Increased labile iron pool in sorghum embryonic axes after the exogenous application of nitric oxide is independent on the nature of the NO donor.

The objective of this work was to explore the hypothesis that nitric oxide (NO) affects Fe bioavailability in sorghum (Sorghum bicolor (L.) Moench) embryonic axes. NO content was assessed in embryonic axes isolated from seeds control or exposed to NO-donors, employing spin trapping electron paramagnetic resonance (EPR) methodology. NO donors such as sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA NONOate), released NO that permeated inside the axes increasing NO content. Under these conditions low temperature EPR was employed to study the labile iron pool. A 2.5 fold increase was observed in NO steady state concentration after 24 h of exposure to NO donors that was correlated to a 2 fold increase in the Fe labile pool, as compared to control axes. This observation provides experimental evidence for a potential role of NO in Fe homeostasis.

Exposure to nitric oxide protects against oxidative damage but increases the labile iron pool in sorghum embryonic axes.

Sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA NONOate), were used as the source of exogenous NO to study the effect of NO upon germination of sorghum (Sorghum bicolor (L.) Moench) seeds through its possible interaction with iron. Modulation of cellular Fe status could be an important factor for the establishment of oxidative stress and the regulation of plant physiology. Fresh and dry weights of the embryonic axes were significantly increased in the presence of 0.1 mM SNP, as compared to control. Spin trapping EPR was used to assess the NO content in axes from control seeds after 24 h of imbibition (2.4+/-0.2 nmol NO g(-1) FW) and seeds exposed to 0.01, 0.1, and 1 mM SNP (3.1+/-0.3, 4.6+/-0.2, and 6.0+/-0.9 nmol NO g(-1) FW, respectively) and 1 mM DETA NONOate (6.2+/-0.6 nmol NO g(-1) FW). Incubation of seeds with 1 mM SNP protected against oxidative damage to lipids and maintained membrane integrity. The content of the deferoxamine-Fe (III) complex significantly increased in homogenates of axes excised from seeds incubated in the presence of 1 mM SNP or 1 mM DETA NONOate as compared to the control (19+/-2 nmol Fe g(-1) FW, 15.2+/-0.5 nmol Fe g(-1) FW, and 8+/-1 nmol Fe g(-1) FW, respectively), whereas total Fe content in the axes was not affected by the NO donor exposure. Data presented here provide experimental evidence to support the hypothesis that increased availability of NO drives not only protective effects to biomacromolecules, but to increasing the Fe availability for promoting cellular development as well.

Reactive nitrogen species-dependent effects on soybean chloroplasts.

Nitric oxide (NO) generation by soybean (Glycine max, var ADM 4800) chloroplasts was studied by electron paramagnetic resonance (EPR) spin-trapping technique.1 Both nitrite and L-arginine (arg) are the required substrates for enzymatic activities considered as possible sources of NO in plants. Soybean chloroplasts showed a NO production of 3.2 +/- 0.2 nmol min(-1) mg(-1) protein in the presence of 1 mM NaNO(2). Chloroplasts incubated with 1 mM arg showed a NO production of 0.76 +/- 0.04 nmol min(-1) mg(-1) protein. This production was inhibited when chloroplasts were incubated in presence of NOS-inhibitors L-NAME and L-NNA. In vitro exposure of chloroplasts to a NO-donor (GSNO) decreased both ascorbyl radical content and the activity of ascorbate peroxidase, without modification of the total ascorbate content. Exposure of the isolated chloroplasts to a NO-donor decreased lipid radical content in membranes, however, incubation in the presence of 25 microM peroxynitrite (ONOO(-)) led to an increase in lipid-derived radicals (34%). The effect of ONOO(-) on protein oxidation was determined by western blotting, showing an increase in carbonyl content either in stroma or thylakoid proteins as compared to control. Taken as a whole, NO seems to be an endogenous metabolite in soybean chloroplasts and reactive nitrogen species could exert either antioxidant or prooxidant effects on chloroplasts, since both a decreased lipid radical content in membranes and a decrease in the activity of ascorbate peroxidase were observed after exposure to a NO donor.

Chloroplasts as a nitric oxide cellular source. Effect of reactive nitrogen species on chloroplastic lipids and proteins.

Nitric oxide (NO) generation by soybean (Glycine max var. ADM 4800) chloroplasts was studied as an endogenous product assessed by the electron paramagnetic resonance spin-trapping technique. Nitrite and l-arginine (Arg) are substrates for enzymatic activities considered to be the possible sources of NO in plants. Soybean chloroplasts showed a NO production of 3.2 +/- 0.2 nmol min(-1) mg(-1) protein in the presence of 1 mm NaNO(2). Inhibition of photosynthetic electron flow by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea resulted in a lower rate (1.21 +/- 0.04 nmol min(-1) mg(-1) protein) of NO generation. Chloroplasts incubated with 1 mm Arg showed NO production of 0.76 +/- 0.04 nmol min(-1) mg(-1) protein that was not affected either by omission of Ca(2+) or by supplementation with Ca(2+) and calmodulin to the incubation medium. This production was inhibited when chloroplasts were incubated in the presence of NO synthase inhibitors N(omega)-nitro-l-Arg methyl ester hydrochloride and N(omega)-nitro-l-Arg. In vitro exposure of chloroplasts to an NO donor (250 mum S-nitrosoglutathione) decreased lipid radical content in membranes by 29%; however, incubation in the presence of 25 mum peroxynitrite (ONOO(-)) led to an increase in lipid-derived radicals (34%). The effect of ONOO(-) on protein oxidation was determined by western blotting, showing an increase in carbonyl content either in stroma or thylakoid proteins as compared to controls. Moreover, ONOO(-) treatment significantly affected both O(2) evolution and chlorophyll fluorescence in thylakoids. Data reported here suggest that NO is an endogenous metabolite in soybean chloroplasts and that reactive nitrogen species could exert either antioxidant or prooxidant effects on chloroplast macromolecules.