Effect of light and nutrients on biomass allocation in Calamagrostis canadensis

The effects of light intensity and nutrient availability on the biomass allocation of Calamagrostis canadensis were studied under both greenhouse and field conditions In the greenhouse, seedlings from forest and wetland populations were grown in sand-peat mixtures, under three light intensities and three fertilizer levels Total above and below ground growth increased with light intensity and nutrient availability, nutrient availability, however, only altered plant growth when light intensity was above moderate levels Numbers of rhizomes were greatest under low and moderate nutrient regimes but high light was also needed for maximum numbers of rhizomes In the field, tillers and rhizomes were examined under open, 40% and 85% canopy cover Tiller and rhizome weight and diameter of rhizomes decreased with canopy closure However, proportional allocation of biomass to rhizomes was greatest and percentage total non-structural carbohydrates of rhizomes was lowest under a 40% canopy     

Experimental documentation of natural hybridization inCactaceae: Origin of Lloyd's Hedgehog Cactus,Echinocereus ×lloydii

The origin ofEchinocereus ×lloydii Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus Engelm. (a species of claret-up cactus) andE. dasyacanthus Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F₁ hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F₂ generation hybrids were also obtained. The known F₁ hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically.     

Effect of monensin on receptor recycling during continuous endocytosis of asialoorosomucoid

The binding of asialoglycoproteins to their liver cell receptor results in internalization of the ligand-receptor complex. These complexes rapidly appear in intracellular compartments termed endosomes whose acidification results in ligand-receptor dissociation. Ligand and receptor subsequently segregate: ligand is transported to lysosomes and is degraded while receptor recycles to the cell surface. The proton ionophore monensin prevents acidification of endosomes and reversibly inhibits this acid-dependent dissociation of ligand from receptor. The present study determined the effect of monensin treatment of short-term cultured rat hepatocytes on cell-surface-receptor content, determined both by their binding activity and immunologically, following continuous endocytosis of asialoorosomucoid. Inclusion of 5 microM monensin in the incubation medium reduced the number of immunologically detectable cell-surface receptors by 20% in the absence of ligand. During continuous endocytosis of asialoorosomucoid, inclusion of monensin resulted in a 30-40% reduction of cell-surface receptor detectable either by ligand binding or immunologically. These results suggest that the reduced liver-cell-surface content of receptor in monensin is due to intracellular trapping of ligand-receptor complexes. The reduction of surface receptor during monensin incubation in the absence of ligand suggests that "constitutive recycling" of plasma membrane components also requires intracellular acidification.     

Estimation of a common odds ratio in case-control studies of familial aggregation

A new estimator of a common odds ratio is proposed for case-control studies of familial aggregation. The proposed estimator is a modification to the usual Mantel-Haenszel estimator that relies on an empirical adjustment for the within-family clustering which is typical of such designs. A simulation study shows that the estimator tends to have smaller mean squared error than the unmodified Mantel-Haenszel estimator under conditions likely to arise in practice. The construction of confidence intervals is also discussed.     

A comparison of confidence interval methods for the intraclass correlation coefficient

Different methods of obtaining confidence intervals for the intraclass correlation coefficient rho in the unbalanced one-way random-effects model are investigated, focusing on applications to family studies. Methods based on simple modifications of formulas for the case of equal group sizes are found to provide adequate coverage at small to moderate values of rho. A method based on the large-sample standard error of the sample intraclass correlation, as derived by Smith (1956, Annals of Human Genetics 21, 363-373), is shown to provide consistently good coverage at all values of rho. A method proposed by Thomas and Hultquist (1978, Annals of Statistics 6, 582-587) also provides consistently good coverage, but generates mean interval widths substantially greater than those generated by Smith's method at values of rho likely to arise in practice.     

Roles of H1 domains in determining higher order chromatin structure and H1 location

Peptides derived from calf thymus H1 and rat liver H1, comprising only the globular and COOH-terminal domains of the intact molecule and therefore lacking NH2-terminal domains, have been shown by reconstitution to be as effective as the complete H1 molecule in inducing higher-order-chromatin structure. As the globular domain of H1 alone cannot induce chromatin folding, our results demonstrate that this function is primarily controlled by the COOH-terminal domain of the molecule. Surprisingly, these peptides do not locate correctly with respect to the nucleosome. This is demonstrated by their failure to confer upon reconstitutes the ability to protect DNA fragments of chromatosome length when digested with micrococcal nuclease. The precise placement of the H1 molecule (globular domain) with respect to the nucleosome is shown to be influenced by the "tail" domains of both H1 and the core histones.     

Transition from somatic to meiotic pairing and progressional changes of the synaptonemal complex in spermatocytes of Aedes aegypti

Aedes aegypti spermatocytes were reconstructed from electron micrographs. The species has tight somatic pairing of the chromosomes, and there are therefore no classical leptotene and zygotene stages, but rather a gradual transition from somatic pairing to meiotic pairing (= pachytene). The term prepachytene has been used for the transitory stage. The first visible sign of impending meiosis was a reorganization of the chromatin, which resulted in the formation of spaces (synaptic spaces) in the chromatin, about the width of the synaptonemal complexes (SCs). Diffuse material, possibly precursor material for the SC, was present in the spaces. Later short pieces of complex were formed throughout the nucleus. Late prepachytene, pachytene, and diplotene complexes were reconstructed. Each chromosome occupied a separate region of the nucleus. The complexes became progressively shorter from prepachytene (maximum complement length 289 m) to diplotene (175 m). The thickness of the SCs increased from prepachytene to pachytene and probably decreased again during diplotene. At the beginning of diplotene the lateral elements (LEs) separated, and the single LEs became two to three times thicker than the LEs of the SC. The centromeres were at all stages attached to the nuclear membrane, whereas the telomeres were free in the nucleoplasm during pachytene and diplotene. A heterochromatic marker was present on chromosome 1 near the sex determining locus, and a diffuse marker on chromosome 3 near the nucleolus organizer region. After breakdown of the complexes, polycomplexes were present in the nucleus.     

The effect of Cd2+ on the biosynthesis of chlorophyll in leaves of barley

The effect of cadmium on the biosynthesis of chlorophyll has been investigated in the leaves of dark-grown seedlings of barley ( Hordeum vulture L. cv. Proctor). Cd2+ inhibited the production of chlorophyll by affecting 1) the synthesis of 5-aminolacvulinic acid and 2) the protoehlorophyllide reductase ternary complex with its substrates. Cd2+ had no effect on the constituent enzymes that catalyse the synthesis of free protoehlorophyllide from 5-aminolaevulinic acid. The results obtained are consistent with Cd2+ inhibiting the formation of chlorophyll by reacting with essential thiol groups in both the protochlorophyllide reductase protein and the enzyme(s) involved in the light dependent synthesis of 5-aminolaevulinic acid.