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.     

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; )     

Coexistence of β1- and β2-Adrenoceptors in the Melanophore of the Goby Tridentiger obscurus*

The effects of β-adrenergic agonists and antagonists on the pigmentary state of denervated melanophores in isolated, split, caudal fins of the goby Tridentiger obscurus were examined to investigate the function and the subtype of the β-adrenoceptors of the melanophores. Salbutamol, terbutaline, and dobutamine partially inhibited the pigment-aggregating response of melanophores to norepinephrine. The effects of these β-agonists were inhibited by propranolol. It was confirmed that the melanophores possess both α-and β-adrenoceptors, and that the activation of the β-adrenoceptors induces the dispersion of pigment in the melanophores. Norepinephrine, epinephrine, isoproterenol, dobutamine, salbutamol, and terbutaline evoked the dispersion of pigment in the melanophores in which pigment had previously been aggregated by treatment with verapamil in the presence of phentolamine. The pigment-dispersing effects of two β₁-selective agonists, norepinephrine and dobutamine, were effectively inhibited by metoprolol, a selective antagonist of β₁-receptors. By contrast, the pigment-dispersing effects of two β₂-selective agonists, salbutamol and terbutaline, were not inhibited by metoprolol. Both the effects of nonselective agonists, epinephrine and isoproterenol, were partially inhibited by metoprolol. The actions of all of the β-agonists used were effectively inhibited by propranolol, and they were partially inhibited by butoxamine. These results suggest coexistence of β₁- and β₂-adrenoceptors in the melanophores. The relative numbers of β₁- and β₂-adrenoreceptors as a percentage of the total population of β-adrenoceptors were estimated to be 18.6% and 81.4%, respectively, from analyses of Hofstee plots of the effects of the β-agonists on the melanophores in the presence of butoxamine or metoprolol.     

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; )     

β-Adrenergic Receptor Subtypes in Melanophores of the Marine Gobies Tridentiger trigonocephalus and Chasmichthys gulosus

The subtype of β-adrenergic receptors in melanophores of the marine gobies Tridentiger trigonocephalus and Chasmichthys gulosus was studied. Pigment of denervated melanophores in isolated, split caudal fins was preliminarily aggregated by incubating the specimens in a physiological saline containing 10 μM phentolamine and 30–100 μM verapamil or 2–10 nM melatonin, and the responses of the melanophores to a β-adrenergic agonist added to the incubating medium were recorded photoelectrically. The β-adrenergic agonists noradrenaline, adrenaline, isoproterenol, salbutamol and, dobutamine were all effective in evoking a dispersion of melanophore pigment in the presence of phentolamine and verapamil or melatonin. The pigment-dispersing effect of noradrenaline (β₁-selective agonist) was inhibited by metoprolol (β₁-selective antagonist), propranolol, and butoxamine. Whereas, the effect of salbutamol (β₂-selective agonist) was hardly inhibited by metoprolol, though it was considerably inhibited by propranolol and ICI-118551. It was estimated that β₁- and β₂-adrenergic receptors coexist at ratios of 8.6:91.4, in the melanophore of Tridentiger trigonocephalus, and 25:75, in the melanophore of Chasmichthys gulosus, through the analyses of Hofstee plots of the effects of the β-adrenergic drugs. It was suggested that the relation between the pigment-dispersing effect of a β-adrenergic agonist on the melanophores and the concentration of the drug follows mass action kinetics, when the effect is mainly caused by the activation of β₂-adrenergic receptors of the melanophores. However, when it is mainly caused by the activation of β₁-adrenergic receptors of the melanophores, the relation does not follow mass action kinetics.     

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.     

Herbivorous insect decreases plant nutrient uptake: the role of soil nutrient availability and association of below‐ground symbionts

1. Plants take nutrients from the rhizosphere via two pathways: (i) by absorbing soil nutrients directly via their roots and (ii) indirectly via symbiotic associations with nutrient‐providing microbes. Herbivorous insects can alter these pathways by herbivory, adding their excrement to the soil, and affecting plant–microbe associations. 2. Little is known, however, about the effects of herbivorous insects on plant nutrient uptake. Greenhouse experiments with soybean, aphids, and rhizobia were carried out to examine the effects of aphids on plant nutrient uptake. 3. First, the inorganic soil nitrogen and the sugar in aphid honeydew between aphid‐infected and ‐free plants were compared. It was found that aphid honeydew added 41 g m^?2 of sugar to the soil, and that aphids decreased the inorganic soil nitrogen by 86%. This decrease may have been caused by microbial immobilisation of soil nitrogen followed by increased microbial abundance as a result of aphid honeydew. 4. Second, nitrogen forms in xylem sap between aphid‐infected and ‐free plants were compared to examine nitrogen uptake. Aphids decreased the nitrogen uptake via both pathways, and strength of the impact on direct uptake via plant roots was greater than indirect uptake via rhizobia. The reduced nitrogen uptake by the direct pathway was as a result of microbial immobilisation, and that by the indirect pathway was probably because of the interaction of microbial immobilisation and carbon stress, which was caused by aphid infection. 5. The present results demonstrate that herbivorous insects can negatively influence the two pathways of plant nutrient uptake and alter their relative importance.