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Assimilation of nitrogen dioxide in response to fumigation with 15 N-labelled nitrogen dioxide was studied in 217 plant taxa. The taxa included 50 wild herbaceous plants collected from roadsides (42 genera, 15 families), 60 cultivated herbaceous plants (55 genera, 30 families) and 107 cultivated woody plants (74 genera, 45 families). Two parameters, the 'NO 2 -N content', or NO 2 -derived reduced nitrogen content in fumigated plant leaves (mg N g -1 dry weight), and the 'NO 2 -utilization index', or percentage of the NO 2 -derived reduced nitrogen in the total reduced nitrogen, were determined. The NO 2 -N content differed 657-fold between the highest (Eucalyptus viminalis; 6·57) and lowest (Tillandsia ionantha and T. caput-medusae; 0·01) values in the 217 taxa; 62-fold in a family (Theaceae) and 26-fold in a species (Solidago altissima). Nine species had NO 2 -utilization indices greater than 10%, of which Magnolia kobus, Eucalyptus viminalis, Populus nigra, Nicotiana tabacum and Erechtites hieracifolia had NO 2 -N contents > 4·9. These plants can be considered 'NO 2 -philic' because in them NO 2 -nitrogen has an important function(s). The Compositae and Myrtaceae had high values for both parameters, whereas the monocots and gymnosperms had low ones. These findings suggest that the metabolic pathway of NO 2 -nitrogen differs among plant species. The information presented here will be useful for creating a novel vegetation technology to reduce the atmospheric concentration of nitrogen dioxide.

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A highly repeated DNA sequence with a repeating unit of approximately 380bp was found in EcoRV digests of the total genomic DNA of Allium fistulosum. Three independent clones containing this unit were isolated, and their repeating units sequenced. These units showed more than 94% sequence homology, and the copy number was estimated to be about 2.8×10(6) per haploid genome. In situ hybridization, with the repeating unit as a probe, and C-banding analyses indicated that the repeated DNA sequence of A. fistulosum is closely associated with the major C-heterochromatin in the terminal regions of all 16 chromosomes at mitotic metaphase. The characters of the repeating unit are similar to those of the A. cepa unit, which is taxonomically closely related to A. fistulosum.

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