Superoxide dismutase (SOD) activity in Scots pine - Wiley Online Library

Eur. J. For. Path. 18 (1988) 343-350 © 1988 Verlag Paul Parey, Hamburg und Berlin ISSN 0300-1237

Department of Botany, University of Oulu

Superoxide dismutase (SOD) activity in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) needles in northern Finland By S. HUTTUNEN and E. HEISKA

Abstract The superoxide dismutase (SOD EC 1.15.1.1) activity in Scots pine {Pinus sylvestris) and Norway spruce {Picea abies L. Karst.) needles in urban and rural trees of northern Finnish populations was studied. Enzyme activity was higher in pine than in spruce needles. Urban forest site trees with SOT pollution had highest enzyme activity in both pine and spruce needles. Two pine clones from eastern Finland and Lapland revealed great differences in specific SOD enzyme activity.

1 Introduction Superoxide dismutase (SOD ;EC 1.15.1.1.) is a metalloprotein catalyzing the dismutation of superoxide radicals (O^.) to molecular oxygen and H2O2. SOD has been found in a wide range of aerobic organisms (FRIDOVICH 1974), in bovine erythrocytes ( M C C O R D and FRIDOVICH 1969), in bacteria (KEELE et al. 1970) and in plant cells (GIANNOPOLITIS and RiES 1977a; GIANNOPOLITIS and RIES 1977b; RABINOWITCH et al. 1982; FEDERICO et al. 1985). At least two pathways of superoxide generation involving chloroplasts have been determined (BADGER 1985). In the first pathway, O2 directly interacts with a component of the electron transfer chain in a single electron transfer to form superoxide, while the second pathway occurs via auto-oxidation of ferredoxin, which in its reduced state readily reacts with O2 to form superoxide. The toxicity of the superoxide is counteracted in photosynthetic systems by SOD, which is the primary defence against the potentially deleterious reactivities of this radical. The physiological function of SOD appears to be to protect cells against the damaging effects of active oxygen. TANAKA and SUGAHARA (1980) have noted that SO2 toxicity is in part due to the superoxide radical, and that SOD participates in the defense mechanism against SO2 toxicity. RABINOWITCH et al. (1982) have suggested that SOD appears to supplement the protective action of carotenoids against photo-oxidative injury. BENNET et al. (1984) concluded that many questions which relate to the enzyme scavenging hypothesis for protection against exogenous oxidants remain unanswered. Perhaps the most significant of these relates to tissue location factors and the primary sites of the reaction. Most information to date indicates that O3 and oxyradical stress and injury is initiated at cell membrane sites. SOD is an enzyme which plays a major role in preserving acquired tolerance to injury in plants (RABINOWITCH et al. 1982). Ghanges in SOD activity, as well as in the activities of other enzymes, have been studied in ozone-fumigated spinach leaves, and these have shown that SOD activities higher than 30 units per gram can be considered as indicating atmospheric pollution (DECLEIRE et al. 1984). U. S. Copyright Clearance Center Code Statement:

0300-1237/88/1806-0343/$ 02.50/0

344

S. Huttunen and E. Heiska

The purpose of the present study was to provide data on the superoxide dismutase activity in pine and spruce needles and on the similarity or dissimilarity of the enzyme activity in urban and rural trees.

2 Materials and methods Measurements were carried out on Scots pine {Pinus sylvestris E.) and Norway spruce {Picea abies E. Karst.) current-year needles in central northern Finland in the town of Oulu (65 °N) and its vicinity. Four different forest sites were selected for the study. Alavuotto, located in Ylikiiminki about 50 km east of Oulu, represents a rural site. The second site was about 300 m from a pulp and paper mill producing SO2, H2S and organic S-composed pollution while the third was situated about 1 km from a fertilizer plant releasing NOx and N H ^ , both in Oulu. The fourth site was in the Botanical Gardens about T km away from the two previously mentioned sites. This last site inludes cloned pines from northern Finland (Sodankyla, 782-P812) about 300 km from Oulu, and from eastern Finland (Kuhmo, 787-P133) about 240 km from Oulu and, in addition, two natural spruces. The pine needles from the third site and the Sodankyla clone were thicker and shorter than the needles from the other sites. In northern Finland, rural forest sites receive a monthly wet deposition of SO^ S-deposition of 4-88 mg/m- and total N2 deposition of 24-35 mg/m-^. Dry deposition is in a range within 7-26 mg/m- and a total N within the range 9 ^ 2 mg/m^ (1984-1985). The urban monthly mean concentrations of SO2 close to the studied trees are 12-28 yu,g m"^ (-gj^g 2) and 11-27 /xg m~3 (site 3). The highest peak concentrations during the study period were 461 /xg m~^ {V2 h, site 3) and 534 /x,g m~^ (site 2). The annual mean concentrations of SO2 varied from 10 to 31 fxg at site 2 and from 12 to 25 at site 3. The NO2 concentrations have varied from 17 to 27 /xg m~^. The NO^ rich site was elected on the basis of the ground vegetation and the nitrogen content of the needles prior to the study. Preparation of the samples and measurements of SOD activity were made essentially according to the methods of KALIR and POLJAKOFF-MAYBER (1981) and M C C O R D and FRIDOVICH (1969), with minor modifications due to the nature of the material investigated. All the operations were performed at 0 to 4°C. Three grams of fresh needles were cut into 0.5 cm pieces and homogenized with an Ultra-Turrax homogenizer at high velocity for 20 seconds in 18 ml cold buffer. The buffer consisted of 0.5 M potassium phosphate of pH 7.8 containing lO"'^ M EDTA: The homogenate was centrifuged at 20000 g for 15 min at 0 to 4°C. 0.75 g of soluble polyvinylpyrroline (PVP) was added to the supernatant to reduce phenolic substances together with a few drops of Antifoam solution. The supernatant was then subjected to ammoniumsulphate precipitation for 85% saturation. After stirring for 1 hr, the yellowish, gluey precipitate formed by the interaction of PVP, ammoniumsulphate and phenolic substances was removed before centrifuging the supernatant as before. The white protein precipitate thus obtained was dissolved in 2 ml of cold buffer. The SOD activity assay was performed at 25 °C in a total volume of 3 ml of buffer. The reaction mixture contained 1x10"^ M cytochrome c, 5x10"'' M xanthine, and sufficient xanthine oxidase to produce a rate of reduction of cytochrome c at 550 nm of 0.025 absorbance unit per min. The amount of xanthine oxidase in the reaction mixture was usually 7.5x10"^ U. The SOD activity units were calculated according to ASADA et al. (1974). The enzymatic unit is equal to (V/v-1), where V and v represent the reduction rates of the assay reaction in the absence and presence of SOD, respectively. The water soluble protein content of SOD extracts was determined by the method of EowRY et al. (1951). PVP was used to reduce phenolic compounds. The total sulphur content of the needles was determined by x-ray fluoresence analysis, using a vacuum spectrometer with a silver anode tube and an EIDDT analyzing crystal and

Superoxide dismutase activity in Scots pine

345

proportional detector. A tube voltage of 30 kV and a current of 30 mA were employed. Standard samples for the x-ray fluorescence analysis were made by adding known amounts of organic sulphur compound to a rural needle matrix.

3 Results 3.1 SOD activity in pine needles The seasonal variation in SOD activity was studied forthnightly from June 1985 till June 1986 using the current-year needles. The SOD activity in pine needles was higher, being at least twice that of the SOD activity in the spruce needles at all of the four forest sites investigated. In addition, the seasonal cycles of SOD activity in pine and spruce needles differed from each other. The SOD activities in pine needles varied from 4.3 Units per gram to 128.8 Units per gram. The rural pines had a mean activity of 30.0 U/g, the sulphur polluted site 35.9 and nitrogen polluted site 43.0 U/g. The Sodankyla clone had the highest mean, 79.6 U/g, while Kuhmo clone had a mean of 41.1 U/g (Table 1). Table 1. Statistics of seasonal total superoxide dismutase activity (enzyme units per gram of fresh needles) in pine needles

Minimum Maximum Range Median Mean Variance S.D. Coeff of var

Rural

Urban SO2

Urban N O ,

Sodankyla clone

Kuhmo clone

n = 20

n = 20

n = 20

n = 19

n = 17

7.9

8.2

49.4 41.5 32.5 30.0 + 2.5 129.8 11.4 38.0

59.7 51.5 38.0 35.9 ±3.1 198.4 14.1 39.2

10.7 70.0 59.3 43.7 43.0 ± 3 . 4

232.0 15.2 35.4

33.0 128.8 95.8 79.8 79.6 ± 5 . 4

548.4 23.4 29.4

4.3

64.7 60.4 41.5 41.1 ±3.6 217.2 14.7 35.8

The seasonal SOD activities in pine needles were highest in July 1985, in October/ November 1985 and in April/May 1986. Generally, the SOD activity of the needles from urban site two was slightly higher (F 1.965, p < 0.25) than that of the needles from the rural site, especially in the late summer and autumn. A significant difference (One way ANOVA four groups) was obtained between all the sampled pines (F 25.469''"•"•', p < 0.0001) and between the cloned test trees (F 38.365^'"^'"='", P < 0.0001). The water soluble protein content in pine needles varied from 0.4 mg/ml to 15.8 mg/ml. The study sites differed significantly in their water soluble protein contents Table 2. Statistics of seasonal water soluble protein content of pine needles


Rural

Urban SO,

Urban N O ,

Sodankyla clone

Kuhmo clone

n = 20

n = 21

n = 20

n = 19

n = 17

0.4 3.0 2.6 2.0

0.5

1.6

4.8

3.8 3.3 2.0

15.8 14.2 10.6

22.8 17.6 11.2

0.6 5.9 5.4 2.8

2.0±0.1

2.0 ±0.2

10.5 ±0.8

11.2±0.9

2.8±0.3

0.4 0.7

0.5 0.7

12.2

16.1

3.5

4.0

1.4 1.2

32.5

34.7

33.2

35.9

42.0

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5. Huttunen and E. Heiska

(F = 70.403--"'-''-, p < 0.0001). The Eappish pine clone from Sodankyla had the highest protein content of between from 4.8 mg/ml and 22.4 mg/ml values for the Kuhmo pine clone were a minimum of 0.6 mg/ml and maximum of 5.9 mg/ml. These clones differed significantly (E = 69.086-'"'"''", p < 0.0001). The maximum protein content was attained in early January. The statistics of water soluble pine proteins are given in Table 2. The specific enzyme activity of pine needles varied from 2.3 units per gram to 63.2 units per gram. The difference between rural and urban trees was highly significant (F = 54.151''"-''"''", P < 0.0001). The needles of the cloned pine from Sodankyla and the pine from the urban NOx site 3 had low specific SOD activities due to the 5-fold water soluble protein content in comparison with the needles of pines from rural and SO2 polluted site and the clone from Kuhmo. The difference between clones was significant (F = 19.902''"''"''", p < 0.0001). The statistics of specific activities are presented in Table 3. The summer time specific SOD activity was most variable in the rural trees (variance 136.4). The autumn time variance of specific SOD activity in pine needles was exceptionally high in the urban SO2 polluted site. Table 3. Statistics of seasonal specific SOD activity in pine needles U/mg prot


Rural

Urban SO2

Urban NO^

Sodankyla clone

Kuhmo clone

n = 20

n = 20

n = 20

n = 19

n = 17

3.9

5.8

45.2 41.3 24.4 24.9 ±2.4 119.9 10.9 44.0

63.2 57.4 25.0 29.1 ±3.0 178.2 13.4 45.8

2.3

3.1

11.6 9.3

21.8

6.1 6.6 ± 0 . 7 8.8 3.0

44.9

18.7 10.6 11.7± 1.1 21.8 4.7

29.9

10.5 53.4 42.9 24.9 24.1 -^2.7 123.3 11.1 46.1

3.2 SOD activity in spruce needles The SOD activity in spruce needles varied from 0.6 U/g to 45.4 U/g. The statistics show the greatest variance in the needles of the test tree on the SO2 polluted site (Table 4). The variance between sites was also significant (F = 18.634''"''''''", p < 0.005). Table 4. Statistics of seasonal total superoxide dismutase activity in spruce needles


Rural

Urban SO2

Urban NO^

Urban I

Urban II

n = 20

n = 20

n = 19

n = 19

n = 19

1.7

26.6 24.9 12.1 12.1 ± 1.4 40.9 6.4

52.9

1.0

45.4 44.4 18.6 20.0 ±2.5 129.7 11.4 57.0

0.7

0.6

0.6

15.9 15.2

30.8 30.2 10.6

40.1 39.5 10.6

7.7

8.5± 1.0 19.2 4.4

51.3

11.6± 1.7

12.4 ±2.2

56.6 7.5 64.8

91,5 9.6

77.1

The water soluble protein content of the spruce needles was very low, from 0.4 mg/ml to 3.2 mg/ml. The specific SOD activity varied from 0.0 U/mg to 62.6 U/mg. With respect to water soluble protein the single natural spruces at the Botanical Gardens differed only slightly from the rural trees, and the rural site differed only slightly from the


347

Table 5. Statistics of seasonal spruce needle specific SOD activity

Minimum Maximum Range Median Mean Variance

Rural

Urban SO2

Urban NO^

Urban I

Urban II

n = 20

n = 20

n = 20

n = 19

n = 18

2.1

44.7 43.5 14.9 19.2 ±3.0 183.2 13.5 70.4

62.5 60.4 9.1

14.7±3.2 204.4 14.3 97.3

S.D. Coeff of var

0.015

1.2

0.7

11.6 11.6 8.3

6.5 ±0.8 13.6 3.7

56.4

1.0

40.4 39.7 10.9 13.6 ±2.4 108.9 10.4 76.8

45.6 44.6 16.2 17.6 ±3.5 224.9 15.0 85.1

urban ones (F = 3.983"', p < 0.10). Variance (224.9) was greatest in single natural spruce from the Botanical Gardens (Table 5). The specific activity of nitrogen polluted spruce needles was extremely low varying from 0 to 11.6 U/mg. However in paired T-test rural trees differed significantly from those of SO2 polluted urban site during the summerautumn period. 3.3 Total sulphur content of pine and spruce needles The total sulphur content of the pine and spruce needles at the rural site was lower than that at the urban sites. The total sulphur content was higher in spruce needles than in pine needles with highest values being attained in spruce needles from the urban SO2 polluted site (Fig. 1). The nitrogen content of the needles was not analysed because of its low diagnostic value (Table 6). Table 6. The sulphur content of current year pine and spruce needles at different sites n = 1 (three measurements from the same tree) Rural

Urban SO2

Urban NO^

867 1046

1097 1661

957 1457

PINE

SPRUCE

ppm 2500 2000 1500 1000

500 0

3

2

1

1

Fig. 1. Total sulphur content of pine and spruce needles in rural (1) and in urban SO2 polluted (2) and NOx polluted (3) trees. The former of the same coloured patterns indicates one-year-old and the latter two-year-old needles. The sulphur content has been expressed as ppm form dry weight of needles

348


4 Discussion Superoxide, hydroxide, hydrogen peroxide and particularly the superoxide radicals are potential agents of oxygen toxicity. The formation of hydrogen peroxide in a cell is associated with superoxide radicals in such a way that after the superoxide radicals are formed, they are converted by superoxide dismutase to form hydrogen peroxidase, which, in turn, is eliminated by peroxidase. The more superoxide radicals, the more superoxide dismutase and hydrogen peroxide. TANAKA and SUGAHARA (1980), who studied the effect of SO2 fumigation on the SOD activities of poplar leaves, found that the young leaves with high SOD activity induced by SO2 fumigation were more resistant to SO2 than the control leaves. JAGER et al. (1985) indicated that the superoxide dismutase activity of SO2 sensitive pea cultivars was lower than that of more resistant ones. A growing concentration caused an increase in sulphur concentration and higher SOD activities in spruce needles. In our study the SOD activity of pine needles was higher, being at least twice that of spruce needles. The sulphur content of spruce needles was, however, slightly higher than that of pine. The high sulphur accumulation rate and the low SOD activity may indicate the differences observed in the pollutant sensitivity of pine and spruce. JAGER et al. (1986) discussed the physiological and biochemical aspects of the impact primarily of photo-oxidants on forest trees, but also of SO2, both of which have high chemical reactivity and which can increase the free radical concentration in the plant cell. As a consequence of an increased radical concentration cellular membranes are mainly decomposed. Changes in protective scavenging or buffering mechanisms for free radicals and SO2 can be used as early indicators of metabohc perturbations and may help to elucidate the causes of the pollutant damage to the plant. ELSTNER et al. (1985) measured relative activities of superoxide dismutase in green and bleached needles of Picea abies and Abies alba in Picea abies green needles had an activity of 120-125 U/mg protein and bleached ones 130-260 U/mg protein. Abies alba had correspondingly 17 U/mg protein in green needles and 40 U/mg in bleached. Green needles of central European spruce seem to have twice the SOD activity of northern Finnish pine or spruce. The cloned pine material revealed that the central eastern clone from Kuhmo had twice as high SOD activity compared with the Lappish pine clone from Sodankyla. The mean of enzyme activity of eastern Finnish clone was, however, only 24.9 U/mg protein, which is close to the level of fir. One clone is too small a sample, but if the SOD specific activity variance between clones and sites can be used as an indication of sulphur dioxide or ozone response, the variance between air pollution response in Finnish forests may be very great. The Lappish pines may be far more sensitive than southern ones. Some scientists have already suggested that ambient ozone and sulphur concentrations have affected northern Finnish pines in particular (SUTINEN 1988). On the other hand, WINGSLE et al. (1987) studied the effects of 75±5 ppb NO^ and 75±10 ppb SO2 fumigation on SOD in the needles of Scots pine but did not find any effects after short term fumigation. The seasonal rhythm of SOD activity was most obvious in the needles collected from the rural site. At the urban sites there was additional variance in the SOD activity. The cloned material from Sodankyla, however, had the most variable total activity. The reason was the high water soluble protein content of the clone. The water soluble protein content was greatest in the Sodankyla clone and lowest in the rural pine. The NO^ rich site trees also had a high water soluble protein content. Significant variance indicated that total activity, as such, is a poor indicator of response. The specific activity was highest in SO7 polluted site but the urban NO^ polluted site indicated low values due to high water soluble protein contents. Indication studies of this kind have also been critized on the ground that enzymes are not pollutant specific and the response is variable (MEJNARTOWiGZ 1984). Long-term monitoring with stress enzymes could, however, help us in


349

understanding the development of long-term stress responses in trees, which is important in forest decline areas. The water soluble protein content clearly shows the seasonal response and so the specific activity measures the capability of different trees to eliminate pollutants. In this study the eastern Finnish clone had double the capability compared with the Sodankyla clone at the same site. Acknowledgements This study has been supported by the Academy of Finland. The language was checked by Dr. SHEILA HICKS.

Summary The superoxide dismutase (SOD; EC 1.15.1.1.) activities in homogenates of Scots pine {Pinus sylvestris) and Norway spruce {Picea abies L. Karst.) needles from rural and urban forest sites were analysed. The cloned pines from northern (specific SOD mean 11.7 U/mg protein) and eastern Finland (specific SOD mean 24.1 U/mg protein) had significantly different SOD activity levels, which indicates different responses under pollution stress. The rural pines had a mean specific SOD activity of 24.9 U/mg protein. The corresponding value for rural spruces was 14.7 U/mg protein. The urban pines under SO2 influence had^ a mean of 29.1 U/mg protein, while the urban spruces under SO2 pollution had a mean of 19.2 U/mg protein. The NO^ polluted site revealed high total activity, but low specific activity.

Resume Activite de la superoxyde dismutase dans les aiguilles de pin (Pinus sylvestris L.) et d'epicea (Picea abies L. Karst.) du nord de la Finlande Nous avons analyse les taux d'activite de la superoxyde dismutase (SOD) dans les aiguilles de pins et d'epiceas appartenant a des populations homogenes de la campagne et en m.ilieu urbain. Nous avons observe des differences significatives dans le niveau d'activite du SOD entre les pins clones du Nord de la Finlande (moyenne specifique de SOD de 11,7 U/mg proteine) et ceux de l'Est du pays (moyenne specifique de SOD de 24,1 U/mg proteine), ce qui revele des differences dans les reactions aux impuretes de l'air. A la campagne les pins avaient une moyenne specifique de SOD de 24,9 U/mg proteine, et les epiceas une moyenne de 14,7 U/mg proteine. En milieu urbain, exposes a l'influence du SO2, les pins avaient une teneur de SOD de 29,1 U/mg proteine, et les epiceas de 19,2 U/mg proteine. En milieu pollue par le NO^ l'activite totale de SOD etait elevee tandis que ses activites specifiques etaient basses.

Zusammenfassung Variation der Superoxiddismutaseaktivitdt von Kiefer und Fichte in Nordfinnland Die Superoxiddismutaseaktivitat wurde an Homogenaten analysiert, die aus Kiefern- und Fichtennadeln sowohl landlicher als auch stadtischer Baume gewonnen wurden. Die SOD-Aktivitat von Kiefernklonen zweier Populationen aus Nord- und Ostfinnland zeigte sehr verschiedene Grade der Aktivitat, die eine unterschiedliche Reaktion auf Euftverunreinigungen anzeigt (spezifische SODAktivitat Mittelwert 11.7 U/mg Protein Nord- und 24.1 U/mg Protein ostfinnische Klone). Die Aktivitat von landlichen Kiefernnadeln war 24.9 U/mg Protein, wahrend in schwefeldioxidbeherrschter Umgebung die Aktivitat 29.1 U/mg Protein war. In Fichtennadeln war das Niveau in landlichen Proben 14.7 U/mg und in stadtischen 19.2 U/mg Protein. Die Totalaktivitat in durch Stickstoffoxide belastetem Stadtwald war hoch, aber die spezifische Aktivitat niedrig.

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J., 1985: Basic mechanisms of pigment bleaching and loss of structural resistance in spruce {Picea abies) needles: advances in pnytomedical diagnostics. Experientia 41, 591-597. FEDERICO, R . ; MEDDA, R. R . ; FLORIS, G . , 1985: Superoxide dismutase from Lens esculenta. Purification and properties. Plant Physiol. 78, 357-358. FRIDOVICH, I., 1974: Superoxide dismutases. Adv. Enzymol. 41, 35-97. GIANNOPOLITIS, C . N . ; RIES, S. K . , 1977a: Superoxide dismutases, I Occurrence in higher plants. Plant Physiol. 59, 309-314. 1977b: Superoxide dismutases. II Purification and quantitative relationship with water-soluble protein in seedlings. Plant Physiol. 59, 315-318. JAGER, H . - J . ; BENDER, J.; GRUNHAGE, L . , 1985: Metabolic responses of plants differing in SO2 sensitivity towards SO2 fumigation. Environ. Pollut. 39, 317-335. JAGER, H . - J . ; WEIGEL, H . - J . ; GRUNHAGE, L., 1986: Physiologische und biochemische Aspekte der Wirkung von Immissionen auf Waldbaume. J. For. Path. 16, 98-109. KALIR, A.; POLJAKOFF-MAYBER, A., 1981: Changes in activity of malate dehydrogenase, catalase, peroxidase and superoxide dismutase in leaves oi Halimione portulacoides (L.) Aellen exposed to high sodium chloride concentrations. Ann. Bot. 47, 75-85. KEELE, B . B . J R . ; M C C O R D , J. M.; FRIDOVICH, I., 1970: Superoxide dismutase from Escherichia coli B. A new manganese-containing enzyme. J. Biol. Chem. 245, 6176-6181. LowRY, O. H.; RosEBROUGH, N. J.; FARR, A . L . ; RANDALL, R. J., 1951: Protein measurements with the folin phenol reagent. J. Biol. Chem. 193, 265-275. M C C O R D , J. M.; FRIDOVICH, I., 1969: Superoxide dismutase. An enzymatic function for erythrocuprein (hemocuprein). J. Biol. Chem. 244, 6049-6055. MEJNARTOWICZ, L . E . , 1984: Enzymatic investigations on tolerance in forest trees. In: Gaseous air pollutants and plant metabohsm (eds. KOZIOL, M . J.; WHATLEY, F . R . ) . Butterworths. pp. 381398. RABINOWITCH, H . D . ; SKLAN, D . ; BUDOWSKI, P., 1982: Photo-oxidative damage in the ripening tomato fruit: Protective role of stiperoxide dismutase. Physiol. Plant. 54, 369-374. SuTiNEN, S., 1988: Ultrastructure of^conifer needles exposed to O3 and 03-i-SO2 compared to the needle structure in the field in Finland, Sweden and West Germany. Aquilo Ser. Bot. (in press.). TANAKA, K. ; SUGAHARA, K . , 1980: Role of superoxide dismutase in defense against SO2 toxicity and an increase in superoxide dismutase activity with SO2 fumigation. Plant & Cell Physiol. 21, 601-611. WiNSLE, G.; NASHOLM, T . ; LANDMARK, T . ; ERICSSON, A.; HALLGREN, J . - E . , 1987: Effects of NO^ and SO2 fumigation on NR, GR, SOD and GSH in needles of Scots pine. Abstracts. 2nd Intern. Symp. Air Pollution Plant Metabolism, April 6-1987. Neuherberg, FRG. GSF. ELSTNER, E . F . ; OSSWALD, W . ; YOUNGMAN, R .

Authors' address: Prof. Dr. SATU HUTTUNEN and EEVA HEISKA, University of Oulu, Department of Botany, Linnanmaa, SF-90570 Oulu, Finland Receipt ofms.: 4. 5. 1987