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Tobacco (Nicotiana tabacum L. cv. Xanthi XHFD8) possesses four nitrite reductase (NiR) genes: nii1, nii2, nii3, and nii4. Their differential expression in leaves and roots was investigated by quantitative competitive RT-PCR using gene-specific primer pairs. These results appear to contradict existing views on the expression of these NiR genes: (i) the mRNA of each of the four NiR genes was distinguishable both in leaves and roots; (ii) nitrate treatment increased nii1 and nii3 mRNA in leaves and roots by at least 4-fold (at least 5-fold in nii2 and nii4 mRNA); and (iii) the steady-state levels of nii1 and nii3 mRNA were almost the same in leaves (6–7×105 and about 3×106 copies μg−1 of total RNA before and after nitrate treatment, respectively) and in roots (3–4×104 and 3–6×105 copies μg−1 of total RNA before and after nitrate treatment, respectively). Very similar relationships were obtained for the steady-state levels of nii2 and nii4 mRNA in roots (2–4×105 and 8×106 copies μg−1 of total RNA before and after nitrate treatment, respectively), and in leaves (5–9×104 and 4×105 copies μg−1 of total RNA before and after nitrate treatment, respectively). These results demonstrate that nii1 and nii3 transcripts are a dominating, but not exclusive, NiR mRNA in leaves, and the same is true for nii2 and nii4 transcripts in roots. [ABSTRACT FROM PUBLISHER]

Levels of NO-3, NO-2 and NH+4 ions in leaves of six plant species were determined by capillary electrophoresis. Levels of NO-3 ions differed by a factor of more than 350 in the six species. NO-2 and NH+4 ions were detected in all species examined but at lower and more similar respective levels than NO-3 ions. [ABSTRACT FROM AUTHOR]