ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.     

ATP synthesis in a succinate decarboxylase system from Fasciola hepatica mitochondria

Köhler P. B.,Ryant C. and Behm Carolyn A. 1978. ATP synthesis in a succinate decarboxylase system from Fasciola hepatica mitochondria. International Journal for Parasitology8: 399–404. Succinate decarboxylation was measured by the formation of ¹⁴CO₂ from 1,4-¹⁴C-succinate in a particle free, dialysed mitochondrial extract from liver fluke. It has an absolute requirement for Mg²⁺ and CoA. ATP, ADP and inorganic phosphate are essential for optimal activity. Ap₅A, an inhibitor of adenylate kinase, and glutathione are also necessary. GTP supports decarboxylation as well as ATP, provided ADP is also present. The formation of CO₂ and propionate greatly exceeds the amount of ATP and CoA initially present in the reaction mixture. A net, substrate-level phosphorylation of ADP occurs, the amount of ATP formed being equivalent to the production of CO₂ or propionate. This system is inhibited in flukes incubated in vitro with mebendazole.It is concluded that ATP is required to spark the fermentation system when succinate is the initial substrate and intermediate substrates are absent; that the terminal step in propionate formation is catalysed by a transferase which transfers CoA from propionyl CoA to succinate; and that ATP formation is coupled to the decarboxylation of methylmalonyl-CoA. A reaction scheme is presented.     

Kinetics and morphology of glucose-limited cultures of moulds grown in a chemostat and on solid media

The affinity (K _s value) of Geotrichum candidum for glucose determined from chemostat cultures was ca. 1 mg/l. K _s values for glucose were also estimated from the radial growth rates of colonies of G. candidum and Neurospora crassa grown on media solidified with agar or silica gel. An assessment is made of the use of colony radial growth rate to determine substrate affinities. The length of apical and intercalary hyphal comparte ments, internode length and the diameter of leading hyphaat the margin of colonies grown on solid media were all reduced at low glucose concentrations.     

Crystals of modified fibrinogen: Size,shape and packing of molecules

We have produced several new macroscopic crystal forms and a variety of microcrystals from modified flbrinogens. Bovine and rabbit flbrinogens crystallize after limited digestion by a bacterial protease or α-chymotrypsin. The fibrinogens making up these crystals are largely intact and highly clottable. Tentative molecular packing arrangements for two crystal forms have been deduced. The crystal morphology and cleavage planes were used in this analysis. The characteristic α-helical coiled-coil reflections arid spikes of intensity in certain directions in the crystal X-ray patterns serve as markers for the orientation of the fibrinogen molecules. Changes that occur in one of the forms during preparation for electron microscopy, as shown by comparison with X-ray experiments on crystals in various stains and solvents, support this packing model. These studies provide preliminary evidence that fibrinogen is about 450 Å in length and that the molecules bond end-to-end to form filaments making up the crystals.     

Anaerobic microbial communities and their potential for bioenergy production in heavily biodegraded petroleum reservoirs

Most of the oil in low temperature, non-uplifted reservoirs is biodegraded due to millions of years of microbial activity, including via methanogenesis from crude oil. To evaluate stimulating additional methanogenesis in already heavily biodegraded oil reservoirs, oil sands samples were amended with nutrients and electron acceptors, but oil sands bitumen was the only organic substrate. Methane production was monitored for over 3000 days. Methanogenesis was observed in duplicate microcosms that were unamended, amended with sulfate or that were initially oxic, however methanogenesis was not observed in nitrate-amended controls. The highest rate of methane production was 0.15 μmol CH₄ g⁻¹ oil d⁻¹, orders of magnitude lower than other reports of methanogenesis from lighter crude oils. Methanogenic Archaea and several potential syntrophic bacterial partners were detected following the incubations. GC–MS and FTICR–MS revealed no significant bitumen alteration for any specific compound or compound class, suggesting that the very slow methanogenesis observed was coupled to bitumen biodegradation in an unspecific manner. After 3000 days, methanogenic communities were amended with benzoate resulting in methanogenesis rates that were 110-fold greater. This suggests that oil-to-methane conversion is limited by the recalcitrant nature of oil sands bitumen, not the microbial communities resident in heavy oil reservoirs.     

Association between sexually selected traits and allelic distance in two unlinked MHC II loci in white-tailed deer (Odocoileus virginianus)

Evolutionary Ecology - Body size and secondary sexual characteristics are drivers of male reproductive success among polygynous species. A gene complex found to be associated with morphology in...     

Genetic analysis of Pycr1 and Pycr2 in mice

The final step in proline biosynthesis is catalyzed by three pyrroline-5-carboxylate reductases, PYCR1, PYCR2, and PYCR3, which convert pyrroline-5-carboxylate (P5C) to proline. Mutations in human PYCR1 and ALDH18A1 (P5C Synthetase) cause Cutis Laxa (CL), whereas mutations in PYCR2 cause hypomyelinating leukodystrophy 10 (HLD10). Here, we investigated the genetics of Pycr1 and Pycr2 in mice. A null allele of Pycr1 did not show integument or CL-related phenotypes. We also studied a novel chemically-induced mutation in Pycr2. Mice with recessive loss-of-function mutations in Pycr2 showed phenotypes consistent with neurological and neuromuscular disorders, including weight loss, kyphosis, and hind-limb clasping. The peripheral nervous system was largely unaffected, with only mild axonal atrophy in peripheral nerves. A severe loss of subcutaneous fat in Pycr2 mutant mice is reminiscent of a CL-like phenotype, but primary features such as elastin abnormalities were not observed. Aged Pycr2 mutant mice had reduced white blood cell counts and altered lipid metabolism, suggesting a generalized metabolic disorder. PYCR1 and -2 have similar enzymatic and cellular activities, and consistent with previous studies, both were localized in the mitochondria in fibroblasts. Both PYCR1 and -2 were able to complement the loss of Pro3, the yeast enzyme that converts P5C to proline, confirming their activity as P5C reductases. In mice, Pycr1; Pycr2 double mutants were sub-viable and unhealthy compared to either single mutant, indicating the genes are largely functionally redundant. Proline levels were not reduced, and precursors were not increased in serum from Pycr2 mutant mice or in lysates from skin fibroblast cultures, but placing Pycr2 mutant mice on a proline-free diet worsened the phenotype. Thus, Pycr1 and -2 have redundant functions in proline biosynthesis, and their loss makes proline a semi-essential amino acid. These findings have implications for understanding the genetics of CL and HLD10, and for modeling these disorders in mice.