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Fungal community structure and diversity in two types of agricultural grassland soil were investigated by amplified 18S ribosomal DNA restriction analysis (ARDRA) and 18S ribosomal DNA sequence analysis. These two grassland sites represent a species-rich old hay meadow and an agriculturally improved site with low floristic diversity. Two primer sets were used in combination to amplify approximately 550 bp of rDNA from three major fungal groups, the zygomycetes, basidiomycetes, and ascomycetes, and clone libraries were created for each site. 18S ARDRA was used to analyze 170 rDNA clones, and three diversity indices were calculated. A small-scale culturing analysis was also carried out and the most common isolates analyzed using ARDRA and sequence analysis. The soil fungal community revealed by the rDNA approaches was significantly different from that produced by this limited culture-based analysis. Twenty-eight soil-derived clones were sequenced, and many represented fungal taxa rarely reported in culture-based studies. The PCR-based techniques detected differences in diversity between the two fungal communities and changes in patterns of dominance that paralleled higher plant diversity. The results suggest that 18S rDNA-based approaches are a useful tool for initial screening of fungal communities, and that they represent a more comprehensive picture of the community than plate culturing.

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Polyamines (PAs) are essential metabolites in plants performing multiple functions during growth and development. Copper-containing amine oxidases (CuAOs) catalyse the catabolism of PAs and in Arabidopsis thaliana are encoded by a gene family. Two mutants of one gene family member, AtCuAOδ, showed delayed seed germination, leaf emergence, and flowering time. The height of the primary inflorescence shoot was reduced, and developmental leaf senescence was delayed. Siliques were significantly longer in mutant lines and contained more seeds. The phenotype of AtCuAOδ over-expressors was less affected. Before flowering, there was a significant increase in putrescine in AtCuAOδ mutant leaves compared to wild type (WT), while after flowering both spermidine and spermine concentrations were significantly higher than in WT leaves. The expression of GA (gibberellic acid) biosynthetic genes was repressed and the content of GA1, GA7, GA8, GA9, and GA20 was reduced in the mutants. The inhibitor of copper-containing amine oxidases, aminoguanidine hydrochloride, mimicked the effect of AtCuAOδ mutation on WT seed germination. Delayed germination, reduced shoot height, and delayed flowering in the mutants were rescued by GA3 treatment. These data strongly suggest AtCuAOδ is an important gene regulating PA homeostasis, and that a perturbation of PAs affects plant development through a reduction in GA biosynthesis.