Research into Cd uptake in T. caerulescens ecotypes is providing insight into comparative plant physiology and a unique transport process. Beyond this, given the threat to the human food chain posed by Cd, research into hyperaccumulators does also have more immediate, applied perspectives. Further molecular studies are now important for the high-affinity transporter demonstrated in the Ganges ecotype – and this should also pave the way to improved phytoremediation.
The entry of Cd into the food chain is of concern as it can cause chronic health problems. To investigate the relationship between soil properties and the concentration of Cd in wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) grain, we analyzed 162 wheat and 215 barley grain samples collected from paired soil and crop surveys in Britain, and wheat and barley samples from two long‐term sewage sludge experiments. Cadmium concentrations were much lower in barley grain than in wheat grain under comparable soil conditions. Multiple regression analysis showed that soil total Cd and pH were the significant factors influencing grain Cd concentrations. Significant cultivar differences in Cd uptake were observed for both wheat and barley. Wheat grain Cd concentrations could be predicted reasonably well from soil total Cd and pH using the following model: log(grain Cd) = a + b log(soil Cd) − c (soil pH), with 53% of the variance being accounted for. The coefficients obtained from the data sets of the paired soil and crop surveys and from long‐term sewage sludge experiments were similar, suggesting similar controlling factors of Cd bioavailability in sludge‐amended or unamended soils. For barley, the model was less satisfactory for predicting grain Cd concentration (22% of variance accounted for). The model can be used to predict the likelihood of wheat grain Cd exceeding the new European Union (EU) foodstuff regulations on the maximum permissible concentration of Cd under different soil conditions, particularly in relation to the existing Directive and the proposed new Directive on land applications of sewage sludge.
No abstract is provided for this article.
No abstract is provided for this article.
The ability to locate and quantify elemental distributions in plants is crucial to understanding plant metabolisms, the mechanisms of uptake and transport
Increased incidence of sulphur (S) deficiency in crops has led to a greater need for S determination in plant tissues. Among the methods available for measurement of S, inductively coupled plasma atomic emission spectrometry (ICP‐AES) has been proved to be accurate and rapid. This paper compares digestion with HNO3‐HClO4, fuming HNO3‐KNO3 and alkaline NaOBr prior to the S measurement by ICP‐AES. Both HNO3‐HClO4 and fuming HNO3‐KNO3 were found to give satisfactory results for five certified plant materials, with high accuracy and precision. The HNO3‐HClO4 method involved a rigid temperature control, with slow ramp rates and a final temperature (190°C) lower than the boiling point of HClO4, to minimise the possibility of gaseous losses of S. Both methods can also be used for the simultaneous determination of phosphorus (P), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn), and additionally potassium (K) with HNO3‐HClO4. In contrast, the alkaline NaOBr method was less suitable as a digestion procedure for S measurement by ICP‐AES, because it involved a large dilution factor and produced high blank values.
No abstract is provided for this article.
Sulphur fractionation and availability to plants are poorly understood in calcareous soils. Sixty-four calcareous soils containing varying amounts of CaCO3
Clear influence of N and S applications on the profile of individual glucosinolates in the seeds of winter oilseed rape ( Brassica napus L) was found in field experiments. The major effect of N was on the relative abundance of the four alkenyl glucosinolates. Increasing the N rate increased the relative proportion of 2‐hydroxybut‐3‐enyl at the expense of pent‐4‐enyl, and to a lesser extent, 2‐hydroxypent‐4‐enyl, in the double‐low (low erucic acid and low glucosinolates) variety Cobra, but at the expense of but‐3‐enyl in the single‐low (low erucic acid) variety Bienvenu. The results strongly suggest that a high N supply favours the hydroxylation step from but‐3‐enyl to 2‐hydroxybut‐3‐enyl. In contrast, the major effect of S appeared to be on the relative abundance of the alkenyl and indole groups as a whole. Sulphur deficiency decreased the concentrations of the alkenyl glucosinolates more than those of the indole glucosinolates, whereas S application to a S‐deficient crop resulted in a larger response in the alkenyl group than in the indole group. The more sensitive response of alkenyl glucosinolates to the plant S status is probably due to the requirement of methionine in their biosynthesis, as compared with the indole glucosinolates which are derived from tryptophan. Implications for changes in the glucosinolate profile in rapeseed are discussed.
Changes in the sulphur (S) concentrations in pod walls and seeds of the double low variety Cobra and single low variety Bienveou of winter oilseed rape ( Brassica napus L) were studied during pod development. The S concentration in the seeds of Cobra increased between 47 and 61 days after flowering and thereafter remained stable, whereas in Bienvenu seed S concentration was much higher initially and continued to increase throughout the sampling period (from 57 to 108 days after flowering). These differences in S concentration reflect different patterns of glucosinolate accumulation in the seeds. In contrast, there was a large and progressive build‐up of S in the pod walls of Cobra, such that at maturity the S concentration in the pod walls of Cobra was approximately double that of Bienvenu. A large and progressive accumulation of inorganic sulphate was found to be responsible for the build‐up of S in the pod walls of the double low variety. Short‐term feeding experiments with terminal racemes showed that a smaller proportion of 35 S was translocated from the pod walls to the seeds in Cobra than in Bienvenu. However, the build‐up of S in the pod walls of Cobra did not seem to result from a restricted translocation of glucosinolates, since in both varieties exogenously supplied allylglucosinolate was translocated rapidly from the pod walls to the seeds. These results are therefore consistent with the hypothesis that pod walls are a major site for the biosynthesis of glucosinolates present in the seeds, and a metabolic block in the pathway of glucosinolate biosynthesis is responsible for the low glucosinolate concentration in the seeds of double low varieties, which consequently results in a large build‐up of sulphate in the pod walls.
