Showing papers by "Kenneth V. Thimann published in 1941"

On the relation between growth and respiration in the avena coleoptile

Abstract: 1. The growth of Avena coleoptile sections in sucrose and auxin solutions is inhibited by various substances which are known to act as dehydrogenase inhibitors. 2. Iodoacetate, which is particularly active in this connection, inhibits all growth at a concentration of 5 x 10–5 M, but produces only a slight inhibition of oxygen uptake. 3. The growth inhibition by iodoacetate is completely removed by malate and fumarate, and to a lesser extent by succinate and pyruvate. 4. These acids themselves increase the effect of auxin on growth and also increase the respiration of the coleoptile sections, but only if auxin is present. 5. When sections have been soaked in malate or fumarate, the addition of auxin considerably increases the total respiration. Further, the concentration range over which this increase takes place parallels that active in promoting growth. 6. The four-carbon acids provide a respiratory system which is part of the chain of growth processes, and which is in some way catalyzed by auxin. It represents a small but variable fraction of the total respiration.

Factors affecting root formation of phaseolus vulgaris.

Abstract: The successful rooting of leafy cuttings involves three physiologically distinct processes: initiation of root primordia; development of true roots from these initials; and maintenance of the cutting as an excised organ during the rooting. The first of these, where it does not take place spontaneously, can be brought about in many plants by treatment with auxin. The second (outgrowth of the roots) involves the formation of cell-wall and protoplasm; it therefore requires the supply of carbohydrates and nitrogenous materials, together with such special substances as may be needed for root growth. Normally all of these materials would be supplied from the leaves or from storage in the stem. Too little attention has been paid up to now to the third process, the maintenance of the cutting, which, in view of the special conditions that obtain when leaves are severed from the plant, is of great importance. Thus, as pointed out by Chibnall (4), the detached leaf of many plants, including Phaseolus, undergoes a rapid and extensive proteolysis. The present experiments were, therefore, designed to shed some light on the second and third of these processes. It was our intention to study the influence of nutrition, especially nitrogen nutrition, and other external chemical factors on the rooting and maintenance of leafy herbaceous material. Since internal factors must also be considered in such a study, attention was paid to the r?le of auxin and also to the separate r?les of the leaves and the stem.