ABSTRACT
This study characterizes sunflower response to the levels of Cd encountered in moderately Cd-polluted soils. Two sunflower cultivars differing in their ability to sequestrate Cd in roots were exposed to low concentrations of Cd (0.5 nM or 100 nM) in hydroponics and sampled after 18 days (258 degree-days) when ten leaves were fully expanded. Plant growth, Cd uptake and partitioning among organs were monitored along with the ionomic (ICP-MS) and the metabolic (1H-NMR) composition of the xylem sap. Sunflower tolerance to Cd differed between the two cultivars. The cultivar with the highest ability to sequestrate Cd in roots (Kapllan) was more tolerant to Cd than the one with the lowest ability (ES RICA). The 23% penalization of plant growth observed at 100 nM in cultivar ES RICA was associated with reduced xylem loading fluxes of soluble sugars, perhaps pointing to disruption of carbohydrate metabolism. Retention of Cd in the stem was higher at 100 nM than at 0.5 nM in the Cd-sensitive cultivar ES RICA, which can be seen as a sunflower strategy to restrict the amount of Cd delivered to the leaves under Cd stress. No direct connection was found between the speciation of Cd in the xylem sap and the Cd translocation efficiency, although significant changes in the free ionic fraction of Cd were observed between the two cultivars at 0.5 nM. The relevance of these results in promoting the use of sunflower in phytomanagement of Cd-polluted soils is discussed.
Subject(s)
Cadmium/metabolism , Helianthus/metabolism , Hydroponics , Biological Transport , Plant Development , Plant Leaves/metabolism , Plant Roots/metabolism , Xylem/metabolismABSTRACT
This study aims to characterize the response of durum wheat to different concentrations of Cd found in agricultural soils. One French durum wheat cultivar (i.e. Sculptur) was exposed to low concentrations of Cd (5â¯nM or 100â¯nM) in hydroponics. After anthesis, the plants were fed with a solution enriched with the stable isotope 111Cd to trace the newly absorbed Cd. Plants were sampled at anthesis and grain maturity to assess how plant growth, Cd uptake and partitioning among organs, as well as Cd remobilization, differed between the two Cd exposure levels. Durum wheat did not show any visual symptoms of Cd toxicity, regardless of which Cd treatment was applied. However, post-anthesis durum wheat growth was 14% penalized at 100â¯nM due to the large transpiration-based accumulation of Cd in leaves at this stage. The allocation of Cd to the grains was not restricted but enhanced at 100â¯nM compared to 5â¯nM. Both the root-to-shoot Cd translocation and the fraction of aboveground Cd allocated to grains were higher in plants exposed to 100â¯nM. Cadmium was remobilized exclusively from roots and stems, and remobilized Cd contributed on average to 40-45% of the Cd accumulated in mature grains, regardless of which Cd treatment was applied. The relevance of these results to decreasing the concentration of Cd in durum wheat grains is discussed.
Subject(s)
Cadmium/metabolism , Edible Grain/metabolism , Hydroponics , Triticum/metabolism , Water Pollutants, Chemical/metabolism , Biological Transport , Edible Grain/growth & development , Plant Leaves/growth & development , Plant Leaves/metabolism , Plant Roots/growth & development , Plant Roots/metabolism , Plant Shoots/growth & development , Plant Shoots/metabolism , Triticum/growth & developmentABSTRACT
This work focuses on the exposure of maize plants to nanomolar concentrations of Cd, which is relevant for agricultural soils cropped with food and feed plants. Maize plants were cultivated in nutrient solution at 0.8 or 20 nM Cd during the vegetative growth stages. No significant hormesis or toxic effects of Cd were observed on maize growth, but a decrease in the allocation of Cd to shoots between the 0.8 and 20 nM Cd exposures revealed that the plants already responded to these low concentrations of Cd according to a shoot Cd excluder strategy. The Cd, Cu and Zn concentrations in shoots decreased with time as the result of an early decrease in the root/shoot ratio and of a decrease in the coefficient of allocation to aboveground for Zn and Cd at 20 nM. As a consequence, shoots of young plants were richer in micronutrients Cu and Zn but also in toxic Cd. The rate of delivery of Cd, Cu and Zn from xylem sap was successfully used to predict the time course of concentrations of Cd, Cu and Zn in the shoot. However, it overestimated the actual concentrations of Cd in the shoot, presumably because the reallocation of this trace element from shoots back to roots was not taken into account.
Subject(s)
Cadmium/metabolism , Copper/metabolism , Soil Pollutants/metabolism , Xylem/metabolism , Zea mays/drug effects , Zinc/metabolism , Cadmium/analysis , Copper/analysis , Micronutrients/analysis , Micronutrients/metabolism , Plant Roots/drug effects , Plant Roots/metabolism , Soil Pollutants/analysis , Xylem/drug effects , Zea mays/growth & development , Zea mays/metabolism , Zinc/analysisABSTRACT
Several types of small-dimension graded-reflectance mirrors deposited through rotating masks are compared. Multilayer mirrors provided with single-variable-thickness layers have limitations that are avoided when all the layers in the system are shaped. High-reflectance mirrors of the latter type are demonstrated. Numerical and experimental results are given.