Gravity resistance, another graviresponse in plants--function of anti-gravitational polysaccharides]

The involvement of anti-gravitational polysaccharides in gravity resistance, one of two major gravity responses in plants, was discussed. In dicotyledons, xyloglucans are the only cell wall polysaccharides, whose level, molecular size, and metabolic turnover were modified under both hypergravity and microgravity conditions, suggesting that xyloglucans act as anti-gravitational polysaccharides. In monocotyledonous Poaceae, (1-->3),(1-->4)-beta glucans, instead of xyloglucans, were shown to play a role as anti-gravitational polysaccharides. These polysaccharides are also involved in plant responses to other environmental factors, such as light and temperature, and to some phytohormones, such as auxin and ethylene. Thus, the type of anti-gravitational polysaccharides is different between dicotyledons and Poaceae, but such polysaccharides are universally involved in plant responses to environmental and hormonal signals. In gravity resistance, the gravity signal may be received by the plasma membrane mechanoreceptors, transformed and transduced within each cell, and then may modify the processes of synthesis and secretion of the anti-gravitational polysaccharides and the cell wall enzymes responsible for their degradation, as well as the apoplastic pH, leading to the cell wall reinforcement. A series of events inducing gravity resistance are quite independent of those leading to gravitropism.     

Chromosomes of Temnocephala minor,an ectosymbiotic turbellarian on Australian crayfish found in Kagoshima Prefecture,with karyological notes on exotic turbellarians found in Japan

Records of exotic turbellarian species found in Japan are reviewed from taxonomic and karyological viewpoints. Temnocephala minor Haswell, 1888, an ectocommensal on a freshwater crayfish of Australia, was found from culture ponds of Cherax tenuimanus (introduced from W. Australia) in Kagoshima Prefecture. T. minor had the chromosome number of 2x = 18 (2sm + 2m + 2m + 2sm + 2m + 2m + 2m + 2sm + 2m). The following 3 species of exotic freshwater triclads were recorded from tanks and ponds used for tropical fish culture: Dugesia austroasiatica Kawakatsu, 1985 (2x = 16), Dugesia tigrina (Girard, 1850) (2x = 16) and Rhodax? sp. (3x = 24; 3x = 24 &; 3x + 1LB + 1SB = 25 + 1SB). The following 3 species of exotic terrestrial triclads were recorded: Bipalium nobile Kawakatsu et Makino, 1982 (2x = 10), Bipalium kewense Moseley, 1878 (2x = 18), and Platydemus manokwari de Beauchamp, 1962 (n = 6, 2x = 12). An extensive occurrence of P. manokwari in the Southwest Islands of Japan may be due to an unexpected introduction of the animal in very recent years.     

Elimination of heparan sulfate by heparitinases induces abnormal mesodermal and neural formation in Xenopus embryos

The expression of heparan sulfate glycosaminoglycan (HS-GAG) was examined in Xenopus embryos during the developmental stages. Chemical analysis showed the existence of HS-GAG in the ³⁵S-labeled embryos. By western blot analysis using a specific anti-HS monoclonal antibody, HS-GAG related epitope was found after the neurulation on two protein bands, whose molecular weights were approximately 90 kDa and 100 kDa, respectively. Immunohistochemistry revealed that HS-GAG occurred exclusively in the animal hemisphere in early gastrulae, and then appeared predominantly on the sheath of the neural tube, the notochord and epithelium. To address whether HS-GAG chains contribute to Xenopus embryonic development, we eliminated the embryonic HS-GAG by injecting purified Flavobacterium heparitinases (HSase) into their blastocoels. Most of the injected embryos were aberrant in mesodermal and neural formation, and became acephalic. Histological examination showed that these embryos were completely devoid of the central nervous system and the mesodermal tissues. Neither heat-inactivated heparitinase nor chondroitinase showed such abnormality. The HS-GAG-eliminated embryos showed decreased expression of both muscular and neural-specific markers. These results suggest that HS-GAG plays an indispensable role in establishing the fundamental body plan during early Xenopus development.     

Crystalline hemoprotein from Pseudomonas that catalyzes oxidation of side chain of tryptophan and other indole derivatives.

A new enzyme which catalyzes the oxidation of the side chain of tryptophan and other indole derivatives, has been purified to apparent homogeneity from Pseudomonas and crystallized. The overall purification was about 25-fold with a yield of 4.5%. The purified enzyme was apparently homogeneous as judged by polyacrylamide gel electrophoresis. The molecular weight estimated by gel filtration was approximately 280,000 and sedimentation coefficient (S20,w) was 11 by sucrose density gradient ultracentrifugation. The absorption spectra indicated that the enzyme was a hemoprotein. The purified enzyme was shown to catalyze the reaction in which 1 mol each of NH3 and CO2 was formed at the expense of 1 mol each of L-tryptophan and molecular oxygen. Neither peroxidase nor catalase activity was detected in the purified enzyme and no formation of H2O2 was observed during the enzyme reaction. The product(s) of the reaction was unstable but was converted to and was identified as its stable quinoxaline derivative, 2-(3-indolyl)quinoxaline, in the presence of o-phenylenediamine. These results indicate that the product of the reaction was 3-indolylglycoaldehyde or 3-indolylglyoxal. A variety of other indole derivatives such as D-tryptophan, 5-hydroxyl-L-tryptophan, tryptamine, serotonin, melatonin, N-acetyl-L-tryptophan, N-acetyl-L-tryptophanamide, 3-indoleacetamide, 3-indolelactic acid, 3-indolepropionic acid, 3-indoleethanol, and skatole were also substrates.     

Variation in selectivity of univalent cations in slime moldPhysarum polycephalum caused by reception of polyvalent cations

Summary Specificity of reception on 11 electrolytes in the slime moldPhysarum polycephalum was investigated in the presence of polyvalent cations in media. Membrane potential and motive force of tactic movement were examined with the aid of the double chamber method, and the zeta potential at the membrane surface of the slime mold was measured by electrophoretic mobility. The results obtained are summarized as follows: (1) The presence of polyvalent cations (e.g., Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺, La³⁺, Th⁴⁺) in medium led to an increase in threshold concentration,C _th , determined from the potential measurements for Na- or Li-salts, and to a decrease inC _th for K-, Rb-, or NH₄-salts,C _th for 11 electrolytes changed discontinuously when the concentration of polyvalent cations in medium exceeded their respective thresholds. (2) TheC _th determined from chemotaxis agreed with that from the potential response both in the presence and absence of polyvalent cations. (3) Sequence of selectivity of univalent cations varied extensively in the presence of polyvalent cations. (4) Changes in the zeta potential induced by NaCl reception agreed with those in the membrane potential even in the presence of Ca²⁺ in medium. (5) TheC _th for reception of NaCl changed sharply at about 12 °C in the presence of polyvalent cations, while that for KCl was independent of the temperature.Conformational changes in surface membrane of the slime mold in response to reception of polyvalent cations were then discussed in relation to the discrimination of univalent cations.