Histidine promotes the loading of nickel and zinc, but not of cadmium, into the xylem in Noccaea caerulescens

Revolutionizing soil heavy metal remediation: Cutting-edge innovations in plant disposal technology

Soil contamination with heavy metals has emerged as a global environmental threat, compromising agricultural productivity, ecosystem integrity, and human health. Conventional remediation techniques often fall short due to high costs, operational complexities, and environmental drawbacks. Plant-based disposal technologies, including biochar, phytometallurgy, and phrolysis, have emerged as promising solutions in this regard. Grounded in a novel experimental framework, biochar is studied for its dual role as soil amendment and metal adsorbent, while phytometallurgy is explored for its potential in resource recovery and economic benefits derived from harvested metal-rich plant biomass. Pyrolysis, in turn, is assessed for transforming contaminated biomass into value-added products, thereby minimizing waste. These plant disposal technologies create a circular model of remediation and resource utilization that holds the potential for application in large-scale soil recovery projects, development of environmentally friendly agro-industries, and advancement in sustainable waste management practices. This review mainly discussed cutting-edge plant disposal technologies-biochar application, phytometallurgy, and pyrolysis-as revolutionary approaches to soil heavy metal remediation. The efficacy, cost-effectiveness, and environmental impact of these innovative technologies are especially evaluated in comparison with traditional methods. The success of these applications could signal a paradigm shift in how we approach both environmental remediation and resource recovery, with profound implications for sustainable development and circular economy strategies.

The role of roots and rhizosphere in providing tolerance to toxic metals and metalloids

Human activity and natural processes have led to the widespread dissemination of metals and metalloids, many of which are toxic and have a negative impact on plant growth and development. Roots, as the first point of contact, are essential in endowing plants with tolerance to excess metal(loid) in the soil. The most important root processes that contribute to tolerance are: adaptation of transport processes that affect uptake efflux and long-distance transport of metal(loid)s; metal(loid) detoxification within root cells via conjugation to thiol rich compounds and subsequent sequestration in the vacuole; plasticity in root architecture; the presence of bacteria and fungi in the rhizosphere that impact on metal(loid) bioavailability; the role of root exudates. In this review, we provide details on these processes and assess their relevance on the detoxification of arsenic, cadmium, mercury and zinc in crops. Furthermore, we assess which of these strategies have been tested in field conditions and whether they are effective in terms of improving crop metal(loid) tolerance.

Low-molecular-weight ligands in plants: role in metal homeostasis and hyperaccumulation

Mineral nutrition is one of the key factors determining plant productivity. In plants, metal homeostasis is achieved through the functioning of a complex system governing metal uptake, translocation, distribution, and sequestration, leading to the maintenance of a regulated delivery of micronutrients to metal-requiring processes as well as detoxification of excess or non-essential metals. Low-molecular-weight ligands, such as nicotianamine, histidine, phytochelatins, phytosiderophores, and organic acids, play an important role in metal transport and detoxification in plants. Nicotianamine and histidine are also involved in metal hyperaccumulation, which determines the ability of some plant species to accumulate a large amount of metals in their shoots. In this review we extensively summarize and discuss the current knowledge of the main pathways for the biosynthesis of these ligands, their involvement in metal uptake, radial and long-distance transport, as well as metal influx, isolation and sequestration in plant tissues and cell compartments. It is analyzed how diverse endogenous ligand levels in plants can determine their different tolerance to metal toxic effects. This review focuses on recent advances in understanding the physiological role of these compounds in metal homeostasis, which is an essential task of modern ionomics and plant physiology. It is of key importance in studying the influence of metal deficiency or excess on various physiological processes, which is a prerequisite to the improvement of micronutrient uptake efficiency and crop productivity and to the development of a variety of applications in phytoremediation, phytomining, biofortification, and nutritional crop safety.

Root uptake and translocation of nickel in wheat as affected by histidine

The role of histidine (His) on root uptake, xylem loading and root to shoot transport of nickel (Ni) was investigated in a winter (Triticum aestivum cv. Back Cross) and a durum wheat (Triticum durum cv. Durum) cultivar. Seedlings were grown in a modified Johnson nutrient solution and exposed to 10 μM of Ni and 100 μM of histidine (His) as no His, Ni (10) + His (100) and Ni(His) in a 1:1 mole ratio (1:1) complex. In our study, the presence of vanadate (a metabolic inhibitor) resulted in a significant decrease of root Ni uptake, indicating that a part of Ni uptake by the plant root is energy-dependent. Addition of His significantly increased the Ni content in shoots and roots of both wheat cultivars. The data suggest that the Ni(His) is most likely to be taken up as a complex or receptors at the membrane are able to enhance Ni uptake from Ni(His) complex. This result was indirectly supported by using EDTA as a strong chelating reagent to reduce the uptake of Ni(His) complexes. By using this ligand, the xylem loading of Ni and His was disproportionately reduced. Cycloheximide (a translation inhibitor) strongly decreased the release of His and Ni from the root into the xylem of wheat, suggesting the significance of a symplastic pathway for Ni loading into the xylem.