Selenium (Se) is an essential mineral element for animals and humans, which they acquire largely from plants. The Se concentration in edible plants is determined by the Se phytoavailability in soils. ...Selenium is not an essential element for plants, but excessive Se can be toxic. Thus, soil Se phytoavailability determines the ecology of plants. Most plants cannot grow on seleniferous soils. Most plants that grow on seleniferous soils accumulate <100 mg Se kg(-1) dry matter and cannot tolerate greater tissue Se concentrations. However, some plant species have evolved tolerance to Se, and commonly accumulate tissue Se concentrations >100 mg Se kg(-1) dry matter. These plants are considered to be Se accumulators. Some species can even accumulate Se concentrations of 1000-15 000 mg Se kg(-1 )dry matter and are called Se hyperaccumulators.
This article provides an overview of Se uptake, translocation and metabolism in plants and highlights the possible genetic basis of differences in these between and within plant species. The review focuses initially on adaptations allowing plants to tolerate large Se concentrations in their tissues and the evolutionary origin of species that hyperaccumulate Se. It then describes the variation in tissue Se concentrations between and within angiosperm species and identifies genes encoding enzymes limiting the rates of incorporation of Se into organic compounds and chromosomal loci that might enable the development of crops with greater Se concentrations in their edible portions. Finally, it discusses transgenic approaches enabling plants to tolerate greater Se concentrations in the rhizosphere and in their tissues.
The trait of Se hyperaccumulation has evolved several times in separate angiosperm clades. The ability to tolerate large tissue Se concentrations is primarily related to the ability to divert Se away from the accumulation of selenocysteine and selenomethionine, which might be incorporated into non-functional proteins, through the synthesis of less toxic Se metabilites. There is potential to breed or select crops with greater Se concentrations in their edible tissues, which might be used to increase dietary Se intakes of animals and humans.
Selenium metabolism in plants White, Philip J.
Biochimica et biophysica acta. General subjects,
November 2018, 2018-11-00, 20181101, Letnik:
1862, Številka:
11
Journal Article
Recenzirano
Selenium (Se) is not an essential element for plants, although it can benefit their growth and survival in some envionments. Excess tissue Se concentrations are toxic. The ability to sequester Se in ...vacuoles, synthesise non-toxic Se metabolites, or volatilise Se compounds determines maximum tissue Se concentrations and the ability to colonise seleniferous soils.
This review first classifies plant species on their abilities to accumulate Se in their tissues and to colonise seleniferous soils. It then presents our knowledge of Se uptake by roots and its movement within the plant, the primary and secondary metabolism of Se in plants, effects of Se on sulfur and nitrogen metabolism, and the detoxification of excessive Se by plants. Finally, it presents a current hypothesis for the evolution of seleniferous flora.
Selenium and sulfur share the same primary metabolism. When grown in the same environment, most plant species have similar tissue Se/S quotients. However, Se-hyperaccumulator species, which can have tissue Se concentrations >1 mg g−1 dry matter, have larger Se/S quotients than other species. Secondary Se metabolism determines differences in tissue Se concentration among plant species. Among non-hyperaccumulator species, alliums and brassicas have particularly large tissue Se concentrations. Selenium hyperaccumulation results from the effective metabolic detoxification of Se in tissues.
Differences in Se metabolism determine the maximum Se concentrations in plant tissues, which is important for the delivery of Se to diets of herbivores and for the evolution of plant species to colonise seleniferous soils.
•Selenium (Se) and sulfur (S) share the same primary metabolism in plants.•Most angiosperm (flowering plant) species have similar shoot Se/S quotients.•Secondary Se metabolism determines tissue Se concentration differences among species.•Se hyperaccumulation results from effective metabolic detoxification of Se in tissues.•Se metabolism determines the ecology of seleniferous soils.
Summary
The concept of a root economics space (RES) is increasingly adopted to explore root trait variation and belowground resource‐acquisition strategies. Much progress has been made on ...interactions of root morphology and mycorrhizal symbioses. However, root exudation, with a significant carbon (C) cost (c. 5–21% of total photosynthetically fixed C) to enhance resource acquisition, remains a missing link in this RES. Here, we argue that incorporating root exudation into the structure of RES is key to a holistic understanding of soil nutrient acquisition. We highlight the different functional roles of root exudates in soil phosphorus (P) and nitrogen (N) acquisition. Thereafter, we synthesize emerging evidence that illustrates how root exudation interacts with root morphology and mycorrhizal symbioses at the level of species and individual plant and argue contrasting patterns in species evolved in P‐impoverished vs N‐limited environments. Finally, we propose a new conceptual framework, integrating three groups of root functional traits to better capture the complexity of belowground resource‐acquisition strategies. Such a deeper understanding of the integrated and dynamic interactions of root morphology, root exudation, and mycorrhizal symbioses will provide valuable insights into the mechanisms underlying species coexistence and how to explore belowground interactions for sustainable managed systems.
Breeding for advantageous root traits will play a fundamental role in improving the efficiency of water and nutrient acquisition, closing yield gaps, and underpinning the "Evergreen Revolution" that ...must match crop production with human demand.
This preface provides an overview of a Special Issue of Annals of Botany on "Root traits benefitting crop production in environments with limited water and nutrient availability". The first papers in the Special Issue examine how breeding for reduced shoot stature and greater harvest index during the Green Revolution affected root system architecture. It is observed that reduced plant height and root architecture are inherited independently and can be improved simultaneously to increase the acquisition and utilisation of carbon, water and mineral nutrients. These insights are followed by papers examining beneficial root traits for resource acquisition in environments with limited water or nutrient availability, such as deep rooting, control of hydraulic conductivity, formation of aerenchyma, proliferation of lateral roots and root hairs, foraging of nutrient-rich patches, manipulation of rhizosphere pH and the exudation of low molecular weight organic solutes. The Special Issue concludes with papers exploring the interactions of plant roots and microorganisms, highlighting the need for plants to control the symbiotic relationships between mycorrhizal fungi and rhizobia to achieve maximal growth, and the roles of plants and microbes in the modification and development of soils.
Limitation of plant productivity by phosphorus (P) supply is widespread and will probably increase in the future. Relatively large amounts of P fertilizer are applied to sustain crop growth and ...development and to achieve high yields. However, with increasing P application, plant P efficiency generally declines, which results in greater losses of P to the environment with detrimental consequences for ecosystems.
A strategy for reducing P input and environmental losses while maintaining or increasing plant performance is the development of crops that take up P effectively from the soil (P acquisition efficiency) or promote productivity per unit of P taken up (P utilization efficiency). In this review, we describe current research on P metabolism and transport and its relevance for improving P utilization efficiency.
Enhanced P utilization efficiency can be achieved by optimal partitioning of cellular P and distributing P effectively between tissues, allowing maximum growth and biomass of harvestable plant parts. Knowledge of the mechanisms involved could help design and breed crops with greater P utilization efficiency.
The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, ...or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of 'promoter' substances, such as ascorbate, f-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of 'antinutrients', such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.
To avoid loss of yield, crops must maintain tissue potassium (K) concentrations above 5–40 mg K (g DM)–1. The supply of K from the soil is often insufficient to meet this demand and, in many ...agricultural systems, K fertilisers are applied to crops. However, K fertilisers are expensive. There is interest, therefore, in reducing applications of K fertilisers either by improving agronomy or developing crop genotypes that use K fertilisers more efficiently. Agronomic K fertiliser use efficiency is determined by the ability of roots to acquire K from the soil, which is referred to as K uptake efficiency (KUpE), and the ability of a plant to utilise the K acquired to produce yield, which is referred to as K utilisation efficiency (KUtE). There is considerable genetic variation between and within crop species in both KUpE and KUtE, and chromosomal loci affecting these characteristics have been identified in Arabidopsis thaliana and several crop species. Plant traits that increase KUpE include (1) exudation of organic compounds that release more non‐exchangeable soil K, (2) high root K uptake capacity, (3) early root vigour, high root‐to‐shoot ratios, and high root length densities, (4) proliferation of roots throughout the soil volume, and (5) high transpiration rates. Plant traits that increase KUtE include (1) effective K redistribution within the plant, (2) tolerance of low tissue K concentrations, and, at low tissue K concentrations, (3) maintenance of optimal K concentrations in metabolically active cellular compartments, (4) replacement of K in its non‐specific roles, (5) redistribution of K from senescent to younger tissues, (6) maintenance of water relations, photosynthesis and canopy cover, and (7) a high harvest index. The development of crop genotypes with these traits will enable K fertiliser applications to be reduced.
Excessive N fertilization results in low N-use efficiency (NUE) without any yield benefits and can have profound, long-term environmental consequences including soil acidification, N leaching and ...increased production of greenhouse gases. Improving NUE in crop production has been a longstanding, worldwide challenge. A crucial strategy to improve NUE is to enhance N uptake by roots. Taking maize as a model crop, we have compared root dry weight (RDW), root/shoot biomass ratio (R/S), and NUE of maize grown in the field in China and in western countries using data from 106 studies published since 1959. Detailed analysis revealed that the differences in the RDW and R/S of maize at silking in China and the western countries were not derived from variations in climate, geography, and stress factors. Instead, NUE was positively correlated with R/S and RDW; R/S and NUE of maize varieties grown in western countries were significantly greater than those grown in China. We then testified this conclusion by conducting field trials with representative maize hybrids in China (ZD958 and XY335) and the US (P32D79). We found that US P32D79 had a better root architecture for increased N uptake and removed more mineral N than Chinese cultivars from the 0-60 cm soil profile. Reported data and our field results demonstrate that a large and deep root, with an appropriate architecture and higher stress tolerance (higher plant density, drought and N deficiency), underlies high NUE in maize production. We recommend breeding for these traits to reduce the N-fertilizer use and thus N-leaching in maize production and paying more attention to increase tolerance to stresses in China.
•The scheduling of supplemental irrigation (SI) affected wheat yield components.•Irrigating after anthesis increased photosynthesis without excessive transpiration.•An appropriate delay in SI delayed ...leaf senescence and increased grain yield.•Excess irrigation or drought during late grain-filling reduced water use efficiency.
Food security in the Huang-Huai-Hai Plain of China is threatened by water shortages and the early senescence of wheat induced by water deficit. However, effective water-saving irrigation techniques based on the consideration of precipitation, soil water storage and crop requirements are rudimentary. Information on the responses of transpiration, photosynthesis and plant senescence to Supplemental Irrigation (SI) at different stages of crop development is urgently required. Field experiments were performed in 2007–2008 and 2008–2009 to provide this information. Four irrigation treatments were tested: rainfed (W0), SI at Zadoks stage 31 (Z31) and Z60 (W1), SI at Z34 and Z69 (W2), and SI at Z39 and Z77 (W3). The SI brought soil water content in the 0–140cm profile to 75% field capacity. Supplemental Irrigation increased grain yields and the scheduling of SI affected yield components. Delaying SI from Z31 and Z60 (W1) to Z34 and Z69 (W2) decreased the number of spikes, but increased the number of grains per spike, 1000-grain weight and crop yield. Activities of superoxide dismutase (SOD) and catalase (CAT) in flag leaves of plants from the W2 treatment were greater, and malondialdehyde (MDA) concentrations in flag leaves were lower, than those from the W3 treatment until 24 days after anthesis and those from the W1 and W0 treatments throughout anthesis. Although SI increased both photosynthetic rate (Pn) and transpiration rate (E), the net effect was greater instantaneous water use efficiency (WUEleaf=Pn/E). Supplemental Irrigation also increased agronomic Water Use Efficiency (grain yield/crop evapotranspiration). Delaying SI decreased the grain filling rate at the beginning of grain filling in 2007–2008, but increased the grain filling rate later in grain filling in both 2007–2008 and 2008–2009. An appropriate delay in SI (W2) increased grain yield substantially, but if SI was applied too late (W3), there was less effect on grain yield, probably because of an inhibition of assimilate remobilization to the grain due to delayed senescence.
PDF
