Standardization of the Methylene Blue Reduction Test by the Use of Methylene Blue Thiocyanate.
SINCE the first use of methylene blue reduction as an indicator of bacteriological quality in milk, fluid milk supplies on this continent have undergone notable improvement. Moreover, during this period it has been shown that the inaccuracies in the test increase with increasing reduction times.6' 8, 9 An effort to minimize these inaccuracies is, therefore, worth while. Because of the extensive use of this test in milk control activities, it becomes necessary to duplicate frequently the standard tablets of methylene blue certified by the Commission on Standardization of Biological Stains and recognized by the American Public Health Association in Standard Methods of Milk Analysis.' This duplication involves not only the creation of standards but also the purification or, at least, the determination of purity of the dye. Clark, Cohen, and Gibbs 2 review the difficulty, if not the impossibility, either of purification or of determination of purity of methylene blue chloride, the methylene blue salt used in these tablets.
Concerning the Accuracy of the Methylene Blue Reduction Test
Summary 1.The methylene blue reduction test is based upon the rate of oxygen consumption in the milk by the bacteria present during incubation. This rate cannot be measured with reasonable accuracy where varying proportions of the bacteria are removed from the main body of the milk during the creaming process. 2.The accuracy of the test is greatly increased by periodical inversion of the tubes during incubation. In addition, reduction time is generally shortened and decolorization is more uniform, especially with the better grades of milk. 3.It is believed that these advantages more than compensate for the slight inconvenience entailed by this modification. 4.Milks showing similar reduction times by the modified technic sometimes show wide differences in standard reduction times. These appear to be associated with differences in the degree and rate of creaming. 5.Reduction time is prolonged by approximately 20 per cent with the proposed stronger dye concentration. This is more than compensated for in all but the poorer grades of milk by the shortening of reduction time when inversion is practised.
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.