Different diurnal cycles of expression of two nitrate reductase transcripts in tobacco roots.

In roots and leaves of tobacco (Nicotiana tabacum cv. Samsun) three functional transcripts (3.6 kb, 3.1 kb, and 1.8 kb) were found to at least partly represent nitrate reductase mRNA. With specific probes for the transcripts of the different domains of nitrate reductase it was shown that the smallest transcript was shortened in the region coding for the flavin adenine dinucleotide domain and might be the transcript coding for plasma-membrane-bound nitrate reductase. The expression of the 3.1 kb and 1.8 kb transcripts in roots was differently regulated during the day-night cycle with the maximum amount of the 3.1 kb transcript in the middle and of the 1.8 kb transcript at the end of the light period.