Individual variation in the flavonoid aglycones excreted on the leaves of Alnus glutinosa: influence of culture conditions and origin of flavonoid natural diversity in wild specimens

This work presents a further step in the analysis of flavonoid aglycones excreted in the leaves of Alnus glutinosa as an aid to the characterization of natural specimens of this species. The stability in the flavonoid pattern of specimens growing under different environmental and biological conditions has been examined. The expression of the flavonoid metabolism in each surveyed individual is shown to remain unchanged over the course of a growing season and over successive years. Specimens from vegetative multiplication (cuttings, grafts) show a qualitative composition of the excreted flavonoids mixture identical to that of the parent tree. Individuals of clonal origins (three grown from in vitro bud culture) display identical flavonoid patterns; however, some minor variations are recorded. The flavonoid profiles displayed by individuals of two clonal origins, inoculated with several strains of Frankia of different efficiency in fixing nitrogen, remain unaffected, when compared with the pattern of the reference samples without nodules. In contrast, specimens grown from seeds (collected from different trees, a single tree, or even a single catkin) consistently display important qualitative and quantitative variations in their flavonoid content. However, in some cases, relationships between profiles of a mother tree and its progeny were detectable. It appears that the individual flavonoid content in Alnus glutinosa remains unaffected by the culture conditions and by the process of vegetative multiplication. The natural diversity observed in specimens from sexual reproduction is mainly interpreted in terms of its strictly allogamous reproductive mode. The analysis of the flavonoid material excreted on leaves appears to be a usable tool for the characterization of trees in the selection of individuals of Alnus glutinosa for experimental symbiosis with Frankia.