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Effects of auxins and cytokinins on epigenetic instability of callus-propagated Kalanchoe blossfeldiana Poelln.

A main problem in the vegetative propagation of ornamental plants in vitro is the epigenetic instability of cells removed from their organized environment. With calluses of leaf explants of Kalanchoe blossfeldiana Poelln., cv. Yucatan, the role of plant growth regulators (PGRs) in the occurrence of fasciation was studied.In various combinations of auxins and cytokinins, the auxin 2,4-D (2,4-dichlorophenoxyacetic acid) gave only deformed, inseparable shoot primordia. The most rapid callus induction with regeneration of well-developed sprouts was obtained with the natural IAA (indoleacetic acid) and Z (zeatin).As a first symptom of fasciation, aberration in decussate phyllotaxis can be observed. At increasing concentrations of IAA + Z, this symptom gradually decreased but fasciation proper increased. The optimum concentration was at 1 M for both PGRs. Reduction of exposure to the PGRs from six to three weeks reduced the epigenetic instability.     

31P nuclear magnetic resonance studies of effects of some chlorophenols on Escherichia coli and a pentachlorophenol-degrading bacterium.

A Flavobacterium sp. that mineralizes pentachlorophenol degrades some, but not all, of the other chlorinated phenols. Whole-cell 31P nuclear magnetic resonance was used to compare and observe transmembrane pH gradients and nucleotide pools in the Flavobacterium sp. and Escherichia coli after pentachlorophenol and 3,4,5-trichlorophenol were added to the cell suspensions. The data suggest that those chlorinated phenols which are not degraded by the Flavobacterium sp. may be resistant to degradation because they act as proton dissipators.     

Involvement of the globular domain of histone H1 in the higher order structures of chromatin

We have attacked H1-containing soluble chromatin by α-chymotrypsin under conditions where chromatin adopts different structures.Soluble rat liver chromatin fragments depleted of non-histone components were digested with α-chymotrypsin in NaCl concentrations between 0 mm and 500 mm. at pH 7, or at pH 10, or at pH 7 in the presence of 4 m-urea. α-Chymotrypsin cleaves purified rat liver histone H1 at a specific initial site (CT) located in the globular domain and produces an N-terminal half (CT-N) which contains most of the globular domain and the N-terminal tail, and a C-terminal half (CT-C) which contains the C-terminal tail and a small part of the globular domain. Since in sodium dodecyl sulfate/polyacrylamide-gel electrophoresis CT-C migrates between the core histones and H1, cleavage of chromatin-bound H1 by α-chymotrypsin can be easily monitored.The CT-C fragment was detected under conditions where chromatin fibers were unfolded or distorted: (1) under conditions of H1 dissociation at 400 mm and 500 mm-NaCl (pH 7 and 10); (2) at very low ionic strength where chromatin is unfolded into a filament with well-separated nucleosomes; (3) at pH 10 independent of the ionic strength where chromatin never assumes higher order structures; (4) in the presence of 4 m-urea (pH 7), again independent of the ionic strength. However, hardly any CT-C fragment was detected under conditions where fibers are observed in the electron microscope at pH 7 between 20 mm and 300 mm-NaCl. Under these conditions H1 is degraded by α-chymotrypsin into unstable fragments with a molecular weight higher than that of CT-C. Thus, the data show that there are at least two different modes of interaction of H1 in chromatin which correlate with the physical state of the chromatin.Since the condensation of chromatin into structurally organized fibers upon raising the ionic strength starts by internucleosomal contacts in the fiber axis (zig-zag-shaped fiber), where H1 appears to be localized, it is likely that in chromatin fibers the preferential cleavage site for α-chymotrypsin is protected because of H1-H1 contacts. The data suggest that the globular part of H1 is involved in these contacts close to the fiber axis. They appear to be hydrophobic and to be essential for the structural organization of the chromatin fibers. Based on the present and earlier observations we propose a model for H1 in which the globular domains eventually together with the N-terminal tails form a backbone in the fiber axis, and the nucleosomes are mainly attached to this polymer by the C-terminal tails.     

Multiple forms of porcine pancreatic α-amylase

Porcine pancreatic α-amylase can be fractionated into two components by DEAE-cellulose chromatography and by disc electrophoresis. The basis for fractionation is tentatively ascribed to a charge difference. The two components displayed the same specific activity and their thermal and pH stability, as well as the variation of V_max and K_m with pH, were identical within experimental error. It is concluded that the multiple forms of the amylase are physically distinct, but structurally related, with a common active site.     

Members of two gene families encoding ubiquitin-conjugating enzymes, AtUBC1-3 and AtUBC4-6, fromArabidopsis thaliana are differentially expressed

Covalent attachment of ubiquitin to other intracellular proteins is essential for many physiological processes in eukaryotes, including selective protein degradation. Selection of proteins for ubiquitin conjugation is accomplished, in part, by a group of enzymes designated E2s or ubiquitin-conjugating enzymes (UBCs). At least six types of E2s have been identified in the plantArabidopsis thaliana; each type is encoded by a small gene family. Previously, we described the isolation and characterization of two three-member gene families, designatedAtUBC1-3 andAtUBC4-6, encoding two of these E2 types. Here, we investigated the expression patterns, of theAtUBC1-3 andAtUBC4-6 genes by the histochemical analysis of transgenicArabidopsis containing the corresponding promoters fused to the -glucuronidase-coding region. Staining patterns showed that these genes are active in many stages of development and some aspects of cell death, but are not induced by heat stress. Within the two gene families, individual members exhibited both overlapping and complementary expression patterns, indicating that at least one member of each gene family is expressed in most cell types and at most developmental stages. Different composite patterns of expression were observed between theAtUBC1-3 andAtUBC4-6 families, suggesting distinct biochemical and/or physiological functions for the encoded E2s inArabidopsis.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.