Differential expression of CuZn-superoxide dismutases in Pinus sylvestris needles exposed to SO2 and NO2

Mature Pinus sylvestris trees were exposed to air-pollution strees in an open field fumigation experiment. The trees were exposed to low-levels of sulphur dioxide and nitrogen oxides throughout the whole growing season (June to October 1991). Three age-classes (current, one- and two-year-old) of needles were collected from exposed and control trees and the expression of chloroplastic and cytosolic CuZn-superoxide dismutase (SOD; EC 1.15.1.1) genes was studied. The levels of chloroplastic and cytosolic CuZn-SOD mRNA were significantly (up to 2.3-fold) higher in exposed trees for all age-classes of needles as compared to control trees. No significant differences were observed between different needle age-classes in CuZn-SOD mRNA induction. The chloroplastic and cytosolic CuZn-SOD mRNA were induced to the same extent, however, the level of chloroplastic CuZn-SOD mRNA was higher than the cytosolic one. Small differences were observed in CuZn-SOD mRNA levels for individual trees both within exposed and control areas. Protein activity measurements of the CuZn-SOD isozymes did not reveal any significant differences between control and exposed trees. The results are discussed in relation to protection against oxidant stress from air pollutants.     

Seasonal changes in antioxidant level of Scots pine (Pinus sylvestris L.) needles exposed to industrial pollution. II. Enzymatic scavengers activities

The involvement of enzymic antioxidant system, superoxide dismutase, guaiacol peroxidase, ascorbate peroxidase in defense reaction to environmental stress evoked by air and soil pollution, was seasonally studied on three populations of Scots pine (Pinus sylvestris L.) growing on experimental areas close two industrial objects in Poland. The first of them (Luboón) is localised near a phosphate fertiliser factory, the second (Głogów) near a copper foundry, and control stand is placed in Kórnik. Głogów is the most polluted site, where in 1998 monthly mean daily concentrations was: SO₂ - 17 μg·m⁻³, NO_x- 12 μg·m⁻³ and dust containing heavy metals (Cu, Pb, Cd) - 29 μg·m⁻³. Trees in Luboń were influenced for many years by high concentration of SO₂ and fluor compounds. Few years ago emissions were markedly reduced, but changes in the soil (low pH and high concentration of aluminium ions) still influence the growth of trees. In needles of two populations: 3 (Russia) and 8 (Poland), from the polluted sites Głogów and Luboń, activities of superoxide dismutase (SOD) and guaiacol peroxidase (PO) were significantly higher compared to Kórnik. However, in one population (16 - Slovakia), such dependance was not evident. Activity of ascorbate peroxidase (AP) measured in winter was also higher in needles from polluted sites. The results indicated that the sensitivity of free radical scavenging system in Scots pine needles differs among populations.     

Growth of coniferous trees exposed to SO2 and O3 using an open-air fumigation system

Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2-year-old seedlings in an open-air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO₂ fumigation began in May 1987 and continued until December 1990. Long-term mean SO₂ concentrations were 4,13 and 22 nmol mo^?1. Three plots, one at each SO₂ level, were also exposed to O₃ at an average of 1–3.times the ambient level. O₃ fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO₂ on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO₂-treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO₂-treated plots, in apparent response to codeposition of NH₃-N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O₃ on growth were recorded for any species.     

Photosynthetic acclimation to long-term exposure to elevated CO2 concentration in Pinus radiata D. Don. is related to age of needles

The effects of CO₂ enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO₂ partial pressures. At this age trees were 3·5–4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO₂ concentration [(pCO₂)_a] were lower in 1-year-old needles of trees grown at elevated CO₂ concentrations than in those of trees grown at ambient (pCO₂)_a. At elevated CO₂ concentrations V_cmax (maximum carboxylation rate) was reduced by 13% and J_max (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO₂)_a of 4·68 ± 0·41 μmol m^–2 s^–1 and 6·15 ± 0·46 μmol m^–2 s^–1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO₂)_a were 6·2 ± 0·72 μmol m^–2 s^–1 at 36 Pa and 10·15 ± 0·64 μmol m^–2 s^–1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO₂ treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO₂)_a in fully fexpanded needles of the current year cohort. These data show that enhancement of photosynthesis continues to occur in needles after 4 years’ exposure to elevated CO₂ concentrations. Photosynthetic acclimation reduces the degree of this enhancement, but only in needles after 1 year of growth. Thus, responses to elevated CO₂ concentration change during the lifetime of needles, and acclimation may not be apparent in current year needles. This transitory effect is most probably attributable to the effects of developmental stage and proximity to actively growing shoots on sink strength for carbohydrates. The implications of such age-dependent responses are that older trees, in which the contribution of older needles to the photosynthetic biomass is greater than in younger trees, may become progressively more acclimated to elevated CO₂ concentration.     

Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO2 enrichment

Abstract Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO₂ mol ¹ for 2 years to establish if growth responses to high CO₂ would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO₂ concentration were subjected to phosphorus deficiency and to periodic drought. CO₂ enrichment increased whole-plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole-plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO₂ and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO₂ levels but differed between families. These results suggest that, as the atmospheric CO₂ concentration rises, field-grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.     

Antioxidant status of the potato tuber and Ca2+ deficiency as a physiological stress

The antioxidant status of potato ( Solanum tuberosum L.) tubers of two genotypes, cv. Désirée and clone 10337de40 was investigated in relation to susceptibility to internal rust spot (IRS), a Ca²⁺-related physiological disorder. Concentrations of total calcium within the perimedulla tissue of tubers, grown with a restricted (1 m M CaCl₂) Ca²⁺ supply, were similar in cv. Désirée (IRS resistant) and clone 10337de40 (IRS susceptible). A range of antioxidants was assayed in order to assess antioxidant status in both genotypes under the two Ca²⁺ treatments. Although no appreciable differences were detected between low Ca²⁺ and control treatments, certain antioxidants were present at significantly higher levels in the IRS resistant genotype, cv. Désirée. These included dehydroascorbate reductase (EC 1.8.5.1) activity (more than 100% higher), total glutathione content (ca 40% higher), glutathione reductase (EC 1.6.4.2) activity (almost 50% higher), peroxidase (EC 1.11.1.7) activity (ca 60% higher) and superoxide dismutase (EC 1.15.1.1) activity (almost 80% higher). There was no difference in ascorbate content, ascorbate free radical reductase activity (EC 1.6.5.4), α-tocopherol levels and catalase activity (EC 1.11.1.6) between the two genotypes. The possible relationship between resistance to IRS and a superior antioxidant status, found in cv. Désirée, is discussed.     

Short-term effect of elevated CO2 concentration and high irradiance on the antioxidant enzymes in bean plants

The effect of short-term exposure to elevated CO₂ concentration and high irradiance on the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (GPX) and catalase (CAT), and on the extent of the lipid peroxidation was studied in bean (Phaseolus vulgaris L.) plants. Plants were exposed for 4 d (8 h a day) to irradiance of 100 (LI) or 1000 (HI) μmol m⁻² s⁻¹ at ambient (CA, 350 μmol mol⁻¹) or elevated (CE, 1300 μmol mol⁻¹) CO₂ concentration. Four-day exposure to CE increased the leaf dry mass in HI plants and RuBPC activity and chlorophyll content in LI plants. Total soluble protein content, leaf dry matter and RuBPC activity were higher in HI than in LI plants, although the HI and CE increased the contents of malonyldialdehyde and H₂O₂. Under CA, exposure to HI increased the activity of APX and decreased the total SOD activity. Under CE, HI treatment also activated APX and led to reduction of both, SOD and GPX, enzymes activities. CE considerably reduced the CAT activity at both irradiances, possibly due to suppressed rate of photorespiration under CE conditions.     

The onset of photosynthetic acclimation to elevated CO2 partial pressure in field-grown Pinus radiata D. Don. after 4 years

The effects of CO₂ enrichment on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied in current year and 1‐year‐old needles of the same branch of field‐grown Pinus radiata D. Don trees. All measurements were made in the fourth year of growth in large, open‐top chambers continuously maintained at ambient (36 Pa) or elevated (65 Pa) CO₂ partial pressures. Photosynthetic rates of the 1‐year‐old needles made at the growth CO₂ partial pressure averaged 10·5 ± 0·5 μmol m^?2 s^?1 in the 36 Pa grown trees and 11·8 ± 0·4 μmol m^?2 s^?1 in the 65 Pa grown trees, and were not significantly different from each other. The photosynthetic capacity of 1‐year‐old needles was reduced by 25% from 23·0 ± 1·8 μmol m^?2 s^?1 in the 36 Pa CO₂ grown trees to 17·3 ± 0·7 μmol m^?2 s^?1 in the 65 Pa grown trees. Growth in elevated CO₂ also resulted in a 25% reduction in V_cmax (maximum carboxylation rate), a 23% reduction in J_max (RuBP regeneration capacity mediated by maximum electron transport rate) and a 30% reduction in Rubisco activity and content. Total non‐structural carbohydrates (TNC) as a fraction of total dry mass increased from 12·8 ± 0·4% in 1‐year‐old needles from the 36 Pa grown trees to 14·2 ± 0·7% in 1‐year‐old needles from the 65 Pa grown trees and leaf nitrogen content decreased from 1·30 ± 0·02 to 1·09 ± 0·10 g m^?2. The current‐year needles were not of sufficient size for gas exchange measurements, but none of the biochemical parameters measured (Rubisco, leaf chlorophyll, TNC and N), were effected by growth in elevated CO₂. These results demonstrate that photosynthetic acclimation, which was not found in the first 2 years of this experiment, can develop over time in field‐grown trees and may be regulated by source‐sink balance, sugar feedback mechanisms and nitrogen allocation.     

Physiological effects of long term exposure to low concentrations of SO2 and NH3 on poplar leaves

Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO₂, NH₃ or a mixture of SO₂ and NH₃ for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112 μg m^?3 SO₂ showed a small reduction in maximum CO₂ assimilation rate (P_max) and stomatal conductance (g_s). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112 μg m^?3 SO₂ was more rapidly activated after transition from dark to light. An exposure to 64 μg m^?3 NH₃ had a positive effect on P_max, stomatal conductance and NH₃ uptake of the leaves. This positive effect was counteracted by an SO₂ concentration of 45 μg m^?3. The exposure treatments appeared to have no effect on the relationship between net CO₂-assimilation and g_s. Also, no injury of the leaf cuticle or of epidermal cells was observed. Resistance analysis showed that NH₃ transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H₂O transfer and NH₃ concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH₃ or to a mixture of NH₃ and SO₂. In contrast SO₂ uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO₂ and H₂O molecules is proposed.     

Effects of SO2 on photosynthesis and ribulose bisphosphate carboxylase in pine tree seedlings

Fumigations of 4–7 week old seelings of Pinus silvestris , with ca 400 μg SO₂ m^-3 for 4–5 days resulted in a decrease both in net photosynthetic rate and in the levels of ribulose bisphosphate carboxylase activity of the primary needles. The effect on net photosynthesis was reversible. No visible damages were observed on the needles. Lower concentrations, ca 200 μg SO₂ m^-3, for ca 6 days inhibited net photosynthesis reversibly. The effect on net photosynthesis was not the result of stomata closure or of increased respiration. A dose-response relation for the inhibition of net photosynthesis and ribulose bisphosphate carboxylase is suggested. A similar relation was observed for the chlorophyll content of the needles. The reversible inhibition of photosynthesis was evident only at high quantum flux density, and the quantum yield of photosynthesis at rate limiting quantum flux was not affected. This was also suggested from an experiment with Scots pine in the field.