First Symposium on Chemical-Biological Correlation, May 26-27, 1950 (1951) / Chapter Skim
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Structure-Activity Relationships in Plant Growth-Regulators
Structure-Activity Relationships in Plant Growth-Regulators
Pages 45-72
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From page 45... ...
Repression of Root Elongation and of Seed Germination .
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From page 46... ...
Certain compounds possess activity in many of the types of response enumerated above, thus lending weight to the view that these responses, although not otherwise demonstrated to be related, may be diverse end-effects of a common fundamental reaction. On the other hand, some compounds exhibit high activity in one type of response but none at all in others.
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From page 47... ...
Compounds having auxin-activity, therefore, are those which can be shown to induce cell elongation in standard tests. The available test methods depend upon measurements of overall growth of organs, or segments of organs, comprising a variety of tissues of different cell types.
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From page 48... ...
a particular space relationship between the ring and the carboxyl group More recently these requirements have been restated as "an unsaturated ring system, with a side chain, adjacent to the ring double bond, of at least two carbon atoms ending in a carboxyl group"38 Although it is true that the majority of active compounds which have been discovered in the past fifteen years conform to these principles, there are known also a number of apparent exceptions. Conversely, the existence of some inactive compounds which also possess the stipulated structural features provides evidence that these have been incompletely defined.
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From page 49... ...
-butyric acid CHOHCH2COCH2COOH CH3 CH3 Auxin-b (Auxenolonic acid) CH2COOH H Indole-3-acetic acid CH3 CHCOOH a-(Indole-3)
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From page 50... ...
"hlorophenoxyacetic acid OCH2COOH 2, 4-Dichlorophenoxyacetic acid |CH2COSH 2-Methyl-4-chlorophenyl-thioacetic acid ClOCH2COOH 2,4, 5-Trichlorophenoxyacetic acid CH3 nCHCOOH 2, 4-Dichlorophenyl-o-propionic acid 2, 4-Dichlorophenoxyacetanilide Cl 2, 4-Dichlorophenoxy) -ethylamine TABLE II REPRESENTATIVES OF TYPES OF RING COMPOUNDS ACTIVE IN STIMULATING CELL ELONGATION C CCH,COOH .iCOOH Indene -3 -acetic acid 1-Cyclohexene-1-acetic acid
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From page 51... ...
On the one hand, high activity is exhibited by some benzene derivatives which might be expected to possess relatively unreactive unsaturated linkages, while, on the other hand, low activity is shown by a number of derivatives with highly reactive double bonds in rings such as those shown in Table II Indeed, even the requirement of the presence of a double bond in the ring adjacent to the side chain can scarcely be maintained in view of the activity of coumaran-3-acetic acid3? , a-1, 2, 3-tetrahydronaphthoic acid , and the so-called benzofulvenecarboxylic acidZS.
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From page 52... ...
Furthermore, there are now known several active substances in which the carboxyl group is attached directly to the ring. These include substituted benzoic acids, such as 2-bromo-3nitrobenzoic acid, 2-bromo-3, 5-dichlorobenzoic acid, and 2, 3, 5-trichlorobenzoic acid from among the many benzoic acids studied at Camp Detrick, 2, 3, 6-trichlorobenzoic acidZ, a-naphthoic acid and a-l , 2, 3, 4-tetrahydronaphthoic acid3'.
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From page 53... ...
On the other hand, 2, 3, 6-trichlorobenzoic acid has high activity, and 2,4, 6-trimethylphenoxyacetic acid also is active2,20. From the information presently available, it does not appear possible to conclude generally that any particular position in any ring series must be substituted or unsubstituted in order to permit activity.
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From page 54... ...
Consequently, in testing the root-initiating activity of chemical agents conditions should be selected so as to minimize the rooting of untreated test objects. Stem cuttings have been employed almost exclusively as test objects Because of the great interest in practical application of rooting compounds much of the available information has been obtained from trials made with species of horticultural value, and relatively little attention has been given to development of standard tests.
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From page 55... ...
TABLE III COMPOUNDS INACTIVE IN STIMULATING CELL-ELONGATION BUT REPORTED ACTIVE IN ROOT-INITIATION Cinnamic acid Naphthalene-1-methanesulfonic acid Diphenylacetic acid Uracil-4-acetic acid Nitrocinnamic acid N-Carbethoxymethylquinolinium chloride Coumarin 4-Methylthiarole-5-acetic acid Phenylacetamide Desoxycinchotenine Desoxycinchotenidine In Table IV are included compounds alleged to be active for root initiation but not heretofore tested for auxin activity. It should be pointed out that there has been no published confirmation of some of these reports.
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From page 56... ...
-valeric acid C-Naphthalene-1 ) -hexoic acid Naphthalenediacetic acid Naphthalene-1 -acetylglycine 2-Methylnaphthalene-1-acetic acid 2 -Methylnaphthalene - 1 -acetamide 4-Methylnaphthalene-1-acetic acid 4-Methylnaphthalene-1 -acetamide Vanillic acid Vanillin Sulfanilamide Piperonal Methoxysalicylaldehyde a-(2 -Chlorophenoxy)
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From page 57... ...
TABLE V COMPOUNDS ACTIVE IN INDUCING PARTHENOCARPY 2, 5-Dichlorobenzoic acid Phenylacetic acid a-(Phenoxy) -propionic acid a-(Phenoxy)
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From page 58... ...
-n-butyric acid Naphthalene-1 -acetamide Acenaphthene Naphthalene-1-propionic acid Skatole Naphthalene-I-butyric acid Sulfanilamide p-Naphthoxyacetic acid Oestrone P-Naphthoxypropionic acid Colchicine Parthenocarpic activity, though exhibited by many substances active also in other responses, is by no means restricted to these. The structural requirements for parthenocarpic induction, like those for root initiation, appear considerably less circumscribed than in the cellelongation or formative responses.
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From page 59... ...
On the other hand, 3- and 4-methylphenoxyacetic acids show approximately equal activity, which is, however, of a low order. Introduction of additional ring substituents into a highly active monosubstituted phenoxyacetic acid usually tends to diminish the activity.
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From page 60... ...
60 TABLE VI FORMATIVE ACTIVITY OF SOME DI- ANfl TRI- SUBSTITUTED BENZOIC ACIDS Active 2., 5-Dichlorobenzoic acid 5-Bromo-2-iodobenzoic acid 2-Bromo-3-nitrobenzoic acid 3 - Bromo-2-nitrobenzoic acid 3-Bromo-4-nitrobenzoic acid 2-Chloro-3-nitrobenzoic acid 2 -Iodo-3-nitrobenzoic acid 2-Methyl-3-nitrobenzoic acid 5-Bromo-3-chloro-2-iodobenzoic acid 5-Bromo-2, 3-dichlorobenzoic acid 5-Chloro-2, 3-dibromobenzoic acid 2, 3-Dibromo-5-iodobenzoic acid 3, 5-Dibromo-2-iodobenzoic acid 3, 5-Dichloro-2-iodobenzoic acid 2, 3, 5-Tribromobenzoic acid 2, 3, 5-Trichlorobenzoic acid 3, S-Dicarboxybenzoic acid 2, 4-Dichlorobenzoic acid 3,4-Dichlorobenzoic acid 2,4-Dihydroxybenzoic acid 2, 5-Dihydroxybenzoic acid 2, 5-Diiodobenzoic acid 3,4-Diiodobenzoic acid 2, 3-Dimethoxybenzoic acid 2f 5-Dinitrobenzoic acid 3, 5-Dinitrobenzoic acid 2-Amino-5-iodobenzoic acid 5 -Amino-2 -hydroxybenzoic acid 2-Bromo-4-nitrobenzoic acid 2-Bromo-5-nitrobenzoic acid 3-Bromo-5-nitrobenzoic acid 3 -Bromo-6 -nitrobenzoic acid 4-Bromo-2-nitrobenzoic acid 4-Bromo-3-nitrobenzoic acid 2-Fluoro-3-nitrobenzoic acid 2-Hydroxy-3-methyIbenzoic acid 2-Hydroxy-3-nitrobenzoic acid S-Bromo-Z-hydroxybenzoic acid 2-Hydroxy-S-iodobenzoic acid 5-Methyl-2-nitrobenzoic acid 2-Amino-3, 5-diiodobenzoic acid 2-Broxno-3, 5-dinitrobenzoic acid 2-Fluoro-3, 5-dinitrobenzoic acid 3-Bromo-2-hydroxy-5-sulfobenzoic acic 3, 5-Dinitro-2-hydroxybenzoic acid 2-Hydroxy-5-iodo-3-methylbenzoic acid 2,4, 6-Trihydroxybenzoic acid 2,4, 6-Trinitrobenzoic acid 3,4, 5-Tribromobenzoic acid 3,4, 5-Trichlorobenzoic acid 3,4, 5-Trihydroxybenzoic acid 3,4, 5-Triiodobenzoic acid
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From page 61... ...
-phenylacetic acid Diphenylacetic acid p-Methallyldiphenyl acetic acid Allyldiphenylacetic acid Hydrocinnamic acid cis-Cinnamic acid trans -Cinnamic acid 2-Chlorocinnamic acid 4-Chlorocinnamic acid 2, 4-Dichlorocinnamic acid 2-Methoxycinnamic acid cis -5-Chloro-2 -hydroxycinnamic acid a-Phenylbutyric acid 4-Hydroxyphenylglycine 3, 5-Dibromo-L-tyrosine Coumarilic acid 2-Thiophenecarboxylic acid 3-Pyridinecarboxylic acid (Nicotinic acid) Ni c otinam ide 4-Pyridinecarboxylic acid (Isonicotinic acid)
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From page 62... ...
) Tryptophane 8-Quinolyloxyacetic acid 5, 7-Dibromo-8-quinolyloxyacetic acid 9-Allylfluorene-9-carboxylic acid The impression may be given that the structural requirements for compounds active in producing formative responses are rather clearer and more restricted than for auxin activity or root initiation, and while this may be the case, it cannot be said to be proved at this time.
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From page 63... ...
Additional compounds reported active in inducing abscission include calcium cyanamide, ammonium thiocyanate, carbon tetrachloride, ethylene chlorohydrin, 3, 6-endoxotetrahydrophthalic acid, 3,6endoxohexahydrophthalic acid, and various halogenated benzoic acids. The evidence available from several types of investigations appears to support the view that abscission of an organ is induced when its content of auxin falls to a low level.
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From page 64... ...
A number of compounds active in overcoming bud dormancy are listed in Table IX. TABLE IX COMPOUNDS EFFECTIVE IN OVERCOMING DORMANCY OF BUDS Diethyl ether Chloroform Ethyl bromide Ethyl iodide Ethylene chloride Ethylene chlorhydrin Ammonia Ethylene Trichloroethylene o-Tolylthiourea Ammonium dithiocarbamate Thiosemicarbazide Hydrogen sulfide Ethyl mercaptan Thioglycol Sodium azido-dithiocarbonate Methyl disulfide Potassium sulfocarbonate Thioacetamide Ethyl carbylamine Thiourea Propylene Acetaldehyde Ethanol Acetone Hydrogen cyanide Zinc sulfate Thiocyanates
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From page 65... ...
Interest in this response stems in part from the fact that certain of the compounds possessing auxin activity, e.g. indole -3 -acetic acid and 2, 4-dichlorophenoxyacetic acid, are among the most active root inhibitors, producing measurable effects in concentrations as low as 10'° to lO'^M.
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From page 66... ...
TABLE X UNSATURATED LACTONES EXHIBITING BLASTOKOLIN ACTIVITY H 'C* + H2C ^CH CH3HCX s-C = O Hexene-2-olid-5, 1 (parasorbic acid)
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From page 67... ...
C-COOH Coumarin-3-carboxylic acid H 'C* 6-Phenyl-a-pyrone OH HC^ VC-COCH3 Dehydroacetic acid OH =0 3-Acetyl-4-hydroxycoumarin H Cl 'CH 6-Chlorocoumarin 8" Dicoumarol Coumarin Esculetin
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From page 68... ...
The increasingly widespread utilization of plant growth-regulators for practical ends in recent years has intensified the interest in this subject with the hope that promising directions of search for additional useful compounds may be indicated. In addition, it is expected that insight into the structural requisites will contribute to understanding of the mechanisms concerned in the regulation of plant development.
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From page 69... ...
Thus, in some responses, such as stimulation of cell elongation, initiation of roots, induction of parthenocarpy, inhibition of bud development, and retardation of abscission, the exogenous growth-regulators appear capable of functioning as substitutes for the endogenous hormone. In certain other responses the relationship is less clear.
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From page 70... ...
Boyce Thompson Inst.
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From page 71... ...
V , Plant growth substances (F.
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From page 72... ...
I thought of this particularly when the activity of the naphthoic arid was mentioned. In looking at a naphthalene ring, 'I wonder if we cannot regard it in two fashions: one, as a benzene ring, doubly substituted with an unsaturated side chain.
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