Resistenzphysiologische Grundlagen der evolutiven Kälteakklimatisation von Sproßpflanzen

Gradations in cold resistance of plants with different latitudinal and altitudinal distribution, and the various categories of chilling and freezing resistance are hypothesized to be evolutionary steps of adaptive responses to increasing low temperature stress and annual seasonality. The gradual lowering of the critical phase transition temperature of biomembrane lipids, the capacity of persistent supercooling of tissues, and the development of a dormancy linked freezing-tolerance are considered to be essential mechanisms resulting in improved acclimatation to low temperature climates.

     

Rat hepatic uroporphyrinogen III cosynthase: Purification,properties, and inhibition by metal ions

Rat hepatic uroporphyrinogen III cosynthase has been isolated and purified 50-fold with a 36% yield by ammonium sulfate fractionation and sequential chromatography on DEAE-Sephacel and Sephadex G-100SF. Inhibition of uroporphyrinogen III formation with increasing porphobilinogen concentration was observed. Cosynthase was shown to be thermolabile, and a time-dependent loss of enzyme activity during reaction with uroporphyrinogen I synthase and porphobilinogen was observed. The pH optimum for the complete system (synthase and cosynthase) was pH 7.8 in 50 mm Tris-HCl or 50 mm sodium phosphate buffer. Various metals (KCl, NaCl, MgCl₂, CaCl₂) increased formation of Uroporphyrinogen III. Heavy metals including ZnCl₂, CdCl₂, and CuCl₂ were shown to selectively inhibit cosynthase activity, whereas other metals (HgCl₂, PbCl₂) were less selective and inhibited both synthase and cosynthase at similar concentrations.     

Notes on economic plants

Antibody-mediated sensitivity is not associated with cellular-mediated or delayed sensitivity, most frequently known as contact dermatitis. Compounds causing this response and their origins in plants are usually different, as is the immunological process.     

Co-localization of ecdysteroid receptors and c-fos-like protein in the brain of Manduca sexta larvae

Summary The presence of c-fos, a marker for cell activation, was investigated in cerebral neurons actively expressing ecdysteroid receptors during larval-pupal development in the tobacco hornworm, Manduca sexta. Colocalization was accomplished by ecdysteroid autoradiography using the tritiated high affinity 20-hydroxyecdysone agonist ponasterone A and immunocytochemistry with an antibody to a peptide sequence which is highly conserved in both human and murine c-fos. Immunoreactivity to a c-fos-like protein(s) was present in nuclei of many neurons of all the developmental stages examined. However, with the exception of the optic lobe, cells expressing nuclear ecdysteroid receptors were more immunoreactive than non-ecdysteroid-binding neurons. These data suggest that ecdysteroid-induced gene activation and translation may involve c-fos expression. Offprint requests to: H.-J. Bidmon     

The old REH theory remains unsatisfactory and the new REH theory is problematical - a reply to holmquist and jukes

Summary In response to criticism of REH theory (Fitch 1980), Holmquist and Jukes (1981) have mostly avoided the criticism or misunderstood it. Since they themselves state in their response that Amino acid sequence data alone cannot be used to estimate total nucleotide substitutions, they agree with the criticism. Most of their paper treats the newer theory (here designated as the REHN theory) which attempts to use the nucleotide sequences encoding proteins to better estimate total nucleotide substitutions (Holmquist and Pearl 1980). Since I made no criticism of REHN theory, their comments are frequently beside the point of my original criticism of REH theory. Nevertheless, it is shown here that REHN theory is also unsatisfactory in that: One, the varions are now more clearly defined but in such a way as to preclude the same codon from suffering a nucleotide substitution in more than one evolutionary interval. Two, the set of codons that accepts silent substitutions is identical to the set that accepts amino acid changing nucleotide substitutions. Three, the uncertainty in the REH estimate is considerable in that alternative excellent fits to the same observatuonal data may give alternative REH values that differ significantly even before stochastic variation and selective bias are considered. Four, the fit of their model to data is an irrelevancy where there are zero degrees of freedom.     

External and internal factors regulating metabolic rates of an estuarine benthic community

Summary The structure and metabolism of a soft-sediment estuarine macrofaunal community were measured over an annual cycle at two depth-contours in mesohaline Chesapeake Bay. Additional data for plankton productivity and respiration, as well as seston and sediment organics are also summarized for these communities. Benthic community respiration ranged from 0.24–3.38 g O₂ m^-2 d^-1, and significant differences were detected between the two depths. Similarly, macroinfaunal standing stocks reached 11.2 and 32.3 g (ash free) m^-2 for 3 m and 6 m depth communities, respectively, and both exhibited mid-summer declines in abundance. Inferences drawn from these data facilitated a partitioning of benthic community respiration into macrofaunal and meiofaunal/microbial components with a residual term, much of which could be explained statistically by interactions between these two components. A multi-variate statistical model developed from these data matched benthic respiration measurements within 1–2 S.E. Mass-balances of organic carbon were estimated for water column and benthos at the two depthcontours for early and late summer, as well as for an entire, time-weighted year. These various analyses led to the tentative conclusions that this benthic community was regulated by such internal factors as macrofaunal/meiofaunal grazing and microbial gardening, and by external factors such as temperature and predation by nekton. However, it appears that the ultimate control for this community was the supply of energy from organic carbon.Contribution No. HPEL-1206, USASupported by grants with the Maryland Department of Natural Resources (PS-72-02(77-78)), J.A. Mihursky, Coordinating Principal Investigator