Metabolism of Adenine in Healthy and Blighted Potato Leaves

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Abstract
Analysis of the distribution of 14C in extracts prepared from leaf tissue which had been exposed to labelled adenine by petiolar uptake revealed that this purine is extensively metabolized in both healthy and Phytophthora-infected potato leaves. Incorporation of labelled adenine into the major ribonucleic acid species of the leaf was also extensive as determined by radioactive assays performed on individual fractions which were separated on columns of methylated albumin kieselguhr. Examination of individual nucleotides released by alkaline hydrolysis showed that both the adenylic and guanylic acid moieties were labelled. Although the labelling patterns were similar for RNA from healthy and infected leaf tissue, the specific activity of the latter was consistently higher than the former. When partially purified leaf extracts were assayed for phosphoribosyltransferase, they exhibited relatively high levels of activity with adenine as substrate, but were virtually devoid of activity with hypoxanthine and guanine. However, direct petiolar uptake of labelled hypoxanthine resulted in highly labelled RNA. A comparison of adenine phosphoribosyltransferase activity in extracts from healthy and blighted leaves failed to reveal measurable differences. Therefore, it was concluded that the differential incorporation of labelled adenine into the RNA of healthy and infected leaves was due neither to increased activity of this enzyme in response to infection nor to its differential activation. Apart from its role in the recovery of preformed purines for nucleic acid synthesis, adenine phosphoribosyltransferase may function as part of a mechanism for regulating levels of adenine in the potato leaf.

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