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, Volume:
1862, Issue:
11
Journal Article
Peer reviewed
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.
Background Low phytoavailability of phosphorus (P) limits crop production worldwide. Increasing seed P content can improve plant establishment and increase yields. This is thought to be a consequence ...of faster initial root growth, which gives seedlings earlier access to growth-limiting resources, such as water and mineral elements. It can be calculated that seed P reserves can sustain maximal growth of cereal seedlings for several weeks after germination, until the plant has three or more leaves and an extensive root system. Case study In this issue of Plant and Soil, Muhammad Nadeem and colleagues report (1) that measurable P uptake by roots of maize seedlings begins about 5 d after germination, (2) that the commencement of root P uptake is coincident with the transition from carbon heterotrophy to carbon autotrophy, and (3) that neither the timing nor the rate of uptake of exogenous P by the developing root system is influenced by initial seed P content. Hypothesis Here it is hypothesised that the delay in P acquisition by roots of maize seedlings might be explained if the expression of genes encoding phosphate transporters is not upregulated either (1) because the plant has sufficient P for growth or (2) because a systemic signal from the shoot, which relies on photosynthesis or phloem development, is not produced, translocated or perceived.
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.
Intercropping is a farming practice involving two or more crop species, or genotypes, growing together and coexisting for a time. On the fringes of modern intensive agriculture, intercropping is ...important in many subsistence or low‐input/resource‐limited agricultural systems. By allowing genuine yield gains without increased inputs, or greater stability of yield with decreased inputs, intercropping could be one route to delivering ‘sustainable intensification’. We discuss how recent knowledge from agronomy, plant physiology and ecology can be combined with the aim of improving intercropping systems. Recent advances in agronomy and plant physiology include better understanding of the mechanisms of interactions between crop genotypes and species – for example, enhanced resource availability through niche complementarity. Ecological advances include better understanding of the context‐dependency of interactions, the mechanisms behind disease and pest avoidance, the links between above‐ and below‐ground systems, and the role of microtopographic variation in coexistence. This improved understanding can guide approaches for improving intercropping systems, including breeding crops for intercropping. Although such advances can help to improve intercropping systems, we suggest that other topics also need addressing. These include better assessment of the wider benefits of intercropping in terms of multiple ecosystem services, collaboration with agricultural engineering, and more effective interdisciplinary research.
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.
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