Somatic embryogenesis - Stress-induced remodeling of plant cell fate.

IT IS WELL RECOGNIZED at present that the vast majority of compounds which display auxin activity have a distinct molecular configuration (recent summaries by Thimann, 1951; van Overbeek, 1950). Among these requirements is a rather specific steric relationship regarding the position of the side chain relative to the ring. This was realized as early as 1935 when Haagen-Smit and Went found that cis-cinnamic acid has auxin activity, while the trans-form is totally inactive. It has also become increasingly apparent in recent years that a close resemblance in molecular structure often exists between a physiologically active compound and its antagonists (summaries by Roblin, 1949; Sexton, 1950). A single deviation from the structure necessary for activity is often most effective in converting a metabolite into its anti-metabolite. In line with this reasoning it was, therefore, suspected that trans-cinnamic acid would display an action antagonistic to the growth promoting activity of the cis-isomer. And, because cis-cinnamic acid has the general qualifications of an auxin, the possibility was considered that trans-einnamic acid might be a general anti-auxin. These possibilities were indeed verified by experiment, and are reported below. In this paper the criterion by which anti-auxin activity is determined, is the capacity of transcinnamic acid to diminish the growth-promoting effect of added auxin. It is realized that reactions which would inactivate the auxin molecule per se, such as oxidations, would also diminish the auxin effect. However, it seems very likely that transcinnamic acid actually does compete with auxin, rather than inactivate it in a chemical sense. LITERATURE ON TRANS-CINNAMIC ACID AND ANTIAUXINS.-Trans-cinnamic acid has not been reported heretofore as an anti-auxin. It is more closely related to the auxin structure, without being an auxin, than any of the many other compounds reported to be antagonistic to auxins. Coumarin, closely related to cinnamic acid, was reported by Veldstra and Havinga (1943) to be antagonistic to naphthaleneacetic acid, together with several other lactones. Further unsaturated lactones having, antiauxin activity have been reported by Larsen (1947), and Thimann and Bonner (1949). Triiodobenzoic acid was shown to have anti-auxin activity by Galston (1946), de Waard and Florschutz (1948), and Thimann and Bonner (1948). Bonner (1949) reported still another type of compound having antiauxin activity: 2,4-dichloranisole. In

Trans-cinnamic acid as an anti-auxin

Changes in the Activities of Several Enzymes during Germination and Seedling Development in Corn (Zea mays L.).

Growth inhibition by applied indoleacetic acid (IAA), naphthaleneacetic acid (NAA), or 2,4-dichlorophenoxyacetic acid (2,4-D) was studied using change in fresh weight of pea root segments as the criterion of growth. Auxin metabolism of these tissues was investigated with 14C-labeled auxins applied under conditions similar to those used in the growth studies.Growth inhibition by applied auxins is independent of the rate of auxin uptake, accumulation of auxin or auxin metabolites in the tissues, or the subsequent loss of accumulated auxin from the tissues. It is also independent of the metabolic processes leading either to auxin conjugation with aspartic acid or to decarboxylation. All three auxins inhibit growth to a similar degree, which depends only on the concentration of auxin applied and the pH of the solution. Inhibition persists undiminished as long as the auxin is applied. It is suggested that growth inhibition by applied auxin occurs at a site external to the cytoplasm, i.e. the cell wall or the c...

Uptake and metabolism of indoleacetic acid, naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid by pea root segments in relation to growth inhibition during and after auxin application

20. MYRBACK, K., and G. NEUMULLER. 1950. Amylases and the hydrolysis of starch and glycogen. In: The Enzymes, J. B. Sumner and K. Myrback eds. Volume I, 1st edition. Academic Press, New York. 21. O'BRIEN, J. A., JR. 1942. Cytoplasmic inclusions in the granular epithelium of wheat and rye. Amer. Jour. Bot. 29: 479-491. 22. OHLSSON, E. 1922. Sur l'existence de deux ferments amylolytiques dans la diastase du malt. Compt. rend. soc. biol. 87: 1183-1184. 23. OHLSSON, E. 1930. Uber die beiden Komponenten der Malzdiastase, besonders mit Riichsicht auf die Mutarotation der bei der Hydrolyse der Stirke gebildeten Produkte. Zeits. Physiol. Chem. 189: 17-63. 24. PEAT, S. 1951. The biological transformations of starch. Advances in Enzymol. 11: 339-373. 25. PIGMAN, W. 1957. The Carbohydrates, Academic Press, New York. 26. PIGMAN, WV., and R. M. GOEPP. 1948. The Chemistry of the Carbohydrates, Academic Press, New York. 27. POLLOCK, M. R. 1959. Induced formation of enzymes. In: The Enzymes. P. D. Boyer, L. Lardy, and K. Myrback., eds. Volume I, 2nd ed. Academic Press, New York. 28. REED, H. S. 1904. A study of the enzyme-secreting cells in the seedlings of Zea mays and Phoenix dactylifera. Ann. Bot. 18: 267-287. 29. SCHWIMMER, S. 1950. Kinetics of malt alpha amylase action. Jour. Biol. Chem. 186: 181-193. 30. SUMNER, J. B., and G. F. SOMERS. 1953. The Chemistry and Methods of Enzymes. Academic Press, New York. 31. TOOLE, E. 1924. The transformations and the course of development of germinating maize. Amer. Jour. Bot. 11: 325-350. 32. TORREY, J. C. 1902. Cytological changes accompanying the secretion of diastase. Bulletin of the Torrey Botanical Club 29: 421-435.

Effects of indoleacetic acid and kinetin on scopoletin-scopolin levels in relation to growth of tobacco tissues in vitro.

Many reports are available in the literature on the effects of 2,4-D on numerous physiological and biochemical processes. Among these are increased cell proliferation (5), increased respiration (20), increased carbohydrate depletion (17), decreased respiration of roots (27), decreased uptake of potassium by roots (18), decreased accumulation by the root system of KNO3 and KC1 (13), inhibition of lipase activity (9), inhibition of ascorbic acid oxidase (27), stimulation of phosphatase activity (15), stimulation of beta-amylase activity (22, 28), inhibition of alphaand beta-amylase activity (14), etc. Useful though these observations are for the understanding of auxin action, they do not tell us if these physiological changes are the specific reasons 2,4-D has such a high herbicidal activity. It would rather seem that these phenomena are not specific for 2,4-D but are caused as well by other auxins such as indoleacetic acid and naphthaleneacetic acid (for terminology see 22). Thus, an increased respiration, a stimulated proliferation, and a considerable loss of carbohydrate are caused in the Jerusalem artichoke tuber by indoleacetic acid (8). Increased phosphatase activity is found in Avena roots after treatment with indoleacetic acid and other auxins (4). Inhibition of amylase activity by indoleacetic acid and by a variety of other auxins has been demonstrated (26). Indoleacetic acid, though capable of affecting many reactions in a fashion similar to 2,4-D is definitely not an efficient herbicide. The clue to the solution of why 2,4-D displays such a high herbicidal activity appears to lie in a different direction. Rather than only asking: "What physiological changes does 2,4-D bring about?" it would appear to be more profitable to ask first: "In what fundamental aspect does 2,4-D differ from the other auxins?" The present paper will largely deal with this question.

Difference in activity between 2,4-dichloro-phenoxyacetic acid and other auxins, and its significance in herbicidal action

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Difference in activity between 2,4-dichloro-phenoxyacetic acid and other auxins, and its significance in herbicidal action