INCLUSIONS OF THE PROPLASTIDS AND VACUOLES IN THE SHOOT APICES OF BRYOPHYLLUM AND KALANCHOË

Spherical, membrane-bound inclusions occur in the proplastids and vacuoles of cells of Bryophyllum and Kalanchoë shoot apices. Evidence is presented indicating that the inclusions arise by the accumulation of material within the cisternae of certain tubular proplastid membranes and are then transferred to vacuoles. The results obtained from electron microscopy and from histochemical studies indicate that the contents of the inclusions are predominantly lipid.     

Insolubility of Cr2O3 in Bioaccessibility Tests Points to Requirement for a New Human Oral Reference Dose for Trivalent Chromium

Bioaccessibility measurements have the potential to improve the accuracy of risk assessments and reduce the potential costs of remediation when they reveal that the solubility of chemicals in a matrix (e.g., soil) differs markedly from that in the critical toxicity study (i.e., the key study from which a toxicological or toxicity reference value is derived). We aimed to apply this approach to a brownfield site contaminated with chromium, and found that the speciation was Cr^III, using a combination of alkaline digestion/diphenylcarbazide complexation and X-ray absorption near edge structure analysis. The bioaccessibility of Cr₂O₃, the compound on which a reference dose for Cr^III is based, was substantially lower (<0.1%) than that of the Cr^III in the soils, which was a maximum of 9%, giving relative bioaccessibility values of 13,000% in soil. This shows that the reference dose is based on essentially an insoluble compound, and thus we suggest that other compounds be considered for toxicity testing and derivation of reference dose. Two possibilities are CrCl₃·6H₂O and KCr(SO₄)₂·12H₂O, which have been used for derivation of ecological toxicity reference values and are soluble at a range of dosing levels in our bioaccessibility tests.     

A comparison of three methods for the determination of available lysine in barley

The protein quality of barley was determined by the measurement of the protein efficiency ratio (PER). Available lysine in the same samples was determined chemically and by microbiological assay, and relationships were obtained between PER and either total or available lysine content.In the PER test, groundnut meal was found to be a suitable protein supplement to barley for the purpose of detecting differences in the protein quality of barley. The method was sufficiently sensitive to detect a reduction in protein quality of one variety as a result of micronization. Available lysine values obtained by the modified Tetrahymena method were significantly correlated (r = 0.99) with PER values; there was no significant correlation between total lysine content and the PER value.The available lysine values measured by the two chemical methods were higher than the Tetrahymena values. The Silcock method gave results better correlated (r = 0.93) with the Tetrahymena values than did the Carpenter method (r = 0.82). The results of chemical methods were not significantly related with PER values, but the methods ranked the barleys in an order similar to that obtained with the PER and Tetrahymena tests.