Growth substances derivatives

IV. Glycosides and Other Carbohydrate Derivatives as Plant-growth Substances.. 408... 

The enzyme choline esterase has been shown to have two binding points on its protein surface for these substances—one site for the quaternary ammonium group and one for X. This enzyme catalyzes the hydrolysis of an ester at the X position. From a consideration of the structure of the (2-chloroethyl)trimethylammonium chloride derivatives which were active as plant growth substances, a similar protein-binding site in the plant has been postulated. This site would have a point of attachment for both the ammonium cation and the X constituent of the molecule. This postulated site in the plant is thus similar, but not identical, to cholinesterase, which is an enzyme not known to occur in plants. There is no direct proof for this hypothetical site in the plant. 

Of the derivatives of (2-chloroethyl)trimethylammonium chloride which have been synthesized and tested as plant growth substances for the reduction of the height of plants, numerous substituents at the X site produced derivatives with biological effect (15). The most active derivatives were the chloride or bromide salts of CH0CI-CH0-N+ (CH3)3, CH>Br-CH -N+ (CH3) 3, CHo=CH-CH2-... 

Tannins and lignins are also derived from these pathways but are not included in Table 1. To make the list as simple as possible, all compounds of aromatic nature, viz., simple phenols, benzoic and cinnamic acid derivates, coumarins, flavonoids and quinones are condensed into one group - aromatic compounds. Thus I will attempt to cover systematically the secondary plant growth substances that fall into 11 major groups as shown in Table 1. 

The cytokinines (e.g. kinetine. Table 43) are plant growth substances which promote cell division. They are all adenine derivatives, the first of which to be isolated from a natural Source [Zea mays) was zcatin, A -[( )-4-hydroxy-3-methylbut-2-enyl]adenine (4). 

CytoMnins. Term derived from cyto and Greek kinein=movement for a group of plant growth substances that are predominately formed in young roots, stimulate cell division, and in some case together with... 

Four main classes of natural and synthetic plant growth substances are distinguished 1) The 3-indolylacetic acid derivatives (lAA) and other C-3 substituted indoles, previously known as auxins, induce a pronounced longitudinal growth, stimulate the formation of roots and flowers, the activity of the cambium, and influence fruit ripening and numerous other developmental processes in the plant. In the literature many compounds with different constitutions are also designated as auxins if they have activities similar to those of lAA. These include, e. g., 2-naphthyloxyacetic acid, benzoic acid, phenoxycarboxylic acid derivatives. 

At the previous (12th) International Conference on Plant Growth Substances we reported on the design of GA-derivatives to probe for GAs and GA-receptors in plants [1]. The application of such derivatives to the study of GA-receptor(s) in aleurone cells is described elsewhere in these Proceedings by Hooley et al. [10]. The preparation of monoclonal antibodies with high epitope specificity for GAs from the GA-protein conjugates, described by Beale et al. [1], has been published by Knox et al. [14, 15]. 

As soon as he had identified indoleacetic acid as a plant growth substance, Thimann proposed that it must be derived from tryptophan (III). Since tryptophan is the most prominent indole in plant tissues, occurring both in protein and as a free amino acid, this still seems reasonable. However, numerous workers have investigated various plant tissues for their capacity to produce indoleacetic acid from tryptophan and in aU cases the capacity of their systems has been feeble indeed. The best conversions obtained have fallen in the range of 0.3%, and most are less. As it is not difficult to obtain comparable amounts of indoleacetic acid from tryptophan non-enzymatically under mild conditions, the specificity of the systems investigated is still... 

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