Superoxide Dismutase Activity In Leaves Research Articles

Comprehensive evaluation and screening identification indexes of heat‐resistance indices in cotton (Gossypium hirsutum L.)

AbstractCotton (Gossypium hirsutum L.) cultivars exhibit varying responses to heat stress. To investigate the heat resistance of various cotton and establish an index system for evaluating their heat resistance, 21 cotton cultivars were selected and subjected to two temperature regimes (CK, average temperature 28°C, 32/24°C; HT, average temperature 38°C, 42/34°C). The results showed that under high temperatures, different changes occurred in individual indexes of cotton, reflecting the differences in heat resistance in cotton cultivars. A total of 21 cotton cultivars could be classified into four types: heat‐tolerant, moderate heat‐tolerant, moderate heat‐sensitive and heat‐sensitive cultivars by multivariate statistical analysis. Moreover, the indexes of net photosynthetic rate (Pn), leaf superoxide dismutase activity (LSOD), the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (ΦPSII), leaf malondialdehyde content (LMDA), leaf catalase activity (LCAT), dry matter weight of shoot (SDW) and root malondialdehyde content (RMDA) were determined to be useful for evaluating the cotton heat tolerance by stepwise regression analysis. The pot experiment showed that the reduction of boll number, boll weight and seed cotton yield was more remarkable under HT in the heat‐sensitive cultivar CCRI‐92 than in the heat‐resistant cultivar CCRI‐69, which further verified the screening results. In conclusion, the heat‐sensitive cultivars CCRI‐92 and heat‐resistant cultivar CCRI‐69 which are identified by seedling experiment could serve as ideal experimental materials for studying heat resistance in cotton. The physiological indices such as Pn, LSOD, Fv/Fm, ΦPSII, LMDA, LCAT, SDW and RMDA be employed for assessing the heat tolerance in cotton.

Effects of field soil warming on the growth and physiology of Juglans mandshurica seedlings.

Global climate change will increase surface soil temperature, with consequences on plant seedling growth and population dynamics. In this study, we carried out a field experiment to investigate the effects of 2 ℃ soil warming on the growth and physiological characteristics of 1- and 2-year-old seedlings of a dominant tree species in broadleaved Korean pine forest, Juglans mandshurica. The results showed that soil warming significantly increased basal diameter, root length, total leaf area, leaf dry weight, root dry weight, total biomass, apparent photosynthetic electron transfer rate (ETR), PSⅡ actual photochemical efficiency (ΦPSⅡ), and apparent photosynthetic electrophotochemical quenching coefficient (qP) of 1-year-old seedlings by 18.3%, 66.7%, 94.4%, 105.9%, 95.8%, 37.8%, 89.5%, 100.0%, and 71.4%, respectively. Soil warming significantly increased basal diameter, total leaf area, leaf dry weight, total biomass, leaf superoxide dismutase activity, peroxidase activity, catalase activity and free proline content, ETR, ΦPSⅡ, and qP of 2-year-old seedlings by 12.5%, 180.5%, 97.3%, 42.5%, 23.9%, 20.4%, 14.9%, 20.7%, 66.7%, 283.3% and 284.6%, respectively. There was an interaction between seedling age and soil warming on the root-shoot ratio and the ΦPSⅡ and qP in chlorophyll fluorescence parameters, in that soil warming significantly reduced the root-shoot ratio of 2-year-old seedlings and that the increase of chlorophyll fluorescence parameters of 2-year-old seedlings (4.1-4.6 times) was much higher than that of 1-year-old seedlings (1.5-1.8 times). Soil warming of 2 ℃ was beneficial to the growth of 1- and 2-year-old J. mandshurica seedlings and increased their regeneration potential. In particular, 2-year-old J. mandshurica seedlings responded to soil warming by increasing leaf area, improving leaf photochemical efficiency, and enhancing protective enzyme activity to increase resistance.

Effects of pesticide application and plant sexual identity on leaf physiological traits and phyllosphere bacterial communities

AbstractPesticides are widely used to enhance food production on a global scale. However, little information is available on the effects of pesticide application on leaf physiology and phyllosphere bacterial communities of dioecious plants. Therefore, this study aimed to assess the impact of λ-cyhalothrin, a broad-spectrum pesticide, on leaf physiology and phyllosphere bacterial communities in the dioecious Populus cathayana. Physiological leaf traits such as photosynthetic apparatus (net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration (E)) of males were significantly higher than those of females, independent of pesticide use. In contrast, pesticide application significantly reduced the photosynthetic apparatus for both sexes, and the reduction was greater in males relative to females. Also, pesticide application significantly increased peroxidase (POD) activity and malondialdehyde (MDA) content and maintained superoxide dismutase (SOD) activity and total chlorophyll content in leaves of males. The phyllosphere bacteria showed some conserved characteristics, in which, Simpson and Shannon diversity indices were not affected by sex or pesticide application. Phyllosphere bacterial community composition differed between females and males, indicating that intrinsic sex significantly shapes the phyllosphere bacterial community. However, pesticide application significantly increased the relative abundance of Actinobacteria but reduced the relative abundance of Proteobacteria. Principal component analysis showed associations between leaf physiology and specific bacterial taxa. For instance, Proteobacteria negatively correlated with leaf SOD activity and MDA content, while Actinobacteria showed an opposite pattern. Our study highlights sex-specific phyllosphere bacterial community composition and leaf physiological traits in dioecious plants.

Lipid Peroxidation Rates, Hydrogen Peroxide Content, and Superoxide Dismutase Activity in Leaves of a Facultative CAM Plant Hylotelephium triphyllum (Haw.) Holub and a C3 Plant Plantago media L. under Natural Environmental Conditions

Lipid Peroxidation Rates, Hydrogen Peroxide Content, and Superoxide Dismutase Activity in Leaves of a Facultative CAM Plant Hylotelephium triphyllum (Haw.) Holub and a C3 Plant Plantago media L. under Natural Environmental Conditions

Indole-3-acetic acid promotes cadmium (Cd) accumulation in a Cd hyperaccumulator and a non-hyperaccumulator by different physiological responses

To study the effects of indole-3-acetic acid (IAA) on cadmium (Cd) accumulation and the physiological responses of the Cd hyperaccumulator Solanum nigrum and non-hyperaccumulator Solanum melongena, a pot experiment was conducted in soil containing 2mgkg-1 Cd in which different concentrations of IAA (0, 10, 20, or 40mgL-1) were sprayed on plant leaves. The results showed that Cd accumulation in shoots of S. nigrum was significantly increased by 30% after the addition of 10mgL-1 IAA under 2mgkg-1 Cd stress compared to that in the control, but shoot Cd accumulation showed no significant change in S. melongena after this IAA treatment. Additionally, the growth and the proline content in the two species were significantly increased by 20mgL-1 IAA. The activities of peroxidase and catalase in leaves of S. nigrum and the activity of superoxide dismutase (SOD) in S. melongena were significantly increased and their malondialdehyde content was significantly decreased compared to those in the control. The root activity of S. nigrum was significantly improved after 10 and 20mgL-1 IAA treatments, but no significant difference was observed in S. melongena. The correlation analysis results showed that the Cd concentration in leaves of S. nigrum was significantly and positively correlated with the carotenoid and proline contents, and there was also a significant positive correlation between the Cd concentration and SOD activity in leaves of S. melongena. Therefore, S. nigrum is an ideal plant for the phytoextraction of Cd-contaminated soil assisted by IAA. IAA promotes Cd accumulation in plant shoots by enhancing the accumulation of carotenoids and proline in S. nigrum and maintaining a high leaf SOD activity in S. melongena.

Oxidative stress and antioxidant responses to direct and bicarbonate-induced iron deficiency in two quince rootstocks

The aim of this research was to investigate some physiological parameters underlining the differences in the sensitivity of quince rootstocks to iron (Fe) deficiency. Two quince rootstocks, Fe-chlorosis tolerant “hawthorn” and Fe-chlorosis sensitive “quince” were subjected to direct or bicarbonate-induced Fe deficiency. One-year-old seedlings of each rootstocks were grown in nutrient solution containing 50 μM Fe-EDTA, pH 5.5 (control), 5 μM Fe-EDTA, pH 5.5 (direct Fe-deficiency) or bicarbonate-lime-induced Fe-deficiency including 5, 10, 15, or 20 mM NaHCO3 in the absence or presence of 0.5 g l−1 CaCO3, containing 50 μM Fe-EDTA, pH 7.8. Both Fe-deficiency treatments decreased leaf chlorophyll, carotenoid and Fe concentrations in quince seedlings, whereas the presence of bicarbonate had no or small effect on these parameters in hawthorn leaves. In both rootstocks, leaf malondialdehyde and hydrogen peroxide (H2O2) concentration were increased in response to direct Fe-deficiency and HCO3- induced Fe-deficiency, though to a higher level in the quince seedlings. Iron-deficiency (direct and indirect) conditions resulted in an increase in the leaf superoxide dismutase activity in both rootstocks, whereas catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) activities decreased significantly, but only in leaf of sensitive quince seedlings. This proposed that CAT, APX, and GPX activities could be an important feature associated with the tolerance to Fe deficiency by inhibiting an increase in H2O2 concentration and protect the cell from oxidative injury.

Efficient superoxide scavenging and metal immobilization in roots determines the level of tolerance to Vanadium stress in two contrasting Brassica napus genotypes

Brassica napus also known as Rapeseed is a member of the Brassicaceae family which is mainly cultivated for its oil-rich seeds. Indeed, B. napus is ranked the third-largest source of vegetable oil in the world. Brassica napus growth, development and yield are negatively affected by heavy metals. Vanadium is a heavy metal and presence in high concentrations impact plant growth and development negatively. However, the impact of Vanadium on B. napus growth and development is unknown. Therefore, in this study we assessed the effects of Vanadium stress on leaf physiology and biochemistry response of two B. napus cultivars (namely Agamax and AV Garnet). A randomised pot-experiment under controlled conditions was used to grow B. napus cultivars under control (distilled water) and Vanadium (350 μM NaVO3) treatments. Results showed that Vanadium caused yellowing of AV Garnet leaves but not Agamax leaves. Furthermore, Vanadium stress caused a more severe decrease in leaf dry and fresh weight of AV Garnet as compared to the decrease in leaf dry and fresh weight of Agamax. We also observed that Vanadium stress only decreased leaf chlorophyll content (a, b and total) of AV Garnet but had no effect on chlorophyll content of Agamax. In addition, Vanadium stress induced an increase in toxic superoxide (O2-) content in leaves of both AV Garnet and Agamax however; we observed more O2- content in AV Garnet leaves than Agamax leaves. Furthermore, we observed a more drastic increase in leaf lipid peroxidation and leaf cell death (assessed by Evans blue uptake) of AV Garnet when compared to Agamax. In order to investigate whether Vanadium regulates O2- metabolising enzymes we assessed superoxide dismutase (SOD) activity (total SOD enzymatic activity and SOD isoform activity). Vanadium inhibited the total leaf SOD activity of AV Garnet more than the total leaf SOD activity of Agamax. The SOD isoform analyses displayed that Vanadium treatment did not alter the leaf MnSOD as well as leaf Cu/ZnSOD isoforms of both Agamax and AV Garnet. However, we observed that FeSOD 1 and FeSOD 3 activity was upregulated in Agamax leaves in response to Vanadium treatment but decreased in AV Garnet following Vanadium treatment. Furthermore, we observed that the leaf FeSOD 2 activity was inhibited in both Agamax and AV Garnet. In addition, we also analysed the Vanadium contents in the two cultivars following Vanadium treatment and observed more Vanadium content in Agamax roots than in AV Garnet roots. Furthermore, translocation factor (TF) analysis showed that AV Garnet had a higher Vanadium TF from roots to leaves than Agamax following Vanadium treatment. In conclusion, Vanadium stress tolerance in B. napus is possibly controlled by SOD activity and Vanadium content root immobilisation.

Apoplastic hydrogen peroxide and superoxide anion exhibited different regulatory functions in salt-induced oxidative stress in wheat leaves

The present work aimed to investigate the mechanisms of nitric oxide (NO) and reactive oxygen species (ROS) generations and to explore their roles in the regulation of antioxidative responses in the wheat leaves under salinity. Except for an insignificant change of NO content and nitrate reductase (NR) activity due to 50 mM NaCl, NO, hydrogen peroxide, superoxide anion (O2•-), hydroxyl radical (•OH), chlorophyll and malondialdehyde content, as well as activities of nitric oxide synthase, NR, peroxidases (POD), catalase (CAT), and ascorbate peroxidase rose in response to different NaCl concentrations. Meanwhile, leaf superoxide dismutase activity lowered only at 50 mM NaCl. NaCl-stimulatory effects on NO content as well as POD and CAT activities could be partly alleviated by the application of 2-phenyl-4,4,5,5-tetrame-thylimidazoline-3-oxide-1-oxyl (PTIO, NO scavenger), exogenous CAT, or diphenylene iodonium (DPI, NADPH oxidase inhibitor). Native polyacrylamide gel electrophoresis also showed that the amount of POD (especially POD4, POD5, and POD7) and CAT (especially CAT1, CAT2, and CAT3) isozymes increased with increasing salinity but decreased by application of PTIO, CAT, or DPI. Furthermore, histochemical staining showed a similar change of O2•- generation. In addition, the inhibition of diamineoxidase (DAO), polyamine oxidase (PAO), and cell wall-bound POD (cw-POD) activities in NaCl-stressed seedlings seemed to be insensitive to the application of PTIO or DPI. Taken together, salinity-induced NO, H2O2, and O2•- generation influenced each other and played different roles in the regulation of antioxidant enzyme activities in the leaves of wheat seedlings under NaCl treatment.

Superoxide dismutase activity in transgenic canola

Superoxide dismutase (SOD) activity was investigated in leaves of transgenic canola plants which expressed heterologous genes of different origin, namely 1) herbicide resistance genes (bar and simultaneously bar and epsps); 2) DesC desaturase gene (desC) of cyanobacterium Synechococcus vulcanus; 3) human interferon alpha2b gene (huLFN-alpha2b); 4) esxA::fbpB(deltaTMD) fused gene, encoding ESAT-6 and Ag85b Mycobacterium tuberculosis proteins, inducing immune response against tuberculosis; 5) cyp11A1 gene of cytochrome P450(scc) from bovine adrenal cortex mitochondria. Introduction of herbicide resistance genes as well as desaturase gene of cyanobacterium and mycobacterium's genes did not change leaf SOD activity. At the same time it was shown that cyp11A1 and huIFN-alpha2b canola have increased leaf SOD activity up 58 and 33%, respectively, compared with control ones in non-stress conditions. It may be a prerequisite for improved resistance of these plants to the stressors of different origin.

Antioxidant response of the invasive herb Ambrosia artemisiifolia L. to different irradiance levels

The exotic invasive Ambrosia artemisiifolia L. and a native co-occurring species in southern China, Urena lobata L., were compared to investigate the possible protective role of leaf antioxidant systems in the acclimation of invasive plants to different irradiance levels. Antioxidant activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were examined under four irradiance regimes: 10% (dense shade), 30% (low irradiance), 55% (medium irradiance) and 100% (full irradiance). Free proline (Pro) content and the rate of lipid peroxidation in terms of malondialdehyde (MDA) content, glutathione reductase (GR), and tea polyphenols (TP) were also assessed under the different irradiance regimes. Antioxidant enzyme activity of SOD and CAT and the MDA, GR and TP contents for the two species increased with increasing irradiance levels. Invasive A. artemisiifolia was able to scavenge oxygen radicals more efficiently at higher irradiance levels by enhancing CAT activity and GR and TP contents although leaf SOD activity was not greatly enhanced. This exotic species also maintained normal physiological functions when subjected to low irradiance, which might be attributed to the increase in POD activity with decreasing irradiance levels. The higher efficiency of adaptive responses of antioxidant enzymes may protect plants from irradiance-induced stress and may contribute to the invasiveness of A. artemisiifolia in subtropical and tropical regions.

Effect of electrostatic field on seed germination and seedling growth of Sorbus pohuashanesis

A study was conducted to determine the effects of electrostatic field (ESF) treatment on seed germination and seedling growth of Sorbus pohuashanesis. The experiments were arranged by uniform design computed by the Data Processing System (DPS), including three levels of seeds soaking time, four levels of ESF intensity and four levels of ESF treatment time, with 12 treatments. Ten seeds were used in each treatment with three replicates. Seed vigor, seed germinating ability, emergence rate of seedling, survival rate of seedling, and seedling height and diameter, as well as the change in activities of superoxide dismutase (SOD), soluble protein contents, total chlorophyll contents, soluble total sugar contents in leaves of S. pohuashanensis seedlings were measured after ESF treatments. The experiment results show that ESF treatment could improve the water absorption ability of dry seeds of S. pohuashanensis, resulting in fast germination at room temperature under light conditions. Combined treatment of ESF with cold stratification could increase seed germination percentage significantly (to 42.20%), promote seedling height growth, affect leaf SOD activity, and could raise contents of total chlorophyll, soluble protein, and total soluble sugar in leaves. Seed soaking time had a significant effect on seed relative electroconductivity, seed germination under light, SOD activity, soluble protein content and total soluble sugar content of seedling leaves. ESF intensity exerted a moderate effect on these indexes. ESF treatment time only had significant effect on total chlorophyll contents, no evident effect on other indexes.

Enhancement of superoxide dismutase activity in the leaves of white clover (Trifolium repens L.) in response to polyethylene glycol-induced water stress

Effects of polyethylene glycol (PEG)-induced water stress on the activities of total leaf superoxide dismutase (SOD) and chloroplast SOD (including thylakoid-bound SOD and stroma SOD) are described in white clover (Trifolium repens L.) grown in solution culture from rooted cuttings. Both leaf SOD and chloroplast SOD activities were markedly enhanced with increasing concentration of PEG stress, generating osmotic potentials around the roots 0, −0.5, −1.0, −1.5 MPa. The effects increased with time up to 72 h. Chloroplast Fe-containing SOD represented about 30% of the total leaf SOD activity in the control plants and a significant increase in chloroplast SOD activity was found during the stress period. This accounted for about 35.5–71.1% of the total leaf SOD activity. The proportion of chloroplast SOD in total leaf SOD not only increased with the decreasing of osmotic potential, but also increased with incubation time. Furthermore, the increase in thylakoid-bound SOD activity was much higher than that of stroma SOD in chloroplast of plants under water stress. The enhanced chloroplastic SOD activity, especially thylakoid-bound SOD activity, demonstrated in Trifolium repens suggests that Fe-SOD located in chloroplasts play a more important role than cytosolic Cu/Zn-containing SODs in scavenging O2−.

Enhanced Tonoplast H+-ATPase Activity and Superoxide Dismutase Activity in the Halophyte Suaeda salsa Containing High Level of Betacyanin

In this study, high-betacyanin Suaeda salsa seedlings were developed and used to explore whether the betacyanin accumulation is related to salinity tolerance in S. salsa. After 8 days of culture, betacyanin content decreased markedly in both high-betacyanin S. salsa seedlings and the control under nonsalt stress, but the decreases were suppressed by NaCl treatments. Betacyanin content in high-betacyanin seedlings was much higher than that in the control throughout the salt treatments. Growth of S. salsa plants was significantly promoted by NaCl treatments, and the fresh weight of high-betacyanin seedlings was much higher than that of the control when grown in 400 mmol L−1 NaCl. Similar cell sap osmolarity and K+/Na+ ratios were observed in high-betacyanin seedlings and the control. No obvious differences in V-ATPase (tonoplast H+-ATPase) activity, leaf SOD (superoxide dismutase) activity, and total chloroplast SOD (including thylakoid-bound SOD and stroma SOD) activity were detected between high-betacyanin seedlings and the control under nonsalt stress conditions. However, V-ATPase hydrolytic activity increased dramatically in S. salsa seedlings when subjected to different levels of NaCl, and the increases in V-ATPase activity in high-betacyanin seedlings were much higher than that in the control. No clear pattern was observed for NaCl-dependent activity changes of P-ATPase (plasma membrane H+-ATPase) and V-PPase (tonoplast H+-pyrophosphatase). Similar changes were demonstrated in leaf SOD activity and chloroplast SOD activity under salt stress. Both leaf SOD activity and chloroplast SOD activity were markedly enhanced with the increase of NaCl or with time, especially thylakoid-bound SOD activity. Furthermore, the increases in chloroplast SOD activity and thylakoid-bound SOD activity were much higher in high-betacyanin seedlings than that in the control at different levels of NaCl treatment. The higher V-ATPase activity, chloroplastic SOD activity, and thylakoid-bound SOD activity demonstrated in high-betacyanin seedlings, but lower in the control, suggest that high-betacyanin S. salsa seedlings may have higher potential to be energized by the electrochemical gradient for ion uptake into the vacuole and to scavenge O2−• in situ produced in the chloroplasts, which may lead to higher salt tolerance than the control under salt stress. Thus, betacyanin may be involved in salt tolerance of S. salsa.

Trinexapac-ethyl, Propiconazole, Iron, and Biostimulant Effects on Shaded Creeping Bentgrass

Creeping bentgrass (Agrostis stolonifera) is used extensively on temperate zone golf course greens, tees, and fairways, but often performs poorly in shade. Previous research has indicated that sequential applications of gibberellic acid (GA) inhibiting plant growth regulators (PGRs) such as trinexapac-ethyl (TE) increase cool-season turfgrass performance in 70-90% shade. This research was conducted to: 1) confirm appropriate TE application rates and frequencies for maintaining `Penncross' creeping bentgrass in dense shade in the mid-Atlantic region of the U.S.; 2) determine the efficacy of other PGRs, biostimulants, and iron (Fe); and 3) assess whether the addition of a biostimulant with TE would have additive, synergistic, or negative effects. The other compounds tested against TE and the control were: propiconazole (PPC), iron sulfate, CPR (a seaweed and iron containing biostimulant), and a generic seaweed extract (SWE) (Ascophyllum nodosum) plus humic acid (HA) combination. These treatments were applied to 88% shaded bentgrass every 14 days from May or June through October in 2001 and 2002, with turf quality, leaf color, root strength, photochemical efficiency, and antioxidant enzyme superoxide dismutase (SOD) activity being determined. While the quality of control plots fell below a commercially acceptable level by the second month of the trial, repeated foliar TE application provided 33% to 44% better quality throughout the experiment. Propiconazole resulted in 13% to 17% better quality through September of each year. Trinexapac-ethyl and PPC resulted in darker leaf color and increased mid-trial root strength by 27% and 29%, respectively. Canopy photochemical efficiency and leaf SOD activity were also increased due to TE in August of both years. Treatment with Fe, CPR, or SWE+HA did not have an effect on quality, root strength, SOD, or photochemical efficiency, but periodic increases in color were observed. The addition of CPR to TE in 2002 provided results that were not different from those of TE-alone. This and previous studies indicate that restricting leaf elongation with anti-GA PGRs is of primary importance for improving shade tolerance, while treatments that increase leaf color or chlorophyll levels without restricting leaf elongation are relatively ineffective.

Effect of Salt Stress on the Superoxide Dismutase Activity in Leaves of Citrus limonum in Different Rootstock-Scion Combinations

The effect of salinity on leaf superoxide dismutase (SOD) activity of lemon trees of different rootstock-scion combinations was studied. In leaves from Citrus limonum cv.Verna scions on Citrus macrophylla and C. reticulata rootstocks, salinity treatment clearly caused a significant depression in both Fe-SOD and Mn-SOD activities and an increase in Cu,Zn-SOD activity. However, in leaves from Citrus limonum on Citrus aurantium rootstook, the reduction observed in the activity values of Fe-SODs and Mn-SODs was not statistically significant. Salt stress also produced a decrease in the content of soluble proteins and chlorophylls. However, this drop was greater in C. limonum leaves on C. macrophylla than for other combinations.

Over-expression of chloroplast-targeted Mn superoxide dismutase in cotton (Gossypium hirsutum L., cv.Coker 312) does not alter the reduction of photosynthesis after short exposures to low temperature and high light intensity.

Transgenic cotton plants from several independently-transformed lines expressing a chimeric gene encoding a chloroplast-targeted Mn superoxide dismutase (SOD) from tobacco exhibit a three-fold increase in the total leaf SOD activity, strong Mn SOD activity associated with isolated chloroplasts, and a 30% and 20% increase in ascorbate peroxidase and glutathione reductase activities, respectively. The Mn SOD plants did exhibit a slightly enhanced protection against light-mediated, paraquat-induced cellular damage but only at 0.3 µM paraquat. In addition, photosynthetic rates at 10°C and 15°C were similar to those of controls, and the immediate recovery of photosynthesis after a 35-min exposure to 5°C and full sun was only slightly better than that for wild-type plants. The recovery for longer exposure times was comparable for both genotypes as was the deactivation of the H2O2-sensitive, Calvin-cycle enzyme, stromal fructose 1,6-bisphosphatase (FBPase). Compared to the controls, Mn SOD plant leaves in full sun prior to chilling stress had a lower activation of FBPase, a higher ratio of oxidized to reduced forms of ascorbate, and a higher total glutathione content. After 35 min at 5°C in full sunlight, total glutathione had risen in control leaves to 88% of the Mn SOD plant values, and oxidized to reduced ascorbate ratios were higher for both genotypes. However, an 80% increase in the ratio of oxidized to reduced glutathione occurred for Mn SOD plant leaves with no change for controls. This increased demand on the ascorbate-glutathione cycle is circumstantial evidence that high Mn SOD activity in the chloroplast leads to increased H2O2 pools that could, in some manner, affect photosynthetic recovery after a stress period. We postulate that the pool sizes of reduced ascorbate and glutathione may restrict the ability of the ascorbate-glutathione cycle to compensate for the increased activity of SOD in cotton over-producing mitochondrial Mn SOD in chloroplasts during short-term chilling/high light stress.