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Titre : A BIOCHEMICAL INVESTIGATION OF CALLUS TISSUE IN THE SAGUARO CACTUS (CARNEGIEA GIGANTEA ((ENGELM.)) BRITT. & ROSE)

Auteur : Caldwell, Roger L.

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1966

Résumé
The tallest cactus in the United States, the saguaro, is restricted to southern Arizona in this country. When the saguaro is wounded, either mechanically (knives, rocks) or naturally (birds, wind), it responds by forming a hard tissue layer (callus) around the injured area. Paper and thin layer chromatographic analyses together with ultraviolet spectral analysis of saguaro callus extracts indicated the presence of several phenolic acids. Among these were : 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and 3-methoxy-if-hydroxybenzoic acid. Following the same procedure, extracts of the pulpy cortex indicated the presence of 4-hydroxycinnamic acid, 3,4-dihydroxycinnamic acid, and 3-methoxy-4-hydroxycinnamic acid. One flavonoid, quercetin, and a second unidentified flavonoid were found to occur in the callus. There was apparently no flavonoid content in the vascular elements of the cactus, the woody ribs. Although no structural identification of alkaloids was attempted, chromatographic analysis of the callus, the ribs, and the intermediate pulpy area indicated the presence of at least five alkaloids. Previously, only one alkaloid, carnegine, had been found in the saguaro. Chromatographic analysis of the intermediate pulpy cortex indicated the presence of a glycoside of 4-hydroxybenzoic acid. This glycoside was also found in the "slime flux" of a decomposing saguaro (decomposition due to bacterial necrosis). In addition, dopamine (3,4-dihydroxyP-phenylethylamine) was shown to occur as the major phenol in the pulpy cortex. The concentration of dopamine increased markedly in areas of the cactus that were wounded. The high lignin content (30.4$) of the callus may result from hormonal influence of dopamine on early lignin precursors. Dopamine as a melanin precursor may also play an important role in the wound metabolism, as a temporary response. A plausible mechanism for the formation of callus tissue is given.

Mots clés : Cactus — Diseases and pests. ; Saguaro — Diseases and pests.

Présentation

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