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Crop production is often limited by low phytoavailability of essential mineral elements and/or the presence of excessive concentrations of potentially toxic mineral elements. In this overview, White and Brown (pp. 1073–1080) describe how current research in plant mineral nutrition is addressing the problems of mineral toxicities in agricultural soils to provide food security, the optimization of fertilizer applications for economic and environmental sustainability, and the production of edible crops that contribute sufficient mineral elements for adequate animal and human nutrition.
Understanding cell-specific processes is fundamental to understanding whole-plant physiology. With respect to plant nutrition, certain elements are accumulated preferentially in specific cell types. Conn and Gilliham (pp. 1081–1102) provide a comprehensive review, highlighting the robust distributions of cadmium, calcium and sodium within plant tissue, the consequences for storage of other elements, and likely control mechanisms through cell-specific expression of defined solute transporters.
Boron (B) is toxic to plant growth at high concentrations, but is also essential in cross-linking pectic polysaccharides in primary cell walls. Miwa and Fujiwara (pp. 1103–1108) review the role of transporters in maintaining homeostasis and show that plants sense internal and external B conditions and regulate B transport by modulating the expression and/or accumulation of these transporters. Results obtained in model plants are applicable to other plant species, and such knowledge may be useful in producing plants or crops tolerant to soils containing low or high B.
The rice transcription factors IDEF1 and IDEF2 mediate the plant's response to iron deficiency. Kobayashi et al. (pp. 1109–1117) report the spatial expression and regulation of IDEF1 and IDEF2, clarifying that these genes are constitutively expressed during both vegetative and reproductive stages. The spatial expression patterns and gene regulation of IDEF1 and IDEF2 in roots are generally conserved under conditions of iron sufficiency and deficiency, suggesting complicated interactions with unknown factors for sensing and transmitting iron-deficiency signals.
Aluminium (Al) resistance in common bean (Phaseolus vulgaris) is known to be due to exudation of citrate from the roots after a lag phase, indicating the induction of gene transcription and protein synthesis. Eticha et al. (pp. 1119–1128) show that the expression of a citrate transporter MATE gene is crucial in this process; however, sustained citrate release and genotypic Al resistance requires, in addition, the continuous synthesis and maintenance of a cytosolic citrate pool in the root apex.
Barley is much more Mn-sensitive than rice. Using physiological and proteomic approaches, Führs et al. (pp. 1129–1140) provide evidence that Mn toxicity in barley involves apoplastic lesions mediated by peroxidases, whereas the high Mn tolerance of old leaves of rice involves a high Mn-binding capacity of the cell walls. In young rice leaves Mn toxicity is related to Mn-induced nutrient deficiencies.
Productive agriculture needs a large amount of expensive nitrogenous fertilizers. Improving nitrogen-use efficiency (NUE) of crop plants is thus of key importance. For most plant species, NUE mainly depends on how plants extract inorganic nitrogen from the soil, assimilate nitrate and ammonium, and recycle organic nitrogen. Masclaux-Daubresse et al. (pp. 1141–1157) present an integrative examination of the physiological, metabolic and genetic aspects of nitrogen uptake, assimilation and remobilization in this review. The approaches used to detect limiting factors may enable manipulation of enzymes and regulatory processes to improve NUE components.
The role of plant amino acid transporters in the context of seasonal nitrogen cycling has to date not received as much attention as it merits. Couturier et al. (pp. 1159–1169) establish a relationship between glutamine synthesized in leaves and arginine synthesized in stems during senescence in poplar, Populus trichocarpa, and suggest a key role for the cationic amino acid transporter Pt-CAT11in N remobilization by facilitating glutamine loading into phloem vessels.
Nitrogen-use efficiency (NUE) of cereals needs to be improved by N management, traditional plant breeding methods and/or biotechnology, while maintaining – or optimally increasing – crop yields. Beatty et al. (pp. 1171–1182) compare spring barley (Hordeum vulgare) genotypes grown on different nitrogen levels in field and growth-chamber conditions in order to determine the effects on N uptake, N utilization and, ultimately, NUE. With similar growth and NUE characteristics across both field and chambers, they demonstrate that simplified, low-variable growth environments can help pinpoint genetic targets for improving spring barley NUE.
Phosphorus acquisition depends on rhizosphere processes that are not accounted for in plant nutrition models. Devau et al. (pp. 1183–1197) use a mechanistic geochemical model to show that on top of P uptake and rhizosphere alkalization, Ca uptake is implied in the changes of P availability occurring in the rhizosphere of durum wheat, Triticum turgidum durum.
Crops with greater potassium-acquisition efficiency (KUpE) and/or K-utilization efficiency (KUtE) require less K-fertilizer. Studying several hundred accessions, White et al. (pp. 1199–1210) find sufficient species-wide genetic variation to breed for both KUtE and KUpE in Brassica oleracea. However, quantitative trait loci (QTL) affecting these traits differ between glasshouse- and field-grown plants. A QTL affecting KUtE in glasshouse-grown plants, which encompasses genes encoding K+ transporters, is confirmed using substitution lines.
Micronutrient malnutrition afflicts three billion people worldwide. Chatzav et al. (pp. 1211–1220) report a wide genetic diversity in grain nutrients among accessions of emmer wheat, Triticum turgidum ssp. dicoccoides, with zinc, iron and protein concentrations in wild accessions being about twice those found in domesticated genotypes. Wild emmer wheat germplasm thus offers unique opportunities to exploit favourable alleles for grain nutrient properties that have been excluded from the domesticated wheat gene pool.
The genetic basis of mineral accumulation in crop seeds is not well understood. Ding et al. (pp. 1221–1234) examine quantitative trait loci (QTLs) for seed mineral concentrations in oilseed rape, Brassica napus, grown with either normal or low phosphorus supply. They find a total of 78 putative QTLs for seven minerals, and 21 genes involved in ion homeostasis are mapped to the QTL intervals. QTLs are often clustered within a linkage group, suggesting that common mechanisms might control the accumulation of several mineral elements in seeds.