Morphologische Interaktionen und molekulare Regulation vor und während der Ektomykorrhiza-Bildung zwischen Quercus robur L. und Piloderma croceum

Abstract

In order to study the events occurring before mycorrhization between oaks (Quercus robur L.) and the ectomycorrhizal fungus Piloderma croceum, oak seedling morphogenesis was highlighted as basis to characterize the developmental behaviour of micro-propagated oaks in a semi-sterile Petri-dish mycorrhization system. As well as in seedlings, shoots of the micro-cuttings remained characterized be an endogen rhythmic growth under controlled culture conditions (25°C and 16 h illumination). Lateral roots of the micro-propagated oaks also displayed a rhythmic growth, whereby the root and shoot flushes were out of phase, with concomitance of apical bud swelling and maximal growth rate of the roots. In micro-cuttings inoculated with P. croceum, this concomitance was maintained, in spite of a strongly enhanced root and shoot growth induced by the fungus in its long premycorrhizal stage. The specificity of morphological modifications (for example enhanced leaf area and lateral root growth) during the prolonged pre-mycorrhizal stage was demonstrated using activated charcoal and auxine (IAA). Both compounds simultaneously advanced mycorrhizal formation and stopped the enhanced development of first order mother roots. In order to elucidate molecular mechanisms involved during this prolonged pre-mycorrhizal stage, a subtractive cDNA bank was established between roots sampled before mycorrhization and control roots mixed with fungal mycelium. After southern blot analysis 60 differentially expressed genes were sequenced and homology was determined for about 30 of them. Northern blot analysis revealed an up regulation during the pre-mycorrhizal stage of two genes encoding for metallothionein and formate-dydrogenase, respectively. The model will serve for further analyses of gen regulation at different stages of mycorrhiza formation.