Jan K. Schjørring

Zinc biofortification of cereals: problems and solutions

The goal of biofortification is to develop plants that have an increased content of bioavailable nutrients in their edible parts. Cereals serve as the main staple food for a large proportion of the world population but have the shortcoming, from a nutrition perspective, of being low in zinc and other essential nutrients. Major bottlenecks in plant biofortification appear to be the root-shoot barrier and--in cereals--the process of grain filling. New findings demonstrate that the root-shoot distribution of zinc is controlled mainly by heavy metal transporting P1B-ATPases and the metal tolerance protein (MTP) family. A greater understanding of zinc transport is important to improve crop quality and also to help alleviate accumulation of any toxic metals.

Iron fortification of rice seeds through activation of the nicotianamine synthase gene

The most widespread dietary problem in the world is mineral deficiency. We used the nicotianamine synthase (NAS) gene to increase mineral contents in rice grains. Nicotianamine (NA) is a chelator of metals and a key component of metal homeostasis. We isolated activation-tagged mutant lines in which expression of a rice NAS gene, OsNAS3, was increased by introducing 35S enhancer elements. Shoots and roots of the OsNAS3 activation-tagged plants (OsNAS3-D1) accumulated more Fe and Zn. Seeds from our OsNAS3-D1 plants grown on a paddy field contained elevated amounts of Fe (2.9-fold), Zn (2.2-fold), and Cu (1.7-fold). The NA level was increased 9.6-fold in OsNAS3-D1 seeds. Analysis by size exclusion chromatography coupled with inductively coupled plasma mass spectroscopy showed that WT and OsNAS3-D1 seeds contained equal amounts of Fe bound to IP6, whereas OsNAS3-D1 had 7-fold more Fe bound to a low molecular mass, which was likely NA. Furthermore, this activation led to increased tolerance to Fe and Zn deficiencies and to excess metal (Zn, Cu, and Ni) toxicities. In contrast, disruption of OsNAS3 caused an opposite phenotype. To test the bioavailability of Fe, we fed anemic mice with either engineered or WT seeds for 4 weeks and measured their concentrations of hemoglobin and hematocrit. Mice fed with engineered seeds recovered to normal levels of hemoglobin and hematocrit within 2 weeks, whereas those that ate WT seeds remained anemic. Our results suggest that an increase in bioavailable mineral content in rice grains can be achieved by enhancing NAS expression.

Policies for agricultural nitrogen management—trends, challenges and prospects for improved efficiency in Denmark

With more than 60% of the land farmed, with vulnerable freshwater and marine environments, and with one of the most intensive, export-oriented livestock sectors in the world, the nitrogen (N) pollution pressure from Danish agriculture is severe. Consequently, a series of policy action plans have been implemented since the mid 1980s with significant effects on the surplus, efficiency and environmental loadings of N. This paper reviews the policies and actions taken and their ability to mitigate effects of reactive N (Nr) while maintaining agricultural production. In summary, the average N-surplus has been reduced from approximately 170 kg N ha?1 yr?1 to below 100 kg N ha?1 yr?1 during the past 30 yrs, while the overall N-efficiency for the agricultural sector (crop?+?livestock farming) has increased from around 20?30% to 40?45%, the N-leaching from the field root zone has been halved, and N losses to the aquatic and atmospheric environment have been significantly reduced. This has been achieved through a combination of approaches and measures (ranging from command and control legislation, over market-based regulation and governmental expenditure to information and voluntary action), with specific measures addressing the whole N cascade, in order to improve the quality of ground- and surface waters, and to reduce the deposition to terrestrial natural ecosystems. However, there is still a major challenge in complying with the EU Water Framework and Habitats Directives, calling for new approaches, measures and technologies to mitigate agricultural N losses and control N flows.

Redistribution of sulphur during generative growth of barley plants with different sulphur and nitrogen status

The effect of S and N application on the distribution and redistribution of S compounds in spring barley (Hordeum vulgareL.) was investigated in pot experiments by determination of changes in the content of total-, sulphate- and thiol-S in leaves, ears and stems during the grain-filling period. Nitrogen and sulphur had a clear interactive effect on the yield of all plant parts with little or no effect of S at low N application rates and similar low effect of N without S application. The sulphate concentration in the different plant parts was markedly affected by the S application rate. This effect was most pronounced in leaves, less in stems and least in ears. In S-replete plants, leaf S decreased during grain development by an average of 28%, while in S-deficient plants the leaf S content did not change during the grain-filling period. About 70% of leaf N was redistributed to the ears in plants growing at adequate S supply compared with about 35% of leaf N in S-deficient plants. The proportion of ear N and S originating from the redistribution of leaf N and S was 49% and 23%, respectively. This study verifies that S is relatively immobile in plants as the proportion of S redistributed from leaf tissue was considerably smaller than that of N. The results suggest that the availability of soil or root S during grain-filling is important for an adequate S supply to the developing grains as the distribution of S to the ears considerably exceeded the amount exported from the leaves.

Model of how plants sense zinc deficiency

Plants are capable of inducing a range of physico-chemical and microbial modifications of the rhizosphere which can mobilize mineral nutrients or prevent toxic elements from entering the roots. Understanding how plants sense and adapt to variations in nutrient availability is essential in order to develop plant-based solutions addressing nutrient-use-efficiency and adaptation to nutrient-limited or -toxic soils. Recently two transcription factors of the bZIP family (basic-region leucine zipper) have been identified in Arabidopsis and shown to be pivotal in the adaptation response to zinc deficiency. They represent not only the first regulators of zinc homeostasis identified in plants, but also a very promising starting-point that can provide new insights into the molecular basis of how plants sense and adapt to the stress of zinc deficiency. Considering the available information thus far we propose in this review a putative model of how plants sense zinc deficiency.

Regulation of Phosphate Influx in Winter Wheat: Root-Shoot Phosphorus Interactions

Summary Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown at various external phosphate (Pi) levels for 10 days in order to investigate the effects of P nutritional status of roots and shoots on Pi influx and efflux measured at intervals the following 7 days. When external Pi was supplied to plants previously deprived of phosphate, P accumulated in the shoots to levels around four times that of controls due to high influx rates and proportionally large P-transport to the shoot. Efflux was, however, comparatively low. Split-root experiments with plants where one or two of the three seminal roots were pretreated with Pi for a period of up to 5 h showed increased phosphate influx in the non-treated root(s) when transferred to 32P-labelled Pi solution. Pretreatment with elevated light intensity for 5 h prior to split-root uptake experiments resulted in higher Pi influx in the part of the root system formerly exposed to Pi. The findings indicate that the shoot P concentration exerted a great effect in regulating the phosphate influx. The mechanisms involved are discussed.