SummaryTo investigate the uptake and long-distance translocation of sulphate in plants, we have characterized three cell-type-speci®c sulphate transporters, Sultr1;1, Sultr2;1 and Sultr2;2 in Arabidopsis thaliana. Heterologous expression in the yeast sulphate transporter mutant indicated that Sultr1;1 encodes a high-af®nity sulphate transporter (K m for sulphate 3.6 K 0.6 mM), whereas Sultr2;1 and Sultr2;2 encode low-af®nity sulphate transporters (K m for sulphate 0.41 K 0.07 mM and > 1.2 mM, respectively). In Arabidopsis plants expressing the fusion gene construct of the Sultr1;1 promoter and green¯uorescent protein (GFP), GFP was localized in the lateral root cap, root hairs, epidermis and cortex of roots. bglucuronidase (GUS) expressed with the Sultr2;1 promoter was speci®cally accumulated in the xylem parenchyma cells of roots and leaves, and in the root pericycles and leaf phloem. Expression of the Sultr2;2 promoter±GFP fusion gene showed speci®c localization of GFP in the root phloem and leaf vascular bundle sheath cells. Plants continuously grown with low sulphate concentrations accumulated high levels of Sultr1;1 and Sultr2;1 mRNA in roots and Sultr2;2 mRNA in leaves. The abundance of Sultr1;1 and Sultr2;1 mRNA was increased remarkably in roots by short-term stress caused by withdrawal of sulphate. Addition of selenate in the sulphate-suf®cient medium increased the sulphate uptake capacity, tissue sulphate content and the abundance of Sultr1;1 and Sultr2;1 mRNA in roots. Concomitant decrease of the tissue thiol content after selenate treatment was consistent with the suggested role of glutathione (GSH) as a repressive effector for the expression of sulphate transporter genes.

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Sulfur is an essential macroelement in plant and animal nutrition. Plants assimilate inorganic sulfate into two sulfur-containing amino acids, cysteine and methionine. Low supply of sulfate leads to decreased sulfur pools within plant tissues. As sulfurrelated metabolites represent an integral part of plant metabolism with multiple interactions, sulfur deficiency stress induces a number of adaptive responses, which must be coordinated. To reveal the coordinating network of adaptations to sulfur deficiency, metabolite profiling of Arabidopsis has been undertaken. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry techniques revealed the response patterns of 6,023 peaks of nonredundant ion traces and relative concentration levels of 134 nonredundant compounds of known chemical structure. Here, we provide a catalogue of the detected metabolic changes and reconstruct the coordinating network of their mutual influences. The observed decrease in biomass, as well as in levels of proteins, chlorophylls, and total RNA, gives evidence for a general reduction of metabolic activity under conditions of depleted sulfur supply. This is achieved by a systemic adjustment of metabolism involving the major metabolic pathways. Sulfur/carbon/nitrogen are partitioned by accumulation of metabolites along the pathway O-acetylserine to serine to glycine, and are further channeled together with the nitrogen-rich compound glutamine into allantoin. Mutual influences between sulfur assimilation, nitrogen imbalance, lipid breakdown, purine metabolism, and enhanced photorespiration associated with sulfur-deficiency stress are revealed in this study. These responses may be assembled into a global scheme of metabolic regulation induced by sulfur nutritional stress, which optimizes resources for seed production.For living organisms with a complex hierarchical organization, such as plants, the necessity for close coordination of various elements requires systemic organization at the level of the whole organism. Additional complexity is imposed on the system through environmental variability. Due to the inability to escape unfavorable environmental conditions, plants have evolved complex mechanisms to sense and transmit external signals to the internal decision points to trigger the adaptive response program for homeostatic maintenance. Such adaptive programs are accomplished at multiple organizational levels, e.g. gene and enzymatic activities, being finally manifested in altered metabolite concentrations. This study describes the metabolic component of the whole-system response to sulfur deficiency, as an environmental perturbation, with special emphasis on the mechanisms of the response coordination.Despite the difficulties in measuring metabolites due to their dynamic behavior and complex chemistry, new methods allow profiling of low molecular weight compounds, with gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) being the most robust (Stitt and Fernie, 2003). In th...

Se is an essential element for animals. In man low dietary Se intakes are associated with health disorders including oxidative stress-related conditions, reduced fertility and immune functions and an increased risk of cancers. Although the reference nutrient intakes for adult females and males in the UK are 60 and 75 μg Se/d respectively, dietary Se intakes in the UK have declined from >60 μg Se/d in the 1970s to 35 μg Se/d in the 1990s, with a concomitant decline in human Se status. This decline in Se intake and status has been attributed primarily to the replacement of milling wheat having high levels of grain Se and grown on high-Se soils in North America with UK-sourced wheat having low levels of grain Se and grown on low-Se soils. An immediate solution to low dietary Se intake and status is to enrich UK-grown food crops using Se fertilisers (agronomic biofortification). Such a strategy has been adopted with success in Finland. It may also be possible to enrich food crops in the longer term by selecting or breeding crop varieties with enhanced Se-accumulation characteristics (genetic biofortification). The present paper will review the potential for biofortification of UK food crops with Se.

Winter wheat (Triticum aestivum L.) was grown for 4 years in multi-factorial field trials at Rothamsted, southern England. Thirty nine elite commercial cultivars (primarily short-straw) were grown including those released in the UK over a 25-year period, a selection of continental varieties, and three older, tall varieties. Varieties spanned the quality spectrum from 'bread' to 'feed'. The crops were given ammonium nitrate at five rates in the range 0-350 kg-N/ha as a 3-way split. The aim was to quantify the genotypic variation in total nitrogen uptake by grain and straw (total-Nup), and in nitrogen utilization efficiency for grain yield (grain yield per unit of N taken up) (grain-NutE). Depending on treatment, grain yield ranged from 2.1 to 11.8 t/ha (85% DM), grain %N from 1.1% to 2.8% (in DM), total-Nup from 31 to 264 kg-N/ha, and grain-NutE from 27 to 77 kg-DM/kg-N. There were significant varietal differences in total N-uptake and grain-NutE both between 'tall' and 'short' varieties and within 'short' varieties. The best short varieties took up 31-38 kg/ha more N than the worst, and grain-NutE was 24-42% better, depending on N-rate. Up to 77% of the variation in grain-NutE was accounted for by yield. All interactions between the factors 'Variety', 'Year', and 'N-rate' were highly significant, but only 'Year × N-rate' made an important contribution to the variation. There was a near-functional inverse relationship between grain-NutE and grain %N; high-quality wheat (high grain %N) can be expected to have a low grain-NutE. The four key variables determining N-efficiency in a wheat crop-grain yield, grain %N, total N-uptake and nitrogen harvest index (NHI)-are ultimately constrained by the law of conservation of matter. Improving grain-NutE for fixed total-Nup and NHI can only be achieved at the expense of grain %N. To improve grain-NutE and maintain grain %N requires a simultaneous increase in NHI and grain starch yield which may be difficult to achieve in practice. The law of conservation of matter ultimately sets a limit on the physiological and agronomic processes that determine crop N requirements. A high yield of high-quality grain (high grain %N) requires a high input and uptake of nitrogen.

Abstract:There is a growing need to increase global crop yields, whilst minimising use of resources such as land, fertilisers and water. Agricultural researchers use ground-based observations to identify, select and develop crops with favourable genotypes and phenotypes; however, the ability to collect rapid, high quality and high volume phenotypic data in open fields is restricting this. This study develops and assesses a method for deriving crop height and growth rate rapidly from multi-temporal, very high spatial resolution (1 cm/pixel), 3D digital surface models of crop field trials produced via Structure from Motion (SfM) photogrammetry using aerial imagery collected through repeated campaigns flying an Unmanned Aerial Vehicle (UAV) with a mounted Red Green Blue (RGB) camera. We compare UAV SfM modelled crop heights to those derived from terrestrial laser scanner (TLS) and to the standard field measurement of crop height conducted using a 2 m rule. The most accurate UAV-derived surface model and the TLS both achieve a Root Mean Squared Error (RMSE) of 0.03 m compared to the existing manual 2 m rule method. The optimised UAV method was then applied to the growing season of a winter wheat field phenotyping experiment containing 25 different varieties grown in 27 m 2 plots and subject to four different nitrogen fertiliser treatments. Accuracy assessments at different stages of crop growth produced consistently low RMSE values (0.07, 0.02 and 0.03 m for May, June and July, respectively), enabling crop growth rate to be derived from differencing of the multi-temporal surface models. We find growth rates range from −13 mm/day to 17 mm/day. Our results clearly display the impact of variable nitrogen fertiliser rates on crop growth. Digital surface models produced provide a novel spatial mapping of crop height variation both at the field scale and also within individual plots. This study proves UAV based SfM has the potential to become a new standard for high-throughput phenotyping of in-field crop heights.

Three plant sulfate transporter cDNAs have been isolated by complementation of a yeast mutant with a cDNA library derived from the tropical forage legume Stylosanthes hamata. Two of these cDNAs, shstl and shst2, encode high-affinity H+/sulfate cotransporters that mediate the uptake of sulfate by plant roots from low concentrations of sulfate in the soil solution. The third, shst3, represents a different subtype encoding a lower affinity H+/sulfate cotransporter, which may be involved in the internal transport of sulfate between cellular or subcellular compartments within the plant. The steady-state level of mRNA corresponding to both subtypes is subject to regulation by signals that ultimately respond to the external sulfate supply. These cDNAs represent the identification of plant members of a family of related sulfate transporter proteins whose sequences exhibit significant amino acid conservation in filamentous fungi, yeast, plants, and mammals.All plants need to absorb essential nutrient anions against large gradients of electrochemical potential; this is true for plants in both natural and agricultural environments. Evidently, transport mechanisms of high affinity have evolved, but their precise nature remains obscure, although they have been a major research topic for decades. Despite a wealth of physiological information, the molecular nature of the transporters and the way in which they are regulated are unknown.Sulfate transport in plant roots or cultured cells has highand low-affinity components (1); the former clearly respond to the sulfur-status of the organism, being strongly derepressed by sulfur-starvation and rapidly repressed by the restoration of a sufficient sulfur supply (2-4). High rates of sulfate uptake by previously sulfur-starved cells or roots appear to depend on protein synthesis; treatment with cycloheximide decreases sulfate influx with kinetics very similar to repression by sulfate (4, 5). Such results raised the question as to whether the control of transport activity was translational, or by posttranslational modification of the transporter, rather than by transcription of the genes that encode it. Here we present results demonstrating that changes in the level of the mRNA encoding the transporter are remarkably rapid and are quite compatible with changes in transport activity.Membrane transport proteins from a wide variety of sources may be placed into distinct groups based upon primary sequence similarity or structural features (6, 7). Sequence homologies between the Neurospora crassa sulfate transporter (8) and a number of genes not previously associated with sulfate transport, including a human mucosa protein (9) and a nodulespecific protein (10), have been recognized recently (11). More recent additions to this group are a rat liver sulfate transporter (12), a human gene, DTD, a mutation in which results in diastrophic dysplasia (13), and the yeast high-affinity sulfate transporter (14). In this paper we report the cloning and analysis of plant members of this family,...

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