Summary Despite the great agricultural and ecological importance of efficient use of urea‐containing nitrogen fertilizers by crops, molecular and physiological identities of urea transport in higher plants have been investigated only in Arabidopsis. We performed short‐time urea‐influx assays which have identified a low‐affinity and high‐affinity (Km of 7.55 μM) transport system for urea‐uptake by rice roots (Oryza sativa). A high‐affinity urea transporter OsDUR3 from rice was functionally characterized here for the first time among crops. OsDUR3 encodes an integral membrane‐protein with 721 amino acid residues and 15 predicted transmembrane domains. Heterologous expression demonstrated that OsDUR3 restored yeast dur3‐mutant growth on urea and facilitated urea import with a Km of c. 10 μM in Xenopus oocytes. Quantitative reverse‐transcription polymerase chain reaction (qPCR) analysis revealed upregulation of OsDUR3 in rice roots under nitrogen‐deficiency and urea‐resupply after nitrogen‐starvation. Importantly, overexpression of OsDUR3 complemented the Arabidopsis atdur3‐1 mutant, improving growth on low urea and increasing root urea‐uptake markedly. Together with its plasma membrane localization detected by green fluorescent protein (GFP)‐tagging and with findings that disruption of OsDUR3 by T‐DNA reduces rice growth on urea and urea uptake, we suggest that OsDUR3 is an active urea transporter that plays a significant role in effective urea acquisition and utilisation in rice.

Investigations on concentration of mineral elements including Fe and Zn in wheat grains are important for human health. Two hundreds and sixtyfive cultivars and advanced lines were collected and sown at Anyang experimental station of the Institute of Crop Science of the Chinese Academy of Agriculture Sciences in season 2005-2006 to evaluate the genetic variation of major mineral element concentrations in wheat grain. Twenty-four selected cultivars were also planted at seven representative locations in seasons 2005-2006 and 2006-2007 to evaluate the effects of genotype, environment, and genotype by environment interaction on mineral element concentrations. The 265 genotypes displayed a large variation for all mineral elements investigated including Fe and Zn, ranging from 28.0 to 65.4 mg kg -1 and 21.4 to 58.2 mg kg -1 for Fe and Zn, with mean values of 39.2 and 32.3 mg kg -1 , respectively. Jimai 26, Henong 326, and Jingdong 8 displayed high Fe and Zn concentrations, and Jimai 26 and Henong 326 also displayed high concentrations of Cu, Mg, K, P, and protein content. Jingdong 8 is the most promising leading cultivar for increasing Fe and Zn concentrations. All mineral element concentrations including Fe and Zn were largely influenced by environment effects. Production of high Fe concentration can be best secured at Jiaozuo and Jinan, and high Zn concentration can be best secured at Jinan and Xuzhou, since samples from these locations in the two seasons are characterized by high Fe or Zn concentration, compared with the other locations. High and significant genotype by environment interaction effects on all mineral element concentrations were also observed, with ratios of genotype by environment to genotype variances all larger than 1.20. Grain Fe concentration was highly significant and positively correlated with that of Zn, indicating a high possibility to combine high Fe and Zn traits in wheat breeding. It also indicated strong positive correlations between concentrations of Fe, Zn, and protein content.

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