The photosynthetic mechanism of C4 plants is generally less tolerant to chilling stress than the ... more The photosynthetic mechanism of C4 plants is generally less tolerant to chilling stress than the mechanism of C3 plants. Visible oxidative injuries on the leaf tissue of C4 plants exposed for long periods to the combination of chilling and high light suggest that these plant types are not adequately photoprotected. The energy absorbed under stress at the chloroplasts might be in excess of that required for the carbon reduction metabolism. A process of non-radiative emission disposes of most of this excess but a pseudocyclic flux of electrons to oxygen might also occur acting as a dissipation process. The strong increase of chloroplast antioxidant activities (1) indicates that the oxygenated species formed at the PSI or at the other sides must be quickly and completely scavenged to avoid an irreversible damage to the photochemical apparatus and thus a limitation to photosynthesis. In alternative, a limitation might be initiated by an enzymatic impairment in the carbon reduction metab...
The quantum yield of non-cyclic electron transport from PS II (PS II) and the apparent quantum yi... more The quantum yield of non-cyclic electron transport from PS II (PS II) and the apparent quantum yield of CO2 fixation (CO2) were measured in the maize genotype, R-CH HOPI, which shows a high leaf anthocyanin content when grown at a temperature slightly below 20 C. Thus, the leaf anthocyanin content was thirty-five times higher in plants grown at 18 C when compared to plants grown at 23 C. The relationship between PS II and CO2 obtained at different CO2 partial pressure was linear for plants with both high and low leaf anthocyanin content. The PS II/CO2 ratio was about 16 in plants with high leaf anthocyanin content and about 10 in plants with low leaf anthocyanin content. The leaf light absorptance in the 400–700 nm region was higher in plants with higher leaf anthocyanin content. Since leaf absorptance between 400 and 600 nm and leaf anthocyanin content also resulted in a strict linear relationship, an indirect estimation of the absorbed light by leaf anthocyanins and thus at chloro...
This review will focus on the interaction of the photosynthetic apparatus with Cd and on the role... more This review will focus on the interaction of the photosynthetic apparatus with Cd and on the role that thiols play in buffering the damaging reactivity of this heavy metal towards enzymes and other molecular components of photosynthesis
We examined the photosynthetic properties, the activity of antioxidant enzymes and the amount of ... more We examined the photosynthetic properties, the activity of antioxidant enzymes and the amount of carotenoids of two maize genotypes characterized by different sensitivity to low temperature. Plants of the low-temperature-sensitive genotype A-619 and of the low-temperature-resistant genotype VA-36 were grown at 25/20 degrees C (control plants) and at 16/14 degrees C (plants grown at low temperature). Twenty-five days after seeding, the exposure to low temperature caused, in all plants, a reduction of leaf chlorophyll and carotenoid content, but an increase in the activity of the oxygen-detoxifying enzymes, superoxide dismutase and ascorbate peroxidase. However, the response of photosynthesis, stomatal conductance and the fluorescence properties to light and temperature were not affected by growth at low temperature. Fifty days after seeding, photosynthesis, stomatal conductance, and fluorescence properties of A-619 leaves grown at low temperature were significantly reduced with respe...
Phragmites (Phragmites australis Cav. (Trin.) ex Steud) plants exposed to a high concentration of... more Phragmites (Phragmites australis Cav. (Trin.) ex Steud) plants exposed to a high concentration of CdSO 4 (50 µM) for 21 d were analysed with respect to the distribution of metal, its effects on antioxidants, the antioxidant enzymes and the redox status in leaves, roots and stolons. The highest accumulation of Cd 2+ occurred in roots followed by leaves, and it was not significant in the stolons when compared with the control plants. In particular, in roots from Cd-treated plants, both the high amount of GSH and the parallel increase of glutathione-S-transferase (EC 2.5.1.18; GST) activity seemed to be associated with an induction of the detoxification processes in response to the high cadmium concentration. Superoxide dismutase (EC 1.15.1.1; SOD), ascorbate peroxidase (EC 1.11.1.11; APX), glutathione reductase (EC 1.6.4.2; GR) and catalase (EC 1.11.1.6; CAT) activities as well as reduced and oxidised glutathione contents in all samples of leaves, roots and stolons were increased in t...
Photosynthesis and carbohydrate accumulation in maize genotypes (Zea mays L.) VA-36 and A-619, ra... more Photosynthesis and carbohydrate accumulation in maize genotypes (Zea mays L.) VA-36 and A-619, ranked as possessing low and high sensitivity to low temperature, were studied in relation to regrowth after transfer from day/night temperatures of 16/12˚C to 25/20˚C. Plants were grown for 45 days at 25/20 or 16/12˚C, or transferred after 45 days from 16/12˚C to 25/20˚C for 27 days. Photosynthesis of both genotypes after a 45-day growth at 16/12˚C was lower than at 25/20˚C. When the photosynthesis of plants at 16/12˚C was measured at 25˚C it was as high as the photosynthesis of plants at 25˚C in VA-36, while it remained lower in A-619. A strong reduction of rubisco content was observed in the sensitive genotype and is suggested as the cause of photosynthesis limitation that was still observed after recovery at 25/20˚C. After a 45-day growth at 16/12˚C, a reduction of sucrose and, to a lesser extent, starch content was observed. Biomass accumulation was also reduced in both genotypes. Tra...
We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (... more We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg-1 chlorophyll was found in leaves, and 0.83 nmol Cd mg-1 chlorophyll was found in chloroplasts of plants treated with 50 microm Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 ...
At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surfa... more At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo-inhibition but also photo-synthesis. To investigate this phenomenon, gas exchange, fluorescence, superoxide dismutase activity and xantho-phyll composition of anthocyanin-containing HOPI and anthocyanin-deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO2 supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The ΔF/Fm (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than ΔF/Fm of W22 with either light ...
In temperate climates, plants are more frequently exposed to sudden and strong decrease of temper... more In temperate climates, plants are more frequently exposed to sudden and strong decrease of temperature combined with high light intensity that compromise the photosynthetic efficiency and, often, the development and their survival. To investigate deeper the effects of such a photo-oxidative cold shock on photosynthesis of mandarin (Citrus reticulata Blanco) we used transient fluorescence analysis and gas exchange techniques. Mandarin plants were acclimated at 13 8C or grown at 25 8C for 30 days, then single leaves were exposed for 6 h at 5 8C and 1200 mmol photons m À2 s À1 and again exposed for 72 h under growth conditions. Acclimated leaves showed lower photosynthesis and higher total carotenoid contents than non-acclimated leaves. The photo-oxidative cold shock inhibited photosystem II (PSII) efficiency, as suggested by the reduction of F v /F m ratios, in all leaves. Carotenoid content was reduced in non-acclimated leaves. A time-dependent increase in the initial fluorescence le...
The quantum yield of non-cyclic electron transport from PS II (FPS II) and the apparent quantum y... more The quantum yield of non-cyclic electron transport from PS II (FPS II) and the apparent quantum yield of CO2 fixation (FCO2) were measured in the maize genotype, R-CH HOPI, which shows a high leaf anthocyanin content when grown at a temperature slightly below 20 °C. Thus, the leaf anthocyanin content was thirty-five times higher in plants grown at 18 °C
Cherry ( Prunus avium L.) saplings were grown under natural sunlight (controls) or moderate shadi... more Cherry ( Prunus avium L.) saplings were grown under natural sunlight (controls) or moderate shading (up to 30%, depending on the incident light intensity and the hour of the day). Reduced light intensity increased the dry mass of each of the plant components studied. Consequently, the total dry mass of shaded plants was significantly greater than that of controls at
The photosynthetic mechanism of C4 plants is generally less tolerant to chilling stress than the ... more The photosynthetic mechanism of C4 plants is generally less tolerant to chilling stress than the mechanism of C3 plants. Visible oxidative injuries on the leaf tissue of C4 plants exposed for long periods to the combination of chilling and high light suggest that these plant types are not adequately photoprotected. The energy absorbed under stress at the chloroplasts might be in excess of that required for the carbon reduction metabolism. A process of non-radiative emission disposes of most of this excess but a pseudocyclic flux of electrons to oxygen might also occur acting as a dissipation process. The strong increase of chloroplast antioxidant activities (1) indicates that the oxygenated species formed at the PSI or at the other sides must be quickly and completely scavenged to avoid an irreversible damage to the photochemical apparatus and thus a limitation to photosynthesis. In alternative, a limitation might be initiated by an enzymatic impairment in the carbon reduction metab...
The quantum yield of non-cyclic electron transport from PS II (PS II) and the apparent quantum yi... more The quantum yield of non-cyclic electron transport from PS II (PS II) and the apparent quantum yield of CO2 fixation (CO2) were measured in the maize genotype, R-CH HOPI, which shows a high leaf anthocyanin content when grown at a temperature slightly below 20 C. Thus, the leaf anthocyanin content was thirty-five times higher in plants grown at 18 C when compared to plants grown at 23 C. The relationship between PS II and CO2 obtained at different CO2 partial pressure was linear for plants with both high and low leaf anthocyanin content. The PS II/CO2 ratio was about 16 in plants with high leaf anthocyanin content and about 10 in plants with low leaf anthocyanin content. The leaf light absorptance in the 400–700 nm region was higher in plants with higher leaf anthocyanin content. Since leaf absorptance between 400 and 600 nm and leaf anthocyanin content also resulted in a strict linear relationship, an indirect estimation of the absorbed light by leaf anthocyanins and thus at chloro...
This review will focus on the interaction of the photosynthetic apparatus with Cd and on the role... more This review will focus on the interaction of the photosynthetic apparatus with Cd and on the role that thiols play in buffering the damaging reactivity of this heavy metal towards enzymes and other molecular components of photosynthesis
We examined the photosynthetic properties, the activity of antioxidant enzymes and the amount of ... more We examined the photosynthetic properties, the activity of antioxidant enzymes and the amount of carotenoids of two maize genotypes characterized by different sensitivity to low temperature. Plants of the low-temperature-sensitive genotype A-619 and of the low-temperature-resistant genotype VA-36 were grown at 25/20 degrees C (control plants) and at 16/14 degrees C (plants grown at low temperature). Twenty-five days after seeding, the exposure to low temperature caused, in all plants, a reduction of leaf chlorophyll and carotenoid content, but an increase in the activity of the oxygen-detoxifying enzymes, superoxide dismutase and ascorbate peroxidase. However, the response of photosynthesis, stomatal conductance and the fluorescence properties to light and temperature were not affected by growth at low temperature. Fifty days after seeding, photosynthesis, stomatal conductance, and fluorescence properties of A-619 leaves grown at low temperature were significantly reduced with respe...
Phragmites (Phragmites australis Cav. (Trin.) ex Steud) plants exposed to a high concentration of... more Phragmites (Phragmites australis Cav. (Trin.) ex Steud) plants exposed to a high concentration of CdSO 4 (50 µM) for 21 d were analysed with respect to the distribution of metal, its effects on antioxidants, the antioxidant enzymes and the redox status in leaves, roots and stolons. The highest accumulation of Cd 2+ occurred in roots followed by leaves, and it was not significant in the stolons when compared with the control plants. In particular, in roots from Cd-treated plants, both the high amount of GSH and the parallel increase of glutathione-S-transferase (EC 2.5.1.18; GST) activity seemed to be associated with an induction of the detoxification processes in response to the high cadmium concentration. Superoxide dismutase (EC 1.15.1.1; SOD), ascorbate peroxidase (EC 1.11.1.11; APX), glutathione reductase (EC 1.6.4.2; GR) and catalase (EC 1.11.1.6; CAT) activities as well as reduced and oxidised glutathione contents in all samples of leaves, roots and stolons were increased in t...
Photosynthesis and carbohydrate accumulation in maize genotypes (Zea mays L.) VA-36 and A-619, ra... more Photosynthesis and carbohydrate accumulation in maize genotypes (Zea mays L.) VA-36 and A-619, ranked as possessing low and high sensitivity to low temperature, were studied in relation to regrowth after transfer from day/night temperatures of 16/12˚C to 25/20˚C. Plants were grown for 45 days at 25/20 or 16/12˚C, or transferred after 45 days from 16/12˚C to 25/20˚C for 27 days. Photosynthesis of both genotypes after a 45-day growth at 16/12˚C was lower than at 25/20˚C. When the photosynthesis of plants at 16/12˚C was measured at 25˚C it was as high as the photosynthesis of plants at 25˚C in VA-36, while it remained lower in A-619. A strong reduction of rubisco content was observed in the sensitive genotype and is suggested as the cause of photosynthesis limitation that was still observed after recovery at 25/20˚C. After a 45-day growth at 16/12˚C, a reduction of sucrose and, to a lesser extent, starch content was observed. Biomass accumulation was also reduced in both genotypes. Tra...
We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (... more We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg-1 chlorophyll was found in leaves, and 0.83 nmol Cd mg-1 chlorophyll was found in chloroplasts of plants treated with 50 microm Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 ...
At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surfa... more At suboptimal temperatures, anthocyanins accumulate in the illuminated leaf surface of some maize genotypes and, if the anthocyanins shade chloroplasts, they can effectively reduce the risk of photo-inhibition but also photo-synthesis. To investigate this phenomenon, gas exchange, fluorescence, superoxide dismutase activity and xantho-phyll composition of anthocyanin-containing HOPI and anthocyanin-deficient W22 maize genotypes were measured in either white or red light, where the latter is not absorbed by anthocyanins. Despite differences in light absorption in chloroplasts, photosynthesis did not differ between HOPI and W22 under either light source, suggesting that neither CO2 supply nor photochemistry were more limiting in red leaves than in green leaves. In fact, no major differences in transpiration were detected. The ΔF/Fm (photosystem II quantum yield) of HOPI in white light was higher than in red light and higher than ΔF/Fm of W22 with either light ...
In temperate climates, plants are more frequently exposed to sudden and strong decrease of temper... more In temperate climates, plants are more frequently exposed to sudden and strong decrease of temperature combined with high light intensity that compromise the photosynthetic efficiency and, often, the development and their survival. To investigate deeper the effects of such a photo-oxidative cold shock on photosynthesis of mandarin (Citrus reticulata Blanco) we used transient fluorescence analysis and gas exchange techniques. Mandarin plants were acclimated at 13 8C or grown at 25 8C for 30 days, then single leaves were exposed for 6 h at 5 8C and 1200 mmol photons m À2 s À1 and again exposed for 72 h under growth conditions. Acclimated leaves showed lower photosynthesis and higher total carotenoid contents than non-acclimated leaves. The photo-oxidative cold shock inhibited photosystem II (PSII) efficiency, as suggested by the reduction of F v /F m ratios, in all leaves. Carotenoid content was reduced in non-acclimated leaves. A time-dependent increase in the initial fluorescence le...
The quantum yield of non-cyclic electron transport from PS II (FPS II) and the apparent quantum y... more The quantum yield of non-cyclic electron transport from PS II (FPS II) and the apparent quantum yield of CO2 fixation (FCO2) were measured in the maize genotype, R-CH HOPI, which shows a high leaf anthocyanin content when grown at a temperature slightly below 20 °C. Thus, the leaf anthocyanin content was thirty-five times higher in plants grown at 18 °C
Cherry ( Prunus avium L.) saplings were grown under natural sunlight (controls) or moderate shadi... more Cherry ( Prunus avium L.) saplings were grown under natural sunlight (controls) or moderate shading (up to 30%, depending on the incident light intensity and the hour of the day). Reduced light intensity increased the dry mass of each of the plant components studied. Consequently, the total dry mass of shaded plants was significantly greater than that of controls at
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