Nutrients and mass in litter and top soil of ten tropical tree plantations

The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha^-1 in the H. sonora stand to 27.2 Mg ha^-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have had different influences on the concentration of available nutrients in soil.     

Characterization of a pollen-specific gene family from Brassica napus which is activated during early microspore development

In this paper we describe the isolation and characterization of a genomic clone (Bp4) from Brassica napus which contains three members of a pollen-specific multigene family. This family is composed of 10 to 15 closely related genes which are expressed in early stages of microspore development. The complete nucleotide sequence of the clone Bp4 and of three homologous cDNA clones is reported. One of the genes (Bp4B) contained in the genomic clone is believed to be non-functional because of sequence rearrangements in its 5 region and intron splicing sites. The remaining genes (Bp4A and Bp4C), as well as the cDNA clones, appear to code for small proteins of unique structure. Three different types of proteins can be predicted as a result of the deletion of carboxy or amino terminal portions of a conserved core protein. These proteins all share a common alternation of hydrophobic and hydrophilic domains. A fragment of the genomic clone containing the gene Bp4A, as well as the non-functional gene Bp4B, was introduced into tobacco plants via Agrobacterium-mediated transformation. The functional gene Bp4A is expressed in transgenic tobacco plants and shows spatial and temporal regulation consistent with the expression patterns seen in Brassica napus.     

Eph Family Receptors and Their Ligands Distribute in Opposing Gradients in the Developing Mouse Retina

The Eph family of receptor tyrosine kinases and their ligands can be divided into two specificity subclasses: the Eck-related receptors and their GPI-anchored ligands, and the Elk-related receptors and their transmembrane ligands. Previous reports demonstrated that Eck- and Elk-related receptors in the retina distribute in high temporal–low nasal and high ventral–low dorsal gradients, respectively. While others have focused on complementary ligand gradients in the retinal axon target, the tectum, we report that ligands from each subclass also distribute in gradients opposing those of their corresponding receptors within the retina itself. Moreover, ligand gradients in the retina precede ganglion cell genesis. These results support an intraretinal role for Eph family members in addition to their previously proposed role in the development of retinotectal topography. The distinct distributions of Eph family members suggest that each subclass specifies positional information along independent retinal axes.     

Purification and characteristics of cytosolic chitinase from Piromyces communis OTS1

Abstract A chitinase was purified from the cytosolic fraction of the anaerobic rumen fungus Piromyces communis OTS1 by affinity chromatography using regenerated chitin, gel filtration and chromatofocusing. The chitinase was most active at pH 6.2 and at 60 °C in a 20-min assay. The molecular mass of the purified protein was estimated by SDS-PAGE to be 42 kDa and its pI was 4.9. The enzyme activity, which was of the 'endo' type, was inhibited by A⁺, Hg²⁺ and allosamidin. N -Acetyl- β -glucosaminidase and 'exo' type chitinase activity were absent from the purified preparation.     

A new enzymatic route to the synthesis of 12-ketoursodeoxycholic acid

Summary Cholic acid (3,7,12-trihydroxy-5-cholanoic acid) was completely and selectively transformed into 12-ketoursodeoxycholic acid (3,7-dihydroxy-12-oxo-5-cholanoic acid) by means of two consecutive enzymatic steps catalyzed, the first, by 7- and 12-hydroxysteroid dehydrogenase and, the second, by 7-hydroxysteroid dehydrogenase. Coenzyme regeneration was carried out with -ketoglutarate-glutamate dehydrogenase and glucose-glucose dehydrogenase, respectively.     

Localization of yeast RNA polymerase I core subunits by immunoelectron microscopy.

Immunoelectron microscopy was used to determine the spatial organization of the yeast RNA polymerase I core subunits on a three-dimensional model of the enzyme. Images of antibody-labeled enzymes were compared with the native enzyme to determine the localization of the antibody binding site on the surface of the model. Monoclonal antibodies were used as probes to identify the two largest subunits homologous to the bacterial beta and beta' subunits. The epitopes for the two monoclonal antibodies were mapped using subunit-specific phage display libraries, thus allowing a direct correlation of the structural data with functional information on conserved sequence elements. An epitope close to conserved region C of the beta-like subunit is located at the base of the finger-like domain, whereas a sequence between conserved regions C and D of the beta'-like subunit is located in the apical region of the enzyme. Polyclonal antibodies outlined the alpha-like subunit AC40 and subunit AC19 which were found co-localized also in the apical region of the enzyme. The spatial location of the subunits is correlated with their biological activity and the inhibitory effect of the antibodies.