Difference In Mean Density Research Articles

Untersuchungen zur Funktions�nderung der Microbodies in den Keimbl�ttern von Helianthus annuus L.

The enzyme patterns in sunflower cotyledons indicate that the glyoxysomal function of microbodies is replaced by the peroxisomal function of these organelles during the transition from fat degradation to photosynthesis. The separation of the microbody population into glyoxysomes and peroxisomes during this transition period is reported. The mean difference in density between the activity peaks of glyoxysomal and peroxisomal marker enzymes on a sucrose gradient was calculated to be 0.007±0.004 g/cm3 and turned out to be significant (t=7.8>4.04=t 5;0.01). The activity peak of catalase coincides with that of isocitrate lyase in early stages of development, but shifts to the activity peak of peroxisomal marker enzymes during the transition period. No isozymes of the catalase could be detected by gel electrophoresis in the microbodies with the two different functions. During the rise of the peroxisomal marker enzymes no synthesis of the common microbody marker, catalase, could be demonstrated using the inhibitor allylisopropylacetamide. Using D2) for density labeling of newly-formed catalase, no difference is observed between the density of catalase from cotyledons grown on 99.8% D2O during the transition period and the density of enzyme from cotyledons grown on H2O. The activity of particulate glycolate oxidase is reduced 30–50% by allylisopropylacetamide, but is not affected by D2O. The chlorophyll formation in the cotyledons is strongly inhibited by both substances.

The Value of Historical Data in Population Research, with Particular Reference to Hyphantria cunea Drury

AbstractThree different types of historical population data on the fall webworm, Hyphantria cunea Drury, are examined graphically. Oscillations in population density have peaks at intervals varying from 8 to 16 years, and are generally synchronous over very large areas in eastern and central Canada. Temperature in late summer is a key factor affecting the rate of change in density, particularly during the development of gradations, and this explains the synchronism of the oscillations. Climate and vegetation appear to be the main factors determining differences in mean density from one area to another. However, oscillations about the mean density have discrete limits, which are usually below the limits imposed by the food supply even where climate is generally favorable, and population decline often occurs despite favorable weather. These limits are imposed by other factors, such as the parasite Campoplex validus Cress. which has a delayed response to webworm density in eastern Canada.It is concluded that similar analyses for other insects, perhaps based on the sort of data being accumulated each year by the Forest Insect Survey, would contribute to the development of population principles and would suggest many useful short-cuts when more intensive work is undertaken on additional species.