots, a 30% increase in average weight of root was obtained; which was the lowest increase in yield obtained in this test. Twenty plants were tested, both controls and treated plants. An average weight of controls was 31 grams, and for treated plants, an average weight of 40 grams was obtained.
Red beets showed a 60% greater weight for treated plants, when compared with controls. Eleven control plants and eleven treated plants were tested. The average weight of control plants was 168 grams, while the average weight of treated plants was 385 grams.
Squash plants were stimulated to produce fruit which was twice as large for treated plants when compared to controls. Twelve plants were tested, both controls and treated plants. The average weight of control plants was 1.5 lbs., while the weight of fruit from treated plants was 3.0 lbs.
Treated Marigold plants were twice as large and had twice the number of flowers, when compared to control plants. The average height of twelve control was 6 inches. The height of treated plants was 12 inches.
The control plants had an average of 10 flowers, while treated plants had an average of 20 flowers.
Corn gave much different results, yielding even less average weight per ear for treated plants, as compared to controls. Since only 2 or 3 ears per plant was obtained, the largest ear from each plant was weighed. Twelve plants were measured. The average weight of ears from controls was 162 grams, while the average weight of ears from treated plants was 144 grams. The conclusion reached was that no effect of Stearic Acid on corn was observed.
As previously indicated, subsequent tests confirmed that the most suitable time of application was about one week after germination; for bean plants past the seedling stage.
During the course of still other tests, it was found that some of the same varieties of plants that were stimulated, were inhibited in growth if an excess amount of Stearic Acid was used (radish, red beets and cabbage). This effect occurred when an excess amount of powder material was place in the soil around potted plants in a greenhouse.
Consequently, this method of treatment is not recommended for houseplants, or other potted plants. Watering with a saturated solution of Stearic Acid may be more beneficial in this case.
Similarly, it is speculated that a build-up of this material in outdoor areas used for commercial crops could occur after years of use, resulting in poor seed germination, and loss of plant vigor. So, an evaluation of a spray program during the growing season might give better results; along with requiring less material, and less expense as a result.
This procedure is also suggested due to the possibility of the formation of metal salts of this compound by chemical fertilizers or enriched soils. This occurrence might then interfere with the expected beneficial effects of free Stearic Acid.
A PROPOSED MECHANISM OF ACTION OF STEARIC ACID ON PLANTS
Since only the amount of Stearic Acid dissolved in water is taken up by the plant, the amount utilized by the plants must be very small. The solubility of Stearic Acid in water (0.034grams/100 ml. of water), indicates that only a small amount would be provided to the plant to exert a stimulating effect.
This suggests it is possible that this material may be a plant hormone. Since hormones are known to stimulate enzymes, determining which enzyme system might be affected would be desirable.
The plants shown to be stimulated in this report (beans, red beets for example), are known as C-3 type plants; while corn, which was not stimulated in these tests, is known as a C-4 type plant. The mechanism of action of Stearic Acid, then, might be in its effect on one of the different metabolic pathways that distinguish these two types of plants.
C-3 type plants are those which operate by the Calvin Cycle of photosynthetic reactions, while C-4 type plants are those which have different intermediates in the cycle of photosynthetic reactions. C-3 plants utilize 3-phospho-glyceric acid as the product of carbon dioxide fixation.
C-4 plants utilize Malic, Aspartic and Oxaloacetic acid as the products of carbon dioxide fixation. These two systems also utilize different enzymes to produce these acids.
The mechanism of stimulation in an enzyme system by Stearic Acid, then, is proposed to be in the Calvin Cycle of photosynthetic reactions. Specifically, the rate-limiting step of carbon dioxide fixation, in which ribulose 1, 5 diphosphate is converted into 3 phosphoglyceric acid; a reaction catalyzed by reibulose 3, 5 biphosphate carboxylase, is proposed to be the affected system.
A further consideration might be to try to determine why so much of this enzyme is present in leaf tissue(40% of the dry weight.) Generally, enzymes are present only in small quantities, being limited in activity by the amount of substrate available.
The amount of substrate carbon dioxide seems to be a major limiting factor in the activity of this enzyme. This might suggest a reason for the large amount of enzyme present - to insure that all of the available carbon dioxide is readily used by the plant. Another possibility may be that early in the history of plant evolution, there was probably a quite different atmosphere, with an abundance of carbon dioxide, which would have been more readily used by plants with an abundance of the enzyme.
So, it would seem that to more effectively increase the growth rate of plants, carbon dioxide and Stearic Acid, used together, would be an even more advantageous method of treatment. Of course, the enclosed area of a greenhouse would likely be needed in order to retain excess carbon dioxide released into the atmosphere.