Gianfranco Soldatini

Effect of chronic ozone fumigation on the photosynthetic process of poplar clones showing different sensitivity.

Rooted cuttings from two poplar clones (Populus x euramericana, I-214, and Populus deltoides x maximowiczii, Eridano) were exposed for 15 days to diurnal square-wave treatment with ozone (60 nL L-1 for 5 h day-1). Completely fully expanded leaves exposed to ozone showed a reduction in net CO2 assimilation rate as compared to the control leaves during whole exposure period in both the clones. The reduction was related to a strong stomatal closure in clone I-214, but also to an altered mesophyll activity ascribed to limitation of the dark reactions of photosynthetic process. The results obtained in leaves of I-214 subjected to long-term fumigation seem to support the view that the decrease in quantum yield of electron transport may be a mechanism to down-regulate photosynthetic electron transport so that production of ATP and NADPH would be in equilibrium with the decreased demand in the Calvin cycle. In Eridano the CO2 assimilation was reduced because of the exposure and any alteration in stomatal conductance was observed. Thus, chlorophyll fluorescence parameters showed that an inhibition of photosystem II had occurred (reduction in Fv/Fm ratio), while no alterations in quenching parameters were observed upon illumination. The results seem to indicate that an alternative sink for reducing equivalent, other than carbon metabolism is present.

The decay of O3 through direct reaction with cell wall ascorbate is not sufficient to explain the different degrees of O3-sensitivity in two poplar clones

Summary Ozone (O 3 ) flux to the mesophyll cell walls and its decay in the direct reaction with cell wall-ascorbate were quantified by measuring stomatal conductance, cell wall ozone-exposed area, cell wall thickness and cell wall-ascorbate concentration in two differently-sensitive poplar clones exposed to O 3 (0.150 γl L -1 for 5 h). Stomatal closure under O 3 was more pronounced in the sensitive Eridano than in the resistant I-214 poplar clone. The relative internal area in the ozonated sensitive clone was significantly (−21 %) lower than that in the control one. The concentration of reduced ascorbate in the cell wall ([ASA cw ]) of the sensitive clone was initially 81 % higher than in the resistant one. Following O 3 treatment, [ASA cw ] increased more than 3-fold in both clones, while there was a much more rapid increase in dehydroascorbic acid concentration [DHA cw ] in the sensitive clone. Calculated ozone flux to mesophyll cell wall and to plasmalemma was compared between the two clones. The decay of O 3 flux in cell wall was more rapid in the sensitive clone, due to the more rapid rise of [ASA cw ] under O 3 , but the total (stomatal+cell wall) attenuation of O 3 flow during the exposure was similar in both of the clones. It is concluded that the decay of O 3 through direct reaction with cell wall ascorbate is not sufficient to explain the different O 3 -sensitivity in two poplar clones.

Growth and photosynthesis of Lycopersicon esculentum (L.) plants as affected by nitrogen deficiency

Fully expanded leaves of tomato (Lycopersicon esculentum) growing with either complete or nitrogen-deficient nutrient solution were analysed for leaf water status, gas exchange and chlorophyll fluorescence during the vegetative and reproductive phases. N-deficiency did not affect leaf water relations but did decrease light saturated photosynthetic rate as well as stomatal conductance in the vegetative stage. A lower variable to maximum fluorescence ratio (Fv/Fm) was found in N-limited plants which also showed an increase in leaf starch content and in starch to sucrose ratio. The inhibition of photosynthesis and the alteration of photosynthates partitioning were responsible for the growth reduction in N-stressed plants. During the reproductive phase the limitation of photosynthesis may be due to a large accumulation of starch which determines both a decrease in the carbon demand from the sinks and a decrease in CO2 conductance in the mesophyll.

Screening of bean cultivars for their response to ozone as evaluated by visible symptoms and leaf chlorophyll fluorescence.

Fourteen Italian cultivars of Phaseolus vulgaris were exposed to a single pulse of ozone (O(3), 150 nl l(-1)) or to filtered air (<3 nl l(-1)) for 3.5 h. O(3) sensitivity was assessed by recording the extent of visible symptoms, effects on chlorophyll (Chl) content and changes in Chl a fluorescence parameters. This paper reports the results of an initial screening of 14 bean cultivars that was used to select a small number of cultivars for further work. Seven cultivars showed visible symptoms of injury in the range of 2-60 h after the end of the O(3) fumigation. O(3) significantly depressed total Chl content in most cultivars and a significant correlation was found between Chl content and visible symptoms. Most cultivars showed a significant change in the F(v)/F(m) ratio, even when there were no visual symptoms. There was no relationship between the extent of visual symptoms and quenching coefficients, indicating that these parameters were of no use in the determination of sensitivity to O(3) stress.

Photosynthetic Activity of Ripening Tomato Fruit

Gas exchanges, chlorophyll (Chl) a fluorescence and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) were determined in tomato (Lycopersicon esculentum Mill.) fruits picked at different developmental stages (immature, red-turning, mature, and over-ripe). The fruits did not show signs of CO2 fixation. However, photochemical activity was detectable and an effective electron transport was observed, the values of Chl fluorescence parameters in green fruits being similar to those determined in the leaves. The RuBPCO activity, which was similar to those recorded in the leaves at the immature stage of the fruit, decreased as the fruit ripened. PEPC activity was always higher than RuBPCO activity.

Changes in thylakoid protein patterns and antioxidant levels in two wheat cultivars with different sensitivity to sulfur dioxide

Abstract Plants of two wheat cultivars ( Triticum aestivum L., cultivars ‘Mec’ and ‘Chiarano’), each with a different sensitivity to sulfur dioxide (SO 2 ), were exposed continuously to 2, 23, 64 and 96 nl l −1 SO 2 for 4 months. To investigate whether the higher resistance to SO 2 of Chiarano was due to increased activities of detoxification systems, some antioxidant enzymatic and non-enzymatic systems were analyzed. Moreover, to test whether the different responses of the two cultivars to SO 2 were related to different changes at thylakoid level, we analyzed the thylakoid polypeptide patterns by two-dimensional electrophoresis. Two-dimensional gels of thylakoid membranes revealed a more pronounced generalized decrease of spot optical density in the more SO 2 -sensitive Mec; following SO 2 fumigation, changes were observed in the area with molecular masses 26–29 kDa and isoelectric point (pI) 5–6 and molecular masses 24–27 kDa and pI 5.7–5.8. A significant decrease in optical density of a spot with a molecular mass of 32 kDa and pI 5.4, reported to be D1 protein of the photosystem II reaction centre, was observed in the leaves of both cultivars fumigated with 96 nl l −1 SO 2 . Catalase activity was unaffected by SO 2 exposure. Following SO 2 fumigation, superoxide dismutase activity decreased in Chiarano, but remained unchanged in Mec. Both cultivars were found to increase guaiacol and ascorbic peroxidase activities as a response to SO 2 . The redox status of ascorbic acid was similar in both cultivars and was unaffected by SO 2 . However, the content of ascorbic acid was higher in the more tolerant Chiarano than in Mec at all SO 2 concentrations. The data reported here confirmed the different sensitivities to SO 2 of the two cultivars, as demonstrated by thylakoid protein analysis, and suggest that this difference depends on a differential ability to maintain elevated levels of ascorbic acid rather than on increasing detoxifying enzyme activities.

In Vicia faba leaves Photoinhibition from Ozone Fumigation in Light Precedes a Decrease in Quantum Yield of Functional PSII Centres

Summary Treatment with a single pulse of O 3 (150 ppb, 4 h) on Vicia faba (cv. Gigante d’Ingegnoli) plants induced a decrease in photosynthetic rate at light saturation level but only slight changes in stomatal conductance and transpiration rate. The increase in intercellular CO 2 concentration implied that the predominant factor responsible for the reduction in light-saturated CO 2 uptake was a decrease in the carboxylation efficiency. A slight change in the photochemical efficiency of PS2 (F v /F m ) that decreased in treated plants more than did the quantum yield of functional centres (ΔF/F′ m ) lasted hours after treatment termination; photosynthetic efficiency decrease occurred after an increase in F 0 . Thermal dependence of fluorescence yield of open PS2 reaction centres was modified by O 3 . This eventually led to photosensitizing these leaves to photoinhibition but quantum yield of functional centres was again less sensitive to this combination. Increase in electrolyte leakage kinetics in distilled water indicated that, in the stressed plants, damage at the membrane level was occurring and this was confirmed also by the thiobarbituric reactive substance increase in ozonated leaves, taken as indicators of membrane lipid peroxidation.

Ozone differentially affects physiological and biochemical responses of two clover species; Trifolium repens and Trifolium pratense.

The effect of acute ozone exposure (150 ppb for 3 h) on two clover species, white clover (Trifolium repens L.) and red clover (Trifolium pratense L.) was investigated through the analysis of 10 different physiological and biochemical parameters. Twenty-four hours after fumigation, visible symptoms of injury on leaves were observed only in red clover, but from the biochemical point of view, both species revealed significant ozone-induced modifications. A decrease in the photosynthetic efficiency as well as an increase in the de-epoxidation index and a decrease in the redox state of ascorbate were detected only in T. pratense leaves; no significant change in pigment content was found in either of the two species. On the other hand, both white and red clover showed, although to different extents, significant decreases in the activities of the antioxidant enzymes peroxidase and ascorbate peroxidase. Multivariate statistical analysis revealed not only that ozone affects both species, but also that they differentially respond to the pollutant, confirming the higher sensitivity of Trifolium pratense to ozone exposure.

Effects of elevated ozone on chlorophyll a fluorescence in symptomatic and asymptomatic leaves of two tomato genotypes

Two different genotypes of Lycopersicon esculentum Mill. (cv. Cuor di Bue, O3-sensitive and line 93.1033/1, O3-resistant) were treated with a single dose of ozone (150 mm3 m−3 for 3 h). The PS 2 activity was examined by measurements of chlorophyll a fluorescence on symptomatic and asymptomatic leaves. Symptoms were evident on the 4th leaves from the bottom, in both genotypes, while the 2nd leaves of the line 93.1033/1 were asymptomatic. In these leaves, the net photosynthetic rate (PN) did not change even if the Fv/Fm ratio significantly decreased. A strong reduction in PN, mostly due to the stomatal closure, was observed in Cuor di Bue. The non photochemical quenching coefficient (qNP) and the degree of PS 2 reaction centres closure (1-qP) were higher, while the quantum efficiency of PS 2 photochemistry (ΦPS2) and quantum efficiency of excitation energy capture (Φexc.) were lower in O3 treated leaves of both genotypes. The limitation of photosynthesis was shown also by a decrease in the parameter %P, which diminished compared to controls in both genotypes. The response of the two genotypes for the energy fraction dissipated as thermal energy in the PS 2 antennae (%D) was similar. The fraction of %P remained lower during the recovery in symptomatic leaves of the resistant line as compared to the controls, whereas %X, which represents the amount of light energy that is not utilized in photochemistry or dissipated in the PS 2 antennae, significantly rose in the asymptomatic leaves of this line and in both the leaves of Cuor di Bue. From data obtained we concluded that ozone affected the plants independently on the appearance of visible symptoms of injury because the leaves without visible symptoms of both the genotypes were negatively influenced.

Effect of chronic O3 fumigation on the activity of some Calvin cycle enzymes in two poplar clones

The effects of long-term exposure to ozone (O3, 60 mm3 m-3 for 5 h d-1) on some Calvin cycle enzymes, in particular those modulated by the thioredoxin system, were studied in two poplar clones. These clones differ in sensitivity to O3. In the I-214 clone, the first effects from O3 treatment were seen after 40 d of fumigation, while the Eridano clone showed visible symptoms of damage after only 15 d of the treatment. Specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39) diminished in both the clones, while specific activity of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) increased. Exposure to O3 also caused a reduction in the specific activity of ribulose-1,5-bisphosphate kinase (E.C. 2.7.1.19) in both clones. At the end of the exposure to O3, specific activity of glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.13) increased in I-214 and remained similar to the control in Eridano, whereas specific activity of fructose-1,6-bisphosphate phosphatase (E.C. 3.1.3.11) was higher in Eridano and similar to the control in I-214.