Selenium Isotope Studies In Plants

Selenium (Se), being an essential nutrient and a toxin, enters the food chain mainly via plants. Selenium isotope signatures were proved to be an excellent redox tracer, making it a promising tool for the exploration of the Se cycle in plants. The analytical method is sensitive on organic samples and requires particular preparation methods, which were developed and validated in this study. Plant cultivation setups revealed the applicability of these methods to trace plant internal processes.

Selenium (Se), being an essential nutrient and a toxin, enters the food chain mainly via plants. Selenium isotope signatures were proved to be an excellent redox tracer, making it a promising tool for the exploration of the Se cycle in plants. The analytical method is sensitive on organic samples and requires particular preparation methods, which were developed and validated in this study. Plant cultivation setups revealed the applicability of these methods to trace plant internal processes. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

This book covers many facets of plant selenium (Se) accumulation: molecular genetics, biochemistry, physiology, and ecological and evolutionary aspects. Broader impacts and applications of plant Se accumulation also receive attention. Plant Se accumulation is very relevant for environmental and human health. Selenium is both essential at low levels and toxic at high levels, and both Se deficiency and toxicity are problems worldwide. Selenium can positively affect crop productivity and nutritional value. Plants may also be used to clean up excess environmental Se. Selenium in plants has profound ecological impact, and likely contributes to Se movement in ecosystems and global Se cycling.

Wetlands remove many dissolved pollutants, such as SeO42−-, Cr(IV), NO3−, and perchlorate, from surface waters via reduction, sorption, and assimilation. Isotope fractionation studies can potentially distinguish reduction from other removal processes, and possibly quantify the amount of reduction, assuming that the correct isotope fractionation factor, [alpha], is applied. Typically, [alpha] is determined under laboratory conditions and subsequently applied to field data. In Chapter 2, I present effective fractionation factors, [alpha]eff, determined for a series of selenate reduction experiments in which reduction occurred within sediments and the fractionation was measured in overlying waters. The experiments showed that [alpha]eff measured in open waters overlying an intact sediment core was significantly less than that measured in a continuously-mixed, anoxic slurry of the same sediments. This difference can be attributed to the effect of a diffusion zone separating the reactant pool from the reaction sites in the sediments. Consequently, degree of reduction and dominant reduction pathways may be miscalculated when isotopic fractionation factors obtained from laboratory experiments are directly applied to field data. Chapter 3 presents results of the first comprehensive, multi-year (2003 - 2005) isotope and concentration survey of dissolved Se oxyanions and reduced Se in a wetland/lake setting. Overall, no strong isotopic contrast was observed, with the mean values of Se oxyanions and major reduced reservoirs in plants and sediments of [delta]80/76Se[subscript SRM] = 1.84[permil] to 2.65[permil]. These data are consistent with the results in Chapter 2 in that Se isotopes did not provide a means of detecting Se(VI) reduction or of discerning the dominant removal pathway for Se(VI). Concentration and isotope trends suggest most of the dissolved Se(IV) in the lake is from oxidation of reduced forms of Se within the wetland/lake system, not reduction of Se(VI). Release of Se from weathered shale, and delivery into surface water, induces only minor isotopic fractionation. Limited earlier reports that phytoplankton and macrophytes are slightly depleted in heavier isotopes relative to dissolved Se(VI) are confirmed, though macrophytes may contain a minor, more strongly depleted component. Selenium in zooplankton and fishes may be slightly depleted relative to Se in phytoplankton.

Crop plants growing under field conditions are constantly exposed to various abiotic and biotic stress factors leading to decreased yield and quality of produce. In order to achieve sustainable development in agriculture and to increase agricultural production for feeding an increasing global population, it is necessary to use ecologically compatible and environmentally friendly strategies to decrease the adverse effects of stresses on the plant. Selenium is one of the critical elements from the biological contexts because it is essential for human health; however, it becomes toxic at high concentrations. It has been widely reported that selenium can promote plant growth and alleviate various stresses as well as increase the quantity and quality of the yield of many plant species. Nonetheless, at high concentrations, selenium causes phytotoxicity. In the last decade, nanotechnology has emerged as a prominent tool for enhancing agricultural productivity. The production and applications of nanoparticles (NPs) have greatly increased in many industries, such as energy production, healthcare, agriculture, and environmental protection. The application of NPs has attracted interest for their potential to alleviate abiotic and biotic stresses in a more rapid, cost-effective, and more sustainable way than conventional treatment technologies. Recently, research related to selenium-NPs-mediated abiotic stresses and nutritional improvements in plants has received considerable interest by the scientific community. While significant progress was made in selenium biochemistry in relation to stress tolerance, an in-depth understanding of the molecular mechanisms associated with the selenium- and nano-selenium-mediated stress tolerance and bio-fortification in plants is still lacking. Gaining a better knowledge of the regulatory and molecular mechanisms that control selenium uptake, assimilation, and tolerance in plants is therefore vital and necessary to develop modern crop varieties that are more resilient to environmental stress. This book provides a comprehensive overview of the latest understanding of the physiological, biochemical, and molecular basis of selenium- and nano-selenium-mediated environmental stress tolerance and crop quality improvements in plants. It helps researchers to develop strategies to enhance crop productivity under stressful conditions and to better utilize natural resources to ensure future food security and to reduce environmental contamination. Finally, this book is a valuable resource for promoting future research into plant stress tolerance, and a reference book for researchers working on developing plants tolerant to abiotic and biotic stressors as well as bio-fortification and phytoremediation.

Selenium: Geobotany, Biochemistry, Toxicity, and Nutrition focuses on the properties, characteristics, reactions, applications, chemistry, and transformations of selenium. The book first offers information on the geological distribution of selenium, including the formation of seleniferous soils, chemical forms of selenium in soils, selenium in water, selenium on the sea floor and in sea water, and geobotany. The text then takes a look at selenium indicator in plants and accumulation of selenium by plants. Discussions focus on selenium accumulations in indicator plants; selenium accumulation in farm crops and native grasses; factors that influence selenium accumulation in plants; and identification of indicators by germination tests. The manuscript elaborates on selenium poisoning in animals and prevention and control of selenium poisoning. Acute selenium poisoning, chronic selenium poisoning by inorganic selenium, and recognition of poisonous range plants are also discussed. The text also examines selenium in nutrition and the chemistry of selenium. The publication is a valuable source of data for readers interested in the study of selenium.