Les mycorhizes des plantes actinorhiziennes

Abstract

Resume.-En qualite d'especes pionnieres pour Ia revegetation des sols, les plantes actinorhiziennes sent predisposees a former avec les champignons mycorhiziens des associations symbiotiques aussi indispensables a leur croissance que celles formees avec Frankia. Com me I' on pouvait s'y attendre, les mycorhizes stimulent le developpement et l'activite fixatrice de N, de Ia symbiose actinorhizienne en ameliorant Ia nutrition minerale de Ia plante-hote. En plus des mycorhizes, les plantes actinorhiziennes peuvent former un type de racines tres particulieres appelees " racines proteo"ides " ou " racines en ecouvillon " en reponse aux effets nefastes des carences nutritionnelles dans le sol. Ces " racines en ecouvillon " constituees de touffes de radicelles sent des structures racinaires specialisees tres efficaces pouvant remplacer les mycorhizes et permettre aux plantes porteuses de croitre dans les sols marginaux pauvres en nutriments. II n'y a pas de competition entre Frankia et les champignons mycorhiziens pour les sites d'infection mais I' extension de Ia mycorhization peut affecter Ia croissance de Frankia et le developpement ulterieur des jeunes nodules actinorhiziens. Par centre, Ia presence de Frankia in planta n'a aucune incidence sur !'infection mycorhizienne. En reference a l'aulne et a Allocasuarina, I' auteur a discute des implications possibles de Frankia et des champignons mycorhiziens dans les phenomenes de reconnaissance et d'echanges de signaux chimiques entre Ia plantehote et ces microorganismes symbiotiques. On remarque que, curieusement, Frankia et les champignons endomycorhiziens arbusculaires presentent certaines similitudes dont on peut tenir compte pour developper de futures recherches.Summary.-As pioneer species for land revegetation, actinorhizal plants are predisposed to form with mycorrhizal fungi symbiotic associations that are as essential for plant growth as the associations they form with Frankia. As expected, mycorrhizas stimulate the development and the N, -fixing activity of the actinorhizal symbiosis by improving mineral nutrition of the host plant. In addition to mycorrhizas, actinorhizal plants are also able to form an unique type of roots called " proteoid roots " or " cluster roots " in response to the detrimental effects of nutrient deficiencies in soil. As an alternative of mycorrhizas, cluster ©Societe botanique de France 1996. JSSN 125-8078. 582ACTA BOTANICA GALLICA roots are specialized roots capable of assisting plant growth in marginal, nutrient deficient soils. There is no competition between Frankia and mycorrhizal fungi for infection sites but extensive mycorrhizas can affect Frankia growth and the subsequent development of young lobes of actinorhizal nodules. By contrast, the presence of Frankia in planta has no incidence on mycorrhizal infection processus. With reference to Alnus and Allocasuarina the possible implications of Frankia and mycorrhizal fungi on the mechanisms of recognition and chemical signalisation between the host plant and these microsymbio...

Determining As, Cd, Cu, Pb, Sb, and Zn in Leaves of Trees Collected near Mining Locations of Malé Karpaty Mts. in the Slovak Republic

“…Alnus sp. is known as a species that cooperated with mycorrhizal fungi (ectomycorrhizal and arbuscular endomycorrhizal), which effect heavy metal bioavailability for A. glutinosa [41][42]. The highest pH value was observed in the downflow of Stoličný stream (STOd, Table 4) and truly we observed the highest As concentration in this location in A. glutinosa and S. nigra (Fig.…”

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“…Casuarinaceae family form symbiotic N-fixing associations with actinomycetes (Frankia) as well as ectomycorrhizal and endomycorrhizal fungi. (Diem 1996). This symbiotic enhances the resistance and root plasticity system of Casuarina species in harsh conditions or degraded soils (Duhoux and Franche, 2003).…”

Fungal Endophytes of Alnus incana ssp. rugosa and Alnus alnobetula ssp. crispa and Their Potential to Tolerate Heavy Metals and to Promote Plant Growth

“…As actinorhizal species, alders are able to access atmospheric nitrogen through the activity of their bacterial partners, i.e., Frankia spp. [8,9], which contributes to increasing soil nitrogen levels [10]. Alders are also important to improving the availability of phosphorus [11].…”