Differences in chemical composition of plants grown at constant relative growth rates with stable mineral nutrition

Summary Leaf chemistry of a willow clone (Salix aquatica Smith) differed significantly when grown at constant relative growth rates depending upon the relative availability of nutrients and light. Concentration of amino acids and nitrate were high in plants grown with a relative surplus of nutrients. Concentrations of starch, tannin, and lignin, on the other hand, were high in plants grown with a relative surplus of carbon. Photosynthetic rates, expressed per unit leaf area, were similar when plants were grown under high light conditions, regardless of nutrient availability. Dark respiration was much higher in plants supplied with abundant nutrients than in those with a more limited supply, reflecting differences in nitrogen concentration of the tissue. The experimental approach allows plants to be grown to a standard size with differing, but highly uniform chemistry. Plants grown in such a manner may provide good experimental material to evaluate interactions between herbivores or pathogens and their hosts.     

Ultrasonographic assessment of the endometrium in rhesus monkeys during the normal menstrual cycle

This study was undertaken to determine whether cyclical changes in the endometrium of the rhesus monkey could be observed by using ultrasound. Three indices of endometrial size were examined: the antero-posterior (or ventro-dorsal), longitudinal, and transverse diameters. Changes in the ultrasonic reflectivity of the endometrium were also assessed. We have attempted to correlate these endometrial parameters with the hormonal status of the animal. Ultrasonography was performed for an average of 12 consecutive days during 19 menstrual cycles. All ultrasonic recordings were normalized to the day of the estradiol (E2) peak (Day 0). We found that the reflectivity of the endometrium was dependent on the stage of the cycle: during the follicular phase, the endometrium appeared less echogenic (darker) compared to the myometrium; in the luteal phase, the endometrium was more echogenic (lighter). During the follicular phase (Days -9 to 0), there was a linear increase in the antero-posterior (p less than 0.001), longitudinal (p less than 0.05), and transverse (p less than 0.001) diameters. In the luteal phase (Days 1-15), no significant changes were observed in these diameters. An estimated endometrial volume (EEV) was obtained by the product of the antero-posterior, longitudinal, and transverse diameters. Each animal observed during the follicular phase (n = 14) exhibited a peak in the EEV, which correlated with the day of the E2 peak (p less than 0.01). From this study, we conclude that the sonographic appearance of the endometrium of the rhesus monkey reflects the cyclical changes that occur during the menstrual cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phage P1 Cre-loxP site-specific recombination. Effects of DNA supercoiling on catenation and knotting of recombinant products

Bacteriophage P1 contains a site-specific recombination system consisting of a site, loxP, and a recombinase protein Cre. We have shown that with purified Cre protein we can carry out recombination between two loxP sites in vitro. When that recombination occurs between two sites in direct orientation on the same DNA molecule, we observed the production of free and catenated circular molecules. In this paper we show that recombination between sites in opposite orientation leads to both knotted and unknotted circular products. We also demonstrate that the production of catenanes and knots is influenced by two factors: (1) supercoiling in the DNA substrate, supercoiled DNA substrates yield significantly more catenated and knotted products than nicked circular substrates; and (2) mutations in the loxP site, a class of mutations have been isolated that carry out recombination but result in a distribution of products in which the ratio of catenanes to free circles is increased over that observed with a wild-type site. A more detailed analysis of the products from recombination between wild-type sites indicates: (1) that the catenanes or knots produced by recombination are both simple and complex; (2) that the ratio of free products to catenanes is independent of the distance between the two directly repeated loxP sites; and (3) that for DNA substrates with four loxP sites significant recombination between non-adjacent sites occurs to give free circular products. These observations provide insights into how two loxP sites are brought together during recombination.