Light-induced changes in the amounts of the 36000-Mr polypeptide of NADPH-protochlorophyllide oxidoreductase and its mRNA in barley plants grown under a diurnal light/dark cycle

Seedlings of barley were grown either in continuous darkness or under a diurnal 12 h light/12 h dark cycle and the effects on NADPH-protochlorophyllide oxidoreductase were followed at two different levels. Firstly, the relative content of the mRNA encoding the NADPH-protochlorophyllide oxidoreductase was measured by dot-blot hybridization. Secondly, changes in the enzyme polypeptide were monitored either by the method of immunoblotting or by immunogold labelling of ultrathin sections of Lowicryl-embedded leaf tissue. Our results demonstrate that drastic diurnal changes in the level of mRNA sequences and the enzyme protein are unlikely to occur in plants which have been grown under natural light/dark conditions. In the dark, protein and mRNA accumulation occurs at an early developmental stage. These results are difficult to reconcile with the suggestion that the massive accumulation of mRNA and enzyme protein in dark-grown seedlings is primarily the consequence of an artificially extended darkperiod. In addition to the plastid-specific NADPH-protochlorophyllide oxidoreductase a closely related polypeptide has been detected outside the plastid in the surrounding cytoplasm (Dehseh et al. 1986b, Planta 169, 172–183). During the diurnal light/dark treatment of seedlings the concentrations of the two protein populations did not show any variation indicative of an exchange between the two protein populations across the plastid envelope.Abbreviation poly(A)⁺RNA polyadenylated RNA     

On subspecific taxa ofHypericum empetrifolium (Hypericaceae) from Crete

The morphology, altitudinal distribution and phytocoenology ofHypericum empetrifolium Willd., var.oliganthum Rech. fil. and var.tortuosum Rech. fil. are reassessed and as a result, the taxa are treated at subspecific rank. Essential characters proved to be growth form, number of flowers, foliage and epidermal surface characters, shape of seeds and testa sculpturing.The different growth forms can be interpreted as adaptations to the local habitats.Hypericum empetrifolium Willd. subsp.empetrifolium is a low subshrub of various vegetation types known as phrygana whereasHypericum empetrifolium Willd. subsp.oliganthum (Rech. f.)Hagemann grows as a cushion-like dwarf shrub in chasmophyte associations rich in relic species.Hypericum empetrifolium Willd. subsp.tortuosum (Rech. f.)Hagemann is confined in the high mountain regions and grows as a true dwarf espalier shrub with low spreading shoots.Dedicated to Hofrat Univ.-Prof. DrK. H. Rechinger on the occasion of his 80th birthday.     

Aldosterone regulates paracellular pathway resistance in rabbit distal colon

Summary Regulation of the paracellular pathway in rabbit distal colon by the hormone aldosterone was investigated in vitro in Ussing chambers by means of transepithelial and microelectrode techniques. To evaluate the cellular and paracellular resistances an equivalent circuit analysis was used. For the analysis the apical membrane resistance was altered using the antibiotic nystatin. Under control conditions two groups of epithelia were found, each clearly dependent on the light: dark regime. Low-transporting epithelia (LT) were observed in the morning and high-transporting epithelia (HT) in the afternoon. Na⁺ transport was about 3-fold higher in HT than in LT epithelia. Incubating epithelia of both groups with 0.1 mol·1^-1 aldosterone on the serosal side nearly doubled in LT epithelia the short circuit current and transepithelial voltage but the transepithelial resistance was not influenced. Maximal values were reached after 4–5 h of aldosterone treatment. In HT epithelia due to the effect of aldosterone all three transepithelial parameters remained constant over time. Evaluation of the paracellular resistance revealed a significant increase after aldosterone stimulation in both epithelial groups. This increase suggests that tight junctions might have been regulated by aldosterone. The hormonal effect on electrolyte transport was also dependent on the physiological state of the rabbit colon. Since net Na⁺ absorption in distal colon is, in addition to transcellular absorption capacity, also dependent on the permeability of the paracellular pathway, the regulation of tight junctions by aldosterone may be a potent mechanism for improving Na⁺ absorption during hormone-stimulated ion transport.Abbreviations V _t transepithelial potential difference (mV) - R _t transepithelial resistance (·cm²) - G _t transepithelial conductance (mS·cm^-2) - I_sc calculated short circuit current (A·cm^-2) - V _a apical membrane potential difference (mV) - V _bl basolateral membrane potential difference (mV) - voltage divider ratio - R _a apical membrane resistance (·cm²) - R _bl basolateral membrane resistance (·cm²) - R _c cellular resistance ( of apical and basolateral resistance) (·cm²) - R _p resistance of the paracellular pathway (·cm²) - G _a apical membrane conductance (mS·cm^-2) - G _bl basolateral membrane conductance (mS·cm^-2) - G _p paracellular conductance (mS·cm^-2) - G _t transepithelial conductance (mS·cm^-2) - HT _contr high transporting control epithelia - LT _contr low transporting control epithelia - HT _aldo aldosterone incubated high transporting epithelia - LT _aldo aldosterone incubated low transporting epithelia     

Prosimian juvenile mortality in zoos and primate centers

I review literature on juvenile mortality of captive prosimians in order to evaluate the available information on captive breeding. Juvenile mortality includes abortion, premature mortality, stillbirth, and death of the unweaned young. Prosimian juvenile mortality ranges between 25 and 45% in captive populations. It is generally lower in the Lemuroidea, particularly the Cheirogaleidae, than in the Lorisoidea. Mortality is particularly high in the Lorisinae. Most mortality, including a high stillbirth rate, occurs on the first day and during the first 10 days thereafter. Stress, maternal neglect and traumatic insults, not infrequently linked to each other, are the most frequently reported causes of death. The percentage of congenital malformations tends to be high in some colonies. Sex of the infant and parity seem to be important risk factors for juvenile mortality, whereas litter size does not appear to be important. Based on few data, wild- caught females appear to have higher breeding success than those born in captivity. Synchronized births in lemuroids and isolated births in Galagoare more likely to result in successfully weaned infants.     

The Gram-positive side of plant–microbe interactions

Plant growth and development are significantly influenced by the presence and activity of microorganisms. To date, the best-studied plant-interacting microbes are Gram-negative bacteria, but many representatives of both the high and low G+C Gram-positives have excellent biocontrol, plant growth-promoting and bioremediation activities. Moreover, actinorhizal symbioses largely contribute to the global biological nitrogen fixation and many Gram-positive bacteria promote other types of symbioses in tripartite interactions. Finally, several prominent and devastating phytopathogens are Gram-positive. We summarize the present knowledge of the beneficial and detrimental interactions of Gram-positive bacteria with plants to underline the importance of this particular group of bacteria.     

Virus evolution reveals an exclusive role for LEDGF/p75 in chromosomal tethering of HIV

Retroviruses by definition insert their viral genome into the host cell chromosome. Although the key player of retroviral integration is viral integrase, a role for cellular cofactors has been proposed. Lentiviral integrases use the cellular protein LEDGF/p75 to tether the preintegration complex to the chromosome, although the existence of alternative host proteins substituting for the function of LEDGF/p75 in integration has been proposed. Truncation mutants of LEDGF/p75 lacking the chromosome attachment site strongly inhibit HIV replication by competition for the interaction with integrase. In an attempt to select HIV strains that can overcome the inhibition, we now have used T-cell lines that stably express a C-terminal fragment of LEDGF/p75. Despite resistance development, the affinity of integrase for LEDGF/p75 is reduced and replication kinetics in human primary T cells is impaired. Detection of the integrase mutations A128T and E170G at key positions in the LEDGF/p75-integrase interface provides in vivo evidence for previously reported crystallographic data. Moreover, the complementary inhibition by LEDGF/p75 knockdown and mutagenesis at the integrase-LEDGF/p75 interface points to the incapability of HIV to circumvent LEDGF/p75 function during proviral integration. Altogether, the data provide a striking example of the power of viral molecular evolution. The results underline the importance of the LEDGF/p75 HIV-1 interplay as target for innovative antiviral therapy. Moreover, the role of LEDGF/p75 in targeting integration will stimulate research on strategies to direct gene therapy vectors into safe landing sites.     

Functional proteome analysis of the banana plant (Musa spp.) using de novo sequence analysis of derivatized peptides

We report the use of chemical derivatization with MALDI-MS/MS analysis for de novo sequence analysis. Using three frequently used homology-based search algorithms, we were able to identify more than 40 proteins from banana, a nonmodel plant with unsequenced genome. Furthermore, this approach allowed the identification of different isoforms. We also observed that the identification score obtained varied according to the position of the peptide sequences in the query using the MS-Blast algorithm.     

Development of resistance against diketo derivatives of human immunodeficiency virus type 1 by progressive accumulation of integrase mutations

The diketo acid L-708,906 has been reported to be a selective inhibitor of the strand transfer step of the human immunodeficiency virus type 1 (HIV-1) integration process (D. Hazuda, P. Felock, M. Witmer, A. Wolfe, K. Stillmock, J. A. Grobler, A. Espeseth, L. Gabryelski, W. Schleif, C. Blau, and M. D. Miller, Science 287:646-650, 2000). We have now studied the development of antiviral resistance to L-708,906 by growing HIV-1 strains in the presence of increasing concentrations of the compound. The mutations T66I, L74M, and S230R emerged successively in the integrase gene. The virus with three mutations (T66I L74M S230R) was 10-fold less susceptible to L-708,906, while displaying the sensitivity of the wild-type virus to inhibitors of the RT or PRO or viral entry process. Chimeric HIV-1 strains containing the mutant integrase genes displayed the same resistance profile as the in vitro-selected strains, corroborating the impact of the reported mutations on the resistance phenotype. Phenotypic cross-resistance to S-1360, a diketo analogue in clinical trials, was observed for all strains. Interestingly, the diketo acid-resistant strain remained fully sensitive to V-165, a novel integrase inhibitor (C. Pannecouque, W. Pluymers, B. Van Maele, V. Tetz, P. Cherepanov, E. De Clercq, M. Witvrouw, and Z. Debyser, Curr. Biol. 12:1169-1177, 2002). Antiviral resistance was also studied at the level of recombinant integrase. Single mutations did not appear to impair specific enzymatic activity. However, 3' processing and strand transfer activities of the recombinant integrases with two (T66I L74M) and three (T66I L74M S230R) mutations were notably lower than those of the wild-type integrase. Although the virus with three mutations was resistant to inhibition by diketo acids, the sensitivity of the corresponding enzyme to L-708,906 or S-1360 was reduced only two- to threefold. As to the replication kinetics of the selected strains, the replication fitness for all strains was lower than that of the wild-type HIV-1 strain.