DCMU inhibits in vivo nitrate reduction in illuminated barley (C 3 ) leaves but not in maize (C 4 ): A new mechanism for the role of light?

Abstract

The leaves of C(4) plants possess a superior metabolic efficiency not only in terms of photosynthetic carbon assimilation, but also in terms of inorganic nitrogen assimilation, when compared to C(3)plants. In vivo nitrate assimilation efficiency of leaves is dependent on light, but the obligatory presence of light has been debated and its role remains confounded. This problem has not been addressed from the standpoint of the C(3) vs. C(4) nature of the species investigated, which may actually hold the key to resolve the controversy. Here, we present the first report providing evidence for differential photo-regulation of leaf nitrate reduction in barley ( Hordeum vulgare L.) vs. maize ( Zea mays L.) plants, which may help explain the superior nitrogen-use efficiency (and hence superior productivity) of maize plants. The novel finding that carbohydrate-depleted maize leaves were able to reduce nitrate when photosynthesis was inhibited by 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea (DCMU) in the presence of light, raises a very important question about the possibilities of a new photo-regulatory mechanism for supporting nitrate reduction in maize leaves operating independently of photosynthetic carbon dioxide fixation. On the other hand, leaves of barley could not carry out any in vivo nitrate assimilation, whatsoever, under these conditions. We find another fundamental difference between the two species in terms of differential regulation of nitrate reductase (NR; EC 1.6.6.1). In barley leaves, NR activity and activation state remained unaffected due to DCMU, but in sharp contrast, both were appreciably upregulated in maize. Collectively, the results indicate that enzyme capacity is not limiting for nitrate reduction in leaves, as the NR activity was higher in barley than in maize. The maize leaves may have had a selective advantage due to C(4) morphology/metabolism in terms of maintaining a better reductant/carbon skeleton supply for nitrate reduction.

Guard cell photosynthesis is crucial in abscisic acid‐induced stomatal closure

“…When we used leaves and added DCMU and ABA at the same time, we obtained similar results to theirs: DCMU failed to inhibit ABA‐induced stomatal closure (Figure ). Intact leaves usually require pretreatment with DCMU for several hours to inhibit photosynthesis, perhaps because DCMU does not penetrate to the chloroplasts of intact leaves during a short period (e.g., Basra, Dhawan, & Goyal, ; Tóth, Schansker, & Strasser, ). To avoid the possibility of DCMU not reaching the guard cell chloroplasts, we used epidermal strips pretreated with DCMU.…”

Impact of chloroplastic- and extracellular-sourced ROS on high light-responsive gene expression in Arabidopsis

“…1A (Duysens, 1972;Basra et al, 2002;Fufezan et al, 2002;Fryer et al, 2003;Krieger-Lizskay, 2005;Flors et al, 2006). Further, HL and DCMU treatment, alone or in combination, promotes the production of 1 O 2 in PSII reaction centres.…”

Influences of nitrogen fertilizer application rates on radish yield, nutrition quality, and nitrogen recovery efficiency

“…After incubation at 30°C for 15 min, the reaction was terminated by adding 1∶1 mixture of 1% (w/v) sulphanilamide in 1.5 mol$L -1 HCl and 0.2% (w/v) N-naphtylethylenediamine dihydrochloride. After color development for 15 min, the nitrite formed was determined spectrophotometrically by measuring A 540 (Basra et al, 2002). NR activity was expressed as mg NO 2…”

“…NR activity was determined by a slightly modified method as described by Aslam et al (2001) and Basra et al (2002). In brief, NR activity was assayed using NADH or NADPH as electron donor.…”