Aristolochia sipho

Fig. 71.—Portion of cross-section of four-year-old stem of Aristolochia sipho, as shown by the rings of growth in the wood. The letters are the same as in Pig. 68 but new tissues have been added by the activity of the cambium and a cork cambium has arisen from the outermost collenchyma cells and given rise to cork. The new tissues are I, cork cambium k, cork g, secondary phloem from the cambium, and just outside this is older crushed phloem , secondary xylem produced by the cambium m, secondary medullary ray made by the cambium (notice that this does not extend to the pith). Half of the pith is shown. Notice how it has been crushed almost out of existence. Compare Figs. 68 and 71, tissue for tissue, to find out what changes the primary tissues undergo with age, and to what extent new tissues are added. Photomicrograph x 20. (From Stevens.)...

The biosynthesis of aristolochic acid (68) in Aristolochia sipho has been studied. Tyrosine, dopa, dopamine, and, interestingly enough, noradrenaline serve as precursors, and the nitro-group of aristolochic acid is derived from the amino-group of tyrosine. It is most likely that aristolochic acid is formed by oxidation of a 1,2,8-trisubstituted aporphine. " ... 

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