RELATIONSHIP BETWEEN LIGHT QUALITY DEPENDENCE AND IRRADIANCE ADAPTATION OF PHOTOSYNTHESIS IN Acetabularia mediterranea*

Characteristic differences in the light intensity curves of photosynthesis after growth of cells of Acetabularia mediterranea Lamour. (A. acetabulum (L.) Silva) in weak and strong white light were similar to those for red and blue light-treated cells, respectively. This indicated that responses to white light quantity and those to light quality might be causally related. Small differences in the thylakoid polypeptide composition of cells grown in high and low intensities of white light were not significant and thus did not help to clarify whether the adaptations to blue or red light, respectively, were the same. When the red to blue-light ratio was varied, keeping the total photon fluence rate constant, the photosynthetic capacity (red light saturated O₂-production) was dependent on blue light irradiance in a logarithmic fashion. The specific influence of red light was not detectable, indicating that only blue light was effective for light irradiance adaptation in Acetabularia. The situation was different, at least for a transient period, when adaptation to light irradiance was allowed to proceed from a low photosynthetic activity after preirradiation of the cells with prolonged red light. The effect of low white light irradiances was pronounced, causing a maximum increase of photosynthetic activity within 3 days. The response to blue light was enhanced as well, and a very low photon irradiance added to continuous red light caused a change of the same order as that produced by high irradiances of blue light alone. This elevated action of low intensity white and blue light is most likely due to increased metabolite supply derived from the degradation of starch enhanced by this light quality. Therefore, photosynthetic effectiveness in Acetabularia is regulated by the irradiance of blue light and by feedback via photosynthetic products.     

Stimulation of hydrogen production in algal cells grown under high CO2 concentration and low temperature

When cells ofChlamydomonas sp. MGA 161, a marine green alga, were cultivated at a high CO₂ concentration (15% CO₂) and low temperature (15°C), the growth lag time was much longer, but the starch accumulated was two times higher than under the basal conditions (5% CO₂ 30°C). When the cells grown in the high-CO₂/low-temperature conditions were incubated under dark anaerobic conditions, the degradation of starch and production of hydrogen and ethanol were remarkably higher than those grown under the basal conditions. The lag time of cell growth was shortened, whereas the high capacity of starch accumulation and hydrogen production was maintained, by cultivating the cells alternately every 12 h under the basal and high-CO₂/low-temperature conditions. Using this dual system, in which the cultivation was alternated between the two conditions, the total productivity was significantly improved.     

THE PHOTOSYNTHETIC APPARATUS OF Acetabularia mediterranea GROWN UNDER RED OR BLUE LIGHT. BIOPHYSICAL QUANTIFICATION and CHARACTERIZATION OF PHOTOSYSTEM II and ITS CORE COMPONENTS

Abstract— The photosynthetic activity of white light-grown Acetabularia mediterranea Lamouroux (= A. acetabulum (L.) Silva) decreases under continuous red light to less than 20% within 3 weeks. Subsequent blue light reactivates photosynthesis within a relatively short period of 3 days. In a former publication (Wennicke and Schmid, Plant Physiol. 84 ,1252–1256, 1987) we have shown that the regulated rate limiting step, which is an immediate light driven reaction, is part of photosystem II (PS II). The following biophysical properties of PS II were analyzed in thylakoids isolated from algae grown 3 weeks under either blue or red light with or without subsequent 3 days of blue light illumination: (a) fluorescence induction in the short time domain dominated by Q_A reduction, (b) the slow fluorescence decline reflecting pheophytin photoaccumulation, (c) absorption changes at 320 and 830 nm under repetitive flash excitation as indicator for the turnover of Q_A and P₆₈₀, respectively, (d) oscillation pattern of the oxygen yield by a flash train in dark adapted samples and (e) the binding capacity for atrazine. None of these PS II functions were severely affected, but a minor impairment of20–30% was observed in the thylakoids from algae grown for 3 weeks in red irradiation. The changes do not fully account for the drastic reduction of the electron transport through PS II which was 80% after red light treatment. Therefore, the regulated rate-limiting step appears to not be mainly located in the PS II core complex itself. It seems likely that the regulation process predominantly comprises the antenna system.     

LIGHT REQUIREMENTS FOR THE ENHANCED SYNTHESIS OF A PLASTID mRNA DURING SPIRODELA GREENING

A plastid mRNA (5 × 10⁵ mol wt) appears as a burst 3 h after white light greening of steady state dark grown plants of Spirodela oligorrhiza. In this species, chlorophyll synthesis begins after 12 h. The light requirement is different from the pulse of far-red reversible red light required to abolish the lag of chlorophyll synthesis in many species, including Spirodela. Continuous high energy far-red is not stimulatory. When the illumination is not continued throughout the time of incorporation, the stimulation is minimal. Low energy blue and red light are stimulatory, and green and far-red light are ineffectual. Blue light was > 5 times as effective as red light at many dose levels. Illumination with 3 × 10¹⁷ quanta/m²/s (50pEm/cm²/s) blue light at 476 nm gave about half maximum stimulation.     

复合光催化剂AgI/AgCl/h-BN的制备及光催化性能

以少层六方氮化硼纳米层状材料为载体,通过水溶性盐晶体模板法和离子交换法制备了h-BN稳定AgI/AgCl的三元复合体系。通过XRD、FT-IR、SEM、TEM等手段对样品的结构和形貌进行检测分析,利用UV-Vis DRS测试了样品的吸光性能。可见光光催化降解罗丹明B实验表明,光照24 min,AgI/AgCl/h-BN复合光催化材料对罗丹明B的降解率高达93%,远高于实验合成的大块AgCl、AgCl立方块、AgI/AgCl纳米腰果及文献报道的数值。并且三元材料循环利用4次后,对罗丹明B的降解率几乎保持不变。结合光电化学测试、活性物种捕获和电子自旋共振等实验结果,探讨了复合材料光催化活性和稳定性提高的机理。     

复合光催化剂AgI/AgCl/h-BN的制备及光催化性能

以少层六方氮化硼纳米层状材料为载体,通过水溶性盐晶体模板法和离子交换法制备了h-BN稳定AgI/AgCl的三元复合体系。通过XRD、FT-IR、SEM、TEM等手段对样品的结构和形貌进行检测分析,利用UV-Vis DRS测试了样品的吸光性能。可见光光催化降解罗丹明B实验表明,光照24 min,AgI/AgCl/h-BN复合光催化材料对罗丹明B的降解率高达93%,远高于实验合成的大块AgCl、AgCl立方块、AgI/AgCl纳米腰果及文献报道的数值。并且三元材料循环利用4次后,对罗丹明B的降解率几乎保持不变。结合光电化学测试、活性物种捕获和电子自旋共振等实验结果,探讨了复合材料光催化活性和稳定性提高的机理。     

Color of illumination during growth affects LHCII chiral macroaggregates in pea plant leaves

To determine whether the color of illumination under which plants are grown, affects the structure of photosynthetic antennae, pea plants were grown under either blue-enriched, red-enriched, or white light. Carotenoid content of isolated chloroplasts was found to be insensitive to the color of illumination during growth, while chlorophyll a/b ratio in chloroplasts isolated from young illuminated leaves showed susceptibility to color. Color of illumination affects the LHCII chiral macroaggregates in intact leaves and isolated chloroplasts, providing light-induced alteration of the handedness of the LHCII chiral macroaggregate, as measured with circular dichroism and circularly polarized luminescence. The susceptibility of handedness to current illumination (red light excitation of chlorophyll fluorescence) is dependent on the color under which the plants were grown, and was maximal for the red-enriched illumination. We propose the existence of a long-term (growth period) color memory, which influences the susceptibility of the handedness of LHCII chiral macroaggregates to current light.     

MULCH SURFACE COLOR AFFECTS ACCUMULATION OF EPICUTICULAR WAX ON DEVELOPING LEAVES

Abstract— Leaf waxes are important to plant growth because they impede water loss and may influence entry of light. Leaf wax quantity and composition were studied in Capsicum annuum plants in trickle-irrigated field plots covered with white, black or red plastic mulches. The quantity of reflected blue light (BL) was greatest over white and about the same over black versus red surfaces; and reflected far-red to red ratios (FR/R) were about the same over white versus black and higher over red. The greatest quantity of total epicuticular wax developed on leaves of plants grown over white mulch (443 μg/cm²) while plants grown over black and red mulches had 229 and 227 μg/cm², respectively. When individual lipid classes were expressed as percentages of the totals, esters constituted the highest percentages over white and black surfaces while secondary free fatty alcohols dominated over red. The higher ester content of epicuticular wax on plants grown over black (versus red) was almost exactly equalled by increased contents of free fatty alcohols and free fatty acids in the epicuticular wax of plants grown over red mulch. We conclude that the total wax concentration on leaves of field-grown plants was influenced by quantity of BL, and the percentage of individual components was influenced by the FR/R ratio.     

Efficient production of mannan-degrading enzymes by the basidiomyceteSclerotium rolfsii

Sclerotium rolfsii CBS 191.62 was cultivated on a number of carbon (C) sources, including mono- and disaccharides, as well as on polysaccharides, to study the formation of different mannan-degrading enzyme activities. Highest levels of mannanase activity were obtained when α-cellulose-based media were used for growth, but formation of mannanase could not be enhanced by employing galactomannan as the only carbon source. Although both xylanase and cellulase formation was almost completely repressed whenS. rolfsii was grown on more readily metabolizable carbohydrates, including glucose or mannose, considerable amounts of mannanase activity were secreted under these growth conditions. Enhanced mannanase production only commenced when glucose was depleted in the medium. The maximal mannanase activity of 240 IU/mL obtained in a laboratory fermentation is remarkable. Mannanase activity formed under these derepressed conditions could be mainly attributed to one major, acidic mannanase isoenzyme with a pI value of 2.75.     

Invertase production is related to the nitrogen source in Hansenula anomala

Differences in invertase accumulation of Hansenula anomala cultivated in ammonium and nitrate are reported. Media supplemented with sucrose and ammonium sulfateas the solecarbon and nitrogen source, respectively, show strong media acidification (pH 3.0 or lower), and vigorous cell growth. Invertase activity was not detected under such conditions. A cell-free imitation experiment suggests that, under such low pH, extensive chemical break-down of sucrose (>22%) occurs. Thus, H. anomala is able togrow under strong acidic conditions that permit sucrose metabolism by the uptake of monosaccharides generated from chemical hydrolysis. In addition, invertase activity is not present in cells grown in nitrate as nitrogen source at pH 5.0, but at pH 7.0 activity is detected. If ammonium is supplied instead of nitrate, cells grown at pH 5.0 show invertase activity and at pH 7.0 high levels of activity are detected. These results indicate a specific physiological response of the sucrose metabolism to the presence of alternate nitrogen source.     

REGULATION OF CHLOROPLAST DEVELOPMENT BY RED AND BLUE LIGHT

There are specific differences between red and blue light greening of etiolated seedlings of Hordevm vulgare L. Blue light results in a different prenyl lipid composition of chloroplast as compared to red light of equal quanta density. This is documented by a much higher prenylquinone content, higher chlorophyll a/b ratios, and lower values for the ratio xanthophylls to carotenes (x/c). The photosynthetic activity of “blue light” chloroplasts (Hill reaction) is higher than that of “red light” chloroplasts. These differences in prenylquinone composition and Hill-activity are associated with a different ultrastructure of chloroplasts. “Red light” chloroplasts exhibit a much higher grana content than “blue light” chloroplasts. The difference in thylakoid composition, photosynthetic activity and chloroplast structure found between blue and red light greening are similar to those found between sun and shade leaves and those between plants grown under high and low light intensities.     

Molecular characterization of a gene for aldose reductase (CbXYL1) from Candida boidinii and its expression in Saccharomyces cerevisiae

Candida boidinii produces significant amounts of xylitol from xylose, and assays of crude homogenates for aldose (xylose) reductase (XYL1p) have been reported to show relatively high activity with NADH as a cofactor even though XYL1p purified from this yeast does not have such activity. A gene coding for XYL1p from C. boidinii (CbXYL1) was isolated by amplifying the central region using primers to conserved domains and by genome walking. CbXYL1 has an open reading frame of 966 bp encoding 321 amino acids. The C. boidinii XYL1p is highly similar to other known yeast aldose reductases and is most closely related to the NAD(P)H-linked XYL1p of Kluyveromyces lactis. Cell homogenates from C. boidinii and recombinant Saccharomyces cerevisiae were tested for XYL1p activity to confirm the previously reported high ratio of NADH:NADPH linked activity. C. boidinii grown under fully aerobic conditions showed an NADH:NADPH activity ratio of 0.76, which was similar to that observed with the XYL1p from Pichia stipitis XYL1, but which is much lower than what was previously reported. Cells grown under low aeration showed an NADH:NADPH activity ratio of 2.13. Recombinant S. cerevisiae expressing CbXYL1 showed only NADH-linked activity in cell homogenates. Southern hybridization did not reveal additional bands. These results imply that a second, unrelated gene for XYL1p is present in C. boidinii.     

Effect of yeast extract on growth kinetics of Monascus purpureus

Growth kinetics and red pigment production of Monascus purpureus CCT 3802 was studied. A reproducible inoculum with extremely dispersed hyphae for bioreactor runs was obtained through a two-step cultivation in a shaker. First, the spores were cultivated in a complex medium rendering a suspension of vegetative cells. In the second step these cells were grown in a semisynthetic medium. Two types of media were employed in the bioreactor runs: a semisynthetic (glucose, salts, and yeast extract), and a synthetic, without yeast extract. The inclusion of yeast extract, caused an increase in cell yield on glucose (Y_s/s) as high as 40%. Also, yeast extract probably yielded a higher proportion of red pigment associated with the cell, relative to the synthetic medium. On the other hand, cells grown on the synthetic medium were slightly higher producers of red soluble pigments.     

REDOX DYES AS ARTIFICIAL PHOTORECEPTORS IN LIGHT-DEPENDENT CAROTENOID SYNTHESIS*

Abstract— The photodynamically active dyes methylene blue, toluidine blue, and neutral red act as artificial photoreceptors in light-dependent carotenoid synthesis in Fusarium aquaeductuum. Normally, carotenoid production is only induced by light of wavelengths shorter than 520 nm, but when mycelia are incubated with neutral red, methylene blue, and toluidine blue, red light is also effective in inducing carotenogenesis. Experiments with methylene blue and red light showed that pigments induced under these conditions are qualitatively the same as those induced with white light, and also that, in accord with the results found for photoinduction with white light, the amount of pigment synthesized was proportional to the logarithm of illumination time. In addition to their role in photoinduction, the dyes were also shown to interfere with the biosynthesis of carotenoids, whereas addition after irradiation caused an increase in pigment production that involves a quantitative change in the more unsaturated components.     

Effect of light/dark cycle on bacterial hydrogen production by Rhodobacter sphaeroides RV

Hydrogen production by photosynthetic bacteria provides an efficient energy conversion method under low light intensity. However, under strong illumination, such as midday sunlight, the efficiency drops. This prevents the method from being applied industrially. To overcome this problem, we examined a method to thin out the excessive illumination. Light was given intermittently to reduce the total energy flux. The on/off ratio was set at 1/1 throughout the study, so that the time average of the light energy flux became half the continuous illumination. By keeping the time-average light flux constant (0.6 kW·m⁻²), the effects of the cycle period were examined in the range of hours to seconds. The hydrogen production rate was greatly affected by the cycle period, but cell growth and substrate consumption rates remained almost constant. The 30-min light/dark cycle (30 min on and 30 min off) provided the highest rate of hydrogen production (22 L·m⁻²·24 h⁻¹). At the shorter cycles, the rate decreased except that there was a suboptimum at about 40 s. Under excessive light intensity (1.2 kW·m⁻²), the light-to-hydrogen conversion efficiency was greatly enhanced. The hydrogen production rate during the 30-min cycle was twice as high as during a 12-h cycle under the same conditions.     

PHYTOCHROME CONTROL OF ITS OWN SYNTHESIS IN Sorghum vulgare AND Avena sativa

The accumulation of phytochrome in the dark was measured for Avena sativa seedlings after a white light pretreatment and for Sorghum vulgare seedlings after continuous red or far-red light treatments, using the herbicide Norflurazon to prevent greening under continuous irradiation. In both cases the accumulation of phytochrome depends on the state of the phytochrome at the light-dark transition: high P_fr levels (red light pulse) led to a slower rate of phytochrome accumulation than lower P_fr levels (long wavelength far-red (RG 9) light pulse). Poly-(A⁺)-RNA was isolated fromA. sativa seedlings grown for 48 h in darkness + 24 h WL + light pulse (5 min) (red, RG 9 light, red followed by RG 9 light or RG 9 followed by red light pulse) + 19 h darkness. The poly-(A⁺)-RNA was translated in a rabbit reticulocyte lysate system and the translation products were immunoprecipitated by specific anti-phytochrome antibodies. It was demonstrated that the activity of mRNA coding for phytochrome was under phytochrome control.     

Nitrogen regulation of Saccharomyces cerevisiae invertase

The regulation of extracellular enzymes is of great biotechnological interest. We studied the regulatory role of the URE 2 gene on the periplasmic invertase of Saccharomyces cerevisiae, because its periplasmic asparaginase is regulated by the URE2/GLN3 system. Enzymatic activity was measured in the isogenic strains P40-1B, the ure2 mutant P40-3C, and the P40-3C strain transformed with the pIC-CS plasmid carrying the URE2 gene. The assays were performed using midlog and stationary phase cells and nitrogen-starved cells from these growth phases. During exponential growth, the level of invertase in both wild-type and ure 2 mutant cells was comparable. However, the invertase activity in ure2 mutant cells from stationary phase was sixfold lower than in the wild-type cells. When P40-3C cells were transformed with the pIC-CS plasmid, the wild-type phenotype was restored. On nitrogen starvation in the presence of sucrose, the invertase activity in wild-type cells from midlog phase decreased three times, whereas in stationary cells, the activity decreased eight times. However, invertase activity doubled in ure 2 mutant cells from both phases. When these cells were trans-formed with the aforementioned plasmid, the wild-type phenotype was restored, although a significant invertase decrease in stationary cells was not observed. These results suggested that the URE2 protein plays a role in invertase activity.     

Refractive index modulation in polymeric photochromic films

Photochromic properties of methylacrylate monomers and polymers containing azobenzene groups with heterocyclic sulfonamide functionalities viz sulfisomidyne (4-amino-N-[2,6-dimethylpyrimidyn-4-yl]benzenesulfonamide) and sulfamethoxazole (4-amino-N-[5-methylisoxazol-3-yl]benzenesulfonamide) substituents were investigated. On illumination with light the azobenzene group underwent trans-cis isomerisation, which was manifested by a drop in the absorbance of the maximum absorption peak at ca. 450 nm and by decrease in refractive index. Quantum chemical calculations showed significant differences in UV-VIS spectra, dipole moments, polarizability and refractive index between both cis and trans form of the chromophoric monomers. The illumination of spin-coated polymer films during ellipsometry measurements resulted in a change in refractive index within the range of 0.014 to 0.025. The dynamics of growth and decay of refractive index changes, was described by biexponential functions approach.     

SiO2/TiO2-xCx/C的制备、表征及其吸附和可见光催化性能

以SiO2为成核中心,钛酸四丁酯为钛源,分别以多羟基化合物乙二醇、丙三醇、葡萄糖和聚乙烯醇为联接剂,采用水解沉淀法制备了碳掺杂和包覆的多孔SiO2/TiO2-xCx/C可见光响应型光催化剂。采用X-射线衍射(XRD)、透射电子显微镜(TEM)、X-射线光电子能谱(XPS)、傅里叶变换-红外光谱(FTIR)、比表面积(BET)和紫外-可见(UV-Vis)漫反射光谱对样品进行表征。对不同结构样品的形成机理进行了分析。以次甲基蓝(MB)溶液为模拟废水,对样品的吸附性能和可见光催化性能进行了评价。结果表明,多羟基化合物对材料的结构和性能有重要影响。碳的掺杂和包覆使材料的吸收光谱包含了整个可见光区,而多孔结构使材料的吸附性能得到提高。以聚乙烯醇为原料所得样品吸附性能最好,30 min内吸附率达到70%;而以丙三醇为原料所得样品具有最好的可见光催化性能,40 min内次甲基蓝的降解率达到95%。