OBSERVATIONS ON METAPHLOEM IN THE VEGETATIVE PARTS OF PALMS

Metaphloem was studied in available vegetative parts of 374 species in 164 genera of palms. Sieve elements usually have compound sieve plates except in the subfamilies Lepidocaryoideae and Nypoideae. Sieve elements in roots usually have oblique to very oblique end walls, whereas in stems and leaves they have transverse to oblique walls. Within a phloem strand the degree of compounding of a sieve plate is directly correlated with element diameter. Plastids are normally present in functioning, enucleate sieve elements. Small quantities of “slime” substances have been detected in young sieve elements in stems and petioles of a few species. Many sieve plates in functioning sieve elements lacked callose in materials quick-killed in liquid nitrogen or chilled acetic-alcohol. Definitive callose is confined to sieve elements just before their obliteration. Sieve tubes in leaf and stem are usually ensheathed by contiguous parenchyma cells while those in root have very few contiguous parenchyma cells. Two types of contiguous parenchyma cells can be distinguished by difference in cytoplasmic density, especially with the electron microscope. Cells with denser cytoplasm are interpreted as companion cells. Lignified contiguous parenchyma cells are occasionally present in metaphloem of petioles. The possible diagnostic and taxonomic features of metaphloem are discussed.     

Direct modification of low density lipoprotein by the spin trap 3,5-dibromo-4-nitrosobenzenesulfonic acid.

We have previously reported that the spin trap alpha-phenyl-tert-butyl nitrone (PBN) inhibited the oxidative modification of low density lipoprotein (LDL) (Kalyanaraman, B., Antholine, W.E. and Parthasarathy, S. (1990) Biochim. Biophys. Acta 1035, 286-292). In the present study, we report that 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS), a water-soluble spin trap, also inhibited the oxidation of LDL as measured by the formation of thiobarbituric acid reactive substances (TBARS). However, when compared with LDL incubated without DBNBS, the DBNBS-incubated LDL showed increased negative charge on agarose gel electrophoresis and was avidly degraded by mouse peritoneal macrophages. Despite the suggestion of biological modification, there was no decrease in lysine-amino groups in DBNBS-incubated LDL. Furthermore, reductively methylated LDL in which more than 85% of the amino group of lysines was blocked, was also modified by DBNBS. A sulfonic acid analog of PBN failed to modify LDL in a similar manner, suggesting that the presence of sulfonic acid alone does not ensure modification. When LDL was incubated with DBNBS, radical adducts associated with both lipid and protein were detected by electron paramagnetic resonance (EPR) technique. It is suggested that DBNBS may bind to the apoprotein B100 and lipids of LDL by a lysine-independent mechanism resulting in increased recognition and degradation by macrophages. The present work offers a novel approach for rapid modification of LDL.     

High pressure freezing and freeze substitution improve immunolabeling of S-locus specific glycoproteins in the stigma papillae ofBrassica

Summary High pressure freezing and freeze substitution methods significantly improve the antigenic preservation of S-locus specific glycoproteins (SLSG). The SLSG, which are implicated in the incompatibility response, are localized over the cell wall and cytoplasm. Labeling in the cytoplasm is mainly associated with dictyosomes and rough endoplasmic reticulum. Quantitative analysis show that in cryofixed papillae the labeling was enhanced by approximately 45% over the cell wall and approximately 90% over the dictyosomes compared to chemically fixed papillae.     

Oxidation of low-density lipoprotein by thiol compounds leads to its recognition by the acetyl LDL receptor

Reduced glutathione and other compounds with free -SH groups promoted the oxidation of low-density lipoprotein (LDL) in the absence of cells in Ham's F-10 medium. In contrast, compounds in which the thiol groups were oxidized or blocked were ineffective in oxidizing LDL. Thiol-induced modification of LDL did not occur in media lacking in redox metals. It is suggested that thiols react with redox metal, generating thiol- and oxygen-derived free radicals that promote modification of LDL.     

Influence of phospholipase C on muscarinic acetylcholine receptor binding in rat brain

Treatment of neural membranes from rat cerebral cortex with phospholipase C (phosphatidylcholine cholinephosphohydrolase) inhibited the binding of radiolabelled antagonists to muscarinic acetylcholine receptors. This inhibition was incomplete, was not competitive, and did not appear to be related to the production of inhibitory products. The affinity of carbamylcholine for cortex muscarinic receptors was increased by phospholipase C action. The distribution of receptors between states of high and low affinity was not affected by phospholipase C; rather, the affinity for carbamylcholine of the lowest affinity receptors was selectively increased. This suggests that membrane lipids influence the interaction of the receptor binding subunit with other structures in the synaptic membrane.     

Mixing characteristics of sludge simulant in a model anaerobic digester

This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid–base reaction and analysed to determine the active and inactive volumes as a function of time. The doughnut-shaped inactive region formed above and below the impeller in low concentration simulant decreases in size with time and disappears finally. The ‘cavern’ shaped active mixing region formed around the impeller in simulant solutions with higher concentrations increases with increasing agitation time and reaches a steady state equilibrium size, which is a function of specific power input. These results indicate that the active volume is jointly determined by simulant rheology and specific power input. A mathematical correlation is proposed to estimate the active volume as a function of simulant concentration in terms of yield Reynolds number.     

Isolation,enzyme-bound structure and antibacterial activity of platencin A1 from Streptomyces platensis

Natural products continue to serve as one of the best sources for discovery of antibacterial agents as exemplified by the recent discoveries of platensimycin and platencin. Chemical modifications as well as discovery of congeners are the main sources for gaining knowledge of structure–activity relationship of natural products. Screening for congeners in the extracts of the fermentation broths of Streptomyces platensis led to the isolation of platencin A₁, a hydroxy congener of platencin. The hydroxylation of the tricyclic enone moiety negatively affected the antibacterial activity and appears to be consistent with the hydrophobic binding pocket of the FabF. Isolation, structure, enzyme-bound structure and activity of platencin A₁ and two other congeners have been described.