Lead and Zinc Uptake and Toxicity in Maize and Their Management.

Soil contamination with heavy metals is a global problem, and these metals can reach the food chain through uptake by plants, endangering human health. Among the metal pollutants in soils, zinc (Zn) and lead (Pb) are common co-pollutants from anthropogenic activities. Thus, we sought to define the accumulation of Zn and Pb in agricultural soils and maize. Concentrations of Pb in agricultural soil (in Namibia) could reach 3015 mg/Kg, whereas concentrations of Zn in soil (in China) could reach 1140 mg/Kg. In addition, the maximum concentrations of Zn and Pb were 27,870 and 2020 mg/Kg in maize roots and 4180 and 6320 mg/Kg in shoots, respectively. Recent studies have shown that soil properties (such as organic matter content, pH, cation exchange capacity (CEC), texture, and clay content) can play important roles in the bioavailability of Zn and Pb. We also investigated some of the genes and proteins involved in the uptake and transport of Zn and Pb by maize. Among several amendment methods to reduce the bioavailability of Zn and Pb in soils, the use of biochar, bioremediation, and the application of gypsum and lime have been widely reported as effective methods for reducing the accumulation of metals in soils and plants.

Diurnal in vivo xylem sap glucose and sucrose monitoring using implantable organic electrochemical transistor sensors.

Bioelectronic devices that convert biochemical signals to electronic readout enable biosensing with high spatiotemporal resolution. These technologies have been primarily applied in biomedicine while in plants sensing is mainly based on invasive methods that require tissue sampling, hindering in-vivo detection and having poor spatiotemporal resolution. Here, we developed enzymatic biosensors based on organic electrochemical transistors (OECTs) for in-vivo and real-time monitoring of sugar fluctuations in the vascular tissue of trees. The glucose and sucrose OECT-biosensors were implanted into the vascular tissue of trees and were operated through a low-cost portable unit for 48hr. Our work consists a proof-of-concept study where implantable OECT-biosensors not only allow real-time monitoring of metabolites in plants but also reveal new insights into diurnal sugar homeostasis. We anticipate that this work will contribute to establishing bioelectronic technologies as powerful minimally invasive tools in plant science, agriculture and forestry.

The Spatio-Temporal Distribution of Cell Wall-Associated Glycoproteins During Wood Formation in Populus.

Plant cell wall associated hydroxyproline-rich glycoproteins (HRGPs) are involved in several aspects of plant growth and development, including wood formation in trees. HRGPs such as arabinogalactan-proteins (AGPs), extensins (EXTs), and proline rich proteins (PRPs) are important for the development and architecture of plant cell walls. Analysis of publicly available gene expression data revealed that many HRGP encoding genes show tight spatio-temporal expression patterns in the developing wood of Populus that are indicative of specific functions during wood formation. Similar results were obtained for the expression of glycosyl transferases putatively involved in HRGP glycosylation. In situ immunolabelling of transverse wood sections using AGP and EXT antibodies revealed the cell type specificity of different epitopes. In mature wood AGP epitopes were located in xylem ray cell walls, whereas EXT epitopes were specifically observed between neighboring xylem vessels, and on the ray cell side of the vessel walls, likely in association with pits. Molecular mass and glycan analysis of AGPs and EXTs in phloem/cambium, developing xylem, and mature xylem revealed clear differences in glycan structures and size between the tissues. Separation of AGPs by agarose gel electrophoresis and staining with ß-D-glucosyl Yariv confirmed the presence of different AGP populations in phloem/cambium and xylem. These results reveal the diverse changes in HRGP-related processes that occur during wood formation at the gene expression and HRGP glycan biosynthesis levels, and relate HRGPs and glycosylation processes to the developmental processes of wood formation.

Cadmium Uptake by Wheat (Triticum aestivum L.): An Overview.

Cadmium is a toxic heavy metal that may be detected in soils and plants. Wheat, as a food consumed by 60% of the world's population, may uptake a high quantity of Cd through its roots and translocate Cd to the shoots and grains thus posing risks to human health. Therefore, we tried to explore the journey of Cd in wheat via a review of several papers. Cadmium may reach the root cells by some transporters (such as zinc-regulated transporter/iron-regulated transporter-like protein, low-affinity calcium transporters, and natural resistance-associated macrophages), and some cation channels or Cd chelates via yellow stripe 1-like proteins. In addition, some of the effective factors regarding Cd uptake into wheat, such as pH, organic matter, cation exchange capacity (CEC), Fe and Mn oxide content, and soil texture (clay content), were investigated in this paper. Increasing Fe and Mn oxide content and clay minerals may decrease the Cd uptake by plants, whereas reducing pH and CEC may increase it. In addition, the feasibility of methods to diminish Cd accumulation in wheat was studied. Amongst agronomic approaches for decreasing the uptake of Cd by wheat, using organic amendments is most effective. Using biochar might reduce the Cd accumulation in wheat grains by up to 97.8%.

Arsenic Uptake and Accumulation Mechanisms in Rice Species.

Rice consumption is a source of arsenic (As) exposure, which poses serious health risks. In this study, the accumulation of As in rice was studied. Research shows that As accumulation in rice in Taiwan and Bangladesh is higher than that in other countries. In addition, the critical factors influencing the uptake of As into rice crops are defined. Furthermore, determining the feasibility of using effective ways to reduce the accumulation of As in rice was studied. AsV and AsIII are transported to the root through phosphate transporters and nodulin 26-like intrinsic channels. The silicic acid transporter may have a vital role in the entry of methylated As, dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), into the root. Amongst As species, DMA(V) is particularly mobile in plants and can easily transfer from root to shoot. The OsPTR7 gene has a key role in moving DMA in the xylem or phloem. Soil properties can affect the uptake of As by plants. An increase in organic matter and in the concentrations of sulphur, iron, and manganese reduces the uptake of As by plants. Amongst the agronomic strategies in diminishing the uptake and accumulation of As in rice, using microalgae and bacteria is the most efficient.

Expression of the human UDP-galactose transporter gene hUGT1 in tobacco plants' enhanced plant hardness.

We reported previously that tobacco plants transformed with the human UDP-galactose transporter 1 gene (hUGT1) had enhanced growth, displayed characteristic traits, and had an increased proportion of galactose (hyper-galactosylation) in the cell wall matrix polysaccharides. Here, we report that hUGT1-transgenic plants have an enhanced hardness. As determined by breaking and bending tests, the leaves and stems of hUGT1-transgenic plants were harder than those of control plants. Transmission electron microscopy revealed that the cell walls of palisade cells in leaves, and those of cortex cells and xylem fibers in stems of hUGT1-transgenic plants, were thicker than those of control plants. The increased amounts of total cell wall materials extracted from the leaves and stems of hUGT1-transgenic plants supported the increased cell wall thickness. In addition, the cell walls of the hUGT1-transgenic plants showed an increased lignin contents, which was supported by the up-regulation of lignin biosynthetic genes. Thus, the heterologous expression of hUGT1 enhanced the accumulation of cell wall materials, which was accompanied by the increased lignin content, resulting in the increased hardness of the leaves and stems of hUGT1-trangenic plants. The enhanced accumulation of cell wall materials might be related to the hyper-galactosylation of cell wall matrix polysaccharides, most notably arabinogalactan, because of the enhanced UDP-galactose transport from the cytosol to the Golgi apparatus by hUGT1, as suggested in our previous report.

UDP-galactose transporter gene hUGT1 expression in tobacco plants leads to hyper-galactosylated cell wall components.

We reported previously that tobacco plants transformed with the human UDP-galactose transporter 1 gene (hUGT1-transgenic plants) displayed morphological, architectural, and physiological alterations, such as enhanced growth, increased accumulation of chlorophyll and lignin, and a gibberellin-responsive phenotype. In the present study, we demonstrated that hUGT1 expression altered the monosaccharide composition of cell wall matrix polysaccharides, such as pectic and hemicellulosic polysaccharides, which are biosynthesized in the Golgi lumen. An analysis of the monosaccharide composition of the cell wall matrix polysaccharides revealed that the ratio of galactose to total monosaccharides was significantly elevated in the hemicellulose II and pectin fractions of hUGT1-transgenic plants compared with that of control plants. A hyper-galactosylated xyloglucan structure was detected in hemicellulose II using oligosaccharide mass profiling. These results indicated that, because of the enhanced UDP-galactose transport from the cytosol to the Golgi apparatus by hUGT1, galactose incorporation in the cell wall matrix polysaccharides increased. This increased galactose incorporation may have contributed to increased galactose tolerance in hUGT1-transgenic plants.