Plant Microtubules can be Translocated by a Dynein ATPase from Sea Urchin in Vitro

The latent ability of plant microtubules to translocate or slidein the presence of motor proteinwas examined in a motility assayin vitro. Plant microtubules isolated from tobacco BY-2 cellsmoved over a glass surface covered with outer arm 21S dyneinfrom flagella of sea urchinsperm with an average velocity of3.7 µm s^-1. This velocity was similar to that of microtubulesisolated from bovine brain under the same conditions (averagevelocity, about 4.1 µm s^-1). These results suggest thatplant microtubules have an intrinsic ability to interact withand to be translocated by dynein. It is postulated that microtubule-basedmotor proteins, including dynein ATP-ase,are involved in thefunctioning of microtubules in plant cells. (Received May 20, 1995; Accepted September 18, 1995)     

Roles of actin filaments in cytoplasmic streaming and organization of transvacuolar strands in root hair cells ofHydrocharis

Summary Effects of cytochalasin B and mycalolide-B on cytoplasmic streaming, organizations of actin filaments and the transvacuolar strand were studied in root hair cells ofHydrocharis, which shows reverse fountain streaming. Both toxins inhibited cytoplasmic streaming and destroyed the organizations of actin filaments and transvacuolar strands. However, we found a great difference between these toxins with respect to reversibility. The effects of cytochalasin B were reversible but not those of mycalolide B. The present results suggest that actin filaments work as a track of cytoplasmic streaming and as a cytoskeleton to maintain the transvacuolar strand. The usefulness of root hair cells ofHydrocharis in studying the dynamic organization of actin filaments of plant is discussed.Abbreviations CB cytochalasin B - DMSO dimethylsulfoxide - ML-B mycalolide B     

Promotive and inhibitory effects of uniconazole and prohexadione on the sprouting of bulbils of Chinese yam,Dioscorea opposita

Gibberellin A₁ (GA₁), GA₃ and GA₄ inhibited the sprouting of nondormant bulbils of Chinese yam, Dioscorea opposita, where the effectiveness of the GAs was as follows: GA₄>GA₁+GA₃. Uniconazole and prohexadione, plant growth retardants, promoted the sprouting of half-dormant bulbils. By contrast, these retardants inhibited the sprouting of nondormant bulbils. Gibberellin A₃ (GA₃) and A₄ (GA₄) which were applied to the stems of the sprouted bulbils, promoted stem elongation, but GAs applied to the bulbous parts inhibited this process. The effectiveness of the GAs on stem elongation was as follows: GA₃+GA₄ for the promotion and GA₄ > GA₃ for the inhibition. Uniconazole applied to the stem inhibited the stem elongation of the sprouted bulbils. These results suggest the possible involvement of endogenous GAs in the induction and maintenance of bulbil dormancy of D. opposita, as well as in the bulbil sprouting and subsequent stem elongation.     

Suppression of apoptotic death in hematopoietic cells by signalling through the IL-3/GM-CSF receptors.

Interleukin 3 (IL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) exert their biological functions through acting on a specific receptor which consists of a ligand-specific alpha subunit and the shared common beta subunit. Inhibition by genistein of a subset of IL-3/GM-CSF-mediated signals, including c-myc induction, resulted in the abrogation of DNA synthesis, however, IL-3 still protected cells from apoptotic cell death. Conversely, a C-terminal truncated form of the GM-CSF receptor, which is missing a critical cytoplasmic region required for activation of the Ras/Raf-1/MAP kinase pathway, induced DNA synthesis, but failed to prevent cell death in response to GM-CSF. Consequently, cells died by apoptosis in the presence of GM-CSF, despite displaying a transient mitogenic response. However, expression of activated Ras protein complemented defective signalling through the mutant receptor and supported long-term proliferation in concert with GM-CSF. These results indicate that IL-3 and GM-CSF prevent apoptosis of hematopoietic cells by activating a signalling pathway distinct from the induction of DNA synthesis and that long-term cell proliferation requires the activation of both pathways.     

A Rapid and Sensitive Method for Determination of Relative Specificity of RuBisCO from Various Species by Anion-Exchange Chromatography

A rapid and sensitive method to determine the relative specificity() of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO)using anion-exchange chromatography is described. We employedthe open gas system for the reaction of RuBisCO to get the mostreliable CO₂ and O₂ concentrations in the reaction mixture.3-Phosphoglycerate and 2-phosphoglycolate which were formedin the RuBisCO reaction were completely separated and directlymeasured with anion-exchange chromatography without using radioisotopes.The determination of the value was accomplished in 3 h. The values of RuBisCO enzymes from higher land plants were between90 and 96, and those from bacteria including cyanobacteriumwere close to 45. These values were in agreement with previouslyreported values. The enzyme of the red macroalga Porphyra yezoensisexhibited a value of over 140, as expected from the reportedvalue of the enzyme from the red microalga Porphyridium cruenteum.RuBisCO from the green macroalga Ulva pertusa had a value closeto 70 and similar to that of the enzyme from the green microalgaChlamydomonas reinhardtii. ⁴On leave from Research and Development Center, Unitika Ltd.,23 Kozakura, Uji, Kyoto, 611 Japan. ⁵Present address: Nara Institute of Science and Technology,8916-5 Takayama-Cho, Ikoma, Nara, 630-01 Japan     

Haustoria of Cuscuta japonica, a Holoparasitic Flowering Plant, Are Induced by the Cooperative Effects of Far-Red Light and Tactile Stimuli

When seedlings of Cuscuta japonica were grown with Vigna radiata(the host plant) in a flower pot for 6 d under white light andthen irradiated with far-red or blue light (ca. 6 µmolphotons m^–2 s^–1), the seedlings parasitized V. radiata.However, no parasitism of the seedlings was observed under redor white light or in darkness. The parasitic behavior of seedlingsof C. japonica was observed even if an acrylic rod was usedas a substitute for the host plant. Upon incubation under far-redlight, the seedling twined tightly around the rod and developedhaustoria towards it. Haustoria also developed when apical andsubapical regions of seedlings were held between two glass platesthat were about 0.7 mm apart and were irradiated with far-redlight. However, no haustoria were induced by either the holdor irradiation alone. These results indicate that parasitismof Cuscuta japonica is controlled by the cooperative effectsof two physical signals, far-red light and appropriate tactilepressure. Our findings suggest that parasitism by the genusCuscuta involves a novel strategy. (Received April 10, 1996; Accepted August 21, 1996)     

Mechanism of Glyoxylate Decarboxylation in the Glycolate Pathway in Euglena gracilis Z : Participation of Mn-Dependent NADPH Oxidase in Chloroplasts

The mechanism for decarboxylating the carboxyl carbon of glycolate was studied in Euglena gracilis Z, which liberates more than 70% of the carboxyl carbon as CO₂ during glycolate metabolism.     

Fine localization of serine: pyruvate aminotransferase in rat hepatocytes revealed by a post-embedding immunocytochemical technique

Summary Immunocytochemical localization of serine: pyruvate aminotransferase (SPT) in rat hepatocytes was studied using a protien A-gold technique. Rat liver was fixed by perfusion. Vibratome sections (100 m thick) of the liver were embedded in Epon or Lowicryl K4M. Ultrathin sections were incubated with antiSPT, followed by protein A-gold complex. Gold particles representing the antigenic sites for SPT were seen in three subcellular compartments, peroxisomes, mitochondria, and cytoplasm. In the control experiments the specificity of the immunolabelling was confirmed. Quantitative analysis of the labelling density showed that main subcellular compartments containing SPT are mitochondria and peroxisomes. In addition, the gold particles distributing in the cytoplasm were 16%–29% of the total labelling. The result indicated that the cytoplasm also contains SPT with a low density.     

Identification and nucleotide sequence determination of the gene responsible for Ogawa serotype specificity of V. cholerae 01.

The gene encoding a protein of 27 kDa, which is specifically expressed in Vibrio cholerae of serotype Ogawa, was identified and its nucleotide sequence determined. The plasmid carrying this gene was found to convert serotype specificity from Inaba to Ogawa when introduced into the Escherichia coli DH5(pVCI112) cell which harbors a cloned 20-kilobase genomic DNA fragment of V. cholerae NIH35A3 and expresses the 01 antigen of Inaba serotype.