Subcellular distribution of superoxide dismutase in leaves of ureide-producing leguminous plants

The subcellular localization of superoxide dismutase (SOD; EC. 1.15.1.1) was studied in leaves of two ureide-producing leguminous plants ( Phaseolus vulgaris L. cv. Contender and Vigna unguiculata [L.] Walp). In leaves of Vigna and Phaseolus , three superoxide dismutases were found, an Mn-SOD and two Cu, Zn-containing SODs (I and II). Chloroplasts, mitochondria, and peroxisomes were purified by differential and density-gradient centrifugation using either Percoll or sucrose gradients. The yields obtained in intact chloroplasts and peroxisomes from Vigna were considerably higher than those achieved for Phaseolus . Purified chloroplasts only contained the Cu, Zn-SOD II isozyme, but in mitochondria both Mn-SOD and Cu, Zn-SOD I isozymes were present. In purified peroxisomes no SOD activity was detected. The absence of SOD activity in leaf peroxisomes from Vigna contrasts with results reported for the amide-metabolizing legume Pisum sativum L. where the occurrence of Mn-SOD was demonstrated in leaf peroxisomes (del Río et al. 1983. Planta 158: 216–224; Sandalio et al. 1987. Plant Sci. 51: 1–8). This suggests that in leaf peroxisomes from Vigna plants the generation of O₂^- radicals under normal conditions probably does not take place.     

Scavenger Enzyme Activities in Subcellular Fractions of White Clover (Trifolium repens L.) under PEG-induced Water Stress

Scavenger enzyme activities in subcellular fractions under polyethylene glycol (PEG)-induced water stress in white clover (Trifolium repens L.) were studied. Water stress decreased ascorbic acid (AA) content and catalase (CAT) activity and increased the contents of hydrogen peroxide (H₂O₂), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation), and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX), and glutathione reductase (GR) in cellular cytosol, chloroplasts, mitochondria, and peroxisomes of Trifolium repens leaves. In both the PEG-treated plants and the control, chloroplastic fractions showed the highest total SOD, APOX, and GR activities, followed by mitochondrial fractions in the case of total SOD and GR activities, whereas cytosolic fractions had the second greatest APOX activity. However, CAT activity was the highest in peroxisomes, followed by the cytosol, mitochondria, and chloroplasts in decreasing order. Although Mn-SOD activity was highest in mitochondrial fractions, residual activity was also observed in cytosolic fractions. Cu/Zn-SOD and Fe-SOD were observed in all subcellular fractions; however, the activities were the highest in chloroplastic fractions for both isoforms. Total Cu/Zn-SOD activity, the sum of activities observed in all fractions, was higher than other SOD isoforms. These results suggest that cytosolic and chloroplastic APOX, chloroplastic and mitochondrial GR, mitochondrial Mn-SOD, cytosolic and chloroplastic Cu/Zn-SOD, and chloroplastic Fe-SOD are the major scavenger enzymes, whereas cellular CAT may play a minor role in scavenging of O₂⁻ and H₂O₂ produced under PEG-induced water stress in Trifolium repens.     

Immunocytochemical evidence for a peroxisomal localization of manganese superoxide dismutase in leaf protoplasts from a higher plant

The controversial question of the intracellular location of manganese-containing superoxide dismutase in higher plants was examined under a new experimental approach by applying the more rigorous and specific methods of immunocytochemistry to protoplasts isolated fromPisum sativum L. leaves. Manganese superoxide dismutase (EC 1.15.1.1) was purified to homogeneity from 15 kg of leaves ofPisum sativum L. Rabbits were immunized with the mangano enzyme and the antibody specific for pea manganese superoxide dismutase was purified and found not to contain antigenic sites in common with (i) human manganese superoxide dismutase, (ii) iron superoxide dismutase from eitherEscherichia coli or higher plants, or (iii) plant or animal cuprozinc-superoxide dismutase.Pisum sativum L. manganese superoxide dismutase only appears to have antigenic determinants similar to other manganese superoxide dismutases from higher land plants. The antibody to pea Mn-superoxide dismutase was used to locate the enzyme in protoplasts isolated from young pea leaves by indirect immunofluorescence, and by electron microscopy using the unlabelled antibody peroxidase-antiperoxidase method. Results from immunofluorescence showed that chloroplasts were devoid of specific fluorescence which appeared scattered over the cytosolic spaces among chloroplasts, and demonstrate the absence of manganese superoxide dismutase inside chloroplasts. The metalloenzyme was found to be localized only in peroxisomes, whereas mitochondria, the traditionally accepted site for this enzyme in many eukaryotic organisms, did not show any specific staining. The possible subcellular roles of manganese superoxide dismutase inPisum sativum L. leaves are discussed in the light of its peroxisomal location.     

Alpha-ketoglutarate supply for amino Acid synthesis in higher plant chloroplasts: intrachloroplastic localization of NADP-specific isocitrate dehydrogenase

Isocitrate dehydrogenase was found in Pisum sativum chloroplasts purified on sucrose density gradients. A chloroplast-enriched pellet obtained by differential centrifugation formed two chlorophyll-containing bands. The lower one containing intact chloroplasts had NADP-specific isocitrate dehydrogenase and triose-phosphate isomerase activities. Mitochondria and peroxisomes were observed to band well away from the intact chloroplast region, as indicated by peak activities of fumarase and catalase, respectively. The presence of isocitrate dehydrogenase in chloroplasts suggests that chloroplasts may generate at least some of the α-ketoglutarate required for glutamate synthesis.     

Antioxidative defense to lead stress in subcellular compartments of pea root cells

Lead, similar to other heavy metals and abiotic factors, causes many unfavorable changes at the subcellular and molecular levels in plant cells. An increased level of superoxide anion in Pisum sativum root cells treated with 1 mM Pb(NO3)2 evidenced oxidative stress conditions. We found increased activities of enzymatic components of the antioxidative system (catalase and superoxide dismutase) in the cytosol, mitochondrial and peroxisomal fractions isolated from root cells of Pisum sativum grown in modified Hoagland medium in the presence of lead ions (0.5 or 1 mM). Two isoenzyme forms of superoxide dismutase (Cu,Zn-SOD and Mn-SOD) found in different subcellular compartments of pea roots were more active in Pb-treated plants than in control. Increased amount of alternative oxidase accompanied by an increased activity of this enzyme was found in mitochondria isolated from lead-treated roots. These results show that plants storing excessive amounts of lead in roots defend themselves against the harmful oxidative stress caused by this heavy metal.     

Peroxisome proliferation and oxidative stress mediated by activated oxygen species in plant peroxisomes

The existence of a relationship between clofibrate-induced peroxisome proliferation and oxidative stress mediated by activated oxygen species was studied in intact peroxisomes purified from Pisum sativum L. plants. Incubation of leaves with 1 mM clofibrate produced a remarkable increase in the peroxisomal activity of acyl-CoA oxidase and, to a lesser extent, of xanthine oxidase, whereas there was a nearly complete loss of catalase activity and a decrease in Mn-superoxide dismutase. Ultrastructural studies of intact leaves showed that clofibrate induced a five- and twofold proliferation of the peroxisomal and mitochondrial populations, respectively, in comparison with those in control leaves. Prolonged incubation with clofibrate produced considerable alterations in the ultrastructure of cells. In peroxisomal membranes, the NADH-induced generation of O2- radicals, as well as the lipid peroxidation of membranes, increased as a result of treatment of plants with clofibrate. In intact peroxisomes treated with this hypolipidemic drug, the H2O2 concentration was higher than in peroxisomes from control plants. These results demonstrate that clofibrate stimulates the production of activated oxygen species (O2- and H2O2) inside peroxisomes, as well as the lipid peroxidation of peroxisomal membranes. This effect is concomitant with a decrease of catalase and Mn-SOD activities, the main peroxisomal enzymatic defenses against H2O2 and O2-, and indicates that in the toxicity of clofibrate, at the level of peroxisomes, an oxidative stress mechanism mediated by activated oxygen species is involved.     

Intraorganellar distribution of superoxide dismutase in plant peroxisomes (glyoxysomes and leaf peroxisomes)

The intraorganellar distribution of superoxide dismutase (SOD) (EC 1.15.1.1) in two types of plant peroxisomes (glyoxysomes and leaf peroxisomes) was studied by determinations of SOD latency in intact organelles and by solubilization assays with 0.2 molar KCl. Glyoxysomes were purified from watermelon (Citrullus vulgaris Schrad.) cotyledons, and their integrity, calculated on the basis of glyoxysomal marker enzymes, was about 60%. Under the same conditions, the latency of SOD activity determined in glyoxysomes was 40%. The difference between glyoxysomal intactness and SOD latency was very close to the percentage of isozyme Mn-SOD previously determined in glyoxysomes (LM Sandalio, LA Del Río 1987 J Plant Physiol 127: 395-409). In matrix and membrane fractions of glyoxysomes, SOD exhibited a solubilization pattern very similar to catalase, a typical soluble enzyme of glyoxysomes. The analysis of the distribution of individual SOD isozymes in glyoxysomal fractions treated with KCl showed that Cu,Zn-SOD II, the major SOD isozyme in glyoxysomes, was present in the soluble fraction of these organelles, whereas Mn-SOD was bound to the glyoxysomal membrane. These data in conjunction with those of latency of SOD activity in intact glyoxysomes suggest that Mn-SOD is bound to the external side of the membrane of glyoxysomes. On the other hand, in intact leaf peroxisomes where only a Mn-containing SOD is present (LM Sandalio, JM Palma, LA Del Río 1987 Plant Sci 51: 1-8), this isozyme was found in the peroxisomal matrix. The physiological meaning of SOD localization in matrix and membrane fractions of glyoxysomes and the possibility of new roles for plant peroxisomes in cellular metabolism related to activated oxygen species is discussed.     

Catalase activity and isozyme pattern of the metalloenzyme system, superoxide dismutase, as a function of leaf development during growth of Pisum sativum L. plants

The catalase activity and the isozyme pattern of the metalloenzyme system superoxide dismutase (SOD) have been determined in pea ( Pisum sativum L., cv, Lincoln) leaves of different ages (apical, middle and lower), during several stages of plant development. Pea seedlings were grown in full nutrient solution in a phytotron. Catalase activity was determined polarographically, and superoxide dismutase isozymes (Mn-SOD, Cu, Zn-SOD I and Cu, Zn-SOD II) were separated by acrylamide gel electrophoresis and their relative amounts quantified by densitonietry. The results indicate that the relative amounts of SOD isozymes are slightly different in leaves of different ages during plant growth and, interestingly, each molecular form of SOD shows a clearly distinct pattern during plant development. These changes in the relative percentages of SOD isozymes could be due to the induction of the distinct molecular forms of SOD by the metals Mn, Cu and Zn, translocated to the different leaves as a result of plant development. The relative percentage of the Mn-SOD isozyme showed a similar pattern to that of catalase activity, suggesting a possible link between these two metalloenzymes at subcellular level, both cooperating to remove the toxic effects of O^-₂ and H₂O₂.
An additional conclusion is that before a certain metalloenzyme can be used as a marker to assess the plant micronutrient status, it is essential to have a detalled study of its activity pattern in leaves of different age during plant development.     

Immunological evidence for the presence of peroxiredoxin in pea leaf peroxisomes and response to oxidative stress conditions

Peroxiredoxins (Prxs) constitute a group of thiol-specific antioxidant enzymes which are present in bacteria, yeasts, and in plant and animal cells. Although Prxs are mainly localized in the cytosol, they are also present in mitochondria, chloroplasts, and nuclei, but there is no evidence of the existence of Prxs in plant peroxisomes. Using soluble fractions (matrices) of peroxisomes purified from leaves of pea (Pisum sativum L.) plants, the immunological analysis with affinity-purified IgG against yeast Prx1 revealed the presence of an immunoreactive band of about 50 kDa. The apparent molecular mass of the peroxisomal Prx was not sensitive to oxidizing and reducing conditions what could be a mechanism of protection against the oxidative environment existing in peroxisomes. Postembedment, EM immunocytochemical analysis with affinity-purified IgG against yeast Prx1 antibodies, confirmed that this protein was present in the peroxisomal matrix, mitochondria, and chloroplasts. In pea plants grown under oxidative stress conditions, the protein level of peroxisomal Prx was differentially modulated, being slightly induced by growth of plants with 50 µM CdCl₂, but being significantly reduced by treatment with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The presence in the matrix of peroxisomes of a protein immunorelated to Prx of about 50 kDa, which is in the range of molecular mass of the dimeric form of other Prxs, opens new questions on the molecular properties of Prxs, but also on their function in the metabolism of reactive oxygen and nitrogen species (ROS/RNS) in these plant cell organelles, where they could be involved in the regulation of hydrogen peroxide and/or peroxynitrite.     

Characterization of antioxidant enzymes and peroxisomes of olive (Olea europaea L.) fruits

The presence of peroxisomes in olive (Olea europaea L.) fruits and different antioxidant enzymes occurring in this plant tissue is reported for the first time. Ultrastructural analysis showed that olive cells were characterized by the presence of large vacuoles and lipid drops. Plastids, mitochondria and peroxisomes were placed near the cell wall, showing some type of association with it. Olive fruit peroxisomes were purified by sucrose density-gradient centrifugation, and catalase, glutathione reductase and ascorbate peroxidase were found in peroxisomes. In olive fruit tissue the presence of a battery of antioxidant enzymes was demonstrated, including catalase, four superoxide dismutase isozymes (mainly an Fe-SOD plus 2 Cu,Zn-SOD and a Mn-SOD), all the enzymes of the ascorbate–glutathione cycle, reduced and oxidized glutathione, ascorbate, and four NADPH-recycling dehydrogenases. The knowledge of the full composition of antioxidants (enzymatic and non-enzymatic) in olive fruits is crucial to be able to understand the processes regulating the antioxidant composition of olive oil.     

Copper-binding proteins and copper tolerance in Pisam sativum L.

The effect of high nutrient levels of copper on the low-molecular-weight copper-proteins of leaves from plants of two cultivars of Pisum sativum L., with different sensitivity to copper, was investigated. Gel-filtration chromatography of leaf extracts from Cu-tolerant and Cu-sensitive plants grown with 1 M Cu(II), showed the presence of only two copper peaks (I and II), but growth of plants with 240 M Cu(II) induced two additional copper fractions (III and IV). Fractions II and III were purified by solvent extraction, gel-filtration and ion-exchange chromatography, and their molecular weights, subunit sizes, absorption spectra, metalprotein stoichiometry and amino-acid contents were determined. Fraction II was a polypeptide of M_r 15000 composed of a single chain. The purification of fraction III produced a copper-containing fraction (III-1) of M_r 3700, and a copper-protein (III-2) with an M_r, by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis, of 66000. The metal contents of fractions III-1 and III-2 were higher in Cu-tolerant than in Cu-sensitive plants. On the basis of amino-acid analyses, fraction III-1 appeared to be complexes of Cu(II)-poly-isoleucine and Cu(II)-poly-leucine. The results rule out the existence, in pea leaves, of any protein similar to either animal metallothioneins or to any of the low-molecularweight metal-binding proteins or peptides described in other plants and reported to be involved in metal tolerance. In the mechanism of copper tolerance at the leaf level, fractions III-1 (M_r 3700), III-2 (M_r 66000), and IV (M_r 2000) appear to have a role, fraction IV being specifically induced in the tolerant cultivar by Cu(II). Fractions III-1 and III-2 could participate in a different mechanism, adaptive in character, involving an enhanced capacity to bind copper in Cu-tolerant plants.Abbreviations DEAE diethylaminoethyl - M_r relative molecular mass - SDS sodium dodecyl sulfate - PAGE polyacrylamide-gel electrophoresis J.M. Palma was the recipient of a research fellowship from the Caja General de Ahorros y Monte de Piedad de Granada and CSIC. We are grateful to Dr. J. Moreno-Carretero, R + D Department, UNIASA, Granada, for conducting the amino-acid analyses. This work was supported by grant 603/275 from CAICYT-CSIC (Spain).     

Copper-Adapted Suillus luteus, a Symbiotic Solution for Pines Colonizing Cu Mine Spoils

Natural populations thriving in heavy-metal-contaminated ecosystems are often subjected to selective pressures for increased resistance to toxic metals. In the present study we describe a population of the ectomycorrhizal fungus Suillus luteus that colonized a toxic Cu mine spoil in Norway. We hypothesized that this population had developed adaptive Cu tolerance and was able to protect pine trees against Cu toxicity. We also tested for the existence of cotolerance to Cu and Zn in S. luteus. Isolates from Cu-polluted, Zn-polluted, and nonpolluted sites were grown in vitro on Cu- or Zn-supplemented medium. The Cu mine isolates exhibited high Cu tolerance, whereas the Zn-tolerant isolates were shown to be Cu sensitive, and vice versa. This indicates the evolution of metal-specific tolerance mechanisms is strongly triggered by the pollution in the local environment. Cotolerance does not occur in the S. luteus isolates studied. In a dose-response experiment, the Cu sensitivity of nonmycorrhizal Pinus sylvestris seedlings was compared to the sensitivity of mycorrhizal seedlings colonized either by a Cu-sensitive or Cu-tolerant S. luteus isolate. In nonmycorrhizal plants and plants colonized by the Cu-sensitive isolate, root growth and nutrient uptake were strongly inhibited under Cu stress conditions. In contrast, plants colonized by the Cu-tolerant isolate were hardly affected. The Cu-adapted S. luteus isolate provided excellent insurance against Cu toxicity in pine seedlings exposed to elevated Cu levels. Such a metal-adapted Suillus-Pinus combination might be suitable for large-scale land reclamation at phytotoxic metalliferous and industrial sites.     

Increased level of superoxide dismutase (SOD) activity in larvae of Chironomus ramosus (Diptera: Chironomidae) subjected to ionizing radiation

A battery of enzymes from the eukaryotic antioxidant defense system was measured in salivary gland and in whole body extract of fourth instar larvae of Chironomus ramosus with an objective of finding any clue for the dipteran insect's capacity to tolerate heavy doses of ionizing radiation. Levels of activity of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GSH-Px) were quantified in 30 days old larvae exposed to LD₂₀ dose of gamma radiation. Compared to controls, activity of Cu,Zn-SOD increased 3 to 4 fold and catalase 2 fold in response to ionizing radiation stress, while activities of GR and GSH-Px enzymes were decreased. Among the other SOD isoenzymes, our results showed comparable levels of Mn-SOD and Cu,Zn-SOD activity in control and irradiated groups of larvae. The increase in levels of the Cu,Zn-SOD isoenzyme was also confirmed by Western blot and zymography supported by densitometric quantification. No evidence of Fe-SOD was found in C. ramosus larvae. These findings could help to explain the persistence of natural populations of Chironomus in radioactively contaminated regions.     

Peroxisomal NADP-Dependent Isocitrate Dehydrogenase. Characterization and Activity Regulation during Natural Senescence

The peroxisomal localization and characterization of NADP-dependent isocitrate dehydrogenase (perICDH) in young and senescent pea (Pisum sativum) leaves was studied by subcellular fractionation, kinetic analysis, immunoblotting, and immunoelectron microscopy. The subunit molecular mass for perICDH determined by immunoblotting was 46 kD. By isoelectric focusing (IEF) of the peroxisomal matrix fraction, the NADP-ICDH activity was resolved into four isoforms, perICDH-1 to perICDH-4, with isoelectric points (pIs) of 6.0, 5.6, 5.4, and 5.2, respectively. The kinetic properties of the NADP-ICDH in peroxisomes from young and senescent pea leaves were analyzed. The maximum initial velocity was the same in peroxisomes from young and senescent leaves, while the Michaelis constant value in senescent leaf peroxisomes was 11-fold lower than in young leaf peroxisomes. The protein levels of NADP-ICDH in peroxisomes were not altered during senescence. The kinetic behavior of this enzyme suggests a possible fine control of enzymatic activity by modulation of its Michaelis constant during the natural senescence of pea leaves. After embedding, electron microscopy immunogold labeling of NADP-ICDH confirmed that this enzyme was localized in the peroxisomal matrix. Peroxisomal NADP-ICDH represents an alternative dehydrogenase in these cell organelles and may be the main system for the reduction of NADP to NADPH for its re-utilization in the peroxisomal metabolism.     

Cadmium induces senescence symptoms in leaf peroxisomes of pea plants

The effect of growing pea (Pisum sativum L.) plants with a toxic CdCl₂ concentration (50 µm ) on the metabolism and proteolytic activity of leaf peroxisomes was studied. In peroxisomes purified from plants treated with cadmium, an increase in the total protein concentration and in the activity and protein level of the photorespiratory enzyme glycolate oxidase was found. The glyoxylate cycle enzymes, malate synthase and isocitrate lyase, whose activity is normally very low in leaf peroxisomes, were enhanced by Cd treatment. The activity of the endogenous proteases of leaf peroxisomes was determined. Two leucine‐aminopeptidase isozymes (AP1‐AP2) were detected, and their activity was slightly higher in Cd‐treated plants. Five endopeptidases (EP1‐EP5) were present in pea leaf peroxisomes, and in plants grown with Cd the activity of isozymes EP1‐EP4 was increased. The ultrastructural analysis of pea leaves showed that Cd produced a disorganization of the chloroplast structure, with an increase in the number of plastoglobuli, and the formation of vesicles in the vacuoles. Taken together, these results indicate that Cd induces senescence symptoms in leaf peroxisomes, and probably a metabolic transition of leaf peroxisomes into glyoxysomes, and suggest that the peroxisomal proteases could participate in the metabolic changes produced by Cd.     

Occurrence of Cu,Zn-Superoxide Dismutase in the Intrathylakoid Space of Spinach Chloroplasts

Thylakoids obtained from intact spinach chloroplasts showedno superoxide dismutase (SOD) activity, but Cu,Zn- and Mn-SODactivities were detected in the presence of Triton X-100. Thylakoidmembranes and the lumen fraction were separated by centrifugationafter treatment of the thylakoids with a Yeda pressure cell.Cu,Zn-SOD was found in the lumen fraction. Mn-SOD was detectedin the thylakoid fraction only after addition of 1% Triton X-100.Antibody against spinach Cu,Zn-SOD did not interact with thelatent Cu,Zn-SOD in the thylakoids unless Triton was added.These results indicate that Cu,Zn-SOD occurs in the lumen inaddition to the stroma of spinach chloroplasts, and Mn-SOD bindsto the thylakoid membranes. (Received February 29, 1984; Accepted May 28, 1984)     

Immunolocalization of S-nitrosoglutathione, S-nitrosoglutathione reductase and tyrosine nitration in pea leaf organelles

S-Nitrosoglutathione (GSNO) is a nitrosothiol which plays a major role in the metabolism of NO in higher plants mediating signaling processes. Protein tyrosine nitration (NO₂–Tyr) is a post-translational modification which contributes to protein regulation. The subcellular localization of GSNO, S-nitrosoglutathione reductase (GSNOR), an enzyme which catalyzes its decomposition and protein tyrosine nitration was studied in pea (Pisum sativum L.) leaf plants with the aid of the electron microscopy immunogold-labeling technique. Our findings show that GSNO, GSNOR and nitrated proteins are present in the different subcellular compartments of leaf cells which include chloroplasts, cytosol, mitochondria, and peroxisomes. Given that pea peroxisomes are one of the cell compartments where nitric oxide (NO) has been thoroughly studied, our results provide additional insights into the metabolism of NO in this organelle where NO and GSNO could function as signal molecules in cross talk between the different cell compartments.     

Superoxide dismutase of plant cell vacuoles

Metal-dependent superoxide dismutases (SOD; EC 1.15.1.1) are present in many cell compartments (mitochondria, plastids, nuclei, peroxisomes, endoplasmic reticulum, cell wall and cytosol). We have established that SOD is also localized in the central vacuole. Cyanide-sensitive Cu, Zn-SOD was found in the fraction of isolated vacuoles of red beet roots (Beta vulgaris L.). The enzyme was represented by three isoforms. Comparison of isoenzyme composition and the level of SOD activity in vacuoles, nuclei, plastids and mitochondria isolated from root cells has shown that Cu, Zn-SOD is present in vacuoles and nuclei, two SOD forms (Cu, Zn- and Fe-SOD) are present in plastids, and two SOD forms (Cu, Zn- and Mn-SOD) are present in mitochondria. Cu, Zn-SOD of organelles, unlike vacuolar Cu, Zn-SOD, had only one isoform. The level of enzyme activity from the vacuolar fraction was twice higher than the level of SOD activity from the fractions of isolated organelles. Previously it has been suggested that Cu, Zn-SOD may be localized on the vacuolar membrane or in the near-membrane space from the side of cytoplasm. Our tests have revealed the Cu, Zn-SOD activity in water-soluble extracts of isolated vacuole fractions in the absence of detergent, which may confirm localization of the enzyme inside the organelles.     

Effect of light quality on the organization of photosynthetic electron transport chain of pea seedlings

The activity of NADP and O₂ photoreduction by water is essentially higher in chloroplasts isolated from pea seedlings (Pisum sativum L.) grown under blue light as compared with that from plants grown under red light. In contrast, the photoreduction of NADP and O₂ with photosystem I only is practically the same or even lower in chloroplasts isolated from plants grown under blue light. The addition of plastocyanin does not affect the rate or the extent of NADP photoreduction by water in the chloroplasts isolated from plants grown under blue light, whereas it sharply activates NADP reduction in the chloroplasts isolated from plants grown under red light. The extent of the light-induced oxidation of cytochrome f is appreciably higher in chloroplasts isolated from plants grown under blue light. Cytochrome b₅₅₉ plays the predominant role in the oxidoreductive reactions of these chloroplasts. Furthermore, the fluorescence measurements indicate more effective transfer of excitation energy from chlorophyll to the photosystem II reaction center in chloroplasts isolated from plants grown under blue light.