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Quantitative relation between ozone concentration and reduction of photosynthesis of Euglena gracilis
Atmospheric Environment, Pergamon Press 1968. Vol. 2, pp. 615-616. Printed in Great Britain.
SHORT COMMUNICATION QUANTITATIVE
RELATION BETWEEN OZONE CONCENTRATION
REDUCTION
OF PHOTOSYNTHESIS OF
AND
EUGLENA GRACZLZS
(First received 2 May 1968 and in final form 7 June 1968) Abstract-The percentage reduction of photosynthesis is a logarithmic function of the ozone concentration (0.2-1.0 ppm). Chlorophyll determinations following treatment with 0.8 ppm ozone show a small (5 per cent) loss of chlorophyll b and no loss of chlorophyll a. 1. INTRODUCTION ACUTE symptoms of plant damage are sufficient to indicate the occurrence of adverse levels of a particular air pollutant ; lower concentrations of the air pollutant may however be capable of causing chronic injury without visible damage. A more sensitive indicator of plant injury was therefore proposed by the authors (DE KONING and JEGIER,1968) in an earlier publication whereby the rates of apparent photosynthesis and respiration are related to the presence of air pollutants. Photosynthesis is a complex chain of oxidation-reduction reactions, with carefully balanced equilibria, leading to the reduction of carbondioxide to form high energy sugars. The intake of even a small quantity of a strong oxidant such as ozone may therefore result in a change of the rate of apparent photosynthesis. In the work presented below it is shown that the concentration of ozone is related quantitatively to the reduction of apparent photosynthesis. 2. EXPERIMENTAL Experimental
procedures
have already been described
in detail in a previous
publication
(DE KONINGand JEGIER,1968).
The Euglenas (Eugfena gracifis, strain Z) are grown at room temperature in a mod&d synthetic medium. The age of the Euglena cells used for experimentation ranges from 4 to 5 days. The final dilution of ozone with carbon-filtered air is checked with a Mast 724-2 ozone meter. Photosynthesis is measured in terms of the rate of oxygen evolution and is carried out in daylight plus 3000 ft.-c. The rate of oxygen evolution representing photosynthesis (the light reaction) is corrected with the value found for the respiratory oxygen absorption (the dark reaction) of the same Euglena suspension. For the estimation of chlorophyll a and chlorophyll b a known volume of Eugiena suspension is diluted with acetone to a tInal concentration of 80% acetone. The optical densities of the resulting chlorophyll solution at 663 rnp and 654 rnp permit the calculation of the quantities of chlorophyll a and chlorophyll b using the formulas of McKinley (in SMITHand BE-, 1955). 3. RESULTS
AND
DISCUSSION
The reduction of photosynthesis is calculated as a percentage of the respective control which is taken as 100 per cent. The exposure time to air (control) or air contaminated with ozone is 1 hr in all experiments. The results obtained for the reduction of photosynthesis as related to the various ozone concentrations (FIG.1) shows that there is a quantitative relation between those two variables which could be expressed as a logarithmic function: logy = 1.392x where y = percentage reduction of photosynthesis and x = ozone concentration during 1 hr. Reports have appeared from time to time relating dose injury response of plants to ozone concentrations (for a review see HECK, 1966). DU~GER et al. (1965) have made a detailed study of the effect of peroxyacetyl nitrate (PAN). a component of smog, on certain photosynthesis reactions. Our work however marks the 8rst time that the effects of different ozone concentrations are directly related to the rate of photosynthesis, allowing a mathematical relation to be established. 615
Short Communication
616
Reduction of photosynthesis following exposure to ozone could be related to a loss of chlorophyll. We have therefore estimated chlorophyll a and chlorophyll b after treatment with 0.8 ppm ozone during 1 hr. The results of this work show no decrease of chlorophyll a following the ozone treatment; there is however a small but significant decrease (5 per cent) of chlorophyll b.
0
I
z
3
4
3
b
OZONE CONCENTRATION
FIG, 1. Relation between percentage reduction
i
.B
9
I"
It
(ppml
of photosynthesis
and ozone concentration.
Studies with algal mutants lacking ~~orophyll b (ALLEN,1958) support the theory that chlorophyll b acts as an accessory pigment by preventing the permanent oxidation of chlorophyll a. Loss of chlorophyll b will therefore lead to a reduction of the rate of photosynthesis. Acknowledgements-Thanks are due to MIMYSCHULTHEIS for her technical assistance. This study was assisted by funds provided by a grant No. 604-7-602 of the National Health Grants program. H. W. DEKONING and 2. JEGIER
School of Hygiene, Universite’ de Montrgal, Mont&a& Canada. REFERENCES
ALLEN M. B. (1958) Possible functions of chlorophyll b. Studies with green algae that lack chlorophyll b. Brookhaven Symp. B&f. 11,339-342. DE KONING H. W. and JEG~ERZ. (1968) A study of the effects of ozone and sulfur dioxide on the photosynthesis and respiration of Euglena gracilis. Atmospheric Environment 2, 321-326. DUGGER W. M., MUDD J. B. and KOUKOL J. (1965) Effect of PAN on certain photosynthetic reactions. Archs envir. Hlth 10, 195-200. HECK W. W., DUNNINGJ. A. and HINDAWXI. J. (1966) Ozone: nonlinear relation of dose and injury in plants. Science 151,.577-578. SMITHJ. H. C. and BENITEZH. (1955) Chlorophylls. In: Modern methods ofplant analysis Vol. 4, pp. 142-196, Edited by K. PEACH and M. V. TRACY.Springer, Berlin.
SHORT COMMUNICATION QUANTITATIVE
RELATION BETWEEN OZONE CONCENTRATION
REDUCTION
OF PHOTOSYNTHESIS OF
AND
EUGLENA GRACZLZS
(First received 2 May 1968 and in final form 7 June 1968) Abstract-The percentage reduction of photosynthesis is a logarithmic function of the ozone concentration (0.2-1.0 ppm). Chlorophyll determinations following treatment with 0.8 ppm ozone show a small (5 per cent) loss of chlorophyll b and no loss of chlorophyll a. 1. INTRODUCTION ACUTE symptoms of plant damage are sufficient to indicate the occurrence of adverse levels of a particular air pollutant ; lower concentrations of the air pollutant may however be capable of causing chronic injury without visible damage. A more sensitive indicator of plant injury was therefore proposed by the authors (DE KONING and JEGIER,1968) in an earlier publication whereby the rates of apparent photosynthesis and respiration are related to the presence of air pollutants. Photosynthesis is a complex chain of oxidation-reduction reactions, with carefully balanced equilibria, leading to the reduction of carbondioxide to form high energy sugars. The intake of even a small quantity of a strong oxidant such as ozone may therefore result in a change of the rate of apparent photosynthesis. In the work presented below it is shown that the concentration of ozone is related quantitatively to the reduction of apparent photosynthesis. 2. EXPERIMENTAL Experimental
procedures
have already been described
in detail in a previous
publication
(DE KONINGand JEGIER,1968).
The Euglenas (Eugfena gracifis, strain Z) are grown at room temperature in a mod&d synthetic medium. The age of the Euglena cells used for experimentation ranges from 4 to 5 days. The final dilution of ozone with carbon-filtered air is checked with a Mast 724-2 ozone meter. Photosynthesis is measured in terms of the rate of oxygen evolution and is carried out in daylight plus 3000 ft.-c. The rate of oxygen evolution representing photosynthesis (the light reaction) is corrected with the value found for the respiratory oxygen absorption (the dark reaction) of the same Euglena suspension. For the estimation of chlorophyll a and chlorophyll b a known volume of Eugiena suspension is diluted with acetone to a tInal concentration of 80% acetone. The optical densities of the resulting chlorophyll solution at 663 rnp and 654 rnp permit the calculation of the quantities of chlorophyll a and chlorophyll b using the formulas of McKinley (in SMITHand BE-, 1955). 3. RESULTS
AND
DISCUSSION
The reduction of photosynthesis is calculated as a percentage of the respective control which is taken as 100 per cent. The exposure time to air (control) or air contaminated with ozone is 1 hr in all experiments. The results obtained for the reduction of photosynthesis as related to the various ozone concentrations (FIG.1) shows that there is a quantitative relation between those two variables which could be expressed as a logarithmic function: logy = 1.392x where y = percentage reduction of photosynthesis and x = ozone concentration during 1 hr. Reports have appeared from time to time relating dose injury response of plants to ozone concentrations (for a review see HECK, 1966). DU~GER et al. (1965) have made a detailed study of the effect of peroxyacetyl nitrate (PAN). a component of smog, on certain photosynthesis reactions. Our work however marks the 8rst time that the effects of different ozone concentrations are directly related to the rate of photosynthesis, allowing a mathematical relation to be established. 615
Short Communication
616
Reduction of photosynthesis following exposure to ozone could be related to a loss of chlorophyll. We have therefore estimated chlorophyll a and chlorophyll b after treatment with 0.8 ppm ozone during 1 hr. The results of this work show no decrease of chlorophyll a following the ozone treatment; there is however a small but significant decrease (5 per cent) of chlorophyll b.
0
I
z
3
4
3
b
OZONE CONCENTRATION
FIG, 1. Relation between percentage reduction
i
.B
9
I"
It
(ppml
of photosynthesis
and ozone concentration.
Studies with algal mutants lacking ~~orophyll b (ALLEN,1958) support the theory that chlorophyll b acts as an accessory pigment by preventing the permanent oxidation of chlorophyll a. Loss of chlorophyll b will therefore lead to a reduction of the rate of photosynthesis. Acknowledgements-Thanks are due to MIMYSCHULTHEIS for her technical assistance. This study was assisted by funds provided by a grant No. 604-7-602 of the National Health Grants program. H. W. DEKONING and 2. JEGIER
School of Hygiene, Universite’ de Montrgal, Mont&a& Canada. REFERENCES
ALLEN M. B. (1958) Possible functions of chlorophyll b. Studies with green algae that lack chlorophyll b. Brookhaven Symp. B&f. 11,339-342. DE KONING H. W. and JEG~ERZ. (1968) A study of the effects of ozone and sulfur dioxide on the photosynthesis and respiration of Euglena gracilis. Atmospheric Environment 2, 321-326. DUGGER W. M., MUDD J. B. and KOUKOL J. (1965) Effect of PAN on certain photosynthetic reactions. Archs envir. Hlth 10, 195-200. HECK W. W., DUNNINGJ. A. and HINDAWXI. J. (1966) Ozone: nonlinear relation of dose and injury in plants. Science 151,.577-578. SMITHJ. H. C. and BENITEZH. (1955) Chlorophylls. In: Modern methods ofplant analysis Vol. 4, pp. 142-196, Edited by K. PEACH and M. V. TRACY.Springer, Berlin.