Effect of Supra-High Irradiation on the Photosynthetic System of the Cyanophyte Synechocystis PCC 6714

Stability of thylakoid components under supra-high irradiancewas studied with the cyanophyte Synechocystis PCC 6714. Theactivity of overall photosynthesis was quickly inactivated (T_1/2=20min) under supra-high irradiance (300 W m^–2, white light).In parallel with the inactivation of photosynthesis, QA in PSII was also inactivated. Both inactivations were acceleratedby chloramphenicol (CAP) addition. The reactivation of PS IIrequired weak irradiation and was suppressed by CAP. However,PS I measured as P700 was very stable. The level of PS I measuredas P700 was not significantly reduced by the irradiation for12 h even in the presence of CAP while the level of Cyt b₅₅₉,component of PS II, was decreased markedly. The function ofPS I before and after supra-high irradiation with CAP was examinedby comparing sizes of P700 oxidation induced by a short flash,by a continuous light, and by determination of O₂-and ferredoxin-reduction.No difference was observed in PS I actions before and afterthe irradiation treatment. These results indicate that the PSI complex is very tolerant of supra-high irradiation. However,the cells grown under supra-high irradiance contained much fewerPS I and PS II complexes than Cyt b₆–f complexes. Theformer levels were reduced to a half to one fourth of thosebefore growth while the level of Cyt b₆–f complex wasnot reduced so much. A possible mechanism for changes in thylakoidcomposition under supra-high irradiation was discussed. (Received February 16, 1991; Accepted June 12, 1991)     

Cannibalistic feeding behavior of the brackish-water copepod Sinocalanus tenellus

Cannibalistic feeding behavior of the brackish-water copepodSinocalanus tenellus was examined in the laboratory using CI-II,CIII-IV and CVI female as predators and NI-II, NIII-IV, NV-VIand CI-II as prey. In each prey-predator combination, the ingestionrate increased with increasing prey density to an asymptoticvalue. Cannibalism took place even when phytoplankton was availableas an alternative food supply. Based on a daily ration, theoptimal prey stages for CVI females, CIII-IV and CI-II are NI-VI,NI-IV and NI-II respectively. Under average, natural prey density(10 nauplii l^–1), S tenellus can achieve only a smallfraction (max 9%) of the daily minimum food requirement by cannibalisticfeeding. However, the impact of cannibalism on naupliar survivorshipcan be significant. When adult females occur at a density of10 l^–1, the mortality due to cannibalism attains 99.2%during the naupliar stages.     

Morphological effects of cadmium on proximal tubular cells in rats

Twenty-four male rats of the Wistar strain divided into four groups were injected sc with a dose of 0.8, 1.5, and 3.0 mg Cd/kg body wt as CdCl₂ in saline, and saline alone to the control rats, three times a week for 3 wk. Cadmium levels of whole kidney homogenate, supernatant (cytosol), precipitate, and metallothionein (MT) fraction were measured. Histological changes of the renal proximal tubules were investigated by optical and electron microscopy. In the kidneys, Cd levels were increased with the increment of Cd dosage; 80–90% of Cd was contained in cytosol, and 55–75% was in MT fraction. Non-MT-Cd reached a maximum in the 1.5 mg Cd group, whereas that of the 3.0 mg Cd group showed some decline. With increasing Cd doses, the size of nuclei and nucleoli in the cells of proximal tubule showed significant enlargement and also an increase in the number of nucleoli on light microscopy. At higher doses, chromatin condensation of the tubular nuclei and vacuolar degeneration of the tubular cells were evident. On electron microscopy, perichromatin granules of the proximal tubular nuclei were increased in number, especially in the rats of Cd 0.8 mg and 1.5 mg/kg groups. As the Cd doses increased, ring-shaped nucleoli were increased in number and nucleolar segregation was observed more clearly. Moreover, in the 3.0 mg/kg Cd group, nuclear indentation and nucleoli containing compact dense granules were observed. In the cytoplasm, there was an increase of lysosomes, myelin bodies, ring-shaped mitochondria, and vesiculation; ultimate changes were degeneration and cell necrosis. The injured cells were heterogenously distributed in each nephron and this heterogeneity was attributed in the difference in Cd content and cell cycle in each cell of the nephron.     

Cloning of Candida pelliculosa beta-glucosidase gene and its expression in Saccharomyces cerevisiae

Summary Candida pelliculosa var. acetaetherius is a strain of yeast which can utilize cellobiose as the carbon source. From a gene library prepared from this yeast, the -glucosidase gene has been cloned in a S. cerevisiae host using a chromogenic substrate, 5-bromo-4-chloro-3-indolyl--glucoside as an indicator. It was proved by Southern analysis that the DNA fragment carrying the -glucosidase gene originated from C. pelliculosa. -Glucosidase produced by S. cerevisiae transformants was secreted into the periplasmic space. In Candida, -glucosidase was not induced by cellobiose but was derepressed by lowering the concentration of glucose. The regulation of -glucosidase synthesis in S. cerevisiae carrying the cloned -glucosidase was not clear compared with that in Candida, however, the enzyme activity in low glucose medium (0.05%) was reproducibly higher than in high glucose medium (2%). We have found the sequence that controls the expression of the -glucosidase gene negatively in S. cerevisiae.     

Inhibition of Photosynthesis by Sulfite in Mesophyll Protoplasts Isolated from Vicia faba L. in Relation to Intracellular Sulfite Accumulation

Inhibition of photosynthesis by Na₂SO₃ in mesophyll protoplastsisolated from Vicia faba leaves and uptake of sulfite by theprotoplasts were examined at various pH values of the incubationmedium containing Na₂SO₃. As the pH of the incubation mediumlowered, the rate of photosynthesis in the protoplasts decreasedand the amount of sulfite taken up by the protoplasts increased.Most of sulfite accumulated in the protoplasts was not metabolizedduring the dark incubation, as measured with an ion chromatograph.Photosynthetic O₂ evolution by the chloroplasts isolated fromVicia mesophyll protoplasts was inhibited by exogenously-appliedNa₂SO₃ over pH region examined (7.4–9.0). The sulfiteconcentration required for a half inhibition of photosynthesisby the isolated chloroplasts was similar to the intracellularsulfite level required for that by the protoplasts. These resultsindicate that the intracellular sulfite accumulated in the protoplastsin an unmetabolized state is responsible for the inhibitionof protoplast photosynthesis. (Received January 24, 1985; Accepted May 29, 1985)     

Characterization of rat cytochrome P-450MC synthesized in Saccharomyces cerevisiae

Rat cytochrome P-450MC cDNA was expressed in Saccharomyces cerevisiae AH22, SHY3 and NA87-11A cells under the control of the yeast ADH1 promoter and terminator. Although the three yeast strains transformed with the constructed expression plasmid, pAMC1, contained approximately three copies of the plasmid, the levels of both P-450MC mRNA and the corresponding protein in the AH22 cells carrying plasmid pAMC1 were 1.4- to 1.7-fold and 2-fold higher than in the other two strains, respectively. The P-450MC protein was purified from the microsomal fraction of AH22 cells carrying pAMC1 by a rapid purification method. The apparent molecular weight, chromatographic behavior, spectral properties, substrate specificity and immunochemical properties of the purified P-450MC protein were indistinguishable from those of rat liver P-450MC-I and P-450MC-II (Sasaki, T., et al. (1984) J. Biochem. 96, 117-126). The NH2-terminal amino acid sequence of the purified protein up to 10 residues was the same as those of P-450MC-I and P-450MC-II. In addition, HPLC analysis of the microsomal fraction of AH22 cells containing pAMC1 indicated that the synthesized P-450MC protein corresponds to P-450MC-II, but not P-450MC-I. With another purification method, we obtained the cleaved P-450MC protein which lacked the NH2-terminal 30 amino acids of intact P-450MC. The spectral properties and monooxygenase activities towards benzo(a)pyrene and 7-ethoxycoumarin of the cleaved P-450MC were nearly the same as those of intact P-450MC.     

Electron microscopical findings with special reference to cancer in rats caused by inhalation of nickel oxide

A special exposure system was used for the inhalation of nickel oxide (NiO) aerosol by Wistar male rats. The median aerodynamic diameter and the geometric standard deviation were 1.2 μm and 2.2, respectively. A histopathological study of the rats was performed immediately, and at intervals of 12 and 20 mo after a 1-mo expsoure to NiO. Electron microscopy showed that localization of NiO particles was restricted to the lungs and that each particle had been engulfed by the alveolar macrophages. Type II pneumocytes and nonciliated bronchiolar epithelial cells (Clara cells), as well as numerous tubular myelin (surfactant) in the alveoli were prominent. In rats dissected after 12 mo, clusters of NiO particles were still present within the terminal bronchioli, alveolar walls, and lysosomes of the alveolar macrophages. Pools of tubular myelin were observed in the peribron-chial lymphatics. The Clara cells, which project into the lumen of bronchioli, showed active secretion and were filled with smooth en-doplasmic reticulum (SER) in the apical cytoplasm. In the experimental group sacrificed after 20 mo, one rat had papillary adenocarcinoma and two rats showed adenomatosis in the peripheral portion of the lung, but none in the upper respiratory tract.     

Macrophage Activation by Tetrahymena pyriformis. I. Active Subcellular Fractions of Tetrahymena

Experiments were carried out to determine what subcellular fractions of Tetrahymena pyriformis could, after inoculation into mice, activate macrophages to kill Toxoplasma gondii in vitro. Peritoneal macrophages from mice inoculated intraperitoneally with cilia, pellicles, mitochondria, and microsomes exhibited strong toxoplasmacidal activity and had an enhanced capacity to release hydrogen peroxide (H₂O₂) by stimulation of a membrane-active agent as compared with resident macrophages. In contrast, macrophages from mice inoculated with macronuclei and postmicrosomal supernatant showed no toxoplasmacidal activity and a low level of H₂O₂ release. Similar dose response was observed on the active subcellular fractions with regard to the degree of macrophage activation. Treatment of the active subcellular fractions with heating and trypsin markedly reduced their activity.