Effect of some nitrogenous salts on nitrogen transfer and protease activity in germinatingZea mays L. seeds

Maize seeds were allowed to germinate in the presence of different nitrogenous salts for 72 h. Changes in the ethanol soluble and insoluble nitrogen were studied in the embryo and in the endosperm. Supply of Ca(NC₃)₂ enhanced germination and protease activity in the endosperm resulting in greater solubilisation of protein to soluble nitrogen in the seeds. NH₄NO₃ and (NH₄)₂SO₄ were less effective as compared to Ca(NO₃)₂. Cycloheximide inhibited germination and protease activity. Pretreatment also resulted in increase in growth, soluble and insoluble nitrogen, and nitrate reductase activity in the primary leaves. Ca(NO₃)₂ was more effective than NH₄NO₃ and (NH₄)₂SO₄.     

Contribution of sarcolemmal sodium-calcium exchange and intracellular calcium release to force development in isolated canine ventricular muscle

The aim of this work was to determine the relationship between peak twitch amplitude and sarcoplasmic reticulum (SR) Ca2+ content during changes of stimulation frequency in isolated canine ventricle, and to estimate the extent to which these changes were dependent upon sarcolemmal Na(+)-Ca2+ exchange. In physiological [Na+]o, increased stimulation frequency in the 0.2-2-Hz range resulted in a positive inotropic effect characterized by an increase in peak twitch amplitude and a decrease in the duration of contraction, measured as changes in isometric force development or unloaded cell shortening in intact muscle and isolated single cells, respectively. Action potentials recorded from single cells indicated that the inotropic effect was associated with a progressive decrease of action potential duration and a marked reduction in average time spent by the cell near the resting potential during the stimulus train. The frequency-dependent increase of peak twitch force was correlated with an increase of Ca2+ uptake into and release from the SR. This was estimated indirectly using the phasic contractile response to rapid (less than 1 s) lowering of perfusate temperature from 37 degrees C to 0-2 degrees C and changes of twitch amplitude resulting from perturbations in the pattern of electrical stimulation. Lowering [Na+]o from 140 to 70 mM resulted in an increase of contractile strength, which was accompanied by a similar increase of apparent SR Ca2+ content, both of which could be abolished by exposure to ryanodine (1 x 10(-8) M), caffeine (3 x 10(-3) M), or nifedipine (2 x 10(-6) M). Increased stimulation frequency in 70 mM [Na+]o resulted in a negative contractile staircase, characterized by a graded decrease of peak isometric force development or unloaded cell shortening. SR Ca2+ content estimated under identical conditions remained unaltered. Rate constants derived from mechanical restitution studies implied that the depressant effect of increased stimulation frequency in 70 mM [Na+]o was not a consequence of a decreased rate of refilling of a releasable pool of Ca2+ within the cell. These results demonstrate that frequency-dependent changes of contractile strength and intracellular Ca2+ loading in 140 mM [Na+]o require the presence of a functional sarcolemmal Na(+)-Ca2+ exchange process. The possibility that the negative staircase in 70 mM [Na+]o is related to inhibition of Ca(2+)-induced release of Ca2+ from the SR by various cellular mechanisms is discussed.     

P700 sensitization by low concentration of DCMU in isolated pea chloroplasts

Using steady-state relaxation spectrophotometric technique a P₇₀₀ component ($\text{t}\text{1}\text{2}\text{～20 ms}$) has been detected which was sensitized by low concentration (10^?7M) DCMU in isolated broken chloroplasts of pea. The relative quantum yield of electron flux through DCMU-sensitized P₇₀₀ was similar to that with methyl viologen or NADP as terminal electron acceptor and water as electron donor. Kinetic analysis showed that a small fraction (10%) of the total P₇₀₀ reaction centers was sensitized by low DCMU.     

Exoprotease production by sporogenous and asporogenous mycobacillin non-producer mutants ofBacillus subtilis

Mycobacillin non-producers, whether sporogenous or asporogenous, possess less exoprotease, but effective exoprotease producers are not always good mycobacillin yielders. There might exist a minimum level of exoprotease formation for elaboration of mycobacillin.     

A low frequency mosaicism for monosomy 21 in a live born female

Summary Monosomy 21, whether homogeneous or as a mosaicism, is very uncommon. We report here a 3-month-old white female with a low degree of monosomy 21 in the blood karyotype (6.5%, 110 cells counted) but not in the skin fibroblasts, which contained only the normal chromosome complement.The patient's physical features included microcephaly with frontal slanting; prominent occiput; ridge-shaped sutures; agenesis of the corpus callosum; large, prominent ears; high and narrow palate; micrognathia; tetralogy of Fallot; crowded toes; and dry, thick skin with very little subcutaneous tissue. The case is discussed in light of the suggested clinical features of the monosomy 21 syndrome and the possible implications of such a low-grade mosaicism in prenatal diagnosis.