. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). The influence of growth substances upon sulphydryl compounds competitive interaction in root growth. Housley et al. (1954) have re- examined the evidence and suggested that this inhibitor was in reaHty non- competitive with auxin. The findings reported here, that the anisole may react with thiol groups whereas auxins do not, would seem to be in agreement with these criticisms. Some data on indoleacetic acid and
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). The influence of growth substances upon sulphydryl compounds competitive interaction in root growth. Housley et al. (1954) have re- examined the evidence and suggested that this inhibitor was in reaHty non- competitive with auxin. The findings reported here, that the anisole may react with thiol groups whereas auxins do not, would seem to be in agreement with these criticisms. Some data on indoleacetic acid and naphthalene acetic acid are also presented in Figure 8. We consider the changes with these reagents to be small. 0-150 0-050 2:9 -Phenol. 2:9 -/In/so/e 9x10 ^M c^. -Z 0 to 0 2 9- e;<10 ^M Concn. of growth substances Figure 8. Cysteine disappearance with 2-A-dichlorophenol, lAA, NAA, and 2-A-dichIoroanisole. Conditions as in Figure 4. Sulphydryl reactions of enzymes and coenzymes The evidence presented so far would suggest that some growth substances are able to react with sulphydryl groups and it is implied from this that by so doing they would influence some metabolic processes in a manner which would be reflected in growth. If this is true then the functioning of enzymes which require free sulphydryls for their activity should be inhibited by these growth substances. We selected amylase as being such an enzyme with which we might demonstrate sulphydryl inhibition. Elliott and Leopold (1953) utilized the inhibition of amylase as an assay for a naturally occurring growth inhibitor in oats. Evidence was brought forward that this inhibitor might attack sulphydryl groups and apparently through this function it would inhibit growth. Since amylase activity is a function of its free sulphydryl groups, it could be utilized as a handy quantita- tive assay for the inhibitor. In the present experiments essentially the same scheme was used. Amylase was incubated at room temperature wi
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