Localization and chemical speciation of cadmium in the roots of barley and lettuce

Abstract

Plants have the potential to accumulate toxic amounts of cadmium (Cd), and understanding how and where Cd is stored in plants is important for ensuring food safety.Previous experiments have determined that a greater amount of Cd is translocated into the leaves of lettuce (Lactuca sativa) as compared to barley leaves (Hordeum vulgare).Preferential retention of Cd in root of barley would explain this difference. Hence, the purpose of this study was to determine the localization and coordination environment of Cd (i.e., the ligands to which Cd was bound) in the different root tissues of lettuce and barley using histochemical staining, electron microscopy and micro X-ray spectroscopy.Retention of Cd in barley roots could be explained by accumulation of Cd at the endodermis, comparatively higher amounts of Cd sequestered in the symplast of cortical cells and binding to xylem cell walls. Increased translocation of Cd to lettuce shoots seemed to be due to a less effective barrier at the endodermis and less sequestration of Cd in the cortex. Regardless of the tissue type, most of the Cd 2+ was bound to S ligands in the roots of barley, possibly reflecting accumulation of Cd-phytochelatin and Cd-S molecules in the vacuoles. In lettuce roots, Cd was more evenly distributed among ligands containing S, O and NO 3 groups, which is indicative of proportionately more Cd binding to the cell walls, relative to barley. These results will be useful in uncovering the mechanisms of differential Cd-tolerance and sequestration in lettuce and barley.

Metal accumulation and shoot yield of Miscanthus×giganteus growing in contaminated agricultural soils: Insights into agronomic practices

“…The high transfer from soil to roots could be due to the facts that Cd is generally more available in the rhizosphere and uses various pathways of entry including non-specific transporters, Ca 2+ channels, ZIP and IRP transporters (Lux et al, 2011;DalCorso et al, 2013). Inside root tissues, Cd accumulates in the endodermis and in xylem cell walls, or is chelated by phytochelatins that mediated vacuolar storage (Lux et al, 2011;Akhter et al, 2014).…”

Cadmium stress antioxidant responses and root-to-shoot communication in grafted tomato plants

“…A recent study by Xin et al (2013) who investigated the role of roots in Cd accumulation in two water spinach cultivars using reciprocal grafting is an elegant example of the application of the technique. Current research has shown differential root-to-shoot regulation of photosynthetic proteins, sulphur and glutathione metabolism involved in signaling and secondary metabolism in Cd hyperaccumulation (Akhter et al 2014;DalCorso et al 2013).…”

Trace Metals in Phosphate Fertilizers Used in Eastern Mediterranean Countries

“…S1). Such result is reminiscent of Cd speciation studies in the roots of barley and lettuce , showing that most of cadmium ions were bound to ligands containing .…”

“…In the present study, however, a fairly good correlation was found between Cd and in superphosphate, NPK‐fertilizers, urea phosphate, and potassium phosphate. The substitution of Ca with Cd results from a Cd 2+ ionic radius (0.109 nm) similar to that of Ca 2+ (0.114 nm), thus, leading to a CdP or CdS bond and the formation of Cd 3 (PO 4 ) 2 and/or CdSO 4 within the fertilizers . The relationship between Cd and sulfate is conditioned to the presence of high sulfate contents in the NPK group of higher pH (Supporting Information Tab.…”