Effects of various buffers, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and NaN3 on menadione mediated photophosphorylation in isolated chloroplasts

The effects of DCMU and NaN₃ were studied on menadione-mediated photophosphorylation in broken spinach chloroplasts kept in low oxygen tension in Tricine or HEPES buffers at either high or reduced irradiances. – (A) At high irradiance (131 W. m^?2) and absence of NaN₃ the ATP formation was inhibited by DCMU regardless of the type of buffer used. – (B) At high irradiance and presence of NaN₃ some concentrations of DCMU stimulated, whilst others inhibited the ATP formation in a HEPES buffer. The ATP formation was predominantly inhibited by DCMU in a Tricine buffer. – (C) At reduced irradiance (57 W. m^?2) the chloroplasts in a HEPES buffer were almost insensitive towards DCMU both in the presence and absence of NaN₃. – (D) Chloroplasts in a Tricine buffer were slightly stimulated in their ATP formation by DCMU at reduced irradiance either with or without the presence of NaN₃ in the experimental medium. When menadione acts as a terminal electron acceptor, oxygen is consumed on its reoxidation. The results indicate that this process may occur with oxygen released by the splitting of water as the main oxidant. – The data also demonstrate the importance of caution when selecting buffering substances as well as when choosing light intensities for experiments on photophosphorylation in chloroplasts.     

Effects of 2,5-Dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) on Light Induced and Glycolytic Phosphate Uptake in Scenedesmus

The effects of DBMIB on photophosphorylation and glycolysis in Scenedesmus obtusiusculus Chod. were investigated by measuring the uptake of inorganic phosphate. To analyze the effects of DBMIB on the different energy coupling possibilities in open chain and cyclic photophosphorylation, DBMIB was given to the algae in narrow concentration intervals between 10^?6M to 10^?4M, either alone, or in combination with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) or desaspidin. DBMIB inhibits non-cyclic as well as cyclic photophosphorylation in Scenedesmus. However, the DCMU resistant photophosphorylation reactions are less sensitive to DBMIB than the open chain photophosphorylating system in non-DCMU treated cells. Low concentrations of DBMIB even released a part of the DCMU inhibition. Experiments with combinations of DBMIB and desaspidin also indicated that cyclic photophosphorylation is less sensitive to DBMIB than non-cyclic. The inhibition of DCMU resistant cyclic phosphorylation by DBMIB, which is a competitive inhibitor of quinones, indicated a participation of plastoquinones in this type of energy coupling as well as in the non-cyclic and DCMU-sensitive processes. The cyclic and the non-cyclic photophosphorylation pathways probably use different parts of the plastoquinone pool. For the purpose of the experiments, it was necessary to produce data for the effect of DBMIB (10^?6–10^?4M) on glycolysis. The highest concentration gave 50% inhibition.     

Growth Cycles in Lemna gibba Cultures and Their Effects on Growth Rate and Ultrastructure

A long-established axenic culture of Lemna gibba G3 was maintained in exponential growth phase under controlled conditions. Weekly analyses for 2 years showed that the individual plants of the Lemna gibba clone fluctuated between two forms. One extreme consisted of plants light in weight, small in size, and with a high relative growth rate (RGR), the other of heavy, large, and more slowly growing plants. At intervals plants having intermediate characteristics dominated in the stock culture. Indication of an annual growth-cycle was also found. The magnitude of growth response (weight, RGR, area, and dry matter content) after treatment with abscisic acid (ABA), 6-benzylaminopurine (BAP), and a combination of the two was different for low-weight and heavy plants. The heavy plants were more sensitive to ABA and BAP treatment than the low-weight ones. The accumulation of starch was least in small untreated plants and greatest in ABA treated plants. Large electron transparent globules were found in the chloroplasts of the ABA treated plants and in heavy plants regardless of how they had been treated. The different physiological and ultrastructural characteristics of the two forms of Lemna plants probably reflect an ageing-rejuvenation cycle. Emphasis is placed on the importance of this cycle when Lemna is used as a model plant in physiological experiments.     

Community Structure of Wetland Birds During Spring Migration Through the Rainwater Basin

Abstract: Staging areas and migratory stopovers of wetland birds have the potential to function as geographic bottlenecks; entire populations within a flyway may be affected by the quality and quantity of available wetland habitat at stopover sites. Although approximately 90% of playa wetlands in the Rainwater Basin (RWB) region of south-central Nebraska, USA, have been destroyed, the area still provides essential stopover habitat for >10 million waterfowl each spring. We evaluated community patterns and species associations to assess importance of assembly rules in structuring wetland bird communities during migration and to better facilitate multispecies conservation and management strategies. We surveyed 36–40 playas twice weekly in the RWB and observed approximately 2.6 million individual migratory wetland birds representing 72 species during 3 spring migrations 2002–2004. We evaluated spatial and temporal species co-occurrence patterns of geese, dabbling ducks, diving ducks, and shorebirds using null model analysis. Goose species co-occurrence scores did not differ from random in any year of the study, suggesting that goose species frequently use the same habitats during migration. Co-occurrence patterns among dabbling ducks were not different than expected by chance in any year; however, when we evaluated co-occurrence at a weekly scale, dabbling ducks co-occurred less often than expected during weeks of peak migration (high abundance), indicating that dabbling duck species spatially segregated at high densities. Diving duck co-occurrence patterns did not differ from random in any year, suggesting that diving duck species used the same habitats during migration. Shorebird species co-occurred less often than expected in 2002 and 2004, and during weeks of high shorebird abundance, indicating that shorebird communities were distinctly structured during those times. Most association values among lesser snow geese (Chen caerulescens) and dabbling duck species were positive, indicating dabbling ducks did not avoid wetlands with snow geese, a concern for waterfowl managers. However, we frequently observed snow geese and dabbling ducks using different microhabitats within a wetland, which indicate species associations and co-occurrence patterns may have occurred at a finer spatial scale than we measured. This approach of co-occurrence analysis will allow wildlife managers charged with multispecies management at migration stopover sites to make informed conservation and management decisions based on community structure rather than historic single-species approaches.     

Indirect Immunofluorescence Microscopy of Microtubular Structures in Male Germ Cells of Wildtype and l(3)pl (lethal-polyploid) Drosophila hydei

Tubulin-containing structures of the male germ cells of Drosophila hydei crossreact in indirect immu-nofluorescence microscopy with antibody directed against homogeneous porcine brain tubulin. There is no detectable difference in reactivity between germ cells of wildtype flies and the mutant l(3)pl (lethal-polyploid) which is characterized by microtubular abnormalities. However, the technique of indirect immunofluorescence microscopy allows the direct visualization of several abnormalities in the arrangement of the microtubular system of the mutant, particularly in the axonemal complex.     

Contamination Expérimentale In Vivo et In Vitro par Aggregata eberthi: Etude Ultrastructurale1

The mechanism of host invasion by Aggregata has been experimentally investigated both in vivo (in the crab), and in vitro (in mollusc cell cultures) and followed by electron microscopy. A few hours after the infesting meal, sporozoites escaped from sporocysts in the crab stomach: then they reached the small intestine. There, they pussed through the epithelium, making their way between the cells. Perforation of the thick basal lamina was induced by means of the elaboration of a dense product, probably an enzyme. Sporozoites stretched themselves passing through the basal lamina and entered the connective tissue surrounding the digestive tract. Damages inflicted on the host were minimal. In vitro, merozoites were able to enter cells from several molluscs by penetrating the cell's plasmalemma. A nucleolus appeared in the nuclei of intracellular merozoites.