Studies on a Growth Inhibitor in Guayule

Citation

Gottlieb, Sidney (1943) Studies on a Growth Inhibitor in Guayule. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/TBXH-5W50. https://resolver.caltech.edu/CaltechTHESIS:01242017-111743193

Abstract

1. Evidence is presented to show that when guayule plants (6 months to 2 years of age) are grown in gravel culture, an influence is exerted which is inhibitory to the growth of guayule seedlings.

2. The development of two types of semi-quantitative assay for the detection of the inhibiting principle is described.

3. A method is described for the collection of large quantities of nutrient solution containing the inhibiting principle, and for the subsequent concentration of this material to small volume. It is pointed out that the production of the inhibiting principle decreases sharply during the winter months.

4. Evidence is presented to show that the inhibiting principle is an organic substance. The critical evidence consists of the disappearance of activity on ashing and of the extractability of the inhibitor by organic solvents.

5. It is estimated that a guayule plant (6 months to 2 years of age), growing in gravel culture gives up to the nutrient medium, on the average, a minimum of 200 gammas per day of organic matter.

6. Various chemical properties of the inhibitor are given. It is shown to be relatively stable to heat, stable to drying, non-volatile, non-adsorbable by charcoal, and probably non-precipitable by lead.

7. An experiment is described in which a crude crystalline material was obtained which was very active.

8. Evidence is presented to show that the effect of the inhibitor is not due to an influence on the pH of the nutrient solution.

9. The occurance of growth stimulatory organic substances in the guayule leachate is described. These stimulatory fractions were active at concentrations as low as 2 mg. per liter.

10. A number of pure synthetic organic acids were tested for inhibitory activity, of these only one, cis-9,10 dihydroxy stearic acid was found to be active. This compound caused marked inhibition in concentrations as low as 3.5 mg. per liter.

11. The chemical fractionation of a soil on which guayule plants had grown is described and it is shown to contain inhibitory organic substances having some chemical properties similar to those of the substances in the guayule leachates.

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