Conclusion

Micromolecular macrosystematics is based on the joint consideration of biosynthetic and evolutionary metabolic sequences. With the advent of angio-sperms, all enzymatic catalysts necessary for the full expression of the biosynthetic pathway featured in Table. 11 must have been existent in order to explain the concomitant occurrence of neolignans, lignins, and proanthocyanidins in the primitive Myristica-ceae. The biosynthesis of all these metabolites requires the intervention of phenylalanine-ammonia lyase (PAL) for the decompositions of the amino acid into cinnamic acid and ammonia.

Possibly for the sake of economy, resulting from the avoidance of dumping enormous quantities of raw material into lignins, natural selection favored the elaboration of inhibitors of PAL, the most active ones being caffeic and vanillic acids (Boudet et al. 1971). In consequence of diminishing efficiency of deamination, phenylalanine would become available for the production of benzylisoquinoline alkaloids or betalains. The sum of such phenomena rationalizes the negative diversificatory correlation of cinnamic acid derivatives vs. benzylisoquinolines-betalains noted above for the development of the lineage Mag-noliidae-Ranunculidae-Caryophyllidae.

However, formation of alkaloids diminishes the quantity of ammonia for recycling into general metabolism. Thus inhibition of PAL is not always fully advantageous and life under nitrogen-poor conditions must require the evolutionary reversal of the inhibitor's action. Since gallic acid is known to be able to effect such reversals and even to function as an activator of PAL (Boudet et al. 1971), the Hamamelidae may well constitute an alternative development of primitive Magnoliidae.

Comparative phytochemistry, conceivably a fragile clue for the confirmation of affinity, at least does not contribute negative evidence for such a possibility, since both these groups are characterized by a high flavonol/flavone ratio, low oxidation level of constituents, high lignosity, presence of proanthocyanidins, absence of gallates, and lack of prenylation. Only one experimental method exists, permiting a glimpse into the past chemical composition of a lineage: the derepression of evolutionarily inactivated genes by fungal infection of the plant. The resulting ex novo bio-synthesized compounds, the so-called phytoalexins (Deverall 1982), would seem to constitute a kind of micromolecular fossil. By such direct, if serendipitous, experimentation Cercidiphyllum japonicum (Cercidiphyllaceae) yielded magnolol (Takasugi and Katui 1986), a common neolignan of Magnoliaceae and other magnolialean families, while Morns alba and Broussonetia papyrifera (Moraceae) yielded respectively stilbenes (Takasugi et al. 1978) and 1,3-dia-rylpropanes (Takasugi et al. 1980), common constituents of Myristicaceae.

The major chemosystematic problem concerning the possible relationship of the angiosperm blocks 1 and 2 having been discussed, some less general questions remain to be considered. First, with respect to the Magnoliidae, it is chemically very difficult to perceive clearcut distinctions among Magnoliales, An-nonales, and Laurales. The major families of these orders fit better in a continuum. Most of the relatively minor families bear neolignans and should thus be rather primitive, ancient segregates. One of the small families, the Nelumbonaceae, contains benzyl-isoquinoline alkaloids. Their rather simple types make it advisable, nevertheless, to keep the family within the Magnoliidae.

Furthermore, with respect to the Ranunculidae benzylisoquinoline alkaloid evidence suggests their derivation from annonaceous stock in three lineages represented by the Berberidaceae, the Menisperma-ceae, and the Papaveraceae-Fumariaceae. The same type of evidence demonstrates the affinity of the first of these families and of the Thalictrum branch of the Ranunculaceae. Other branches of the Ranuncula-ceae develop strikingly differentiated chemistries. Such is the case of the Aconitum-Delphinium complex, an unparalleled champion of molecular flexibility involving the diterpene alkaloid theme.

Next, with respect to the Caryophyllidae, the absence of betalains in the Molluginaceae and Caryo-phyllaceae (Table 4) is, considering all other chemical markers, insufficient evidence for their segregation from the order Caryophyllales. If indeed the Molluginaceae (with anthocyanin pigments) and Ai-zoaceae (with betalain pigments) were placed into different orders, by an analogous presence/absence criterion the Myristicaceae (with neolignans) and the Annonaceae (with benzylisoquinoline alkaloids) also should not both belong to the Annonales.

Finally, with respect to the Hamamelidae, as is usual in plant groups that contain gallotannins, the existence of chemosystematically useful markers is the exception rather than the rule. Each of the families possesses a rather specialized assortment of secondary metabolites that makes the suggestion of affinities between them a rather speculative endeavor. Either these families represent small remnants of previously more diversified taxa, or indeed, as noted above, the presence of galloyl esters favors the production of cinnamic acids, thus channeling organic material into biosynthetic pathways leading to metabolic classes such as flavonoids rather than to the major classes of dicotyledonous markers (e.g., aromatic amino acid derived alkaloids, polyace-tylenes, sesquiterpene lactones) efficiently and selectively.

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