Caracterisation du rajeunissement du noyer (Juglans sp.) pour une etude spectrophotometrique globale du contenu polyphenolique

English. Although positive results on the vegetative propagation of Paradox (Juglans hindsii x Juglans regia) were obtained, many difficulties with regard to the in vitro culture or the propagation via cuttings of Walnut hybrids (Juglans nigra x Juglans regia) remain. Therefore, attempts have been made to find biochemical markers of juvenility in the annual shoots of Walnut. In this respect the paper describes research on : 1) The identification of the more favorable physiological stages for vegetative propagation (optimalization of the sampling time for cuttings). 2) The improvement of the different treatments for propagation (temperature, light, culture, medium, etc.) on mother trees or cuttings. In order to achieve the above aims, polyphenols of different Walnut material (seedlings, adult trees, sprouts, grafts, pruned trees) were extracted and subsequently the polyphenol content of the alcoholic and aqueous extracts were analyzed by U.V.-spectrophotometry and T.L.C. In addition, optical densities read at six wavelengths (268, 280, 290, 342, 352 and 360 nm) or ratios between these readings (transformed data) were used for discriminant analysis of all extracts ; the latter analyses giving an idea of the « biochemical separation » of the different types of shoots (fig. 2 and 3) (Additional discriminating variables being shown in tables 1 and 2). A comparison of the crude spectrophotometric data demonstrates further a clear cut difference between juvenile and mature shoots (fig. 2, points 1 and 8) ; the more important variables characterizing the latter physiological stages being the two ratios between the optical densities read at four different wavelengths : 268/280 nm, 342/360 nm. Moreover, rejuvenated shoots (stump sprouts) appeared to be closely related to juvenile shoots (fig. 3, points 1, 2 and 3). In a second set of analyses (fig. 3) and again using transformed data, a regular distribution with the physiological age along the first <<mathematical component>> of the samples was observed. The same « component » allowed also the characterization of the rejuvenation phenomena of Walnut.After bidimensional T.L.C. several of the separated polyphenols were eluted with alcohol and subsequently analysed by means of U.V.-spectrophotometry (fig. 4). These analyses contributed to the better understanding of the spectra of the crude extracts. From the results obtained follows further that the phenolic composition of the plant tissues may be related to the distance between the buds and the roots and to the morphology of the stems.Finally, the results described in this paper suggest that discriminant analysis may help in determining the juvenility level of the plant material and that the phenolic compounds could be used as biochemical markers of juvenility. H.P.L.C.-analyses of the foregoing extracts have already confirmed the latter statement (Jay-Allemand 1985).

French. Cette étude a eu pour objet de rechercher des marqueurs biochimiques de la juvénilité chez le Noyer pour permettre d’apprécier l’état d’aptitude à la multiplication végétative des boutures et des microboutures avant et pendant l’application des traitements (température, lumière, milieux de culture...). A partir d’analyses spectrophotométriques effectuées sur des extraits purifiés de composés phénoliques de différentes catégories de pousses annuelles (selon l’âge du pied-mère, la taille, le greffage, le recépage), nous avons pu estimer les distances biochimiques entre les états juvéniles, matures et rajeunis par l’étude des fonctions discriminantes. Il a été montré en particulier que d’importantes variations permettent de différencier les pousses juvéniles (jeunes plants issus de semis) des axes d’arbres adultes alors que de fortes affinités biochimiques existent entre des situations juvéniles et rajeunies (rejets de souches). Ces données ont permis, en particulier, de caractériser le phénomène de rajeunissement (processus par lequel la plante retrouve des caractères juvéniles) sur le plan biochimique. L’analyse spectrophotométrique individuelle de certains polyphénols, élués après séparation en chromatographie bidimensionnelle sur couche mince de cellulose, a permis de comprendre en partie la structure des spectres globaux et de pouvoir ainsi rendre crédible les résultats obtenus. Enfin, les aspects physiologiques liés à l’influence du recépage sur le contenu polyphénolique des rejets ont été abordés.