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Aflatoxins B1, B2, G1 and G2, highly toxic mycological metabolic products occurring as food contaminants, were capable in minute quantities of causing delayed hypersensitivity in guinea pigs. Structurally related compounds, sterigmatocystin (a mycotoxin), coumarin, 8-methoxypsoralen and furazolium chloride were also equally or more active in causing delayed hypersensitivity in guinea pigs. Animals which were strongly sensitized to aflatoxin B1 showed cross-reactivity to other aflatoxins (B2, G1 and G2), sterigmatocystin, coumarins, 8-methoxypsoralen, furans and commerical perfumes. Less strongly immunized animals, on the other hand, showed differential cross-reactivity in that other aflatoxins produced frank erythema whereas closely related compounds were more moderate in action. None of these immunized animals showed any circulating antibodies. [ABSTRACT FROM AUTHOR]

Effects of coumarin on fresh weight, dry matter, protein and nucleic acid content per cell in attached roots of maize and wheat and in whole excised elongation zones of maize were determined. The inhibition in cell length exerted by coumarin did not correspond to an inhibition of the net synthetic capacity. Coumarin treatment increased the cell surface, the production of dry matter and the protein content per cell. The dry matter and the protein content per unit surface was slightly increased or unaffected. The effect of coumarin on cell shape seemed to be independent of that on dry matter production and net protein synthesis. The same was found in excised elongation zones. — The net DNA-synthesis per cell was slightly increased in attached roots by coumarin treatment, but this effect was probably not correlated with the morphogenetic changes. Inhibition of DNA-synthesis with hydroxyurea did not alter the coumarin induced changes in cell shape. — The net RNA-synthesis per cell was slightly decreased after coumarin treatment, but the net RNA-synthesis per cell and the morphogenetic effects exerted by coumarin were not related with each other. Inhibition of m-RNA synthesis with actinomycin D did not prevent the effects of coumarin on cell division, cell expansion, dry matter production and net protein synthesis. The same was true for inhibitors of protein synthesis, puromycin and p-fluorophenylalanine. The findings are in support of the view that coumarin affects already existing structures or enzymes. — Comparisons between coumarin and the uncouplers, DNP and dicoumarol, showed that the effects of coumarin were not, solely, due to uncoupling. SH-protecting agents, BAL, DTE and glutathione, did, with few exceptions, not reduce the morphogenetic effects of coumarin. [ABSTRACT FROM AUTHOR]

The effect of coumarin on the root growth was studied on roots from intact plants, isolated roots and isolated elongating zones. All material was cultivated aseptically. A new method was developed for sterile culture of intact plants in flowing nutrient medium. The effects on cell division and cell elongation were studied separately. An effect on both these processes can be established at all concentrations that affect the root growth. The concentration‐growth curve has an “all‐or‐none” appearance. Coumarin inhibits the transverse divisions in all cell layers; the perivascular layers seem to be more sensitive. Also the mitotic activity that is involved in the initiation of laterals is inhibited. The longitudinal divisions within the stele are enhanced. Coumarin decreases the cell length in all cell layers, most likely with greater relative sensitivity in the perivascular layers. Studies on the time course of cell elongation in both attached corn roots and isolated elongating zones reveal that the decrease in cell length is caused exclusively by a decrease in the maximal rate of elongation, whereas the duration of the elongation is unchanged. With each decrease of the cell length, the cell diameter is increased. The two changes are intimately connected within the greater part of the active region of concentration. Studies on the time course of the radial expansion in isolated elongating zones show a strict connection in time between cell elongation and radial expansion. The radial expansion leads to unchanged or increased cell volume at most concentrations and for most cell types. Coumarin causes an inhibition of the longitudinally directed processes and a stimulation of the radially directed ones. This is interpreted as indicating that the formative system is disengaged or reorientated, i.e., the polarity of the cells is changed. Through experiments partly with isolated elongating zones and partly by disruption of the linear phase by means of mannitol, the inhibitory effect of coumarin could be localized to the first non‐linear phase of the elongation. The results were compared with earlier findings in the literature. The microtubuli are proposed as a conceivable main Component in the formative system common to both cell division and cell elongation. These are assumed to be affected by changes in the SH/SS balance produced by coumarin. [ABSTRACT FROM AUTHOR]