Essential trace metals: micronutrients with large impact

Essential trace metals: micronutrients with large impact Among the metals found in the environment, plants utilize copper, iron, manganese, molybdenum, nickel, and zinc as micronutrients. Understanding of their uptake, behaviour in plant cells, and interactions at the molecular level is essential not only to improve plant nutrition and crop yield but also to improve human diet. The translation of experimental results obtained in model species to crops is an important goal that will eventually help improve micronutrient levels in food. This review collection discusses current state of the art and possible future directions related to the plant-essential metal relationship, including both basic molecular research and applied aspects related to agriculture and human nutrition. One of the earliest research fields in experimental plant sciences deals with the plant-metal relationship. From the 18th century, this field has examined in detail the uptake, accumulation , translocation, speciation, and physiological role of trace metals, as well as the diverse effects of their deficiency and excess on plant physiology and molecular processes. Owing to the active research in the past decades, specific primary and secondary active transport systems have been revealed through which land plants are able to absorb, distribute, and sequester essential metal ions. Essential trace metals have diverse biological roles in plants, but in general they are enzyme cofac-tors and participate in vital processes such as the mitochondrial and photosynthetic electron transport chains, CO 2 fixation, the antioxidant defence system, nitrogen and sulfur metabolism, and phytohormone synthesis. The limited amount or bioavail-ability of essential metals causes various deficiency symptoms in plants, such as growth retardation, yellowing, susceptibility to abiotic and biotic stresses, and yield reduction. Furthermore, plant nutrient deficiencies are closely related to human malnutrition , which is partly due to the importance of plant-based diets in human nutrition. Beyond enrichment through agricultural biofortification practices (e.g. fertilization), crop breeding for higher mineral micronutrient content is an available strategy to alleviate trace metal deficiencies in humans. Some of the articles in this special issue summarize the latest molecular-level knowledge and emphasize future directions, while others focus on applied aspects in plant essential metal homeostasis research. All the authors draw attention to the need for a better knowledge of trace metal homeostasis. Zinc and iron homeostasis in plants: understanding of molecular mechanisms It has long been known that zinc (Zn) has diverse regulatory functions in a wide range of plant proteins, including enzymes and transcription factors (Broadley et al., 2007). However, the question of which processes regulate the availability of Zn in the cell for proteins, transporters, and sensor partners remains unanswered. The review by Clemens (2022) details the intra-cellular forms and distribution of Zn, which determine 'free Zn' and 'Zn buffers', that is, Zn bound by metabolites or pep-tides. The main Zn storage organelles are the vacuole and the endoplasmic reticulum, and the influx and efflux transporters localized in their membranes serve as a dynamic control of local Zn concentrations in space and time. Based on results obtained in animal systems, the author rightly assumes that spatially controlled cytosolic Zn may also modulate phosphorylation cascades and influence protein-protein interactions in plant cells. Owing to the diverse biological role of Zn and its frequently limited availability in soils, Zn deficiency in plants has received special attention in basic molecular biology research (Assunção et al., 2010; Campos et al., 2017; Lilay et al., 2021). Thiébaut and Hanikenne (2022) provide a valuable summary of the knowledge gained so far in Arabidopsis, which emphasizes the urgent need for this knowledge to be translated to dicotyledonous crop species. They consider Zn requirements, the impact of Zn deficiency, the function and regulation of Zn transporters, Zn sensing, and the role of phytohormones in the Zn deficiency response in economically important dicot crops, providing a gap-filling review of the field. Iron (Fe) deficiency is one of the most common nutrient deficiencies in the world, and multiple studies have therefore focused on Fe uptake, transport, and homeostasis in plants (e.g. Hell and Stephan, 2003). Although a lot of attention has been given to Fe uptake by roots in order to biofortify crops and limit dietary Fe deficiency in humans, less information is available on Fe metabolism in leaves. In their review, Sági-Kazár et al. (2022) focus on the Fe-ligand interactions in leaves and

Publication year:2022

Keywords:Agriculture, deficiency, homeostasis, human nutrition, molecular, mechanisms, trace metals

Accessibility:Open