Role of the pentose phosphate pathway during callus development in explants from potato tuber

Metabolic change during callus formation in explants from potatotuber (Solarium tuberosum L.) was investigated. Under the presentculture conditions, callus starts exponential growth (estimatedby the fresh weight increase) with a 5-day lag period, at whichtime marked production of DNA occurs. In the lag period, respirationis very much resistant to malonate, and the value of the C6/C1ratio and activities of both G6PDH 6PGDH pass their peaks. Onthe basis of these and relevant findings, glucose metabolismthrough the PP pathway is surmised to play a significant rolein the initial DNA multiplication phase of callus development. (Received October 15, 1969; )     

Ribulose-1, 5-diphosphate carboxylase of Chromatium strain D

RuDP carboxylase isolated from autotrophically grown cells ofphotosynthetic sulfur bacterium, Chromatium strain D, was partiallypurified by (NH₄)₂SO₄ precipitation and Sephadex G-200 gel filtration.The molecular size of the bacterial RuDP carboxylase was foundto be large, analogous to that of the plant enzyme, in agreementwith results of previous workers. Sucrose density gradient centrifugationshowed the S_rel to be approximately 18; the omission of Mg⁺⁺caused no dissociation of the enzyme molecule in its subunits.Chromatium RuDP carboxylase showed similarities to the plantenzyme in some of its kinetic properties; (a) a shift of pHoptimum to the neutral side from the alkaline side on the additionof Mg⁺⁺, (b) deviation of the substrate concentration (NaHCO₃)-activityrelationship from the MICHAELIS formula and (c) a marked stimulativeeffect of Mg⁺⁺. A unique sigmoidal saturation curve of the enzymeto RuDP, which had been detected in Rhodospirillum rubrum andRhodopseudomonas spheroides RuDP carboxylase in the absenceof Mg⁺⁺, was not found. Another characteristic feature of ChromatiumRuDP carboxylase is its partial immunological response to therabbit anti-spinach RuDP carboxylase serum as detected by theinhibition of the carboxylation reaction due to the antibody-antigenreaction. ¹Part X, Structure and Function of Chloroplast Proteins. Supportedin part by research grants from the Ministry of Education ofJapan (No. 8719) and USPHS (AM-10792-03) (Received July 4, 1969; )     

Failure of Immunological Memory in DMBA-treated Mice

SEVERAL chemical carcinogens show immunosuppressive activity in various experimental systems^1–4. Stjernswärd⁵ reported a remarkable correlation between carcinogenic activity and immunosuppressive capacity of chemicals, that is, potent carcinogens such as 3-methylcholanthrene (MCA), benz(a)pyrene and 7,12-dimethylbenzanthracene (DMBA) suppressed the immune response to sheep red blood cells (SRBC) but noncarcinogenic analogues did not. Stutman² showed that administration of MCA depressed the immune response to SRBC in mice (C3Hf/Bi strain) sensitive to oncogenic effect of the drug, but the drug was not immunosuppressive in the I strain, which is relatively resistant to its oncogenic effect. These suggest an important role of immunosuppressive activity of the carcinogens on the process of carcinogenesis, perhaps by weakening the immune surveillance capacity of the host. On the other hand, many potent carcinogens, such as urethane, do not seem to have an immunosuppressive effect⁶. Here we have analysed the effect of DMBA on the antibody response of C3H/He mice to soluble protein antigen, bacterial α-amylase (BαA). Our findings suggest a marked effect of DMBA on the immunological memory.     

EFFECT OF VARIOUS ANIONS ON THE TRANSPORT OF STRONTIUM WITHIN PLANTS

With a view to finding a means of reducing contamination offoods by radiostrontium, the inhibiting effects of various anionson the transport of strontium in plants are investigated. Pea and bean plants were pretreated with silicate, phosphateand nitrate ions, and the distribution of strontium in variousparts of the plants was examined.

1. In the case of pretreatment with silicate or phosphate ions,strontium absorption by the plant was decreased even if theseanions were absent in the culture solution at the time of applicationof ⁸⁹Sr.
2. The absorption of strontium by the plants pretreatedwith nitrateions was similar to that of the controls.
3. Strontiumabsorbed by the plants pretreated with silicate orphosphatewas found to be accumulated in the roots and its quantitytransportedto the aboveground parts was remarkably small; especiallyinthe case of application of silicate, no measurable amountofstrontium was transported to the upper parts of the plant.
4. Inthe control and nitrate-pretreated plants, strontium absorbedin the roots was readily transported to the aboveground parts.

(Received March 15, 1965; )     

Phylogenetic Relationships Among Microsporidia Based on rDNA Sequence Data, With Particular Reference to Fish-Infecting Microsporidium Balbiani 1884 Species.

Recently, large discrepancies have been identified between microsporidian systematics based on molecular and traditional characteristics. In the current study the 530f-580r region of the rRNA gene of eight microsporidian species was cloned and sequenced. Included were two unclassified species of Microsporidium Balbiani, 1884 and an unidentified microsporidian that infects the musculature of different sea bream species. Sequence identities in excess of 98% indicated that these three species almost certainly are members of the same genus. Phylogenetic analyses of all microsporidian sequence data available for this region of the gene (20 species) and for partial small subunit sequences (51 species of 21 genera) revealed these species to be distinct from the family Pleistophoridae Doflein, 1901 and closely related them to the genus Sproguea Weissenberg, 1976. This clade was found to comprise a sister taxon to that containing the vast majority of fish-infecting species. Broad cladistic divisions were found between terrestrial insect-infecting and fish-infecting species, which together are distant from the aquatic insect-infecting microsporidia. The rRNA gene of certain fish-infecting genera was found to be more highly conserved than previously reported. This has implications for its utility in diagnostic assays and phylogenetic studies at, or close to, the species level.     

Effects of elevated CO2 on the size structure in even-aged monospecific stands of Chenopodium album

To investigate the effect of elevated CO₂ on the size inequality and size structure, even‐aged monospecific stands of an annual, Chenopodium album, were established at ambient and doubled CO₂ with high and low nutrient availabilities in open top chambers. The growth of individual plants was monitored non‐destructively every week until flowering. Elevated CO₂ significantly enhanced plant growth at high nutrients, but did not at low nutrients. The size inequality expressed as the coefficient of variation tended to increase at elevated CO₂. Size structure of the stands was analyzed by the cumulative frequency distribution of plant size. At early stages of plant growth, CO₂ elevation benefited all individuals and shifted the whole size distribution of the stand to large size classes. At later stages, dominant individuals were still larger at elevated than at ambient CO₂, but the difference in small subordinate individuals between two CO₂ levels became smaller. Although these tendencies were found at both nutrient availabilities, difference in size distribution between CO₂ levels was larger at high nutrients. The CO₂ elevation did not significantly enhance the growth rate as a function of plant size except for the high nutrient stand at the earliest stage, indicating that the higher biomass at elevated CO₂ at later stages in the high nutrient stand was caused by the larger size of individuals at the earliest stage. Thus the effect of elevated CO₂ on stand structure and size inequality strongly depended on the growth stage and nutrient availabilities.     

Proliferation and Neoplastic Transformation of Pigment Cells in Metallothionein/ret Transgenic Mice

Although melanoma is a common human disease, there were few animal models in which melanoma developed at high incidence. To date, the Xiphophorus fish has been used as a model system to study melanoma formation. Studies on this fish showed the presence of a dominant oncogene, Tu, which encodes a transmembrane, tyrosine kinase of epidermal growth factor receptor type (Wittbrodt et al., Nature, 341:415–421, 1989). Recently, we succeeded in establishing novel transgenic mouse lines in which melanosis and melanocytic tumors developed stepwise by introducing another transmembrane tyrosine kinase oncogene, ret (Iwamoto et al., EMBO J., 10:3167–3175, 1991). In our transgenic mice, high levels of expression of the ret transgene induced proliferation and neoplastic transformation of melanin-producing cells. In addition, crossbreeding experiments between transgenic mice and W^v mice showed that the ret oncogene can also induce melanogenesis and melanocyte development in W^v/W^v mice.     

Six polymorphic microsatellite loci in the Japanese Spanish mackerel,Scomberomorus niphonius

Six polymorphic microsatellite loci were isolated for genetic structure studies of the Japanese Spanish mackerel, Scomberomorus niphonius, a severely exploited marine fish species. The number of observed alleles for each locus ranged from seven to 41, and the values of expected and observed heterozygosities were 0.546–0.946 and 0.602–1.000, respectively. These microsatellite markers should prove to be a useful tool for estimating the population genetic structure and genetic variability of Japanese Spanish mackerel.     

DEFORMATION MOVEMENT INDUCED BY DIVALENT IONOPHORE A23187 IN THE TUBIFEX EGG

Deformation movement (groove-forming activity of the equatorial surface) was induced in the spherical Tubifex egg by treatment with ionophore A23187 (5–10 μg/ml). The degree of induced movement was maximal when the treatment was commenced at the beginning of the round stages, i.e. , immediately after disappearance of the grooves formed in the preceding normal deformation movement; it gradually decreased as the onset of the treatment was delayed. This induction was independent of either external Ca²⁺ or Mg²+. Ultrastructural examination of eggs undergoing the induced movement revealed the presence of organized microfilaments in the cortical layer of the grooving regions. It is assumed that the absence of contractile activity during the round stages of the Tubifex egg is attributed basically to the low availability of intracellularly stored Ca²⁺. The results also suggest that the distribution and/or the amount of the contractile elements change during these stages.