Growth and Metabolism of Bean Cuttings Subsequent to Rooting with Indoleacetic Acid

1. Cuttings of kidney bean seedlings were treated by immersing their bases in water, 0.002 per cent, or 0.01 per cent indoleacetic acid for 3 hours. They were then set in quartz sand contained in 4 inch clay pots. The pots were systematically distributed on each of two greenhouse benches which were then inclosed by glass to maintain a relatively high humidity. Cuttings were harvested 5 days after treatment and every second day thereafter until 15 days had elapsed. Each sample was divided into roots, hypocotyls, first internodes, primary leaves and petioles, and tips. Fresh weight, dry weight, total and insoluble nitrogen, reducing sugars, and sucrose were determined for each sample. 2. Treatment with 0.01 per cent indoleacetic acid significantly increased the weight of the hypocotyls and roots over the corresponding portions of the controls until the thirteenth day after treatment. The same treatment significantly decreased the growth of the first internode throughout the course of the experiment and also the growth of the tips, and the difference became statistically significant on the ninth day and remained approximately constant through the rest of the experiment. Treatment with even a strong solution (0.01 per cent) of acid did not appreciably affect the dry weight of the primary leaves. Weak treatment (0.002 per cent) caused slight growth responses that were qualitatively like the strong treatment but statistically insignificantly different from the controls. Neither the weak nor the strong treatment increased the weight of the whole plant above that of the control. 3. During the rooting process nitrogen was transported from the leaves to the first internodes and hypocotyls, the strong treatment being by far the most effective in increasing the amount mobilized. This nitrogen was subsequently translocated to other portions of the cuttings. In the case of cuttings treated with 0.01 per cent acid, a large amount of this mobilized nitrogen was temporarily deposited in the hypocotyls in an insoluble form, but it was subsequently translocated to other portions of the cuttings. Since all of this accumulated nitrogen subsequently disappeared, it is evident that the treatment stimulated the proteolytic enzymatic activity of the cuttings. 4. Application of nutrient solution after the cuttings were rooted increased their nitrogen content by about 35 per cent. The larger number of roots induced as a result of treatment resulted in the uptake of only a slightly greater amount of nitrogen and inorganic substances than were absorbed by the controls. 5. The treatment of cuttings with 0.002 per cent acid resulted in slightly greater accumulation of sugars than in the controls at the end of the experiment. Treatment with 0.01 per cent acid significantly reduced the sugar content of cuttings below that of controls at all times. No starch was present at any time in the roots, leaves, or tips, and only traces in the hypocotyls and first internodes. Interpretation of the carbohydrate metabolism in relation to growth requires further information as to the effect of the acid on the rates of photosynthesis, respiration, and enzymatic activity.