Nitrate reductase in cotyledons of cucumber seedlings as affected by nitrate, phytochrome and calcium

Abstract

1994. Nitrate reductase in cotyledons of cucumber seedlings as affected by nitrate, phytochrome and calcium. -Physiol. Plant. 91: 257-262.Regulation by the active form of phytochrome (PRJ) and the effect of Ca-* was examined with nitrate re.ducta.se (NR) in etiolated cucumber (Cucumis sativus cv. Beilpuig). Nitrate reductase activity (NRA) was studied in excised coty'iedons of cucumber seedlings grown io distilled water and in darkness for seven days at 24 ± 0.5°C. All experiments were performed in the dark and a dim green safeiight was used during analyses, lo etiolated cucumber cotyledons NRA was induced by nitrate and a brief irradiation (15 min) with red light (R) resulted in 62% increase in NRA. This effect was nullified when R was followed immediately by a brief (5 min) far-red light (FR). NRA also showed a semidian (12 h) rhythmicity. Both PpR, and nitrate effects were age depefideot. Calcium seemed to be involved since the phytochrome effect was only obseri'ed when calcium was supplied in the external solution. The effect of R on NRA depended on the period of calcium nitrate incubation. An extensal supply of calcium ionophore mimicked the effect of R and, if supplied to R-irradiated cotyledons, produced a higher NR level than that caused by R alone. This suggested that intracellolar free calciutn was involved.

A Chlorate-Resistant Mutant Defective in the Regulation of Nitrate Reductase Gene Expression in Arabidopsis Defines a New HY Locus

“…Therefore, the light-induced gene expression shown in Figure 5 is most likely dueto the response to light signals, not to the products of photosynthesis. This conclusion is consistent with previous observations in which light acts as a signal to induce the expression of NR genes in etiolated seedlings (Rajasekhar et al, 1988;Melzer et al, 1989;Becker et al, 1992;Bergareche et al, 1994). In addition to NR2, the mRNA levels of light-regulated nuclear-encoded photosynthetic genes CAB and RBCS were also reduced in cr88, further supporting the conclusion that cr88 is defective in the direct role that light plays in the regulation of NR2.…”

“…Light signals induce NR gene expression in etiolated seedlings (Rajasekhar et al, 1988;Melzer et al, 1989;Becker et al, 1992;Bergareche et al, 1994). The phenotypes of slow greening and underdeveloped chloroplasts suggest the possibility that cr88 is defective in light-regulated processes.…”

“…All of the studies on photoreceptor-mediated light induction of NR gene expression were performed with seedlings (Rajasekhar et al, 1988;Melzer et al, 1989;Becker et al, 1992;Bergareche et al, 1994). In addition, cr88 was selected for chlorate resistance during the seedling stage.…”

“…This suggests that white light induces NR gene transcription indirectly through photosynthates. On the other hand, the steady state NR mRNA levels of etiolated seedlings of various species increase in response to red (Rajasekhar et al, 1988;Melzer et al, 1989;Becker et al, 1992;Bergareche et al, 1994) and blue (Melzer et al, 1989) light. In the constitutive photomorphogenic mutant copl, NRZ, along with many other light-regulated genes, is derepressed in the dark (Deng et al, 1991).…”

Light Quality Effect on Internal N Retranslocation in Podocarpus macrophyllus Precultured with Exponential Nutrient Loading

“…The red light spectrum induced a depression in the NR activity in needles, suggesting a lowered nitrate assimilation rate. In previous studies, it was identified that the spectra effects on NR activity depend on the length of vegetation [ 56 , 57 ] and that, when a significant effect occurred, it was the blue light spectrum that promoted NR activity through activation of the expression level [ 48 ]. Although the red light spectrum may exhibit night degradation of NR activity in Gracilaria tenuistipitata , it can also modify the circadian rhythm in the activity of NR, resulting in a decline in accumulation [ 58 ].…”