The Influence of Temperature on Nitrate Reductase Activity of Agrostis palustris and Cynodon dactylon

The influence of temperature was studied in relation to nitrate reductase activity of creeping bentgrass (Agrostis palustris Huds. cv. ‘Toronto’) a cool season grass and bermudagrass (Cynodon dactylon L. cv. ‘Tifgreen’) a warm season grass. Maximum nitrate reductase activity of both species occurred at 20°C. The nitrate reductase level in bentgrass leaves was reduced when grown at 35°C while bermudagrass leaves were relatively unaffected. The activity per se of the bentgrass enzyme preparation was inhibited rather than synthesis of the enzyme.     

Genetic Control of Variable and Constant Regions of Immunoglobulin Heavy Chains

IMMUNOGLOBULIN polypeptide chains consist of two well defined regions designated the “variable region” and the “constant region”. Whereas great diversity exists in amino-acid sequences of variable regions, the constant regions of a given subclass of heavy chains (C_H)^* are essentially invariant in sequence^{1, 2}. Exceptions are the allelic forms, such as the rabbit allotypes A14 and A15^{3, 4}, where a threonine-alanine interchange occurs in the constant region of γ chains (Appella, Chersi, R. G. M. and Dubiski, in preparation). The markers unique to a chains (for example, A14-A15) are closely linked to allotypic markers at the a locus (a1, a2, a3)^{3, 4} which seem to be present on four different Ig heavy chain classes (α, γ, ε, µ)^5–7. These puzzling observations can be explained if the a locus determinants are variable region markers which reflect genetically controlled differences in some relatively constant residues within the V_H region sequences⁷.     

Synthesis by Ribosomes of Viral Coat Protein containing Ester Linkages

Peptidyl transferase, the ribosomal enzyme which synthesizes peptide bonds, can catalyse the formation of ester linkages between α-hydroxyacyl-tRNA and aminoacyl-tRNA when ribosomes carry out a specific translation of phage R17 RNA in vitro.     

Phosphorus availability and nitrogenase activity in aquatic blue-green algae

Metabolically active phosphorus-starved cultures of blue-green algae assimilate ³²P rapidly in the light and in the dark. The uptake of phosphorus results in a rapid (within 15 min) stimulation in acetylene reduction by Anabaena cylindrica, A. flosaquae, Anabacnopsis circuiaris and Chlorogloea fritschii, with a response being obtained to less than 5 μg/1 of phosphorus. Uptake of phosphorus also causes a rapid increase in respiration in the dark but not in photo respiration, and the size of the cellular ATP pool and the ¹⁴CO₂ fixation rate both increase more slowly. The metabolism of phosphorus-sufficient cells, which assimilate phosphorus more slowly, shows little response when phosphorus is provided. Excess phosphorus is stored in the vegetative cells of blue-green algae as polyphosphate bodies which may form within 60 min of adding phosphorus to phosphorusstarved cells and which serve as a source of phosphorus for the algae when exogenous phosphorus is limiting. Preliminary results from Scottish waters suggest that urban effluents are important sources of available-phosphorus for algal growth and that the levels entering fresh waters from agricultural land are, per unit volume, lower. In both types of water the levels of available-phosphorus are rather similar to the levels of orthophosphate-phosphorus present. Most detergents tested serve as a source of phosphorus for nitrogen-fixing blue-green algae and cause a rapid stimulation in reduction when added to phosphorus-starved cultures. Of the detergents assayed, the biological types were richest in available phosphorus. The addition of detergents may result in a rapid increase in number of polyphosphate bodies present in the algae. Detergents in general also contain an inhibitor of algal metabolism. Whether a stimu-lation or an inhibition occurs depends on the quantities of detergent added and on whether or not the alga is phosphorus-deficient.     

Studies on plant growth-regulating substances XXVIII. Halogen-substituted benzoic acids

The plant growth-regulating activities of chloro-, bromo- and iodo-isomers in 2,5-, 2,3,5- and 2,3,6-substituted benzoic acids were assessed in the wheat cylinder, pea segment and pea curvature tests. Their effects in the tomato-leaf epinasty test were also investigated. Replacing an ortho-chloro atom by bromine had little or no effect on activity. An ortho-iodo substituent, however, reduced activity in the 2,3,6-substituted series and almost completely inhibited it in the 2,5- substituted series. This decreased activity of ortho-iodo-substituted isomers is visualized as being due to a steric inhibition of the attachment of the carboxyl group to its receptor unit prior to the initiation of the growth response.     

Bistable properties of the hock joint of horses (Equus spp.)

The hock (ankle) joint of horses is bistable: if placed in an intermediate position it springs either to full extension or to strong flexion. We have performed experiments to measure the torques involved and to elucidate the mechanism. The torques were much smaller in hocks of Przewalski's horse ( E. ferus ) and zebra ( E. grevyi ) than in those of domestic horses. We suggest that the bistability of the hock is too slight to have much importance for wild horses but may have been enhanced in the breeding of domestic horses by selection for elegance of gait. The elbow joint is also bistable but the stifle (knee) and carpal joints are not.     

Growth Rate, Photosynthesis and Respiration in Relation to Leaf Area Index

This work examined three possible explanations of growth rateresponses to leaf area index (LAI) in which growth rate perunit of ground area (crop growth rate, CGR) increased to a plateaurather than decreasing above an optimum LAI at which all lightwas intercepted. Single leaf photosynthetic measurements, andwhole plant 24 h photosynthesis and respiration measurementswere made for isolated plants and plants in stands using Amaranlhushybridus, Chenopodium album, and two cultivars of Glycine maxgrown at 500 and 1000 µimol m^–2 S^–1 photosyntheticphoton flux density at 25 °C. CGR, relative growth rate(RGR), and LAI were determined from 24 h carbon dioxide exchangeand leaf area and biomass measurements. Respiration increasedrelative to photosynthesis with crowding in A. hybridus andthere was an optimum LAI for CGR. In contrast, the ratio ofrespiration to photosynthesis was constant across plant arrangementin the other species and they had a plateau response of CGRto LAI. Neither increased leaf photosynthetic capacity at highLAI nor a large change in biomass compared to the change inLAI could account for the plateau responses. It was calculatedthat maintenance respiration per unit of biomass decreased withdecreasing RGR in C. album and G. max, but not A. hybridus,and accounted for the plateau response of CGR to LAI. Sincesimilar decreases in maintenance respiration per biomass atlow RGR have been reported for several other species, a constantratio of respiration to photosynthesis may occur in more speciesthan constant maintenance respiration per unit of biomass. Amaranlhus hybridus L., Chenopodium album L., Glycine max L Merr, soybean, photosynthesis, respiration, growth, leaf area index     

Colony development and formation in halysitid corals

Lee, D.-J. & Noble, J. P. A. 1990 04 15: Colony development and formation in halysitid corals. Lethaia , Vol. 23. pp. 179–193. Oslo. ISSN 0024–1164.
Modes of colony formation and their relationship with colony morphology, size and substrate characteristics in species of halysitid corals have been studied. Two distinctive modes of colony formation in halysitids are proposed. In the monoplanulate mode. represented by Catenipora snnplex . the colony is developed from a single protocorallite and colony formation is achieved by a combination of asexual increase and intracolony fusions. In contrast, the polyplanulatc mode is demonstrated by C. escharoides . in which the early colony formation is achieved primarily by fusions of many 'incipicnt colonies' of more than a single planulate origin and of different generations. The latter mode has not previously been described in tabulates and has significant implications for coloniality, reproductive and life history characteristics, histo-compatibility and adaptative ecology. The colony size and morphology. and The distribution of halysitid species were primarily determined by the modes of colony formation and the substrate characteristics. Colonies of the monoplanulate mode. when developed on soft substrates, exhibit a small and spherical morphology with isolated distribution patterns, while those developed on hard substrates are tabular and variable in size. depending on the availability of substrate. In colonies of the polyplanulate mode, on the other hand. the size of the colony is largely dependent on The frequency and timing of allograft fusion. They are characteristically found on soft substrates. often as dense mono specific thickets. The mode of colony formation in halysitids is probably species-specific and results in the adaptation to substrates. * Colony development, halysitid corals, Anticosti Island. Gotland .     

Secondary production of chironomid communities in insecticide-treated and untreated headwater streams

SUMMARY.

• 1 Production of chironomid communities of three first order, Appalachian Mountain streams was estimated and the effects of an insecticide-induced disturbance on chironomid production was examined.
• 2 Annual production of non-Tanypodinae chironomids in the streams during the first study year (no treatment) ranged from 1366 to 3636 mg m^?2, while production of Tanypodinae chironomids ranged from 48 to 116 mg m ^?2. Production/biomass ratios ranged between 19 and 23 for non-Tanypodinae and from 6 to 7 for Tanypodinae chironomids.
• 3 Insecticide applications resulted in significantly lower chironomid densities and biomass in the treated stream relative to the pretreatment year and reference stream. Annual production of non-Tanypodinae (703 mg m^?2) and Tanypodinae (32 mg m ^?2) chironomids in the treated stream decreased by 64% and 67%, respectively, compared with the pretreatment year. In contrast, production of non-Tanypodinae (2084 mg m^?2) increased by 34% and production of Tanypodinae (96 mg m^?2) by 57% in the reference stream.

     

Nolleria pulicis N. Gen., N. Sp. (Microsporida: Chytridiopsidae), a Microsporidian Parasite of the Cat Flea, Ctenocephalides felis (Siphonaptera: Pulicidae)

A new species of microsporidium, Nolleria pulicis, is described and named here from the cat flea, Ctenocephalides felis. The genus Nolleria is created and placed within the family Chytridiopsidae. The family is slightly modified to accommodate certain features of intracellular development seen in N. pulicis, which is otherwise very similar to other species in the family Chytridiopsidae. Sporulation is described from ultrastructural analysis of infected midgut epithelial cells of adult C. felis. The term “multiple division by vacuolation” is proposed for describing sporogony as it occurs in this species and certain related species of microsporidia. The probable mode of transmission and apparent absence of merogony are discussed.