A COMPARATIVE STUDY OF MITOSIS IN THE ONAGRACEAE

Kurabayashi , Masataka , Harlan Lewis , and Peter H. Raven . (U. California, Los Angeles.) A comparative study of mitosis in the Onagraceae. Amer. Jour. Bot. 49(9): 1003–1026. Illus. 1962. —Mitotic cycles of 46 species of Onagraceae, representing 15 genera and all of the tribes, have been examined and were found to fall into 3 modally distinct groups: (1) the tribes Fuchsieae, Lopezieae, and Circaeae; (2) the Epilobieae and Jussiaeae; (3) the Onagreae and Hauyeae. All species characterized by translocation systems, whether complex heterozygotes or variable frequencies of individual translocations, belong to group 3. Group 1 has no definite chromocenters during interphase and the chromosomes contract more or less evenly along a gradient during prophase. Groups 2 and 3 have definite chromocenters during interphase and the chromosomes become differentiated at early prophase into dense proximal and diffuse distal regions; contraction of the chromosomes does not seem to follow a gradient. In group 2, the chromosomes within a genome are much more heterogeneous in size and in the relative proportions of the differentiated segments than in group 3. Only in species belonging to group 3 are all or most of the chromosomes metacentric, subequal in size, and uniformly differentiated. The differences between the groups and within group 3 are discussed in relation to the development of translocation systems. Chromosome numbers of 9 taxa are reported for the first time.     

Cellular expression of C<Subscript>3</Subscript> and C<Subscript>4</Subscript> photosynthetic enzymes in the amphibious sedge<Emphasis Type="Italic"> Eleocharis retroflexa</Emphasis> ssp.<Emphasis Type="Italic"> chaetaria</Emphasis>

The amphibious leafless sedge Eleocharis retroflexa ssp. chaetaria expresses C₄-like biochemical characteristics in both the terrestrial and submerged forms. Culms of the terrestrial form have Kranz anatomy, whereas those of the submerged form have Kranz-like anatomy combined with anatomical features of aquatic plant leaves. We examined the immunolocalization of C₃ and C₄ enzymes in culms of the two forms. In both forms, phosphoenolpyruvate carboxylase; pyruvate, Pi dikinase; and NAD-malic enzyme were compartmentalized between the mesophyll (M) and Kranz cells, but their levels were somewhat reduced in the submerged form. In the terrestrial form, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) occurred mainly in the Kranz cells, and weakly in the M chloroplasts. In the submerged form, the rubisco occurred at higher levels in the M cells than in the terrestrial form. In both forms, the C₄ pattern of enzyme expression was clearer in the M cells adjacent to Kranz cells than in distant M cells. During the transition from terrestrial to submerged conditions, the enzyme expression pattern changed in submerged mature culms that had been formed in air before submergence, and matched that in culms newly developed underwater. It seems that effects of both environmental and developmental factors overlap in the C₄ pattern expression in this plant.     

Role of Vanilloid Receptors in the Capsaicin-Mediated Induction of iNOS in PC12 Cells

The vanilloid receptor 1(VR1) is a nonselective cation channel that is activated by pungent vanilloid compound, extracellular protons, or noxious heat. mRNA of VR1 and vanilloid receptor 1-like receptor (VRL1) were expressed in PC12 cells, and only VRI mRNA was detected in glioma and A10 cell lines. VRI protein was demonstrated in PC12 cells by immunocytochemistry and Western blotting. Capsaicin (CPS), the VRI receptor agonist, led to an increase in intracellular calcium ion, and this effect was blocked by pretreatment with VR1 receptor antagonist capsazepin (CPZ). Treatment of PC12 cells with low concentration of CPS (5-50 microM) increased reactive oxygen species (ROS) production, and inducible nitric oxide synthase (iNOS) was expressed after CPS treatment for 24 h. These CPS-induced changes are inhibited by pretreatment of CPZ. These findings suggest that CPS-induced iNOS expression through the VR1 and/or VRL1-mediated pathway, and this may explain the CPS-mediated physiological and pathological effects in neuron system.     

Strategies for bioremediation of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are serious environmental pollutants that threaten both the natural ecosystem and human health. For remediation of environments contaminated with PCBs, several approaches that exploit the potential of microbes to degrade PCBs have been developed. These approaches include improvement of PCB solubilization and entry into the cell, pathway and enzyme engineering, and control of enzyme expression. In this mini-review, we briefly summarize these strategies and provide potentially useful knowledge for the further improvement of the bacterial breakdown of PCBs.     

Migration from plant to plant: an important factor controlling densities of the epiphytic cladoceran <Emphasis Type="Italic">Alona</Emphasis> (Chydoridae,Anomopoda) on lake vegetation

We investigated seasonal changes in the density of epiphytic cladocerans Alona spp. (Chydoridae, Anomopoda) in two habitats, emergent and submerged aquatic plants, in Lake Suwa, Japan, from April to August 1998 and from April to November 2000. Alona had a density peak in early June on reeds (emergent) and in late June on Potamogeton malaianus (submerged). In summer, Alona density remained low in both habitats. Although density was positively correlated with the abundance of epiphytic algae, the birth rate was constant and no correlation between algal abundance and clutch size was detected. In a field experiment using ropes as an artificial substrate covered with high and low densities of epiphytic algae as food, more Alona attached to the ropes with the high density of algae. These results suggest that Alona may select food-rich habitats and migrate seasonally, and that migration is an important factor in the population dynamics of epiphytic chydorid cladocerans such as Alona. In Lake Suwa, Alona may migrate from the reed zone to the submerged macrophyte zone in June.     

Protein folding by the effects of macromolecular crowding

Unfolded states of ribonuclease A were used to investigate the effects of macromolecular crowding on macromolecular compactness and protein folding. The extent of protein folding and compactness were measured by circular dichroism spectroscopy, fluorescence correlation spectroscopy, and NMR spectroscopy in the presence of polyethylene glycol (PEG) or Ficoll as the crowding agent. The unfolded state of RNase A in a 2.4 M urea solution at pH 3.0 became native in conformation and compactness by the addition of 35% PEG 20000 or Ficoll 70. In addition, the effects of macromolecular crowding on inert macromolecule compactness were investigated by fluorescence correlation spectroscopy using Fluorescence-labeled PEG as a test macromolecule. The size of Fluorescence-labeled PEG decreased remarkably with an increase in the concentration of PEG 20000 or Ficoll 70. These results show that macromolecules are favored compact conformations in the presence of a high concentration of macromolecules and indicate the importance of a crowded environment for the folding and stabilization of globular proteins. Furthermore, the magnitude of the effects on macromolecular crowding by the different sizes of background molecules was investigated. RNase A and Fluorescence-labeled PEG did not become compact, and had folded conformation by the addition of PEG 200. The effect of the chemical potential on the compaction of a test molecule in relation to the relative sizes of the test and background molecules is also discussed.     

Synthesis and properties of bifunctional chloroalkyl nitrosamines with an intercalating moiety

Three N-nitroso-N-(arylcarbonyloxymethyl)-3-chloropropylamines were synthesized, and their chemical and biological properties were studied. All arylcarboxylates intercalated with double-stranded DNA, and their mutagenicity and DNA cross-linking activity were affected by their ring structure. The DNA interstrand cross-link formation increased dose dependently after treatment with the acridine analog. The anthraquinone analog showed the highest bacterial mutagenicity among the three nitrosamines in Salmonella typhimurium TA100, while in Salmonella typhimurium TA92, which can detect cross-linking agents, the acridine analog showed the highest mutagenicity. This agreed with the result of a cross-linking assay. These results suggest that the three-ring aromatic moiety gives DNA-intercalating ability to cross-linkable chloropropyl nitrosamine, and the acridine analog is considered as a possible new antitumor lead compound.     

Regulation mode of evaporative cooling underlying a strategy of the heat-tolerant FOK rat for enduring ambient heat

Compared with other rat strains, the inbred FOK rat is extremely heat tolerant. This increased heat tolerance is due largely to the animal's enhanced saliva spreading abilities. The aims of the present study were to 1) quantify the heat tolerance capacity of FOK rats and 2) determine the regulatory mode of the enhanced salivary cooling in these animals. Various strains of rats were acutely exposed to heat. In the heat-intolerant strains, saliva spreading was insufficient and the core temperature (Tc) rose rapidly. In contrast, FOK rats maintained an elevated Tc plateau (39.5 +/- 0.7 degrees C) for 5-6 h over a wide range of ambient temperatures (Ta) (37.5-42.5 degrees C). In hot environments the FOK rats secreted copious amounts of saliva and spread it over more than the entire ventral body surface. FOK rats had a low Tc threshold for salivation, and the salivation rate increased linearly in proportion to the Tc deviation from the threshold. No strain difference or temperature effect was observed in the saliva secretion rate from in vitro submandibular glands perfused by sufficient doses of ACh. These results suggest that 1) the ability of FOK rats to maintain a moderate steady-state hyperthermia (39.5 +/- 0.7 degrees C) over a wide Ta range is enabled by a lowered threshold Tc for salivation and functional negative-feedback control of saliva secretion and 2) strain differences in ability to endure heat stress are mainly attributable to changes in the thermoregulatory control system rather than altered secretory abilities of the salivary glands.     

Nicotine enhances neovascularization and promotes tumor growth

Solid tumors require vascularization for their growth. Bone marrow-derived endothelial progenitor cells participate in tumor angiogenesis. Here, we show that nicotine markedly accelerated growth of colon cancer cells inoculated subcutaneously in mice but had no effect on proliferation of carcinoma cells in vitro. We found that the tumor growth was associated with increased vascularization of the tumor and that bone marrow-derived cells contributed to the formation of the new blood vessels. Our findings show that nicotine promotes tumor growth, at least in part, by stimulating tumor-associated neovascularization.     

AIP is a mitochondrial import mediator that binds to both import receptor Tom20 and preproteins

Most mitochondrial preproteins are maintained in a loosely folded import-competent conformation by cytosolic chaperones, and are imported into mitochondria by translocator complexes containing a preprotein receptor, termed translocase of the outer membrane of mitochondria (Tom) 20. Using two-hybrid screening, we identified arylhydrocarbon receptor-interacting protein (AIP), an FK506-binding protein homologue, interacting with Tom20. The extreme COOH-terminal acidic segment of Tom20 was required for interaction with tetratricopeptide repeats of AIP. An in vitro import assay indicated that AIP prevents preornithine transcarbamylase from the loss of import competency. In cultured cells, overexpression of AIP enhanced preornithine transcarbamylase import, and depletion of AIP by RNA interference impaired the import. An in vitro binding assay revealed that AIP specifically binds to mitochondrial preproteins. Formation of a ternary complex of Tom20, AIP, and preprotein was observed. Hsc70 was also found to bind to AIP. An aggregation suppression assay indicated that AIP has a chaperone-like activity to prevent substrate proteins from aggregation. These results suggest that AIP functions as a cytosolic factor that mediates preprotein import into mitochondria.