A comparison of plants regenerated from a variegated <Emphasis Type="Italic">Epipremnum aureum</Emphasis>

In order to study chloroplast biogenesis, we chose natural variegated Epipremnum aureum (golden pothos) and regenerated pale yellow, variegated and green plants from all three types of tissue explants. The percentage of three types of regenerated shoots from three different explants was very close. Regenerated plants have been maintained for a year and show no sign of a colour switch. By comparing their protein profiles, two major differences between pale yellow and green plants were observed at the 15 and 40 to 50 kDa proteins. Moreover, pale yellow plants had unexpected high molecular mass proteins (greater than 60 kDa). Both variegated and green plants had more chlorophyll (Chl) a than Chl b, the ratios were about 1.46 and 1.93, respectively. In contrast, the pale yellow plants not only had less total Chl, but also the reduction of Chl a was much greater than Chl b, resulting in a higher content of Chl b than Chl a. Microscopic analysis revealed that pale yellow plants contained predominantly undeveloped chloroplasts with low Chl contents, even though their mesophyll cells were similar to green and variegated plants. PCR amplification of chloroplast DNA with 14 universal chloroplast primers did not reveal any difference among these regenerated plants.     

Chlorophylls <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">f</Emphasis> and their role in primary photosynthetic processes of cyanobacteria

The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Q_y) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria.     

Seasonal dynamics of chlorophyll and microelement content in developing conifer needles of <Emphasis Type="Italic">Abies sibirica</Emphasis> and <Emphasis Type="Italic">Picea abies</Emphasis>

Composition of microelements and photosynthetic pigment content (chlorophylls (Chl) a and b) were monitored in growing needles of spruce (Picea abies (L.) Karst.) and Siberian fir (Abies sibirica Ledeb.) during spring-autumn vegetation period. The dynamics of fresh weight and needle length for the first-year needles of spruce and fir revealed a number of shared and species-specific features in growth patterns of photosynthetic organs. In the beginning of growth period (in May), the needles elongated rapidly, while June–July were marked by the increase in needle weight. In P. abies the needle weight accumulated rapidly (specific growth rates μ_max up to 0.20 day⁻¹) over a short period (14 days), while in A. sibirica the needle weight increased slower (μ_max ≤ 0.11 day⁻¹) but over a longer period (≥30 days). The dynamics of Chl a and Chl b content and their ratio were identical in needles of both species over the growth period, although changes in Chl a were pronounced stronger than those in Chl b. In spring (May), a relatively high total Chl content per needle dry weight was noted. In summer (June–August), the total Chl content declined appreciably. In autumn (September–November), the total chlorophyll content in first-year needles increased slightly. Microelements were classified into two groups according to seasonal dynamics of their relative content in first-year needles. The first group includes Ba, Mn, Zn, B, Cu, Co, Cr, Pb, and Mo, whose relative content had a distinctive maximum in July, coincident with the peak in Chl content. The second group comprises Ni, V, Ag, Be, Cd, and As, whose relative content was minimal at this period. Seasonal changes in microelement composition were similar for the two conifer species examined, which is likely due to different physiological values of various microelements for photosynthetic organs.     

Responses of chlorophyll <Emphasis Type="Italic">b</Emphasis>-less <Emphasis Type="Italic">chlorina</Emphasis> 3613 mutant of barley to a prolonged decrease in illuminance: 2. Dynamics of carotenoids in leaf chloroplasts

Barley (Hordeum vulgare L.) mutant chlorina 3613 is notable for a lack of chlorophyll b (Chl b), low content of chlorophyll a (Chl a) and carotenoids in the chloroplasts, as well as reduction in the majority of components of LHCI and LHCII. Incompletely developed photosynthetic machinery of chlorina 3613 results in suppressed growth, lower biomass, and the declined rate of photosynthesis (as compared with the wild-type cv. Donaria). The lack of Chl b and greater part of peripheral antenna suggests that this mutant will have difficulties during acclimation to long-term shading because the light-harvesting role of Chl b-containing antenna becomes more important under the shortage of light. Earlier, our experiments with the mature chlorina 3613 plants shaded for one week at PAR photon flux density of 60 and 40% of that in full sunlight showed a stimulating effect of shading on growth, biomass accumulation, and Chl a synthesis in chlorina 3613 when biosynthesis of Chl b did not occur [1]. In this work, we investigated in more detail the changes in the content of carotenoids in chlorina 3613. We found that in Donaria at both investigated levels of illumination (60 and 40% of full sunlight) and in chlorina 3613 at 60% illumination, moderate reversible changes typical of shade-enduring plants occur in the content of carotenoids. In chlorina 3613 at 40% illumination, the content of β-carotene increased considerably (by 3 times) with simultaneous accumulation of Chl a. When full illumination was restored, the content of β-carotene decreased and remained on the level, which exceeded its initial content in the plants without shading by 38%; this level, was maintained by the end of vegetation. The changes in the contents of β-carotene and Chl a in chlorina 3613 were not accompanied by any accumulation of xanthophylls or changes in the relative content of active violaxanthin. The obtained results suggest that a long-term shading of the leaves of mature chlorina 3613 plants induced the formation of certain components of photosynthetic apparatus: reactive centers and core parts of photosystems’ antennae as well as proteins CP26 and CP29 and in this way contributed to partial restoration of photosynthetic activity and production process in the mutant lacking Chl b.     

Cadmium and zinc induced chlorosis in Indian mustard [<Emphasis Type="Italic">Brassica juncea</Emphasis> (L.) Czern] involves preferential loss of chlorophyll <Emphasis Type="Italic">b</Emphasis>

Plants of Indian mustard (Brassica juncea) were treated with either 50 μM Cd, 250 μM Zn, or 25 μM Cd+125 μM Zn and the progression of chlorosis in the mature leaves monitored. As relative chlorophyll (Chl) contents in the mature leaves decreased to 75, 50, and 25 % relative to controls, both mature and young leaves were harvested and the Chl pools extracted. The metal treatments caused a greater loss of Chl b than Chl a. As mature leaves underwent progressive chlorosis, the young leaves displayed a characteristic over-greening, due largely to increased content of Chl b. However, as the young leaves began to experience chlorosis, a greater loss of Chl b was also observed. Thus during metal induced chlorosis, there is a preferential turnover of the Chl b pool in mature and young leaves.     

Viable nonsense mutants for the essential gene <Emphasis Type="Italic">SUP45</Emphasis> of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Background  

Termination of protein synthesis in eukaryotes involves at least two polypeptide release factors (eRFs) – eRF1 and eRF3. The highly conserved translation termination factor eRF1 in Saccharomyces cerevisiae is encoded by the essential gene SUP45.     

Expression profiling and integrative analysis of the <Emphasis Type="Italic">CESA</Emphasis>/<Emphasis Type="Italic">CSL</Emphasis> superfamily in rice

Background  

The cellulose synthase and cellulose synthase-like gene superfamily (CESA/CSL) is proposed to encode enzymes for cellulose and non-cellulosic matrix polysaccharide synthesis in plants. Although the rice (Oryza sativa L.) genome has been sequenced for a few years, the global expression profiling patterns and functions of the OsCESA/CSL superfamily remain largely unknown.     

Universal chlorophyll equations for estimating chlorophylls <Emphasis Type="Italic">a,b, c</Emphasis>, and <Emphasis Type="Italic">d</Emphasis> and total chlorophylls in natural assemblages of photosynthetic organisms using acetone,methanol, or ethanol solvents

A universal set of equations for determining chlorophyll (Chl) a, accessory Chl b, c, and d, and total Chl have been developed for 90 % acetone, 100 % methanol, and ethanol solvents suitable for estimating Chl in extracts from natural assemblages of algae. The presence of phaeophytin (Ph) a not only interferes with estimates of Chl a but also with Chl b and c determinations. The universal algorithms can hence be misleading if used on natural collections containing large amounts of Ph. The methanol algorithms are severely affected by the presence of Ph and so are not recommended. The algorithms were tested on representative mixtures of Chls prepared from extracts of algae with known Chl composition. The limits of detection (and inherent error, ±95 % confidence limit) for all the Chl equations were less than 0.03 g m⁻³. The algorithms are both accurate and precise for Chl a and d but less accurate for Chl b and c. With caution the algorithms can be used to calculate a Chl profile of natural assemblages of algae. The relative error of measurements of Chls increases hyperbolically in diluted extracts. For safety reasons, efficient extraction of Chls and the convenience of being able to use polystyrene cuvettes, the algorithms for ethanol are recommended for routine assays of Chls in natural assemblages of aquatic plants.     

Effect of phosphorus and temperature on chlorophyll <Emphasis Type="Italic">a</Emphasis> contents and cell sizes of <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> and <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis>

An experiment was carried out to evaluate the effects of phosphorus concentration (1, 4 and 10 mg l⁻¹) and temperature (15 and 25°C) on chlorophyll a (chl a) contents and cell size/volume of green alga Scenedesmus obliquus and blue green alga Microcystis aeruginosa. Long-term field data from Lake Taihu, a large, shallow eutrophic lake between Jiangsu and Zhejiang Provinces, China, was also used to evaluate the effect of temperature on the model between chl a and total phosphorus (TP). The chl a content of both algae increased with an increase in phosphorus concentration and temperature. Temperatures showed a significantly different effect on chl a content of S. obliquus at a phosphorus concentration of 10 mg l⁻¹, whereas there was no significant difference at the two lower phosphorus levels. For M. aeruginosa, temperatures presented significantly different effects on the chl a contents at three phosphorus concentrations. Chl a content of neither alga presented an interaction between the nutrient and the temperature. Long-term field data from Lake Taihu also indicated that the addition of temperature to the model increased predictability of chl a by TP. The length/diameter and volume of both algae were greater at the lower temperature and phosphorus concentration. Moderate negative correlations were observed between algal size, volume, and chl a content. Our results suggest that phosphorus concentration and temperature could change chl a contents and size in species-specific algal cells and that temperature should be considered when building the model of TP and chl a concentration.     

Natively oxidized amino acid residues in the spinach cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript><Emphasis Type="Italic">6</Emphasis></Subscript><Emphasis Type="Italic">f</Emphasis> complex

The cytochrome b ₆ f complex of oxygenic photosynthesis produces substantial levels of reactive oxygen species (ROS). It has been observed that the ROS production rate by b ₆ f is 10–20 fold higher than that observed for the analogous respiratory cytochrome bc₁ complex. The types of ROS produced (O₂^{??, 1}O₂, and, possibly, H₂O₂) and the site(s) of ROS production within the b ₆ f complex have been the subject of some debate. Proposed sources of ROS have included the heme b _p , PQ _p ^?? (possible sources for O₂^??), the Rieske iron–sulfur cluster (possible source of O₂^?? and/or ¹O₂), Chl a (possible source of ¹O₂), and heme c _n (possible source of O₂^?? and/or H₂O₂). Our working hypothesis is that amino acid residues proximal to the ROS production sites will be more susceptible to oxidative modification than distant residues. In the current study, we have identified natively oxidized amino acid residues in the subunits of the spinach cytochrome b ₆ f complex. The oxidized residues were identified by tandem mass spectrometry using the MassMatrix Program. Our results indicate that numerous residues, principally localized near p-side cofactors and Chl a, were oxidatively modified. We hypothesize that these sites are sources for ROS generation in the spinach cytochrome b ₆ f complex.     

Attenuation of fibrosis <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> with <Emphasis Type="Italic">SPARC</Emphasis> siRNA

Introduction  

SPARC is a matricellular protein, which, along with other extracellular matrix components including collagens, is commonly over-expressed in fibrotic diseases. The purpose of this study was to examine whether inhibition of SPARC can regulate collagen expression in vitro and in vivo, and subsequently attenuate fibrotic stimulation by bleomycin in mouse skin and lungs.     

Enhancement of susceptivity to photoinhibition and photooxidation in rice chlorophyll <Emphasis Type="Italic">b</Emphasis>-less mutants

Two rice chlorophyll (Chl) b-less mutants (VG28-1, VG30-5) and the respective wild type (WT) plant (cv. Zhonghua No. 11) were analyzed for the changes in Chl fluorescence parameters, xanthophyll cycle pool, and its de-epoxidation state under exposure to strong irradiance, SI (1 700 μmol m⁻² s⁻¹). We also examined alterations in the chloroplast ultrastructure of the mutants induced by methyl viologen (MV) photooxidation. During HI (0–3.5 h), the photoinactivation of photosystem 2 (PS2) appeared earlier and more severely in Chl b-less mutants than in the WT. The decreases in maximal photochemical efficiency of PS2 in the dark (F_v/F_m), quantum efficiency of PS2 electron transport (Φ_PS2), photochemical quenching (q_P), as well as rate of photochemistry (P_rate), and the increases in de-epoxidation state (DES) and rate of thermal dissipation of excitation energy (D_rate) were significantly greater in Chl b-mutants compared with the WT plant. A relatively larger xanthophyll pool and 78–83 % conversion of violaxanthin into antheraxanthin and zeaxanthin in the mutants after 3.5 h of HI was accompanied with a high ratio of inactive/total PS2 (0.55–0.73) and high 1–q_P (0.57–0.68) which showed that the activities of the xanthophyll cycle were probably insufficient to protect the photosynthetic apparatus against photoinhibition. No apparent difference of chloroplast ultrastructure was found between Chl b-less mutants and WT plants grown under low, LI (180 μmol m⁻² s⁻¹) and high, HI (700 μmol m⁻² s⁻¹) irradiance. However, swollen chloroplasts and slight dilation of thylakoids occurred in both mutants and the WT grown under LI followed by MV treatment. These typical symptoms of photooxidative damage were aggravated as plants were exposed to HI. Distorted and loose scattered thylakoids were observed in particular in the Chl b-less mutants. A greater extent of photoinhibition and photooxidation in these mutants indicated that the susceptibility to HI and oxidative stresses was enhanced in the photosynthetic apparatus without Chl b most likely as a consequence of a smaller antenna size.     

Responses of photosynthetic parameters of <Emphasis Type="Italic">Mikania micrantha</Emphasis> and <Emphasis Type="Italic">Chromolaena odorata</Emphasis> to contrasting irradiance and soil moisture

Photosynthetic parameters were measured in two invasive weeds, Mikania micrantha and Chromolaena odorata, grown in soil under full, medium, and low irradiance and full, medium, and low water supply. Both species showed significantly higher net photosynthetic rate, quantum yield of PS 2 photochemistry and photochemical quenching coefficient under high than low irradiance. For M. micrantha, low irradiance caused decreased chlorophyll content (Chl), Chl a/b ratio and maximum photochemical efficiency of PS 2 (F_v/F_m), while drought decreased Chl content and F_v/F_m and increased nonphotochemical quenching (NPQ). However, these parameters were much less affected in C. odorata except that Chl content and NPQ slightly increased under drought and high irradiance. High irradiance increased xanthophyll pools in both species, especially M. micrantha under combination with drought.     

Inactivation of NMD increases viability of <Emphasis Type="Italic">sup45</Emphasis> nonsense mutants in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Background  

The nonsense-mediated mRNA decay (NMD) pathway promotes the rapid degradation of mRNAs containing premature termination codons (PTCs). In yeast Saccharomyces cerevisiae, the activity of the NMD pathway depends on the recognition of the PTC by the translational machinery. Translation termination factors eRF1 (Sup45) and eRF3 (Sup35) participate not only in the last step of protein synthesis but also in mRNA degradation and translation initiation via interaction with such proteins as Pab1, Upf1, Upf2 and Upf3.     

Effects of site-directed mutagenesis of <Emphasis Type="Italic">mglA</Emphasis> on motility and swarming of <Emphasis Type="Italic">Myxococcus xanthus</Emphasis>

Background  

The mglA gene from the bacterium Myxococcus xanthus encodes a 22kDa protein related to the Ras superfamily of monomeric GTPases. MglA is required for the normal function of A-motility (adventurous), S-motility (social), fruiting body morphogenesis, and sporulation. MglA and its homologs differ from all eukaryotic and other prokaryotic GTPases because they have a threonine (Thr78) in place of the highly conserved aspartate residue of the consensus PM3 (phosphate-magnesium binding) region. To identify residues critical for MglA function or potential protein interactions, and explore the function of Thr78, the phenotypes of 18 mglA mutants were characterized.     

Photosystem 2-activity and thylakoid membrane polypeptides of <Emphasis Type="Italic">in vitro</Emphasis> cultured chrysanthemum as affected by NaCl

Long-term (30 d) effects of 100, 200, 300, and 400 mM NaCl on photosystem 2 (PS 2)-mediated electron transport activity and content of D1 protein in the thylakoid membranes of chrysanthemum (Dendranthema grandiflorum) cultured in vitro at low irradiance 20 μmol(photon) m⁻² s⁻¹ were investigated. 100 mM NaCl increased contents of chlorophylls (Chl) a and b, carotenoids (Car; xanthophylls + carotenes), and the ratio of Chl a/b, and Car/Chl a+b. However, further increase in NaCl concentration led to the significant reduction in the contents of Chl a, and Chl b, and increase in the ratio of Chl a/b and Car/Chl a+b. NaCl treatment decreased the PS 2-mediated electron transport activity and contents of various thylakoid membrane polypeptides including D1 protein.