Cytokinin enhancement of the light induction of nitrate reductase transcript levels in etiolated barley leaves

Abstract

To investigate the molecular mechanism of cytokinin regulation of nitrate reductase (NR) activity, the influence of benzyladenine (BA) on the level of NR transcript was studied in etiolated barley leaves using a barley NR cDNA as a probe. Northern blot analyses of the levels of NR poly (A)+ RNA indicate that the amount present is proportional to the concentration of BA (2 x 10(-8) to 2 x 10(-4) M) applied to the leaves. Enhancement of NR mRNA by 2 x 10(-5) M BA was clearly detected after 15 minutes of exposure of the leaves to light. The enhancement is cytokinin-specific and adenine is ineffective. Brief treatment with the protein synthesis inhibitor, cycloheximide, inhibited BA-enhanced NR activity but did not inhibit BA-enhanced NR transcript level, thus the enhancement was independent of concurrent protein synthesis. Nuclear runoff transcription studies showed that the enhancement of NR mRNA was at least partially due to increased transcription rates.

5[prime] Proximal Regions of Arabidopsis Nitrate Reductase Genes Direct Nitrate-Induced Transcription in Transgenic Tobacco

“…Light signals at red/far-red (Rajasekhar et al, 1988;Melzer et al, 1989) and at blue (Melzer et al, 1989) regions of the spectrum both increase the NR mRNA levels of etiolated seedlings. Cytokinin enhances, whereas ABA suppresses, the light induction of NR transcription in etiolated barley leaves (Lu et al, 1990(Lu et al, , 1992. The biological significance of light signal and hormonal regulation is unclear.…”

The early nodulin gene SrEnod2 from Sesbania rostrata is inducible by cytokinin

“…Cytokinin-enhanced nitrate reductase gene expression in etiolated barley leaves has been shown to occur at least partially on the transcriptional level (Lu et a/., 1990). This response has been shown to be cytokinin-specific, rapid and dependent on the hormone concentration.…”

Co‐regulated expression of nitrate and nitrite reductases

“…The NR mRNA concentration drops to undetectable levels in the leaves of tobacco plants grown in constant darkness for 60 h, but increased after 4 h of exposure to light (Deng etal., 1990). Cytokinins and light have a synergistic effect on NR mRNA induction in etiolated barley leaves (Lu et a/., 1990) and on NR activity in Agrostemrna githago L. embryos (Schmerder and Horbs, 1986). A plastidic factor appears to be involved in the regulation of NR expression in mustard cotyledons (Schuster et a/., 1989).…”