PRODUCTIVITY AND PRODUCTION EFFICIENCY OF AN UPPER SONORAN DESERT EPHEMERAL COMMUNITY

During years with good winter rainfall, ephemeral plants can contribute considerably to primary production in the upper Sonoran Desert. This study was designed to compare ephemeral community productivity and production efficiency within the different microhabitats created by trees, shrubs and open spaces in a Sonoran Desert ecosystem. Ephemerals were periodically harvested in the different habitats and dried for biomass and caloric determinations. The caloric data were compared to total solar input into the different microhabitats in order to determine production efficiencies of each stand. Productivity rates were also determined for the total community for the sample period, winters of 1972-74. Both productivity and production efficiency were highest under the shade of Cercidium. The highest production efficiency occurring in the shaded sites was 5.03% which approaches the theoretical maximum photosynthetic efficiency level. The production efficiency of the entire ephemeral community for the whole growing season was only 0.17% during an optimal year, demonstrating the influence of the environment in the interspaces on productivity and solar conversion in the desert.     

Identification of a region of mouse zona pellucida glycoprotein mZP3 that possesses sperm receptor activity.

The ability of mouse zona pellucida glycoprotein ZP3 (mZP3) to function as a sperm receptor is attributable to certain of its oligosaccharides, not to its polypeptide (P. M. Wassarman, 1990. Development 108, 1-17). Here, purified, radioiodinated mZP3 was digested by either papain or V8 protease, and the glycopeptides produced were fractionated by HPLC and assayed for sperm receptor activity in vitro. Each proteolytic digest of mZP3 contained a heavily glycosylated peptide, approximately 55,000 apparent M(r), that exhibited sperm receptor activity in vitro. To determine the region of mZP3 polypeptide from which the active glycopeptides were derived, Western gel immunoblotting, employing an antiserum directed against a specific mZP3 peptide epitope, and automated amino-terminal amino acid sequencing were employed. Results of these experiments strongly suggest that the active glycopeptides produced by digestion of mZP3 with either papain or V8 protease are derived from the same region of the carboxy-terminal half of the mZP3 polypeptide. These and other findings are discussed in terms of mZP3 structure and function.     

Tiron as a spin-trap for superoxide radicals produced by the respiratory chain of submitochondrial particles

Tiron can be used as a spin-trap for O2 radicals generated by the respiratory chain of submitochondrial particles (SMP). Using this sensitive method, it was shown that the O2 (radical) production by the succinate-oxidizing SMP can be reduced by antimycin or 4-nonyl-2-hydroxyquinoline-N-oxide, the effects of both antibiotics being abolished and prevented by cyanide. It is suggested tht the O2 radicals are produced due to autooxidation of ubisemiquinone which is formed as an intermediate upon one-electron oxidation of CoQH2 by cytochrome c1. The effects of antimycin, 2-nonyl-4-hydroxyquinoline-N-oxide and cyanide on the O2 (radical) generation correlate with the effects of these inhibitors on a steady-state concentration of ubisemiquinone predicted by the Mitchell's Q-cycle hypothesis.