The action of the plant growth hormone

Although the control of cell elongation in plant tissues by a special growth-promoting substance or substances has been well established for some time, the processes by which this substance is able to bring about growth have remained obscure. Since the general properties of the response to growth substance by plant tissues, in particular of the Arena coleoptiles which have been most extensively studied, have been recently summarized by Thimann and Bonner (1933), only the principal points of interest for the present discussion need be given. These are briefly as follows: (a) The growth-promoting substance of the Avena coleoptile is produced only in the coleoptile tip and passes from there downward (Went, 1928). After removal of the tip new growth substance is formed by the uppermost cells of the stump ("physiological regeneration," Dolk, 1926). (b) The growth of the Avena coleoptile is for some time proportional to the amount of growth substance supplied to it (Thimann and Bonner, 1933). (c) The growth substance which enters the plant and causes growth cannot be recovered; i.e., is used up (Went, 1928). (d) Growth substance is an unsaturated acid of empirical formula C18H32O5 (Kögl, Haagen-Smit and Erxleben, 1933) and readily loses its growth-promoting activity by oxidation. (e) The growth substance is a true hormone, i.e., it acts in minute amounts and bears no direct stoichiometrical relationship to the number of molecules of soluble substance transformed during growth into, for example, cell walls. Thus one molecule of growth substance causes an amount of growth of the Avena coleoptile at 27°C. which requires the changing of 3 X 10^5 molecules of hexose to cellulose in cell walls (Thimann and Bonner, 1933). The changes in the physical properties of coleoptiles under the influence of growth substance have been studied to some extent. Heyn (1931), and independently, Söding (1931, 1932) have shown that the plasticity, and also to a considerable extent the elasticity, of the coleoptile is increased after action of growth substance, and that this increase is independent of whether growth has occurred or not; i.e., this action of growth substance is preliminary to active elongation. Heyn also found an increase in extensibility in coleoptiles which had been plasmolyzed after growth substance action, so that it is the physical properties of the cell wall, and not of the protoplasm, which are changed. The action of growth substance has now been further studied, and a few of the results will be described in the present paper. This study has been made easier by discovery of the fact that short sections of coleoptiles grow at a rapid rate if immersed in a growth substance solution of suitable concentration. This method of using coleoptiles is convenient because, under proper conditions, a large amount of growth takes place in a relatively short time, and the "physiological regeneration" mentioned in (a) occurs slightly or not at all. It has the added advantage that the effect of known concentrations of growth substance upon the growth of younger and older portions of the same coleoptile may be examined independently

The growth and respiration of the Avena coleoptile

In a previous paper (1) a relation was shown to exist between the respiration of the plant cell and its elongation under the influence of the plant growth hormone. A more extensive investigation of this relation was therefore undertaken with the hope that elongation would exhibit a close correlation with some relatively accessible property of the respiration, for example with the magnitude or the respiratory quotient of the latter. It may be said at once, however, that this was not the case, and that the work reported in the present paper, while revealing several points of interest and defining more clearly the dependence of elongation upon respiration, has not resulted in any explanation of the way in which respiration is essential to growth

A reversible growth inhibition of isolated tomato roots

Introduction. - It is known that certain bacteria are inhibited in their growth by the presence of sulfanilamide or related compounds in the nutrient medium, and it has been suggested by Fildes(1) and by Woods(2) that this inhibition is due to specific interference with the utilization of essential metabolites, in particular p-amino benzoic acid. In the present paper data will be presented which show that the growth of isolated tomato roots(3) is inhibited in the presence of appropriate concentrations of sulfanilamide or its derivatives, but that this growth inhibition can be in whole or in part abolished by the further presence of p-amino benzoic acid, a substance not otherwise essential as a supplement for the growth of isolated tomato roots

Plant tissue cultures from a hormone point of view

A botanist, Haberlandt,(1) first pointed out the possibilities of the culture of isolated tissues. He suggested that not only could the potentialities of individual cells be determined, but that also some insight might be gained as to the reciprocal influences of tissues upon one another, that is, as to "correlation.

The wound hormones of plants. I. Traumatin, the active principle of the bean test

An attempt has been made in the present investigation to work out a specific test for wound hormone activity, and to use this test in the purification of the active principle of plant tissue extracts. In this way we have isolated a substance, possessing high wound hormone activity, for which we propose the name “traumatin.” This name seems particularly appropriate in view of the historical background of the subject

The growth of plant embryos in vitro. Preliminary experiments on the role of accessory substances

The aseptic culture of plant embryos isolated from the seed dates back to the work of Brown and Morris,(1) Hannig(2) and Dietrich.(3) More recent contributions to our knowledge concerning the culture in vitro of excised embryos have been made by Tukey,(4) Brunner(5) and LaRue,(6) among others. It has been recognized by, for example, Ray(7) that the embryo culture technique offers a useful tool for biochemical investigations, and it has also been recognized(4,8) that it may be used as a practical measure to circumvent the abortion of embryos. It has, however, been found that in general the growth of the excised embryo, even upon a medium containing essential inorganic materials and sugar, is far less than that of normal intact seedlings. This has led to the suggestion(5) that "accessory growth factors" which are needed in minute amounts, are required by the developing plant as they are by the developing animal organism. The present work, as well as that of Kogl and Haagen-Smit,(9) furnish final proof that this is the case; that these accessory substances, although normally furnished by the seed, may be replaced to some extent by pure compounds added in small amounts to the embryo culture medium. These investigations, taken up early in 1936, are concerned particularly with orienting experiments undertaken with an ultimate view toward the elucidation of the nature and mode of action of these accessory growth factors. The embryo culture technique is here to be used as a tool in the "hormonal" analysis of plant development

Studies on the growth hormone of plants VII. The fate of growth substance in the plant and the nature of the growth process

Since the early work of Went (1928), it has been known that the growth substance of the Avena coleoptile may be obtained in the usual way, i.e. by diffusion into agar blocks, only from that part of the plant which produces it, namely the tip. The hormone is not recoverable in this way from those parts of the plant, such as the lower zones, which only make use of it. Recent work (Thimann, 1934) has, however, shown that by extraction with chloroform some growth substance is recoverable from the lower zones of the coleoptile. The results of this extraction method confirmed the earlier view that there is a marked concentration gradient of growth substance from tip to base

Studies of the physiology, pharmacology, and biochemistry of the auxins

Several excellent reviews of auxin matters have appeared during the past few years dealing broadly with the subject as a whole, such as the Wisconsin Symposium on Plant Growth Substances whleh is referred to repeatedly below, as well as reviews of more restricted scope such as those of Thimann (116) and of the previous volumes in this series. The present review need not, therefore, attempt to cover the entire spectrum of auxin physiology. It will concern a few aspects of the subject only, aspects in which particular progress has been made in recent years. It will attempt to evaluate the work which has been done in each of the several fields, to see in how far an integrated picture can be made of each and to make a few suggestions

The site of ribonucleic acid synthesis in the isolated nucleus

There is still controversy concerning the primary site of RNA synthesis in the cell.(1) When tissues are radioautographed after administration of radioactive inorganic phosphorus or radioactive RNA(2) precursors such as tritiated uridine or cytidine, it is commonly observed that radioactivity appears in the nucleus first and in the cytoplasm later. It has furthermore been shown that isolated nuclei of both animal(3) and plant(4) material are able to synthesize RNA in vitro but that enucleated cytoplasm is unable to carry on such synthesis.(5) Although the problem of whether or not RNA is synthesized in both nucleus and cytoplasm is not completely understood,(6-8) there is increasing cytological evidence that a substantial portion of the cytoplasmic RNA is synthesized in the nucleus (9-17) and subsequently migrates to the cytoplasm