Aluminum Induces Distinct Changes in the Metabolism of Reactive Oxygen and Nitrogen Species in the Roots of Two Wheat Genotypes with Different Aluminum Resistance

Aluminum (Al) toxicity in acid soils is a primary factor limiting plant growth and crop yield worldwide. Considerable genotypic variation in resistance to Al toxicity has been observed in many crop species. In wheat (<i>Triticum aestivum</i> L.), Al phytotoxicity is a complex phenomenon involving multiple physiological mechanisms which are yet to be fully characterized. To elucidate the physiological and molecular basis of Al toxicity in wheat, we performed a detailed analysis of reactive oxygen species (ROS) and reactive nitrogen species (RNS) under Al stress in one Al-tolerant (Jian-864) and one Al-sensitive (Yang-5) genotype. We found Al induced a significant reduction in root growth with the magnitude of reduction always being greater in Yang-5 than in Jian-864. These reductions were accompanied by significant differences in changes in antioxidant enzymes and the nitric oxide (NO) metabolism in these two genotypes. In the Al-sensitive genotype Yang-5, Al induced a significant increase in ROS, NO, peroxynitrite (ONOO^–) and activities of NADPH oxidase, peroxidase, and S-nitrosoglutathione reductase (GSNOR). A concomitant reduction in glutathione and increase in S-nitrosoglutathione contents was also observed in Yang-5. In contrast, the Al-tolerant genotype Jian-864 showed lower levels of lipid peroxidation, ROS and RNS accumulation, which was likely achieved through the adjustment of its antioxidant defense system to maintain redox state of the cell. These results indicate that Al stress affected redox state and NO metabolism and caused nitro-oxidative stress in wheat. Our findings suggest that these molecules could be useful parameters for evaluating physiological conditions in wheat and other crop species under adverse conditions

Tracing Copper Derived from Pig Manure in Calcareous Soils and Soil Leachates by ⁶⁵Cu Labeling

Copper is used as a growth promoter in animal husbandry, resulting in high Cu concentrations in animal manure. We tested whether Cu would be mobilized in soils receiving excessive loads of manure, both from recently added and from aged fractions. To discriminate between these Cu sources, manure was labeled with ⁶⁵Cu. After soil application of 0, 15, and 30 Mg manure ha^–1, leachate was collected in free-draining lysimeters (40 cm depth) under undisturbed soil over a 53 day period. Determining the total amounts of Cu and the fractions of ⁶⁵Cu in leachate and the soil profile enabled us to trace the translocation of Cu derived from labeled manure. More than 84% of the applied Cu was retained in the top 2 cm of soil. Less than 0.01% of the applied Cu was detected overall in the leachate. Of this amount, however, 38% (±8.9 SE) was leached within 8 days after application. The total Cu concentration in leachates (32–164 μg L^–1) frequently exceeded the Chinese groundwater quality standard of 50 μg L^–1. The added ⁶⁵Cu, however, accounted for less than 3.6% of the total Cu leaching load, suggesting that Cu from older sources and/or geological background controls contamination, regardless of current land management