Hydroponic growth test of maize sprouts to evaluate As, Cd, Cr and Pb translocation from mineral fertilizer and As and Cr speciation

Differences of cadmium uptake and accumulation in roots of two maize varieties (Zea mays L.)

Different maize varieties respond differentially to cadmium (Cd) stress. As the first organ in contact with the soil, the response of the root is particularly important. However, the physiological mechanisms that determine the response are not well defined. Here, we compared the differences in Cd-induced related gene expression, ionic homeostasis, and ultrastructural changes in roots of Cd-tolerant maize variety (XR57) and Cd-sensitive maize variety (LY296), and assessed their effects on Cd uptake and accumulation. Our findings indicate that XR57 absorbed a significantly lower Cd than LY296 did, and that the expression levels of genes related to Cd uptake (ZmNRAMP5 and ZmZIP4) and efflux (ZmABCG4) in the root were consistent with the Cd absorption at the physiological levels. Compared with LY296, the lower Cd concentration in the roots of XR57 caused less interference with the ion balance. Transmission electron microscope images revealed that the roots from XR57 exposed to Cd had developed thicker cell walls than LY296. In addition, the large increase ZmABCC1 and ZmABCC2 expression levels in XR57 mediated the appearance of numerous electron-dense granules in the vacuoles present in the roots. As a result, the high Cd tolerance of XR57 is the result of a multi-level response that involves increased resistance to Cd uptake, a stronger capacity for vacuolar regionalization, and the formation of thicker cell walls. These findings may provide a theoretical basis for maize cultivation in Cd-contaminated areas.

Speciation of macro- and nanoparticles of Cr2O3 in Hordeum vulgare L. and subsequent toxicity: A comparative study

Chromium (Cr) is reported to be hazardous to environmental components and surrounding biota when levels exceed allowable thresholds. As Cr is extensively utilized in different industries, thereby comprehensively studied for its toxicity. Along with Cr, the applications of nano-Cr or chromium oxide nanoparticles (Cr₂O₃-NPs) are also expanding; however, the literature is scarce or limited on their phytotoxicity. Thereby, the current work investigated the morpho-physiological insights of macro- and nanoparticles of Cr in Hordeum vulgare L. plants. The increased accumulation and translocation of Cr under the exposure of both forms disturbed the cellular metabolism that might have inhibited germination and growth as well as interfered with the photosynthesis of plants. The overall extent of toxicity was noticeably higher under nanoparticles' exposure than macroparticles of Cr. The potential cue for such phytotoxic consequences mediated by Cr nanoparticles could be an increased bioavailability of Cr ions which was also supported by their total content, mobility, and factor toxicity index. Besides, to support further these findings, synchrotron X-ray technique was used to reliably identify Cr-containing compounds in the plant tissues. The X-ray spectra of the near spectral region and the far region of the spectrum of K-edge of Cr were obtained, and it was established that the dominant crystalline phase corresponds to Cr₂O₃ (eskolaite) from the recorded observations. Thus, the obtained results would allow revealing the mechanism of macro- and nanoparticles of Cr induced impacts on plant at the tissue, cellular- and sub-cellular levels.

Arsenate phytotoxicity regulation by humic acid and related metabolic mechanisms

The use of irrigation water containing arsenic (As) had led to large areas of As-contaminated farmland, and as a result, plants and food have become severely poisoned. Humic acid (HA) can be complexed with metals, which in turn affects the metals' behavior. Herein, we explored the accumulation of arsenate in lettuce treated with different concentrations of arsenate and studied the effects of HA on the accumulation and toxicity of arsenate. The addition of HA did not cause significant changes in the arsenate content in lettuce but had a significant effect on the activity of antioxidant enzymes, which improved the antioxidant capability of the lettuce plants. Furthermore, HA promoted the accumulation of nutrients, such as magnesium (Mg), calcium (Ca), molybdenum (Mo) and manganese (Mn), in the leaves. Arsenate disrupted metabolic pathways, such as amino acid metabolism, carbohydrate metabolism, and aminoacyl-tRNA biosynthesis. The addition of HA increased the contents of amino acids and sugars, thereby improving lettuce growth. The present study explored the effects of HA on As accumulation and related physiological changes (antioxidant enzyme activities, absorption of nutrients and metabolic mechanisms) and provided insights into the regulation of As contamination by HA, which is relatively inexpensive.