The role of cytokinins in shoot organogenesis in apple

Effective regeneration in vitro is a necessary precondition for the implementation of different biotechnological approaches in plant breeding. Numerous studies have reported on regeneration from apple somatic tissues, and organogenesis has been proved to be influenced by several factors including mother shoots (genotype, size, type, and age of explant), in vitro conditions (dark period, light intensity, and quality), and others (wounding, orientation of leaf explants). However, one of the most important factors before and during the regeneration process is the type and concentration of cytokinin applied. Thidiazuron and benzyladenine are the most frequently used cytokinins in the regeneration systems, but their efficiency depends on genotype and other factors. Other cytokinins (e.g., zeatin and kinetin) have also been tested in several experiments and they were found in general to be less active. The organogenic ability of explants can also be increased by a properly selected cytokinin pre-treatment. Cytokinins applied in the pre-treatments can influence the leaf structure, which in turn can alter the regeneration capacity of the leaf explant. Interactions between factors of pre-treatments (hormones, light, and culture conditions) and factors of the regeneration phase should be considered. This review brings into focus the role of different cytokinins during in vitro shoot development, discussing their effects on the histology of leaves developed in vitro, and how this affects the subsequent regeneration process.     

Design, synthesis, and in vitro activity of novel drug delivery systems containing tuftsin derivatives and methotrexate

During the past decade, biodegradable polymers or oligopeptides recognized by cell-surface receptors have been shown to increase drug specificity, lowering systemic drug toxicity in contrast to small-size fast-acting drugs. The goal of the present study was to develop anticancer bioconjugates based on chemotactic drug targeting (CDT). These constructs are composed of methotrexate (Mtx) attached to a tuftsin-like peptide carrier through an enzyme-labile pentapeptide spacer (GFLGC) and several copies of a chemotactic targeting moiety (H-TKPR, For-TKPR, H-TKPKG, and Ac-TKPKG). Carriers with targeting moieties in the branches were prepared by solid-phase synthesis using mixed Boc and Fmoc strategies. The drug molecule connected to an enzyme-labile spacer was attached to the branched oligopeptide in solution. In vitro chemotaxis, cellular uptake, and cytotoxicity assays were carried out on the MonoMac6 cell line. The most effective conjugates with H-TKPR or Ac-TKPKG targeting moieties in the branches, which have the most advantageous chemotactic properties, can be internalized rapidly, and these conjugates trigger higher toxic effect than the free drug (Mtx). The results suggest that our tuftsin-based drug delivery systems might be potential candidates for targeting cancer chemotherapy.     

Aggregation of Abeta(1-42) in the presence of short peptides: conformational studies

CD and infrared spectroscopic studies were performed on (i) the inhibitory effects of equimolar quantities of LPFFD-OH and LPYFD-NH(2) on the time-dependent aggregation of amyloid beta-protein (Abeta) (1-42) and (ii) the beta-sheet-breaker effects of two-fold molar excess of the pentapeptides on aggregated Abeta(1-42) aged 1 week. The data obtained from the time-dependent studies demonstrated that LPFFD-OH did not significantly influence, whereas LPYFD-NH(2) exerted some inhibitory effect on the aggregation of Abeta(1-42). When added to a solution of Abeta(1-42) aged 1 week, LPFFD-OH accelerated, while LPYFD-NH(2) delayed, but did not prevent further fibrillogenesis. The difference in the effects of these two pentapeptides on the aggregational profile of Abeta(1-42) is probably due to the difference in their conformational preferences: LPFFD-OH adopts a beta-turn and extended structures, while LPYFD-NH(2) adopts a prevailing beta-turn conformation.     

A piRNA pathway primed by individual transposons is linked to de novo DNA methylation in mice

piRNAs and Piwi proteins have been implicated in transposon control and are linked to transposon methylation in mammals. Here we examined the construction of the piRNA system in the restricted developmental window in which methylation patterns are set during mammalian embryogenesis. We find robust expression of two Piwi family proteins, MIWI2 and MILI. Their associated piRNA profiles reveal differences from Drosophila wherein large piRNA clusters act as master regulators of silencing. Instead, in mammals, dispersed transposon copies initiate the pathway, producing primary piRNAs, which predominantly join MILI in the cytoplasm. MIWI2, whose nuclear localization and association with piRNAs depend upon MILI, is enriched for secondary piRNAs antisense to the elements that it controls. The Piwi pathway lies upstream of known mediators of DNA methylation, since piRNAs are still produced in dnmt3L mutants, which fail to methylate transposons. This implicates piRNAs as specificity determinants of DNA methylation in germ cells.     

Novel design principle validated: glucopyranosylidene-spiro-oxathiazole as new nanomolar inhibitor of glycogen phosphorylase, potential antidiabetic agent

2-Naphthyl-substituted glucopyranosylidene-spiro-oxathiazole prepared following a novel design principle was found to be the best known glucose analogue inhibitor of rabbit muscle glycogen phosphorylase b (K(i) 160 nM).     

Polymorphic genotypes of the HRES-1 human endogenous retrovirus locus correlate with systemic lupus erythematosus and autoreactivity

 Antinuclear autoantibodies are a hallmark of systemic lupus erythematosus (SLE). Autoantibodies to HRES-1/p28, a 28 000 M _r nuclear protein, commonly occur in patients with SLE. HRES-1 is a single-copy endogenous retroviral element mapped to human Chromosome 1 at q42. A polymorphic Hin dIII site defines two different allelic forms of the genomic locus. The HRES-1/1 probe [5.5 kilobases (kb)] anneals to three polymorphic fragments and three genotypes can be differentiated: I, 5.5 kb fragment only; II, 3.7 kb and 1.8 kb fragments only; and III, all three polymorphic fragments. By cloning of the HRES-1 locus from homozygous type I and type II human DNA samples, the polymorphic Hin dIII site was identified as a G to C transition at position 653 of the long terminal repeat region. Family studies showed that Hin dIII genotypes of the HRES-1 locus are inherited in a Mendelian pattern. The relative frequency of genotype I with respect to genotype III was 3.1-fold lower in patients with SLE (14 : 40=0.35) in comparison to 100 ethnically matched control donors (47 : 43=1.09;P=0.0084). Frequency of genotype I vs genotype II alleles was lower in SLE (68/52) than in normal donors (137/63;P=0.033), suggesting that a genotype I allele of the HRES-1 locus may be protective against SLE. Western blot seroreactivity with recombinant HRES-1/p28 was noted in 4/14 (29%) of genotype I patients and 13/19 (68%) of genotype III patients (P<0.025). These data raise the possibility that the HRES-1 element or a gene in linkage disequilibrium with this genomic locus may influence autoimmunity in SLE. Received: 20 February 1999 / Revised: 15 April 1999     

Regeneration capacity of microspore-derived structures produced in anther cultures of maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.)

The regeneration capacity of microspore-derived structures, with various morphological characteristics produced in anther cultures of maize (Zea mays L.) were studied in order to identify the morphotype resulting in the highest yield of spontaneous doubled haploid regenerants. Parallel to the morphological studies the ploidy level of microspore-derived structures and regenerants was analysed by flow cytometry. Neither the growth conditions of the anther donor plants nor the media used in the experiment had any effect on the frequency distribution of different morphotypes. The highest number of spontaneous doubled haploid plants was regenerated from white compact structures 2–3 mm in size, derived from the anthers of phytotron-grown donor plants.