Utilization of phosphate diester by the marine diatom Chaetoceros ceratosporus

Utilization of phosphate diester (PDE) and phosphodiesterase(PDEase) production by five marine phytoplankton species wereexamined in the laboratory to evaluate the contribution of PDEto the growth of phytoplankton. Among the five marine phytoplanktonspecies tested, only Chaetoceros ceratosporus was able to usethe PDE compound, bis(p-nitrophenyl) phosphate (bis-NPP), effectivelyas a sole phosphorus source. In addition, C. ceratosporus simultaneouslyproduced both PDEase and alkaline phosphatase (APase) at almostequal activity levels under the phosphate-deficient condition.These results suggest that PDE compounds presumably play animportant role as a phosphorus source for PDEase-producing phytoplanktonin coastal environments.     

Conservation of molecular structure of DNA polymerase beta in vertebrates probed by tryptic peptide mapping

DNA polymerase beta's from mouse myeloma, chick embryo, and cherry salmon testis were all composed of a single polypeptide of about 40K daltons as judged by a sodium dodecyl sulfate-polyacrylamide gel electrophoresis of extensively purified enzyme preparations. Although the enzyme from bullfrog ovary was not fully purified, its molecular weight was estimated to be the same as that of the chick enzyme by immunological detection after electrophoresis. All the enzymes tested cross-reacted immunologically with the antibody against chick DNA polymerase beta, indicating that they have a common molecular structure, at least in part. Two-dimensional maps of radioiodinated tryptic peptides directly showed the presence of highly conserved amino acid sequences among mouse, chick, and cherry salmon enzymes. This conserved structure is thought to be essential for the enzyme activity, which is very similar among all these vertebrates.     

The anticonvulsant effect of citalopram on El mice,and the levels of tryptophan and tyrosine and their metabolites in the brain

Serotonin (5-HT) plays an important role in the seizures of El mice since the seizure threshold of El mice correlates with the 5-HT concentration in the central nervous system. In this study, the anticonvulsant effect of a 5-HT reuptake blocker, citalopram, was evaluated behaviorally and biochemically. El mouse convulsions were inhibited by oral administration of citalopram for 2 weeks. Citalopram increased tryptophan and tyrosine amounts, and decreased the 5-HT, 5-hydroxy-indoleacetic acid, kynurenine, and dopamine amounts in the brain. These findings show that citalopram depresses monoaminergic metabolism. Given the known convulsant effect of kynurenine, it is suggested that its decrease by citalopram may involve attenuation of El mice seizures.     

The SV2 Protein of Synaptic Vesicles Is a Keratan Sulfate Proteoglycan

Abstract: We have determined that synaptic vesicles contain a vesicle-specific keratan sulfate integral membrane proteoglycan. This is a major proteoglycan in electric organ synaptic vesicles. It exists in two forms on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, i.e., the L form, which migrates like a protein with an M_r of 100, 000, and the H form, with a lower mobility that migrates with an M_r of ∼250, 000. Both forms contain SV2, an epitope located on the cytoplasmic side of the vesicle membrane. In addition to electric organ, we have analyzed the SV2 proteoglycan in vesicle fractions from two other sources, electric fish brain and rat brain. Both the H and L forms of SV2 are present in these vesicles and all are keratan sulfate proteoglycans. Unlike previously studied synaptic vesicle proteins, this proteoglycan contains a marker specific for a single group of neurons. This marker is an antigenically unique keratan sulfate side chain that is specific for the cells innervating the electric organ; it is not found on the synaptic vesicle keratan sulfate proteoglycan in other neurons of the electric fish brain.     

Changes in Levels of Heme a, Protoheme and Protochlorophyll(ide) in Submerged Rice Seedlings after Exposure to Air

Rice (Oryza sativa L. cv. Yamabiko) seedlings germinated underwater for 5 days contained small amounts of heme a and protohemebut no protochlorophyll(ide) [Pchl(ide)]. Levels of hemes andPchl(ide) increased rapidly upon transfer to air. When expressedin terms of fresh weight of tissue, hemes reached the levelsin aerobic controls after 24 h of contact with air, but Pchl(ide)did not. A comparison of the increases during 24-h adaptationto air in levels of heme a and Pchl(ide), which are specificto mitochondria and plastids, respectively, suggested that thedevelopment of mitochondria preceded that of plastids. The rateof synthesis of 5-aminolevulinic acid (ALA) was low in submergedseedlings, as compared to the rate in aerobic controls, butit increased during air adaptation. The sum of the amounts ofheme a, protoheme and Pchl(ide) increased in parallel with theamount of porphyrins, equivalent to the amount of ALA synthesizedduring the experimental period. When submerged seedlings thathad been pretreated with levulinic acid were exposed to air,no Pchl(ide) was formed. In contrast, Pchl(ide) accumulatedunder water when submerged seedlings were fed with ALA. Theseresults indicate that the synthesis of ALA, the limiting stepin the synthesis of Pchl(ide), is repressed under hypoxic conditions. ¹ Present address: KRI International, Inc., Kyoto Research Park17, Chudoji Minami-machi, Shimogyo-ku, Kyoto, 600 Japan. ² Present address: Research Institute for Bioresources, OkayamaUniversity, Kurashiki, 710 Japan.     

Growth Characteristics and Intraspecies Host Specificity of a Large Virus Infecting the Dinoflagellate Heterocapsa circularisquama

The growth characteristics and intraspecies host specificity of Heterocapsa circularisquama virus (HcV), a large icosahedral virus specifically infecting the bivalve-killing dinoflagellate H. circularisquama, were examined. Exponentially growing host cells were more sensitive to HcV than those in the stationary phase, and host cells were more susceptible to HcV infection in the culture when a higher percent of the culture was replaced with fresh medium each day, suggesting an intimate relationship between virus sensitivity and the physiological condition of the host cells. HcV was infective over a wide range of temperatures, 15 to 30°C, and the latent period and burst size were estimated at 40 to 56 h and 1,800 to 2,440 infective particles, respectively. Transmission electron microscopy revealed that capsid formation began within 16 h postinfection, and mature virus particles appeared within 24 h postinfection at 20°C. Compared to Heterosigma akashiwo virus, HcV was more widely infectious to H. circularisquama strains that had been independently isolated in the western part of Japan, and only 5.3% of the host-virus combinations (53 host and 10 viral strains) showed resistance to viral infection. The present results are helpful in understanding the ecology of algal host-virus systems in nature.     

Mercurial-sensitive water transport in barley roots

An isolated barley root was partitioned into the apical and basal part across the partition wall of the double-chamber osmometer. Transroot water movement was induced by subjecting the apical part to a sorbitol solution, while the basal part with the cut end was in artificial pond water. The rate of transroot osmosis was first low but enhanced by two means, infilitration of roots by pressurization and repetition of osmosis. Both effects acted additively. The radial hydraulic conductivity (Lp_r) was calculated by dividing the initial flow rate with the surface area of the apical part of the root, to which sorbitol was applied, and the osmotic gradient between the apical and basal part of the root. Lp_r which was first 0.02–0.04 pm s⁻¹ Pa⁻¹ increased up to 0.25–0.4 pm s⁻¹ Pa⁻¹ after enhancement. Enhancement is assumed to be caused by an increase of the area of the plasma membrane which is avallable to osmotic water movement. The increased Lp_r is in the same order of magnitude as the hydraulic conductivity (Lp) of epidermal and cortical cells of barley roots obtained by Steudie and Jeschke (1983). HgCl₂, a potent inhibitor of water channels, suppressed Lp_r of non-infiltrated and infiltrated roots down to 17% and 8% of control values, respectively. A high sensitivity of Lp_r to HgCl₂ suggests that water channels constitute the most conductive pathway for osmotic radial water movement in barley roots.     

Studies on factors in sweet potato root which induce spore germination of Ceratocystis fimbriata

Spore germination of Ceratocystis fimbriata was studied in termsof host-parasite specificity. The sweet potato, coffee and cacaostrains of Ceratocystis fimbriata germinated well in a fractionof sweet potato root water extract which had been passed througha column of cation exchange resin. The results showed that germinationof these strains was independent of exogenous cations. On theother hand, the prune, oak, taro and almond strains requiredfor germination both the absorbed and unabsorbed fractions ofsweet potato root water extract which were separated from eachother with a cation exchange resin column. Divalent cationssuch as Ca²⁺ Mg²⁺, Mn²⁺ and Zn²⁺ were identified as the activeprinciples in the absorbed fraction and Ca²⁺ showed the highestinductive activity for spore germination in the presence ofthe unabsorbed fraction. The active principle(s) in the unabsorbedfraction has not yet been identified. There was no relationshipbetween the Ca²⁺ and Mg²⁺ contents of the spores and the requirementof exogenous Ca²⁺ for germination. Ca²⁺ appeared to functionas a trigger of spore germination, not as a normal nutrient.These results suggest that the divalent cations such as Ca²⁺and Mg²⁺ in sweet potato contribute to the establishment ofhost-parasite specificity of this system. (Received August 10, 1977; )