SUMMARY A histochemical method was used to investigate the distribution of applied lead in the seed and seedling stage of Raphanus sativus. Lead contamination of the embryo was inhibited by the testa until it ruptured during imbibition. In seedlings, lead moved into the root cortex predominantly along the cell walls as far as the endodermis. Beyond the endodermis lead was localized extensively in the vascular tissues. There was little movement of lead from the vascular tissue into the surrounding tissue of the stem and cotyledons.

In vitro studies of IAA-induced cell elongation in Triticum aestivum have demonstrated that lead causes a large reduction in elongation. Inhibition of elongation can be reduced by increasing the concentration of IAA, or by the addition of calcium. The inhibitory effect appears to be linked with changes in the properties of the cell walls. Experiments are described which show that lead becomes bound strongly to certain chemical substances involved in cell wall architecture.

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The culture extracts of 21 micro-organisms were screened in vitro for anti-microbial activity against a range of test contaminants isolated from plant tissue cultures. Extracts produced by Trichoderma viride Pers. (strain A) and Bacillus subtilis Ehrenberg (strain 2) had the highest antifungal activity and extracts from Pseudomonas fluorescens Migula (strain X) had the highest antibacterial activity. When extracts of these organisms were applied to Nicotiana tabacum L. cultures, they reduced the growth of accidental contaminants. In the case of B. subtilis and P. fluorescens strains, equivalent extracts did not reduce fresh weight yields of uncontaminated N. tabacum cultures over four growth passages.