Excitation-energy distribution in green algae. The existence of two independent light-driven control mechanisms

Three distinct states can be identified for cells of the green alga Chlorella vulgaris; State 1 and State 2 obtained by preillumination in far-red and red light, respectively, and the dark state obtained by dark-adaptation. Addition of the inhibitor DCMU to algal cells leads to an initial rapid increase in chlorophyll-a fluorescence reflecting the closure of Photosystem II traps. This, in the case of dark and state-2-adapted algae is followed by a slow light-dependent increase to a fluorescence yield typical of State-1-adapted cells. Measurements of low temperature (77 K) emission spectra indicate that the low fluorescence yields of dark and State-2-adapted algae reflect similar balances in excitation-energy distribution between the two photosystems. In both cases, the balance favours PS I and the slow fluorescence increase seen in the poisoned algae reflects a redressing of this balance in favour of PS II. The low fluorescence yield of State-2-adapted algae is thought to be associated with the phosphorylation of chlorophyll a/b light-harvesting protein (Biochim. Biophys. Acta (1983) 724, 94–103). Measurements of the uncoupler and ATPase sensitivity of the light-dependent increases seen in DCMU-poisoned cells indicate that the low fluorescence yield of dark-adapted algae is of different origin. Evidence is presented showing that the light-driven changes in excitation-energy distribution seen in green algae involve two distinct processes; a low-intensity, wavelenght-independent change reflecting simple light/dark changes and a higher intensity, wavelength-dependent change reflecting State 1/State 2 adaptation. The former changes appear to be associated with changes in the local ionic environment within the algal chloroplast, whilst the latter appear to reflect changes in the phosphorylation state of chlorophyll a/b light-harvesting protein.     

Orientation of photosystem-I pigments. Investigation by low-temperature linear dichroism and polarized fluorescence emission

Using absorption and fluorescence experiments at low temperature with polarized light on oriented samples, the orientation of PS-I-related pigments, both in green plants and in Chlamydomonas reinhardtii, has been investigated on isolated pigment-protein complexes and intact thylakoids. The following observations have been made. (i) The isolation procedure of PS I₁₁₀, PS I₆₅, LHC I and CP0) particles from pea and C. reinhardtii do not alter significantly the intrinsic orientation of the pigments inside the complexes; (ii) Chl b is a structural component of PS I, linked to the peripheral antenna, with an orientation with respect to the thylakoid plane different from that observed in the main light-harvesting complex (iii) PS I₆₅ (i.e., ‘core’ PS I) of pea and C. reinhardtii contains identical chromophores having the same orientation with respect to the geometrical longest axis (axes) of the complexes. (iv) LHC I and CP0 (i.e., PS I ‘peripheral antenna’) of pea and C. reinhardtii have identical oriented chromophores, except that a long-wavelength component with a high anisotropy is only present in green plants. This set of pigments, which absorbs at 705–725 nm, has the same orientation as the dipoles emitting F₇₃₅ and also as the Q_Y transition of P-700. (v) All the long-wavelength fluorescence properties of the various studied membranes are explained by these data on isolated PS I complexes: wild-type C. reinhardtii and Chl-b-less barely fluoresce from the core pigments, while a CP1 deficient mutant of C. reinhardtii and wild-type barley fluoresce from the antenna pigments.     

A study of the primary charge separation in green bacteria by means of flash spectroscopy

A reaction-center pigment-protein complex of the green bacterium Prosthecochloris aestuarii was studied by means of nanosecond-flash spectroscopy. In this complex electron transfer between the primary and secondary acceptor is blocked. The spectra and kinetics of the absorption changes induced by a short flash indicated the formation of the radical pair P-840⁺I^?, which decayed in 20–35 ns, mainly to the triplet state of the primary electron donor P-840. The absorption difference spectrum of the initial absorption change indicated that the primary acceptor I is either bacteriopheophytin c or another pigment with absorption maximum at 665 nm.     

1 alpha, 25-Dihydroxyvitamin D3 directly induces fusion of alveolar macrophages by a mechanism involving RNA and protein synthesis, but not DNA synthesis

The results of our present study indicate that 1 alpha, 25-dihydroxyvitamin D3[1 alpha, 25(OH)2D3] directly induces fusion of mouse alveolar macrophages without any participation of T-lymphocytes by a mechanism involving RNA and protein synthesis but not DNA synthesis. We have reported that 1 alpha, 25(OH)2D3 induces fusion of alveolar macrophages by a direct mechanism and by a spleen cell-mediated indirect mechanism [(1983) Proc. Natl. Acad. Sci. USA 80, 5583-5587]. Alveolar macrophages pretreated with or without anti-Thy 1.2 antibody and complement fused similarly when they were incubated with 1 alpha, 25(OH)2D3. The vitamin suppressed DNA synthesis, but it significantly enhanced RNA and protein synthesis. The 1 alpha, 25(OH)2D3-induced fusion was blocked by adding actinomycin D or cycloheximide, but not by hydroxyurea.     

Cytotaxonomy and breeding system of the genusBiscutella (Cruciferae)

Chromosome counts were determined for 46 populations ofBiscutella representing 28 taxa. The genus was found to contain diploid taxa with 2n = 12, 16 and 18, tetraploid taxa with 2n = 36 and hexaploid taxa having 2n = 54.B. laevigata L. s. l. consists of diploid and tetraploid populations which are poorly differentiated morphologically. TetraploidB. laevigata s. l. and hexaploidB. variegata Boiss. & Reuter (s. l.) are characterized by chromosomal instability. The variation in chromosome numbers and the occurrence of polyploidy is discussed in relation to the taxonomy of the genus. An investigation of the breeding system showed that most of the annual species were self-compatible and partly inbreeding and most of the perennial species self-incompatible and, therefore, outbreeding, while one annual species,B. cichoriifolia Loisel., showed both systems.     

Differential regulation of the accumulation of the light-harvesting chlorophyll a/b complex and ribulose bisphosphate carboxylase/oxygenase in greening pea leaves

The photoregulation of chloroplast development in pea leaves has been studied by reference to three polypeptides and their mRNAs. The polypeptides were the large subunit (LSU) and the small subunit (SSU) of ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO), and the light-harvesting chlorophyll a/b protein (LHCP). The polypeptides were assayed by a sensitive radioimmune assay, and the mRNAs were assayed by hybridization to cloned DNA probes. LSU, LSU mRNA, and LHCP mRNA were detectable in etiolated seedlings but LHCP, SSU, and SSU mRNA were at or below the limit of detection. During the first 48 hr of de-etiolation under continuous white light, the mRNAs for LSU, SSU, and LHCP increased in concentration per apical bud by about 40-fold, at least 200-fold, and about 25-fold, respectively, while the total RNA content per apical bud increased only 3.5-fold. In the same period, the LSU, SSU, and LHCP contents per bud increased at least 60-, 100-, and 200-fold, respectively. The LHCP increased steadily in concentration during de-etiolation, whereas the accumulation LSU, SSU, and SSU mRNA showed a 24-hr lag. The accumulation of SSU, SSU mRNA, and LHCP mRNA showed classical red/far-red reversibility, indicating the involvement of phytochrome in the regulatory mechanism. LSU and LSU mRNA were induced equally well by red and far-red light. The LHCP failed to accumulate except under continuous illumination. These results indicate that the accumulation of SSU is controlled largely through the steady-state level of its mRNA, which is in turn almost totally dependent on light as an inducer and on phytochrome as one of the photoreceptors. The accumulation of LSU is largely but not totally determined by the level of its mRNA, which appears to be under strong photoregulation, which has yet to be shown to involve phytochrome. Phytochrome is involved in the regulation of LHCP mRNA levels but substantial levels of the mRNA also occur in the dark. LHCP accumulation is not primarily governed by the levels of LHCP mRNA but by posttranslational stabilization in which chlorophyll synthesis plays a necessary but not sufficient role.     

“Naked” spinal cord on a non-segmented baton-like bony structure in the tail of the electric fish Eigenmannia virescens (Gymnotoidei)

Summary The caudal spinal cord of Eigenmannia virescens is not enclosed in a neural canal of the vertebral column. In fact, a segmented vertebral column with neural and ventral arches is lacking and replaced by a non-segmented baton-like bony structure on which the free spinal cord is located. The baton consists of calcified bone tissue with bone cells. Individual differences exist as far as the length of the rod is concerned. The electromotor neurons of this caudal part of the spinal cord are histochemically acetylcholinesterase-positive. The electrocytes which surround this part of the spinal cord show strong enzymatic actitivity on the posterior innervated face. However, there is also activity on the non-innervated lateral and anterior faces.     

Titles of related papers in other sections

Electrophoretic analysis by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis showed that the light-harvesting chlorophyll $\text{a}\text{b}\text{-}\text{protein}$ complex of barley thylakoids contains only one polypeptide of apparent molecular weight 26 000. The barley mutant, deficient in chlorophyll b and this light-harvesting complex, lacks this polypeptide.The addition of a nonionic detergent, Triton X-100, to the sodium dodecyl solubilization buffer prior to SDS polyacrylamide tube gel electrophoresis, allowed separation of a relatively stable complex, characterized as an oligomeric form of the light-harvesting complex. The oligomer also contained a polypeptide with an apparent molecular weight of 26 000. The absorption and fluorescence spectral properties of the oligomer are similar to those of the monomer. It is suggested that the oligomer of the light-harvesting chlorophyll $\text{a}\text{b}\text{-}\text{protein}$ is closer to the in vivo form rather than the monomer.     

Effect of cadmium on Golgi complex of freshwater teleost (Pimelodus maculatus) hepatocytes

Summary Freshwater teleost hepatocytes show hypertrophied Golgi complexes 3 days after a single intraperitoneal injection of cadmium chloride (10 mg/Kg).