Effects of Indoleacetic Acid Upon Growth and Respiration of Kidney Bean

Abstract

1. Study was made of the effects upon respiration and growth following unilateral application of IAA in lanolin on or directly below the arch (on the convex side) of young seedlings of Phaseolus vulgaris var. Red Kidney. Both green and etiolated plants were used. 2. IAA incorporated into lanolin with ether was almost ten times as effective in eliciting response as that mixed into lanolin by stirring only. 3. Slices and unsliced pieces of hypocotyl and epicotyl gave comparable results in the measurement of oxygen uptake. 4. The rate of respiration of untreated hypocotyls, though initially high, fell rapidly with time; however, treatment with IAA prolonged the high initial rate of respiration. The respiratory quotient of untreated hypocotyls, though initially below 1, rose rapidly to 1; however, treatment with IAA delayed this rise. These results corroborate the previously reported histological evidence of a delay in maturation resulting from IAA treatment. 5. The rate of anaerobic respiration of treated hypocotyls was higher than that of untreated; however, the ethyl alcohol produced accounted for 92%-95% of the carbon dioxide released by both treated and untreated hypocotyls. 6 Respiration and growth of epicotyl and upper hypocotyl were initially inhibited by treatment. Later these returned to about the same rates found in untreated parts of the same age. Two possible explanations of this response are proposed. 7. The effects of treatment upon the lower hypocotyl were inhibition of elongation; more rapid increase in diameter, volume, dry weight, and fresh weight; and reduction in the rate of fall of the respiratory rate. The high rate of respiration of the treated lower hypocotyl was correlated more nearly with the rapid dry-weight increase than with the slower fresh-weight or volume increases. 8. Oxidation of IAA in the hypocotyl cannot account for the effects upon respiration. 9. The effect of treatment upon the respiration of the hypocotyl was detectable within 1 hour. 10. Treatment produced no significant effects on either the cotyledons or the roots. 11. The increased rate of respiration of some parts of the treated plants was counterbalanced by decreases in other parts with the result that the respiration of the plant considered as a whole was not affected by treatment with IAA. 12. Though producing an effect upon the rate of respiration, 0.001% IAA had little effect upon growth. 13. A concentration of 10-3 M IAA in water inhibited the respiration of hypocotyl slices. Lower concentrations produced no significant effects. 14. Juice from untreated and treated hypocotyls added as substrate to hypocotyl slices produced the same effects of initial increase in the rate of respiration followed by a decrease to or below the rate for untreated slices. 15. Similarities and differences in the responses of etiolated plants to treatment of the first internodes and of the hypocotyls are noted and discussed. 16. The possible courses and ultimate dispositions of IAA applied in lanolin paste to the intact hypocotyl are discussed.