Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO₂ under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO₂.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO₂ at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO₂-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO₂was due to superoxide radicals (O₂^–). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO₂-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D₂O. These results suggest thatlipid peroxidation in SO₂-fumigated leaves was due to singletoxygen ¹O₂ produced from O_2^–. (Received May 15, 1980; )     

Effects of 2-month ozone exposure in spinach leaves on photosynthesis,antioxidant systems and lipid peroxidation

The photosynthesis response, antioxidant systems and lipid peroxidation were studied in leaves from spinach plants (Spinacia oleracea L.) in response to ozone fumigation, ambient air and charcoal filtered air treatments. The photosynthetic activity was tested through gas exchange and chlorophyll a fluorescence measurements. Ambient air and ozone fumigation caused a decrease in the photosynthetic rate (25% and 63%, respectively) mainly due to a reduced mesophyll activity, as evidenced by the increased intercellular CO₂ concentration. These data agree with a large reduction in the non-cyclic electron flow (7% and 16%), a lower capacity to reduce the quinone pool and a higher development of non-photochemical quenching upon high O₃ concentration. The results suggest that the oxidative stress produced, together with the stimulation of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11) activities and the increase in lipid peroxidation (20% and 36%, respectively), generated an alteration of the membrane properties.     

Profiles of light absorption and chlorophyll within spinach leaves from chlorophyll fluorescence

Chlorophyll fluorescence was used to estimate profiles of absorbed light within chlorophyll solutions and leaves. For chlorophyll solutions, the intensity of the emitted fluorescence declined in a log–linear manner with the distance from the irradiated surface as predicted by Beer's law. The amount of fluorescence was proportional to chlorophyll concentration for chlorophyll solutions given epi‐illumination on a microscope slide. These relationships appeared to hold for more optically complex spinach leaves. The profile of chlorophyll fluorescence emitted by leaf cross sections given epi‐illumination corresponded to chlorophyll content measured in extracts of leaf paradermal sections. Thus epifluorescence was used to estimate relative chlorophyll content through leaf tissues. Fluorescence profiles across leaves depended on wavelength and orientation, reaching a peak at 50–70 µm depth. By infiltrating leaves with water, the pathlengthening due to scattering at the airspace : cell wall interfaces was calculated. Surprisingly, the palisade and spongy mesophyll had similar values for pathlengthening with the value being greatest for green light (550 > 650 > 450 nm). By combining fluorescence profiles with chlorophyll distribution across the leaf, the profile of the apparent extinction coefficient was calculated. The light profiles within spinach leaves could be well approximated by an apparent extinction coefficient and the Beer–Lambert/Bouguer laws. Light was absorbed at greater depths than predicted from fibre optic measurements, with 50% of blue and green light reaching 125 and 240 µm deep, respectively.     

Correlation between chlorophyll fluorescence and photoacoustic signal transients in spinach leaves

Chlorophyll fluorescence and photoacoustic transients from dark adapted spinach leaves were measured and analyzed using the saturating pulse technique. Except for the first 30 s of photosynthetic induction, a good correlation was found between photoacoustically detected oxygen evolution at 35 Hz modulation frequency and electron flow calculated from the fluorescence quenching coefficients q_P and q_N. The induction kinetics of the photothermal signal, i.e., the photoacoustic signal at 370 Hz, reveal a fast (t _r <10 ms) and a slow (t _r 1 s) rise component. The fast component is suggested to be composed of the minimal thermal losses in photosynthesis and thermal losses from non-photosynthetic processes. The slow phase is attributed to variable thermal losses in photosynthesis. The variable thermal losses were normalized by measuring the minimal photothermal signal (H₀) in the dark-adapted state and the maximal photothermal signal (H_m) during a saturating light pulse. The kinetics of the normalized photochemical loss (H-H₀)/(H_m-H₀) obtained from high-frequency PA measurements were found to correlate with the kinetics of oxygen evolution measured at low frequency.Abbreviations F_m maximum fluorescence - F₀ initial fluorescence - F_v variable fluorescence - H photothermal signal - I in-phase - LED light emitting diode - PA photoacoustic - PL photochemical loss - Q quadrature - q_N non-photochemical quenching - q_P photochemical quenching - VCLS voltage controlled light source     

Subcellular distribution of 35S-sulfur in spinach leaves after application of 35SO 4 2- , 35SO 3 2- , and 35SO2

³⁵SO₂, ³⁵SO ₃ ^2- , and ³⁵SO ₄ ^2- , respectively, were applied to leaves of Spinacia oleracea L. for 60 min in the light. Thereafter, the specific activity was determined in the organelles separated by means of sucrose density gradient centrifugation. In mitochondria and peroxisomes, the specific activity was equally distributed in their protein moieties. After application of ³⁵SO₂ or ³⁵SO ₃ ^2- , the chloroplast lamellae are characterized by elevated specific activity, which is not found after application of ³⁵SO ₄ ^2- . Chloroplast stroma shows a low specific incorporation rate after application of either compound, which may be due to the low turnover rate of Fraction I protein.     

Photosynthetic rate,chlorophyll fluorescence parameters,and lipid peroxidation of maize leaves as affected by zinc deficiency

Pot trial in greenhouse was conducted using cumulic cinnamon soil from North China to study the effects of zinc deficiency on CO₂ exchange, chlorophyll fluorescence, the intensity of lipid peroxidation, and the activity of superoxide dismutase (SOD) in leaves of maize seedlings. Zn deficiency resulted in a reduction of net photosynthetic rate and stomatal conductance to H₂O. The maximum quantum efficiency of photosystem 2 (PS2) and the PS2 activity were depressed, while the pool size of the plastoquinone molecules was not affected by Zn deficiency. The content of super oxygen anion radical (O₂ ^·−) and the intensity of lipid peroxidation as assessed by malonyldialdehyde content in Zn-deficient leaves were higher than those in Zn-sufficient leaves. The activity of SOD increased with Zn application. The adverse influence of Zn-deficiency on the light stage of photosynthesis is probably one of possible reasons for the limitation of photosynthetic capacity in maize leaves.     

Polyamines inhibit lipid peroxidation in senescing oat leaves

Exogenous diaminopropane, spermidine, spermine and guazatine, an inhibitor of polyamine oxidase (EC 1.5.3.3) activity, were able to inhibit loss of chlorophyll and reduce the level of malondialdehyde in dark-incubated Avena sativa L. cv. Victory leaves, as well as in leaves subjected to osmotica used for protoplast isolation. Both lipoxygenase (EC 1.13.11.12) activity and enzyme-protein levels were reduced by incubation with spermine. The results provide support for the contention that the inhibition of lipid peroxidation by polyamines may be one of the mechanisms responsible for their anti-senescence effects.     

Specific inhibition of photosystem II activity in chloroplasts by fumigation of spinach leaves with SO2

The phytotoxic effects of sulfur dioxide (SO₂) were investigatedby fumigating spinach plants with SO₂. Inhibition of 2,6-dichloroindophenol(DCIP) photoreduction was observed in spinach chloroplasts isolatedfrom fumigated leaves. NADP and DCIP photoreductions were inhibitedto a similar extent by fumigation with 2.0 ppm SO₂ but electronflow from reduced DCIP to NADP was not affected. When electronflow from H₂O to NADP was inhibited by 36%, a 39% inhibitionof non-cyclic photophosphorylation was observed. However, phenazinemethosulfate(PMS)-catalyzed cyclic photophosphorylation wasas active as in the control chloroplasts. Moreover, in the presenceof PMS, no significant suppression was observed in the extentof light-induced H⁺ uptake or in the rate of H⁺ efflux in chloroplasts.From these results, it can be concluded that SO₂ inhibits theelectron flow driven by photosystem II when plants have beenfumigated with SO₂. In spinach leaves fumigated with SO₂, the rate of photosyntheticO₂ evolution was reduced under light-limited conditions, whilethe rate of respiratory O₂ uptake changed slightly. (Received February 8, 1979; )     

沈阳市区大气SO2污染程度的叶绿素含量监测分析

沈阳市区大气ＳＯ２污染程度的叶绿素含量监测分析周兴文（沈阳大学师范学院生物系,沈阳１１００１５）ＴｈｅｃｈｌｏｒｏｐｈｙｌｃｏｎｔｅｎｔｍｏｎｉｔｏｒｉｎｇａｎａｌｙｓｉｓｏｆｔｒｅｌｅａｖｅｓｆｏｒＳＯ２ｐｏｌｕｔｉｏｎｉｎＳｈｅｎｙａｎｇＣｉｔｙ...     

Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profiles

Profiles of chlorophyll fluorescence were measured in spinach leaves irradiated with monochromatic light. The characteristics of the profiles within the mesophyll were determined by the optical properties of the leaf tissue and the spectral quality of the actinic light. When leaves were infiltrated with 10^?4M DCMU [3‐(3,4‐dichlorophenyl)‐1, 1‐dimethyl‐urea] or water, treatments that minimized light scattering, irradiation with 2000 μmol m^?2 s^?1 green light produced broad Gaussian‐shaped fluorescence profiles that spanned most of the mesophyll. Profiles for chlorophyll fluorescence in the red (680 ± 16 nm) and far red (λ > 710 nm) were similar except that there was elevated red fluorescence near the adaxial leaf surface relative to far red fluorescence. Fluorescence profiles were narrower in non‐infiltrated leaf samples where light scattering increased the light gradient. The fluorescence profile was broader when the leaf was irradiated on its adaxial versus abaxial surface due to the contrasting optical properties of the palisade and spongy mesophyll. Irradiation with blue, red and green monochromatic light produced profiles that peaked 50, 100 and 150 μm, respectively, beneath the irradiated surface. These results are consistent with previous measurements of the light gradient in spinach and they agree qualitatively with measurements of carbon fixation under monochromatic blue, red and green light. These results suggest that chlorophyll fluorescence profiles may be used to estimate the distribution of quanta that are absorbed within the leaf for photosynthesis.     

镍对水稻离体叶片脂质过氧化作用的影响

杂交水稻离体叶片用１０－３ｍｏｌ／ＬＮｉＳＯ４处理后,镍阻抑了叶片在衰老过程中ＳＯＤ、ＣＡＴ酶活性的下降和ＡｓＡ氧化酶活性的上升,ＡｓＡ和叶绿素含量的下降得到延缓,减少了膜脂过氧化程度。     

Light scattering,chlorophyll fluorescence and state of the adenylate system in illuminated spinach leaves

Scattering of green light and chlorophyll fluorescence by spinach leaves kept in a stream of air or nitrogen were compared with leaf adenylate levels during illumination with blue, red or far-red light. Energy charge and ATP-ADP ratios exhibited considerable variability in different leaves both in the dark and in the light. Variability is explained by different possible states of the reaction oxidizing triose phosphate or reducing 3-phosphoglycerate. Except when oxygen levels were low, there was an inverse relationship between light scattering and chlorophyll fluorescence during illumination with blue or red light. When CO₂ was added to a stream of CO₂-free air, chlorophyll fluorescence increased, sometimes after a transient decrease, and both light scattering and leaf $\text{ATP}\text{ADP}$ ratios decreased. Similar observations were made when air was replaced by nitrogen under blue or high-intensity red light. Under these conditions, over-reduction caused inhibition of electron transport and phosphorylation in chloroplasts. However, when air was replaced by nitrogen during illumination with low-intensity red light or far-red light, light scattering increased instead of decreasing. Under these light conditions, $\text{ATP}\text{ADP}$ ratios were maintained in the light. They decreased drastically only after darkening. Although $\text{ATP}\text{ADP}$ ratios responded faster than light scattering or the slow secondary decline of chlorophyll fluorescence due to illumination, it appeared that in the steady state, light scattering and chlorophyll fluorescence are useful indicators of the phosphorylation state of the leaf adenylate system at least under aerobic conditions, when chloroplast and extrachloroplast adenylate systems can effectively communicate.     

Radiation-induced lipid peroxidation: influence of oxygen concentration and membrane lipid composition

Radiation-induced lipid peroxidation in phospholipid liposomes was investigated in terms of its dependence on lipid composition and oxygen concentration. Non-peroxidizable lipid incorporated in the liposomes reduced the rate of peroxidation of the peroxidizable phospholipid acyl chains, possibly by restricting the length of chain reactions. The latter effect is believed to be caused by interference of the non-peroxidizable lipids in the bilayer. At low oxygen concentration lipid peroxidation was reduced. The cause of this limited peroxidation may be a reduced number of radical initiation reactions possibly involving oxygen-derived superoxide radicals. Killing of proliferating mammalian cells, irradiated at oxygen concentrations ranging from 0 to 100 per cent, appeared to be independent of the concentration of peroxidizable phospholipids in the cell membranes. This indicates that lipid peroxidation is not the determining process in radiation-induced reproductive cell death.     

Effect of lead on the lipid metabolism in spinach leaves and thylakoid membranes

The effects of lead and sodium acetate treatment on the lipid composition of leaves, thylakoid membranes and cell debris of spinach were investigated. The concentration of lead in leaves and cell debris was higher than that in thylakoid membranes, probably due to a protection of photosynthetic apparatus. The lead treatment lead to decrease of contents of monogalactosyl diacylglycerols and phospholipids and to increase of the other glycolipids in the thylakoid membranes. There were no statistically significant differences between the total lipids of thylakoid membranes after incubation with lead and sodium acetate, which was an indication that in this case the effect of metal ion was not specific.     

Phospholipase A2, reactive oxygen species, and lipid peroxidation in cerebral ischemia

Ischemic stroke is caused by obstruction of blood flow to the brain, resulting in energy failure that initiates a complex series of metabolic events, ultimately causing neuronal death. One such critical metabolic event is the activation of phospholipase A2 (PLA2), resulting in hydrolysis of membrane phospholipids and release of free fatty acids including arachidonic acid, a metabolic precursor for important cell-signaling eicosanoids. PLA2 enzymes have been classified as calcium-dependent cytosolic (cPLA2) and secretory (sPLA2) and calcium-independent (iPLA2) forms. Cardiolipin hydrolysis by mitochondrial sPLA2 disrupts the mitochondrial respiratory chain and increases production of reactive oxygen species (ROS). Oxidative metabolism of arachidonic acid also generates ROS. These two processes contribute to formation of lipid peroxides, which degrade to reactive aldehyde products (malondialdehyde, 4-hydroxynonenal, and acrolein) that covalently bind to proteins/nucleic acids, altering their function and causing cellular damage. Activation of PLA2 in cerebral ischemia has been shown while other studies have separately demonstrated increased lipid peroxidation. To the best of our knowledge no study has directly shown the role of PLA2 in lipid peroxidation in cerebral ischemia. To date, there are very limited data on PLA2 protein by Western blotting after cerebral ischemia, though some immunohistochemical studies (for cPLA2 and sPLA2) have been reported. Dissecting the contribution of PLA2 to lipid peroxidation in cerebral ischemia is challenging due to multiple forms of PLA2, cardiolipin hydrolysis, diverse sources of ROS arising from arachidonic acid metabolism, catecholamine autoxidation, xanthine oxidase activity, mitochondrial dysfunction, activated neutrophils coupled with NADPH oxidase activity, and lack of specific inhibitors. Although increased activity and expression of various PLA2 isoforms have been demonstrated in stroke, more studies are needed to clarify the cellular origin and localization of these isoforms in the brain, their responses in cerebral ischemic injury, and their role in oxidative stress.     

Different responses of young and expanded lettuce leaves to fungicide Mancozeb: chlorophyll fluorescence,lipid peroxidation,pigments and proline content

This work aimed to study the effects of commercial doses of the fungicide, Mancozeb, on the photosynthetic apparatus of lettuce young leaves (YL) and expanded leaves (EL). Seven days after Mancozeb application, chlorophyll a fluorescence, pigment contents, lipid peroxidation, and proline content were evaluated. Independently of leaf age, Mancozeb treatment reduced the efficiency of photosystem II photochemistry, increased the nonphotochemical quenching and proline content, decreased pigment contents, and induced lipid peroxidation. Moreover, EL showed a more stable photosynthetic apparatus, less prone to oxidative damages compared with YL. The parameters measured proved to be good markers for the rapid and preliminary diagnosis of fungicide toxicity.     

The role of iron in oxygen radical mediated lipid peroxidation

The role of iron in the peroxidation of polyunsaturated fatty acids is reviewed, especially with respect to the involvement of oxygen radicals. The hydroxyl radical can be generated by a superoxide-driven Haber-Weiss reaction or by Fenton's reaction; and the hydroxyl radical can initiate lipid peroxidation. However, lipid peroxidation is frequently insensitive to hydroxyl radical scavengers or superoxide dismutase. We propose that the hydroxyl radical may not be involved in the peroxidation of membrane lipids, but instead lipid peroxidation requires both Fe2+ and Fe3+. The inability of superoxide dismutase to affect lipid peroxidation can be explained by the fact that the direct reduction of iron can occur, exemplified by rat liver microsomal NADPH-dependent lipid peroxidation. Catalase can be stimulatory, inhibitory or without affect because H2O2 may oxidize some Fe2+ to form the required Fe3+, or, alternatively, excess H2O2 may inhibit by excessive oxidation of the Fe2+. In an analogous manner reductants can form the initiating complex by reduction of Fe3+, but complete reduction would inhibit lipid peroxidation. All of these redox reactions would be influenced by iron chelation.