Cadmium, nickel, copper, and zinc influence on microfilament organization in Arabidopsis root cells

MeGLYI-13, a Glyoxalase I Gene in Cassava, Enhances the Tolerance of Yeast and Arabidopsis to Zinc and Copper Stresses

Although zinc and copper are the two essential nutrients necessary for plant growth, their excessive accumulation in soil not only causes environmental pollution but also seriously threatens human health and inhibits plant growth. The breeding of plants with novel zinc or copper toxicity tolerance capacities represents one strategy to address this problem. Glyoxalase I (GLYI) family genes have previously been suggested to be involved in the resistance to a wide range of abiotic stresses, including those invoked by heavy metals. Here, a MeGLYI-13 gene cloned from a cassava SC8 cultivar was characterized with regard to its potential ability in resistance to zinc or copper stresses. Sequence alignment indicated that MeGLYI-13 exhibits sequence differences between genotypes. Transient expression analysis revealed the nuclear localization of MeGLYI-13. A nuclear localization signal (NLS) was found in its C-terminal region. There are 12 Zn2+ binding sites and 14 Cu2+ binding sites predicted by the MIB tool, of which six binding sites were shared by Zn2+ and Cu2+. The overexpression of MeGLYI-13 enhanced both the zinc and copper toxicity tolerances of transformed yeast cells and Arabidopsis seedlings. Taken together, our study shows the ability of the MeGLYI-13 gene to resist zinc and copper toxicity, which provides genetic resources for the future breeding of plants resistant to zinc and copper and potentially other heavy metals.

Exogenous abscisic acid fine-tunes heavy metal accumulation and plant's antioxidant defence mechanism to optimize crop performance and secondary metabolite production in Trigonella foenum-graecum L. under nickel stress

Nickel (Ni) contamination of farming soil has become currently a recurring global menace to agriculture crop productivity. The purpose of the present study was to investigate the putative contributions of abscisic acid (ABA) to extemporize Ni tolerance in Trigonella foenum-graecum L. (fenugreek) plants. The outcomes of this study exposed that exogenous supplementation of ABA at 10, 20, 40 and 80 µM considerably enhanced the growth and physiological attributes of fenugreek under 80 mg Ni kg^-1 soil, however, 40 µM of ABA exhibited the best results under normal and Ni-stressed conditions. ABA-mediated Ni tolerance was marked by reductions in Ni accumulation and consequent lowering of reactive oxygen species (ROS) like hydrogen peroxide and superoxide radicals. Contrarily, NO (nitric oxide) level increased in response to ABA application under Ni stress conditions, accompanied by promoted antioxidant activities through improved levels of secondary metabolites, proline, and perked-up ROS-detoxification enzymes activities. Exogenous ABA at 40 µM concentration applied to Ni-exposed plants (80 mg Ni kg^-1 soil) improved the total content of alkaloids, phenolics, flavonoids and tannins by 14.3%, 10.2%, 15.4% and 7.0%, respectively, over Ni-stressed plants alone. Additionally, seed trigonelline content imparting several pharmacological actions to the fenugreek plant exhibited a remarkable escalation upto 3.6 and 2.6 mg g^-1 DW under '40 µM ABA' and '40 µM ABA + 80 mg Ni kg^-1 soil' treatments, respectively. The findings of the study suggest that ABA plays a key role in enhancing the overall performance of the fenugreek crop under excessive Ni stress.

Effect of heavy metals on in vitro growth and development of the Momordica cymbalaria Fenzl

Heavy metals have played a great role in the genesis of the present-day civilization. Human beings are affected when these metals are added to the food chain. Although these are the most important plant nutrients, they are phytotoxic at high concentrations. Heavy metals at super optimal concentrations affect different metabolic pathways in plants and result in their ceased growth and development. They may enter plants either by their root system or through foliar uptake; stunted growth, chlorosis, necrosis, and reddish-brown discoloration are visible symptoms of severe metallic phytotoxicity. The study of heavy metal stress tolerance on Momordica cymbalaria shows the effect on the plant growth and metabolism. All heavy metals treated with high concentrations affect the overall plant growth. The Murashige and Skoog (MS) basal medium with ZnSO4 at 100 µM concentration resulted in healthy shoot development (9) with a maximum shoot length of 7.2 cm. MS basal medium with low concentration of CuSO4 (50 µM) achieved a maximum shoot number (7) with healthy leaves and shoots. MS basal medium with higher concentration of CdCl2 (150 µM) affects plant growth and reduced the regeneration capability completely.

Metal crossroads in plants: modulation of nutrient acquisition and root development by essential trace metals

The metals iron, zinc, manganese, copper, molybdenum, and nickel are essential for the growth and development of virtually all plant species. Although these elements are required at relatively low amounts, natural factors and anthropogenic activities can significantly affect their availability in soils, inducing deficiencies or toxicities in plants. Because essential trace metals can shape root systems and interfere with the uptake and signaling mechanisms of other nutrients, the non-optimal availability of any of them can induce multi-element changes in plants. Interference by one essential trace metal with the acquisition of another metal or a non-metal nutrient can occur prior to or during root uptake. Essential trace metals can also indirectly impact the plant's ability to capture soil nutrients by targeting distinct root developmental programs and hormone-related processes, consequently inducing largely metal-specific changes in root systems. The presence of metal binding domains in many regulatory proteins also enables essential trace metals to coordinate nutrient uptake by acting at high levels in hierarchical signaling cascades. Here, we summarize the known molecular and cellular mechanisms underlying trace metal-dependent modulation of nutrient acquisition and root development, and highlight the importance of considering multi-element interactions to breed crops better adapted to non-optimal trace metal availabilities.

Subtoxic levels of some heavy metals cause differential root-shoot structure, morphology and auxins levels in Arabidopsis thaliana

Contamination of soil by heavy metals severely affects plant growth and causes soil pollution. While effects on plant growth have been investigated for metals taken individually or in groups, less is known about their comparative effects. In this study Arabidopsis thaliana seedlings were grown for 14 days in Petri dishes containing medium contaminated by six common heavy metals (Hg, Cd, Pb, Cu, Ni and Zn), at the minimum concentrations defined as toxic by the most recent EU legislation on contamination of agricultural soils. (a) Root structure and morphology, (b) metal composition and translocation, and (c) the levels of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) were analyzed. Metals accumulated more in roots than in shoots, with concentrations that differed by several orders of magnitude depending on the metal: Cd (ca. 700 × and ca. 450 × in roots and shoots, respectively), Hg (150 × , 80 × ), Ni (50 × , 20 × ), Cu (48 × , 20 × ), Zn (23 × , 6 × ), and Pb (9 × , 4 × ). Responses were significant for at least nine of the ten root parameters (with the exception of Hg), and five of the six shoot parameters (with the exception of Zn). Cu and Zn induced respectively the strongest responses in root hormonal (up to ca. 240% the control values for IBA, 190% for IAA) and structural parameters (up to 210% for main root length, 330% for total lateral root length, 220% for number of root tips, 600% for total root surface, and from 2.5° to 26.0° of root growth angle). Regarding the shoots, the largest changes occurred for shoot height (down to 60% for Ni), rosette diameter (down to 45% for Hg), leaf number (up to 230% for Zn) and IBA (up to 240% for Pb and Cu). A microscope analysis revealed that shape and conformation of root hairs were strongly inhibited after Cd exposure, and enhanced under Hg and Pb. The results could have positive applications such as for defining toxicity thresholds (in phytoremediation) and acceptable concentration levels (for policies) for some of the most common heavy metals in agricultural soils.

Polyelectrolyte Gels Formed by Filamentous Biopolymers: Dependence of Crosslinking Efficiency on the Chemical Softness of Divalent Cations

Filamentous anionic polyelectrolytes are common in biological materials. Some examples are the cytoskeletal filaments that assemble into networks and bundled structures to give the cell mechanical resistance and that act as surfaces on which enzymes and other molecules can dock. Some viruses, especially bacteriophages are also long thin polyelectrolytes, and their bending stiffness is similar to those of the intermediate filament class of cytoskeletal polymers. These relatively stiff, thin, and long polyelectrolytes have charge densities similar to those of more flexible polyelectrolytes such as DNA, hyaluronic acid, and polyacrylates, and they can form interpenetrating networks and viscoelastic gels at volume fractions far below those at which more flexible polymers form hydrogels. In this report, we examine how different types of divalent and multivalent counterions interact with two biochemically different but physically similar filamentous polyelectrolytes: Pf1 virus and vimentin intermediate filaments (VIF). Different divalent cations aggregate both polyelectrolytes similarly, but transition metal ions are more efficient than alkaline earth ions and their efficiency increases with increasing atomic weight. Comparison of these two different types of polyelectrolyte filaments enables identification of general effects of counterions with polyelectrolytes and can identify cases where the interaction of the counterions and the filaments exhibits stronger and more specific interactions than those of counterion condensation.