Alicyclic acid metabolism in plants

When the epicotyls of etiolated pea seedlings were fed with 40 mM potassium quinate solution in the dark for 24 hr, a marked accumulation of shikimic acid occurred in the tissue. This effect was much more pronounced in epicotyls preliminarily starved in a phosphate solution for 24 hr. On the other hand, supplying shikimate to the epicotyls brought about no significant accumulation of quinic acid. Tracer studies with¹⁴C-shikimate have shown that, in the epicotyls, shikimic acid was rapidly metabolized and fairly high radioactivities were observed in the amino acid fraction. However, feeding of¹⁴C-shikimate together with unlabeled alicyclic acids resulted in a reduction of shikimate utilization. When³H-quinate was fed to the epicotyls, radioactivities were retained mostly in an acidic fraction, indicating the sluggish conversion of quinic acid. In starved epicotyls, however, nearly half of the absorbed radioactivity was consumed. In tracer experiments the conversion of quinate to shikimate was clearly observed, whereas the reverse reaction was not. From these findings the metabolic role of quinic acid in quinate-less pea seedlings is discussed.