Regulation of Photosynthetic Induction State in High- and Low-Light-Grown Soybean and Alocasia macrorrhiza (L.) G. Don

Alocasia (Alocasia macrorrhiza [L.] G. Don) and soybean (Glycine max [L.]) were grown under high or low photon flux density (PFD) conditions to achieve a range of photosynthetic capacities and light-adaptation modes. The CO2 assimilation rate and in vivo linear electron transport rate (Jf) were determined over a range of PFDs and under saturating 1-s-duration lightflecks applied at a range of frequencies. At the same mean PFD, the assimilation rate and the Jf were lower under the lightfleck regimes than under constant light. The activation state of two, key enzymes of the photosynthetic carbon reduction cycle pathway, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose-1,6-bisphosphatase, and the photosynthetic induction states (ISs) were also found to be lower under flashing as compared to continuous PFD. Under all conditions, the IS measured 120 s after an increase in PFD to constant and saturating values was highly correlated with the Rubisco activation state and stomatal conductances established in the light regime before the increase. Both the fructose-1,6-bisphosphatase and Rubisco activities established in a particular light regime were highly correlated with the mean Jf in that regime. The relationships between enzyme activation state and Jf and between IS and enzyme activation state were similar in soybean and Alocasia and were not affected either by growth-light regime, and hence photosynthetic capacity, or by flashing versus constant PFD. The common relationship between the linear Jf and the activation state of key enzymes suggests that electron transport may be the determinant of the signal regulating IS, at least to the extent that the IS is controlled by the activation state of key stromal enzymes.     

The Magnitude and Duration of Itch Produced by Intracutaneous Injections of Histamine

The magnitude and duration of itch sensation produced by intracutaneous injection of histamine were determined for humans with the procedure of magnitude estimation scaling. Thirteen subjects received a 10-μ1 intracutaneous injection of histamine at doses of 0.0001, 0.001, 0.01, 0.1, 1, and 10 μg into the volar forearm; eight of these subjects also received a 100-μg dose. One subject received multiple injections over several weeks to determine the reliability of the magnitude estimates of itch. Following each injection, the area of flare and duration of itch were also determined.

Intracutaneous injection of histamine produced a pure sensation of itch, without pain. The magnitude of itch increased in a dose-dependent fashion. The lowest histamine dose that produced itch greater than the itch produced by vehicle was 0.01 μg. The greatest itch was produced by the 100-μg dose. A power function fitted to the mean magnitude estimates had an exponent of 0.17, indicating a negatively accelerating relation between the magnitude of itch and histamine dose. The one subject who received histamine over several weeks gave fairly reproducible estimates of itch magnitude.

The duration of itch and the area of flare also increased in a dose-dependent fashion. The lowest dose of histamine that produced a duration of itch longer than the itch produced by the vehicle was 0.1 μg, while the 100-μg dose produced the longest duration of itch. Although the area of flare increased with each increase in dose from 0.1 to 10 μg, the areas of flare produced by 10 and 100 μg of histamine did not differ.

These results indicate that humans can scale the magnitude of itch produced by histamine in a dose-dependent manner. In addition, the duration of itch and the area of flare produced by histamine are dose-dependent, confirming results of previous investigators. Intracutaneous histamine is easily quantifiable and may thus be a useful stimulus in neurophysiological studies of the peripheral neural mechanisms of itch.     

Intraphagosomal Measurement of the Magnitude and Duration of the Oxidative Burst

Generation of an oxidative burst within the phagosomes of neutrophils, dendritic cells and macrophages is an essential component of the innate immune system. To examine the kinetics of the oxidative burst in the macrophage phagosome, we developed two new assays using beads coated with oxidation-sensitive fluorochromes. These assays permitted quantification and temporal resolution of the oxidative burst within the phagosome. The macrophage phagosomal oxidative burst is short lived, with oxidation of bead-associated substrates reaching maximal activity within 30 min following phagocytosis. Additionally, the extent and rate of macrophage phagosomal substrate oxidation were subject to immunomodulation by activation with lipopolysaccharide and/or interferon-γ.     

Induction Phenomena of Photosynthetic Algae at Low Partial Pressures of Oxygen

The effect of a dark period at very low partial pressures ofoxygen (10^–4–10^–1mm. Hg) upon the subsequentphotosynthetic production of oxygen by Chlorella pyrenoidotawith saturating intensities of illumination has been investigated.With the lowest partial pressures of oxygen used the time courseof oxygen production separates into two phases; an initial burstfollowed by a subsequent rise to the final steady state. Theseparation of the two phases in time is greater the lower theconcentration of carbon dioxide and the longer the precedingdark period. The initial burst of oxygen as distinct from thesteady state production is not inhibited by 10^–3 M. iodoacetamide.In contrast with the ‘Hill’ reaction, as measuredafter addition of quinone, the initial burst of oxygen was inhibitedby p-chloromercuribenzoate 10^–4M.). Concentrations ofsodium fluoride and of 2:4-DNP which had no effect on the steadystate of photosynthesis shortened the half-time for attainmentof the steady state so removing or obscuring the initial burst.The effect with fluoride was observed only if added at the beginningof the preceding dark period. It is suggested that the initial oxygen burst results from reductiveamination and carboxylation of keto acids present at the beginningof illumination. Iodoacetamide is assumed to inhibit steadystate photosynthesis by preventing reduction of phosphoglycericacid (PGA) to triose and hence its regeneration. It is assumednot to inhibit reductive amination or carboxylation. With longdark periods the initial burst is separated in time from thefinal acceleration to a steady state; this phase appearing asa decreased rate of production of oxygen may be also due toinhibition by fermentation products or to their conversion toamino acid without change in oxidation-reduction. The separationin time is minimized if fluoride or 2:4-dinitro-phenol is addedat the beginning of the dark period; both probably prevent accumulationof pyruvic acid during fermentation limiting the initial reactionsto the reduction of PGA.     

适合于悬浮培养的枇杷愈伤组织诱导及状态调控

以枇杷不同品种和不同器官为外植体,通过对愈伤组织诱导率、诱导状态、熊果酸（UA）和齐墩果酸（OA）含量的综合考虑,筛选适合于悬浮培养的枇杷愈伤组织,并通过调整2,4-D、6-BA浓度,同时加入酸水解酪蛋白（CH）、谷氨酰胺（Gln）、KCl等物质对花丝愈伤组织状态进行调控。结果表明：枇杷‘早钟6号’幼胚诱导的愈伤组织最适用于枇杷悬浮培养,愈伤诱导率为83.70%,愈伤组织嫩黄、疏松、颗粒明显,UA、OA含量分别为6.90、2.34 mg/g dw。在MS中附加2,4-D 6.0 mg/L、6-BA 0.8 mg/L、CH 200 mg/L、KCl 500 mg/L,花丝诱导的坚硬愈伤出现细软、嫩黄的愈伤组织,但多次继代后水渍化,状态不佳。     

Utilization of Light for Nitrogen Fixation by a New Synechocystis Strain Is Extended by Its Low Photosynthetic Efficiency

Performance of photosynthesis and nitrogenase activity in a novel cyanobacterium, Synechocystis sp. strain BO 8402, isolated from Lake Constance, located at the northern fringe of the Alps in central Europe, and of a stable derivative, strain BO 9201, were examined. Strain BO 8402 is characterized by an extraordinarily high level of autofluorescence originating from paracrystalline phycobiliprotein-linker complexes located in inclusion bodies (W. Reuter, M. Westermann, S. Brass, A. Ernst, P. Böger, and W. Wehrmeyer, J. Bacteriol. 176:896-904, 1994). Energy transfer between paracrystalline phycobiliproteins and the photosystems is inefficient, resulting in a high oxygen compensation point and a decreased growth rate. The derivative strain BO 9201 exhibits hemidiscoidal phycobilisomes that support a high growth rate, even under low light intensities. Because of the differences in photosynthetic performance, anaerobic light-stimulated nitrogenase activity is maintained at higher light intensity in the original strain BO 8402 than in the derivative strain BO 9201. The results indicate that the formation of paracrystalline phycobiliproteins in Synechocystis sp. strain BO 8402 represents a hitherto-unknown means for a unicellular cyanobacterium to extend its capacity to fix nitrogen in the light.     

Modulation of Endothelial Inflammation by Low and High Magnitude Cyclic Stretch

Excessive mechanical ventilation exerts pathologic mechanical strain on lung vascular endothelium and promotes endothelial cell (EC) inflammatory activation; however, the specific mechanisms underlying EC inflammatory response caused by mechanical ventilation related cyclic stretch (CS) remain unclear. This study investigated the effects of chronic exposure to CS at physiologic (5%) and pathologic (18%) magnitude on pulmonary EC inflammatory status in control conditions and bacterial lipopolysacharide (LPS)-stimulated conditions. EC exposure to high or low CS magnitudes for 28–72 hrs had distinct effects on EC inflammatory activation. 18% CS increased surface expression of endothelial adhesion molecule ICAM1 and release of its soluble form (sICAM1) and inflammatory cytokine IL-8 by CS-stimulated pulmonary endothelial cells (EC). EC inflammatory activation was not observed in EC exposed to 5% CS. Chronic exposure to 18% CS, but not to 5% CS, augmented ICAM1 and IL-8 production and EC monolayer barrier disruption induced by LPS. 18% CS, but not 5% CS, stimulated expression of RhoA GTPase-specific guanine nucleotide exchange factor GEF-H1. GEF-H1 knockdown using gene-specific siRNA abolished 18% CS-induced ICAM1 expression and sICAM1 and IL-8 release by EC. GEF-H1 knockdown also prevented disruption of EC monolayer integrity and attenuated sICAM1 and IL-8 release in the two-hit model of EC barrier dysfunction caused by combined stimulation with 18% CS and LPS. These data demonstrate that exacerbation of inflammatory response by pulmonary endothelium exposed to excessive mechanical stretch is mediated by CS-induced induction of Rho activating protein GEF-H1.     

The Regulatory Properties of Rubisco Activase Differ among Species and Affect Photosynthetic Induction during Light Transitions

Rubisco’s catalytic chaperone, Rubisco activase (Rca), uses the energy from ATP hydrolysis to restore catalytic competence to Rubisco. In Arabidopsis (Arabidopsis thaliana), inhibition of Rca activity by ADP is fine tuned by redox regulation of the α-isoform. To elucidate the mechanism for Rca regulation in species containing only the redox-insensitive β-isoform, the response of activity to ADP was characterized for different Rca forms. When assayed in leaf extracts, Rubisco activation was significantly inhibited by physiological ratios of ADP to ATP in species containing both α-Rca and β-Rca (Arabidopsis and camelina [Camelina sativa]) or just the β-Rca (tobacco [Nicotiana tabacum]). However, Rca activity was insensitive to ADP inhibition in an Arabidopsis transformant, rwt43, which expresses only Arabidopsis β-Rca, although not in a transformant of Arabidopsis that expresses a tobacco-like β-Rca. ATP hydrolysis by recombinant Arabidopsis β-Rca was much less sensitive to inhibition by ADP than recombinant tobacco β-Rca. Mutation of 17 amino acids in the tobacco β-Rca to the corresponding Arabidopsis residues reduced ADP sensitivity. In planta, Rubisco deactivated at low irradiance except in the Arabidopsis rwt43 transformant containing an ADP-insensitive Rca. Induction of CO₂ assimilation after transition from low to high irradiance was much more rapid in the rwt43 transformant compared with plants containing ADP-sensitive Rca forms. The faster rate of photosynthetic induction and a greater enhancement of growth under a fluctuating light regime by the rwt43 transformant compared with wild-type Arabidopsis suggests that manipulation of Rca regulation might provide a strategy for enhancing photosynthetic performance in certain variable light environments.The activity of Rubisco, the enzyme that catalyzes CO₂ assimilation in photosynthesis, is regulated by Rubisco activase (Rca), a specific catalytic chaperone (Spreitzer and Salvucci, 2002; Portis, 2003). Like other AAA+ ATPases (Snider et al., 2008), Rca uses the energy from ATP hydrolysis to remodel the conformation of its target protein, Rubisco. The conformational changes induced by Rca restore catalytic competence to Rubisco active sites that have been inactivated by the unproductive binding of sugar phosphates, including the substrate ribulose 1,5-bisphosphate (RuBP; Wang and Portis, 1992). Because of the requirement for ATP hydrolysis and the inhibition of activity by ADP (Robinson and Portis, 1988, 1989), Rca adjusts the rate of CO₂ fixation to the rates of electron transport activity via changes in the activation state of Rubisco (Salvucci et al., 1985). As a result of this coordinate regulation, the light response of Rubisco activation closely resembles the light response of CO₂ assimilation, and the levels of RuBP under steady-state conditions are relatively constant over a wide range of irradiance levels (Perchorowicz et al., 1981; Dietz and Heber, 1984).Many plant species express two isoforms of Rca, α and β, that are both active in ATP hydrolysis and Rubisco activation (Shen et al., 1991; Salvucci et al., 2003). In some plant species, these isoforms are the products of an alternative splicing event that generates two polypeptides, which are identical except for a 20- to 30-amino acid extension at the C terminus of the longer α-isoform (Werneke et al., 1989). In cotton (Gossypium hirsutum), soybean (Glycine max), and presumably other plant species, separate genes encode the two isoforms of Rca (Salvucci et al., 2003; Yin et al., 2010). In these species, the amino acid sequences of the overlapping regions of the α- and β-polypeptides are very similar, and the C-terminal extension of the longer α-isoform is similar to the extension produced by alternative splicing (Supplemental Fig. S1).Our current understanding of the role of the two Rca isoforms is based primarily on investigations with Arabidopsis (Arabidopsis thaliana; Zhang and Portis, 1999; Zhang et al., 2001; Wang and Portis, 2006). The C-terminal extension of the α-Rca contains two redox-regulated Cys residues that are modulated by thioredoxin f (Zhang and Portis, 1999). When these residues are oxidized to a disulfide, the affinity for ATP decreases and enzyme activity is more sensitive to inhibition by ADP. Physiological ratios of ADP to ATP significantly inhibit the activity of the Arabidopsis α-Rca when in the oxidized state, but inhibition is much less when this isoform has been reduced by thioredoxin. In contrast, the shorter Arabidopsis β-Rca is not redox regulated and is less sensitive to inhibition by ADP (Zhang and Portis, 1999). Mixing experiments with recombinant Rca have shown that the properties of α-Rca are conferred to the heterooligomer, providing a mechanism for redox regulating the Rca holoenzyme (Zhang et al., 2001). In this way, Rca is similar to the chloroplastic glyceraldehyde 3-P dehydrogenase (GAPDH), which also has both redox-regulated (GAP-B) and non-redox-regulated (GAP-A) forms that differ by a C-terminal extension (Baalmann et al., 1996). Like Rca (Zhang and Portis, 1999; Zhang et al., 2001), redox regulation of two Cys residues in the extension exerts master control over the mixed GAPDH oligomer.Some plant species, including members of the Solanaceae family, as well as maize (Zea mays) and green algae, express only the shorter β-Rca (Salvucci et al., 1987). The β-Rca in these species is not responsive to redox regulation, even though the activation state of Rubisco in these plants is modulated by irradiance (Salvucci and Anderson, 1987) and seems to be associated with the redox status of the chloroplast (Ruuska et al., 2000). With GAPDH, all higher plants appear to have both chloroplastic isoforms, but the non-redox-sensitive form, Gap-A, can be regulated indirectly by thioredoxin through the binding of the small chloroplast protein CP12 (Trost et al., 2006). By analogy, a similar association with CP12 or a CP12-like protein could provide a means of conferring redox sensitivity to β-Rca in species that have only this Rca isoform. However, no association of Rca was observed when the native CP12 complex and other high-molecular-mass species were isolated from tobacco (Nicotiana tabacum) chloroplasts (Carmo-Silva et al., 2011b).In this study, the regulation of β-Rca activity was examined both in vivo and in vitro in plant species that contain only one (i.e. β-) or both (α- and β-) Rca isoforms. The response of enzyme activity to physiological ratios of ADP to ATP was measured for the native Rca in leaf extracts, as well as for recombinant Arabidopsis and tobacco enzymes, to determine the sensitivity of β-Rca to ADP in different species. In addition, experiments were conducted with transgenic Arabidopsis plants containing variants of β-Rca to determine the link between Rca regulation and photosynthetic induction. The results suggest a new strategy for enhancing photosynthetic performance under variable light environments based on altering the regulatory properties of Rca to increase the rate of photosynthetic induction.     

Carotenoids and Reaction Center II-D1 Protein in Light Regulation of the Photosynthetic Apparatus in Aphanocapsa*

A new cyanobacterial isolate, morphologically closely resembling Aphanocapsa, was characterized for its growth requirements, as well as pigmentation, photosynthetic activity and dynamics of the D1 protein in the reaction center (RC) of photosystem II (PSII). It was shown to be able to grow on glucose in the dark in the presence of DCMU. The cyanobacterium turned light yellow at high light intensity in the absence, and dark emerald green in high light in the presence of sublethal concentrations of the DCMU-type inhibitor atrazine. While total carotenoids per cell slightly decreased with increasing light intensity during growth, the cells still turned pale yellow due to decreased levels of chlorophyll and phycocyanin. In contrast to β-carotene, zeaxanthin and echinenone which decreased with increasing light intensity during growth, the carotenoid glycoside, myxoxanthophyll, continuously increased in concentration. Extremely high rates of light-saturated O₂ evolution were recorded for the high light cultures after a 0.5 h recovery period in the dark. The recovery measured after 2.5 h was shown to be less effective in darkness than in dim light and was prohibited by chloramphenicol. The degree of recovery was dependent on the light intensity during growth. A fast light intensity-dependent RC II-D1 protein turnover was found for the bleached yellow cells rich in myxoxanthophyll. The half-life of the RC II-D1 protein, plotted against the light intensity during growth and experimentation, yielded a curve the slope of which was considerably steeper for Aphanocapsa than for Anacystis. Apparently, the isolated strain of Aphanocapsa reacts more vigorously to changes in the environment than other strains tested and may, therefore, turn out to be a suitable organism in the attempt to elucidate the molecular mechanism of light intensity adaptation.     

Accumulation of Phenylpropanoids in the Cotyledons of Morning Glory (Pharbitis nil) Seedlings during the Induction of Flowering by Low Temperature Treatment, and the Effect of Precedent Exposure to High-Intensity Light

Extracts from the cotyledons of seedlings of Pharbitis nil strain‘Violet’ cultured at low temperature, which inducestheir flowering even in continuous light, with or without precedentexposure to high-intensity light, which shortens the periodof low temperature required for flowering, were analyzed byHPLC for substances correlating with the flower-inducing process.The content of two phenylpropanoids were found to increase duringthe low-temperature, and were identified as 3-O-feruloylquinicacid and dehydrodiconiferyl alcohol-13-O-ß-D-glucoside.The increase was more rapid in the cotyledons exposed to high-intensitylight before the low-temperature. This suggests that the accumulationof these compounds is correlated to the promotive effect ofhigh-intensity light on the flower-induction by low temperature. (Received March 7, 1994; Accepted April 2, 1994)     

Acclimation of Photosynthetic Light Reactions during Induction of Inorganic Carbon Accumulation in the Green Alga Chlamydomonas reinhardtii

Cells of the unicellular green algae Chlamydomonas reinhardtii were grown in high dissolved inorganic carbon (DIC) concentrations (supplied with 50 milliliters per liter CO₂[g]) and transferred to low DIC concentrations (supplied with ≤ 100 microliters per liter CO₂[g]). Immediately after transfer from high to low DIC the emission of photosystem II related chlorophyll a fluorescence was substantially quenched. It is hypothesized that the suddenly induced inorganic carbon limitation of photosynthesis resulted in a phosphorylation of LHCII, leading to the subsequent state 1 to state 2 transition. After 2 hours of low-DIC acclimation, 77 K fluorescence measurements revealed an increase in the fluorescence emitted from photosystem I, due to direct excitation, suggesting a change in photosystem II/photosystem I stoichiometry or an increased light harvesting capacity of photosystem I. After 5 to 6 hours of acclimation a considerable increase in spillover from photosystem II to photosystem I was observed. These adjustments of the photosynthetic light reactions reached steady-state after about 12 hours of low DIC treatment. The quencher of fluorescence could be removed by 5 minutes of dark treatment followed by 5 minutes of weak light treatment, of any of four different light qualities. It is hypothesized that this restoration of fluorescence was due to a state 2 to state 1 transition in low-DIC acclimated cells. A decreased ratio of violaxanthin to zeaxanthin was also observed in 12 hour low DIC treated cells, compared with high DIC grown cells. This ratio was not coupled to the level of fluorescence quenching. The role of different processes during the induction of a DIC accumulating mechanism is discussed.     

Calcium in the Regulation of Gravitropism by Light

The red light requirement for positive gravitropism in roots of corn (Zea mays cv “Merit”) provides an entry for examining the participation of calcium in gravitropism. Applications of calcium chelators inhibit the light response. Calcium channel blockers (verapamil, lanthanum) can also inhibit the light response, and a calcium ionophore, A23187, can substitute for light. One can substitute for red light by treatments which have elsewhere been shown to trigger Ca²⁺ influx into the cytosol, e.g. heat or cold shock. Agents which are known to be agonists of the phosphatidylinositol second messenger system (serotonin, 2,4-dichlorophenoxyacetic acid, deoxycholate) can each partially substitute for the red light, and Li⁺ can inhibit the light effect. These experiments suggest that the induction of positive gravitropism by red light involves a rise in cytoplasmic Ca²⁺ concentration, and that a contribution to this end may be made by the phosphatidylinositol second messenger system.     

Induction of the Viable but Nonculturable State of Ralstonia solanacearum by Low Temperature in the Soil Microcosm and Its Resuscitation by Catalase

Ralstonia solanacearum is the causal agent of bacterial wilt on a wide variety of plants, and enters a viable but nonculturable (VBNC) state under stress conditions in soil and water. Here, we adopted an artificial soil microcosm (ASM) to investigate the VBNC state of R. solanacearum induced by low temperature. The culturability of R. solanacearum strains SL341 and GMI1000 rapidly decreased at 4°C in modified ASM (mASM), while it was stably maintained at 25°C in mASM. We hypothesized that bacterial cells at 4°C in mASM are viable but nonculturable. Total protein profiles of SL341 cells at 4°C in mASM did not differ from those of SL341 culturable cells at 25°C in mASM. Moreover, the VBNC cells maintained in the mASM retained respiration activity. Catalase treatment effectively restored the culturability of nonculturable cells in mASM, while temperature increase or other treatments used for resuscitation of other bacteria were not effective. The resuscitated R. solanacearum from VBNC state displayed normal level of bacterial virulence on tomato plants compared with its original culturable bacteria. Expression of omp, oxyR, rpoS, dps, and the 16S rRNA gene quantified by RT-qPCR did not differ significantly between the culturable and VBNC states of R. solanacearum. Our results suggested that the VBNC bacterial cells in mASM induced by low temperature exist in a physiologically unique state.     

低温弱光对辣椒幼苗光合特性与光合作用启动时间的影响

以辣椒(Capsicum annuumL.)幼苗为试材,研究了偏低温弱光(19℃/12℃昼/夜,90μmol?m-2?s-1)和临界低温弱光(15℃/8℃昼/夜,90μmol?m-2?s-1)胁迫10 d后的光合特性与光合作用启动时间的变化.结果表明:无论是在偏低温弱光还是在临界低温弱光下,辣椒幼苗的光补偿点(LCP)、光饱和点(LSP)、光饱和时的光合速率(Amax)和表观量子产额(AOY)下降;CO2补偿点(CCP)升高,而CO2饱和点(CSP)、CO2饱和时的光合速率(Amax)以及羧化效率(CE)下降;温度补偿点(TCP)降低;光合作用启动时间(STP)延长.在偏低温弱光下,辣椒幼苗有着更高的光与CO2利用能力和利用效率,光合作用启动时间较短,但温度补偿点较高.     

低磷和高照度光下两种不同磷效率玉米幼苗的几种光合参数变化

以完全培养液（HP,1000μmol·L^-1KH2PO4）培养15d的玉米自交系KH5（磷高效）和SD502（磷低效）幼苗转入低磷（LP,5μmol·L^-1KH2PO4）条件下培养20d后,检测叶中几种与光合作用有关参数的结果表明,低磷下两自交系玉米叶中无机磷含量、植株生物量和叶片的净光合速率（Pn）均下降,KH5的降幅小于SD502。两自交系玉米叶片以高照度光（1600μmol·m^-2·s^-1）照射1h后,叶片的PSII实际光化学效率（ФPSII）、PSII最大光化学效率（Fv/Fm）和表观光合电子传递速率（ETR）均下降,而初始荧光（F0）、非光化学猝灭（NPQ）和天线热耗散（HDR）均升高。在强光胁迫过程中,玉米幼苗叶片发生光抑制,自交系SD502在低磷下的光抑制比KH5严重。     

Enhancing Tetrazolium-Based Histochemical Stains by Exposure to Light

In the histochemical determination of glucose-6-phosphate dehydrogenase, with nitro blue tetrazolium used as the electron receptor, cold neutral formalin-fixed or fresh-frozen microtome sections were incubated for 1 hr at 37 C in the appropriate substrate. Following a brief formalin fixation of frozen sections, mounting on slides, and application of a cover glass with 50% glycerol, the sections were exposed to the light from a mercury-quartz lamp at a distance of 10 cm for 30 min. The pale pattern of the reaction product seen immediately after mounting was decidedly intensified and was more easily interpreted after irradiation. Tetrazolium itself was not affected by irradiation. The method was tested on bond paper models, on frozen-sectioned brain tissue, and on substrate-perfused inner-ear structures in temporal bones of guinea pigs.     

The Sensitivity of Light Modulation of Enzyme Activity to Arsenite and Sulphite and of Photosynthetic Induction toArsenite is Determined by a Cytoplasmic Gene

Muschinek, G., Alscher, R. and Anderson, L. E. 1987. The sensitivityof light modulation of enzyme activity to arsenite and sulphiteand of photosynthetic induction to arsenite is determined bya cytoplasmic gene—J. exp. Bot. 38: 1069–1075. The membrane component of the light modulation system was moresensitive to arsenite and to sulphite in the Pisum cultivar‘Nugget’ than in the cultivar ‘Progress No.9’. Likewise, the induction phase of CO₂ fixation wasmore arsenite sensitive in chloroplasts isolated from ‘Nugget’plants. Sensitivity was controlled by a cytoplasmic gene. Key words: Induction, light modulation, arsenite sensitivity     

Photoabatement by Anthocyanin Shields Photosynthetic Systems from Light Stress

Leaves and other chlorophyllous tissues of plants often show transient or permanent anthocyanin coloration. The question of whether anthocyanins can function as effective light screens to modulate photosynthesis in plants was addressed by comparing photosynthetic responses in reddish-purple pods with those in green pods of the ornamental leguminous tree Bauhinia variegata. For these comparisons the actinic radiation employed was either red radiation (RR) which was poorly absorbed by anthocyanin or blue-green radiation (BGR) which was strongly absorbed by anthocyanin. Photon yields of photosystem 2 (PS2) photochemistry and photochemical chlorophyll fluorescence quenching coefficients (q_p), measured over a range of photon flux densities (PFD) up to 1200 μmol m^-2 s^-1 at 23 °C and at five temperatures from 8 to 28 °C at a PFD of 260 μmol m^-2 s^-1, were almost identical in green pods irradiated with either RR or BGR and in purple pods irradiated with RR. However, q_p values remained much higher in purple pods irradiated with BGR, e.g., 0.80 in BGR versus 0.29 in RR at a PFD of 1200 μmol m-2 s^-1 at 23 °C, and 0.67 in BGR versus 0.28 in RR at a PFD of 260 μmol m^-2 s-1 at 8 °C. The higher values of q_p in BGR compared to RR indicated that photoabatement by anthocyanin allowed the first stable acceptor of PS2, Q_A, to be kept in a more oxidized state, thus decreasing the likelihood of photoinhibition. This was confirmed by demonstrating a lower susceptibility to photoinhibition in purple pods than in green pods in the sunlight, either naturally in pods on trees or in detached pods exposed to photoinhibitory conditions. We conclude that photoabatement by anthocyanin is a mechanism for allowing maintenance of higher oxidative levels of PS2 acceptor during episodes of high radiation stress, thereby minimizing photodamage to photosynthetic tissues. This revised version was published online in June 2006 with corrections to the Cover Date.     

氯化胆碱对低温弱光下黄瓜幼苗叶片细胞膜和光合机构的保护作用

1.07mmol／L氯化胆碱处理降低了低温弱光（6℃．PFD100μmol m^-2s^-1）下黄瓜幼苗叶片膜脂组分中主要是磷脂酰甘油（PG）的饱和脂肪酸含量,增加了膜脂不饱和度：减缓了膜透性的下降、MDA的产生速率、叶绿素的降解及PSII最大量子效率（Fv/Fm）、捕光效率（Fv＇／Fm＇）、光化学猝灭系数（qp）、实际光化学效率（ФPSII）和抗氧化酶POD、APX及CAT活性的下降;提高了非光化学猝灭系数（NPQ）和脯氨酸的含量。以上结果表明氯化胆碱处理保护了低温弱光对黄瓜叶片细胞膜和光合机构的伤害。