Flavonoids in phylloclades discriminate endemic Semele androgyna chemotypes from Madeira

Thirty-five randomly-collected Semele androgyna Kunth samples were screened by RP-HPLC for their phenolic composition. Fraction analysis allowed the detection of 17 different compounds. According to their retention times and UV spectra obtained by diode array analysis, these phenolics represent three classes: phenolic acids, flavones and flavonols. Co-chromatography with specific standards enabled identification of quercetin, rutin and quercitrin in Semele tissues for the first time. Polymorphism based on phenolic composition was evaluated using multivariate analysis and showed four distinct S. androgyna clusters. This polymorphism was not associated with morphological diversity or different in ambient light intensities. Biochemical differentiation is thus present in this species. The application of multivariate analysis techniques to RP-HPLC data has allowed the classification of samples into two groups, previously proposed on the basis of morphological and cytotaxonomical information. Therefore, the use of phenolics as chemotaxonomic markers in Semele is highly recommended because of its diagnostic value, even at a subspecies level. Discriminant canonical analysis and Mahalanobis distances confirmed these clusters as recognisable chemosystematic units. However, these units do not support the separation of S. pterygophora.The Portuguese Foundation for Science and Technology (FCT) funded this work through the Centre of Macaronesian Studies (CEM). The authors are grateful to the Madeiran Centre of Science and Technology (CITMA), the Berardo Foundation and European Social Funding for financial assistance given during execution of this work. The assistance rendered by Mr Rogério Correia during field collection is gratefully acknowledged.info:eu-repo/semantics/publishedVersio

An Auxin Transport-Based Model of Root Branching in Arabidopsis thaliana

Root architecture is a crucial part of plant adaptation to soil heterogeneity and is mainly controlled by root branching. The process of root system development can be divided into two successive steps: lateral root initiation and lateral root development/emergence which are controlled by different fluxes of the plant hormone auxin. While shoot architecture appears to be highly regular, following rules such as the phyllotactic spiral, root architecture appears more chaotic. We used stochastic modeling to extract hidden rules regulating root branching in Arabidopsis thaliana. These rules were used to build an integrative mechanistic model of root ramification based on auxin. This model was experimentally tested using plants with modified rhythm of lateral root initiation or mutants perturbed in auxin transport. Our analysis revealed that lateral root initiation and lateral root development/emergence are interacting with each other to create a global balance between the respective ratio of initiation and emergence. A mechanistic model based on auxin fluxes successfully predicted this property and the phenotype alteration of auxin transport mutants or plants with modified rythms of lateral root initiation. This suggests that root branching is controlled by mechanisms of lateral inhibition due to a competition between initiation and development/emergence for auxin

Micropropagation of hybrid walnut trees (Juglans nigra x Juglans regia) through culture and multiplication of embryos

International audienc

Culture in vitro d'embryons isolés de noyer commun (Juglans regia L.)

La technique in vitro de production de pousses à partir des axes embryonnaires de noyer dépend successivement de deux facteurs : - la concentration en saccharose qui, utilisée à 20 ou 40 g/1, permet d’obtenir des plantules enracinées sur un milieu simple de KNOP dilué de moitié, après 60 jours de culture ; - la N6-benzylaminopurine à 1 mg/1 qui déclenche après 30 jours de culture la formation de pousses axillaires sur des épicotyles excisés des plantules précédentes et ensemencés sur le milieu de MILLER à 20 g/1 de saccharose.The main objective of the walnut improvement program of the Forest Tree Improvement Station (INRA-Orléans) is the vegetative propagation of hybrids created by controlled cross. For that purpose, establishment of an in vitro micropropagation technique from embryos could save much time. In this work, we present the technique used to obtain good development of isolated embryos of Juglans regia L. Two main factors studied were the concentration of sucrose in the culture medium and the effect of N6-Benzylaminopurine. 1) Sucrose effect. Naked embryos were transferred from disinfected nuts to Knop’s medium supplemented with sucrose at 0, 10, 20, 40, 80 and 160 g/1. After 50 days of culture (tabl. 1 and fig. 1) the best growth of epicotyls and roots was obtained with 20 g/1 of sucrose. Low concentration (less than 40 g/1) promoted epicotyl growth whereas high concentration (80 g/1) increased root growth. When sucrose was absent or at too high concentration (160 g/1) embryo development did not occure. In all treatments the epicotyls of embryos formed a terminal bud and 10 to 16 lateral buds in two rows. None of those buds flushed. 2) Effect of N6-Benzylaminopurine. The developed embryos obtained on the medium showing the best growth (knop 1 /2 and sucrose 20 g/1) were transferred, with and without roots to the medium of Miller supplemented or not with BAP 1 mg/1 or BAP 1 mg/1 and GA3 10 mg/1. Flushing of at least one bud per plant occured only if there is BAP in the medium (tabl. 2). On BAP alone the mean number of buds elongated per explant was about 2 times greater on excised epicotyls than on whole embryos. There was a depressive effect of GA3 on elongation of buds particularly on excised epicotyls. Apparently there is a strong effect of roots on the development of buds. With this technique, we are able to establish directly walnut embryos in in vitro culture, the first step for a mass micropropagation process

Exodermis structure controls fungal invasion in the leafless epiphytic orchid Dendrophylax lindenii (Lindl.) Benth. ex Rolfe

Leafless and shootless epiphytic orchids rely essentially on CAM photosynthesis in roots for carbon gain. However, it is believed that a proportion of carbon is obtained by endomycorrhizal associations. In this study, we show that Dendrophylax lindenii possesses a dimorphic exodermis with smaller, thin-walled passage cells that are depleted in flavonoids. No hyphae succeeded in penetrating into the cortex from a non-passage cell, but 20% of the hyphae in contact with a passage cell managed to penetrate into the cortex. The passage cells represent 40% of the amount of cells in the centre of the side that touches the substrate, but no passage cells are observed in the upper side of the root. This distribution and density of exodermal passage cells define a strategy for controlling the extent and location of fungal invasion in the orchid root. This strategy provides a mechanism for restricting fungal growth to the lower cortex and thus maximising carbon gain from photosynthesis while enabling further trophic exchanges from mycorrhizal associations

Relation entre les composés phénoliques solubles du bois de noyer (Juglans regia) et sa couleur

National audienc

Carbohydrate reserves and CO2 balance of hybrid walnut (Juglans nigra no.23 x Juglans regia) plantlets during acclimatisation

International audienc