Showing papers by "Kenneth V. Thimann published in 1962"

Some Characteristics of Movement of Indoleacetic Acid in Coleoptiles of Avena. I. Uptake, Destruction, Immobilization, & Distribution of IAA During Basipetal Translocation.

Abstract: Indoleacetic acid (IAA) appears to be the major naturally occurring auxin controlling normal vegetative growth of a wide variety of higher plants. In many plants the auxin of the shoot is produced at or near the apex (8, 12, 32) and must be translocated from the site of production to the many sites where it influences growth and differentiation in the shoot. The translocation of auxin, like that of other organic molecules, can not be attributed to diffusion or purely physical processes; it requires the presence of living cells (28, 29, 23). The movement of auxin differs from the translocation of other organic substances in that it occurs predominantly from the apex toward the base of the shoot. This is not just-a reflection of auxin production at the apex. In Avena coleoptiles, Went showed that even when auxin is supplied at the base of a section it can not be collected at the apex (31). Since the initial work of Went (31) and van der Weij (28, 29), information has been obtained on the ability of plant tissues to translocate natural auxins (13) and on the inhibition of translocation by various substances (e.g. 5,16,17, 18). These studies, however, have been limited by the sensitivity and adaptability of some bioassay for detecting the auxin. Conclusions had to be drawn from the amount of auxin activity appearing at the opposite end of a section from a source of IAA. This experimental system is a complex one, and one would like to know how the uptake from the source, the destruction, and the retention of auxin within the tissue itself influence the amount of auxin recovered at the base of a section. Only with the advent of radioactively labeled IAA has this type of quantitative study become feasible. The information presented here on the normal basipetal transport of IAA by excised sections provides a basis for further studies. For example, the effect of altered oxygen tensions and the characteristics of an acropetal, apolar movement have already been examined and will be described in subsequent papers.

The effects of auxins and kinetin on xylem differentiation in the pea epicotyl

Abstract: growth of this callus causes a characteristic split at the base of the internode. Treatment with kinetin, alone or in combination with the auxin, changes the above structure markedly. It leads to the initiation, over the entire circumference of the core of the internode, of a still more active cambium, which forms several layers of secondary xylem; this consists mainly of long vessel members with pitted walls. Hyperplastic growth is completely absent, and the xylem does not become occluded. Thus the effect of kinetin is to make the xylem more normal and to alter the epicotyl structure from herbaceous to more-or-less woody. THE INITIAL purpose of this investigation was to study the effects of auxins and kinetin on the development of the transport system in the stem and bud of the pea plant during the inhibition of lateral bud development. As the work developed, however, it became clear that the changes in the internode are much more extensive than had been expected, and that they required detailed study before changes in the other parts could be interpreted. This paper, therefore, describes some of the histological changes which occur in excised, etiolated sections of the Pisum epicotyl after treatment with 2,4-dichlorophenoxyacetic acid or indoleacetic acid,2 with and without kinetin, and also after growing decapitated plants on intact roots in 2, 4-D solutions. Attention is devoted here to the internode, and a description of the changes in the node and bud will be given in another paper. There are many earlier studies of the anatomy of stems in relation to treatment with auxins,

Growth-promoting Activity of Caffeic Acid

Abstract: Vendrig and Buffel have recently stated1 that trans-caffeic acid “may be a very important natural growth regulator, not less important than indole-3-acetic acid”. This conclusion was based on the identification of caffeic acid as one of the active growth substances in an ether extract of leaves, and on growth tests with commercial caffeic acid on 2-mm. sections of Avena coleop tiles. We believe that the true explanation of these observations is quite different. In what follows, a good crystalline sample of commercial caffeic acid, m.p. 188°–190°, was used.