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.