Nuclear size and DNA content of the embryo and endosperm during their initial stages of development in Glycine max (Fabaceae)

A technique was developed for isolating embryo sacs from ovules of soybean and for separating embryo from endosperm. Image analysis and cytophotometry were used to determine the relative mass of DNA and size of nuclei of endosperm and embryo cells. Analyses were done at the globular through late heart-shaped embryo stages to correlate ploidy level or nuclear size, and differentiation in these tissues. Mean size of embryo nuclei was fairly constant through all stages studied. Ploidy condition of the embryo was stable, 95%–99% of the nuclei were distributed in a bipolar pattern by relative mass at 2C and 4C. Few embryo nuclei (3%) had ploidy levels above 4C at the late heart-shaped embryo stage. Variability in size of endosperm nuclei seemed correlated with the morphological state of these nuclei (free-nuclear vs. cellular). Most endosperm cells did not show significant polyploidy with 84%–92% of nuclei in the expected 3C–6C range, but some nuclei with elevated ploidy levels were noted during endosperm cellularization. Endosperm senescence was correlated with nuclear DNA loss over time. Polyploidy seems to have no direct role in the early differentiation of the soybean embryo and endosperm, but these stable conditions may be necessary for the early establishment of the embryo.     

Stereochemistry of residues in turning regions of helical proteins

JBIC Journal of Biological Inorganic Chemistry - We have developed a geometrical approach to quantify differences in the stereochemistry of α-helical and turning regions in four iron proteins....     

A demographic analysis of vole population responses to fragmentation and destruction of habitat

 Fragmentation and destruction of natural habitats is currently considered to be the major threat to wildlife populations. We here perform a comprehensive analysis of the demographic effects of habitat fragmentation and destruction on 14 populations of the root vole. The experiment was divided into two consecutive periods. During the first period, we contrasted populations with the same initial size and structure in continuous and fragmented habitat. During the second period, we fragmented the continuous habitat into the same configuration as the permanently fragmented habitat so that the effect of habitat destruction could be evaluated. We estimated survival and fecundity parameters and combined them into population projection matrices to evaluate their relative impact on population growth. In the first period of the experiment there was no difference in population growth rate between fragmented and continuous populations, although litter size was significantly higher in the continuous populations. In the second period, we found higher population growth rates in populations that had experienced habitat destruction. By applying the transition matrix model to empirical estimates of demographic parameters, we demonstrate that the difference in population growth rate in the second period of the experiment was the result of a nonsignificant difference in adult survival. Movements out of the habitat patches were significantly lower in populations that had experienced habitat destruction. We conclude that predator-caused mortality of animals moving out of the habitat patches was the main determinant of demographic variation in this system. Received: January 31, 2002 / Accepted: March 25, 2003