Oxidation-reduction potential dependence of low-temperature photoreactions of chloroplast Photosystem II

The light-induced free-radical signal of Photosystem II (observed after illumination at 77 °K) has been studied in chloroplasts as a function of the oxidation-reduction potential established prior to freezing. The intensity of the light-induced signal is unchanged in the potential region of +590 mV to +760 mV. At higher potential (+850 mV), there is a 30% decrease in signal intensity. The light-induced signal decreases to zero in the low-potential region, with a midpoint potential of +475 mV. These results are considered in terms of a Photosystem II reaction-center complex in which the light-induced free-radical signal arises from the oxidized form of the reaction-center chlorophyll, and this chlorophyll molecule is capable of being reduced at liquid-nitrogen temperature by a secondary electron donor which has a midpoint oxidation-reduction potential of +475 mV.     

Hybrid formation within the genus Leishmania?

Leishmanial organisms isolated from a desert rodent (Psammomys obesus) and a feral dog (Canis familiaris) in the Eastern Province of Saudi Arabia were isoenzymically distinct from Leishmania major and L. arabica, organisms usually associated with human and wild animal cutaneous leishmaniasis in this area. Further examination of isoenzyme banding patterns of cloned populations of these organisms, together with karyotyping using orthogonal field alternation gel electrophoresis and the use of highly specific kinetoplast DNA probes, has produced evidence suggesting that these organisms isolated from the dog and the rodent are hybrids of L. major and L. arabica.     

Concentration and flux of solutes from snow and forest floor during snowmelt in the West-Central Adirondack region of New York

Decreases in pH and increases in the concentration of Al and NO ₃ ^– have been observed in surface waters draining acid-sensitive regions in the northeastern U.S. during spring snowmelt. To assess the source of this acidity, we evaluated solute concentrations in snowpack, and in meltwater collected from snow and forest floor lysimeters in the west-central Adirondack Mountains of New York during the spring snowmelt period, 29 March through 15 April 1984.During the initial phase of snowmelt, ions were preferentially leached from the snowpack resulting in elevated concentrations in snowmelt water (e.g. H⁺ = 140 eq.l^–1; NO ₄ ^2– = 123 eq.l^–1; SO ₃ ^– = 160 eq.l^–1). Solute concentrations decreased dramatically within a few days of the initial melt (< 50 eq.l^–1). The concentrations of SO ₄ ^2– and NO ₃ ^– in snowpack and snowmelt water were similar, whereas NO^– ₃ in the forest floor leachate was at least two times the concentration of SO ₄ ^2– .Study results suggest that the forest floor was a sink for snowmelt inputs of alkalinity, and a net source of H⁺, NO ₃ ^– , dissolved organic carbon, K⁺ and Al inputs to the mineral soil. The forest floor was relatively conservative with respect to snowmelt inputs of Ca²⁺, SO ₄ ^2– and Cl^–. These results indicate that mineralization of N, followed by nitrification in the forest floor may be an important process contributing to elevated concentrations of H⁺ and NO ₃ ^– in streams during the snowmelt period.     

Hormone responses to low-dose GnRH treatment in post-partum beef cows

Acyclic beef cows received 1.0, 2.5 or 5.0 micrograms GnRH/2 h for 48 h as 24 X 2 h repeated i.v. injections or by continuous i.v. infusion. Preovulatory-type LH surges were detected in 9/18 injected and 8/15 infused cows and occurred 30.6 +/- 5.1 h and 3.3 +/- 0.7 h after the start of treatment respectively. Cows receiving the lowest infusion dose did not exhibit gonadotrophin surges. The LH response to individual injections increased with dose but the proportion of injected cows showing preovulatory-type surges at each dose level did not change. A total of 20 cows (10 injected and 10 infused) showed evidence of luteal activity within 7 days of the end of GnRH treatment, although this was transitory in most animals. Cows which exhibited preovulatory-type LH surges in response to treatment had significantly higher plasma oestradiol-17 beta concentrations and lower FSH concentrations before treatment than those which did not. The results suggest that the LH response to GnRH treatment is dependent on follicular status in the immediate pretreatment period.     

Expression of the precore region of an avian hepatitis B virus is not required for viral replication.

The core-antigen-coding region of all hepadnaviruses is preceded by a short, in-phase open reading frame termed precore whose expression can give rise to core-antigen-related polypeptides. To explore the functional significance of precore expression in vivo, we introduced a frameshift mutation into this region of the duck hepatitis B virus (DHBV) genome and examined the phenotype of this mutant DNA by intrahepatic inoculation into newborn ducklings. Animals receiving mutant DNA developed DHBV infection, as judged by the presence in hepatocytes of characteristic viral replicative intermediates; molecular cloning and DNA sequencing confirmed that the original mutation was present in the progeny genomes. Infection could be efficiently transmitted to susceptible ducklings by percutaneous inoculation with serum from mutant-infected animals, indicating that infectious progeny virus was generated. These findings indicate that expression of the precore region of DHBV is not essential for genomic replication, core particle morphogenesis, or intrahepatic viral spread.     

An upper limit to the abundance of aquatic organisms

Summary The maximum density achievable by aquatic organisms is an inverse linear function of their body size. As a consequence, the maximum achievable biomass is independent of body size, and is 2 orders of magnitude higher than the biomass in natural populations. The minimum interorganismic terorganismic distance, calculated from the maximum density to allow comparison between aquatic and terrestrial organisms, scales as the 1/3 power of body size in both habitats. The similarities in the interorganismic distance of terrestrial and aquatic plant and animal communities suggest a fundamental regularity in the way organisms use the space.