Fluxes and enzyme activities in central metabolism of myeloma cells grown in chemostat culture

Activities of enzymes in glycolysis, the pentose phosphate pathway, the tricarboxylic acid cycle, and glutaminolysis have been determined in the mouse myeloma SP2/0.Ag14. Cells were grown on IMDM medium with 5% serum in steady-state chemostat culture at a fixed dilution rate of 0.03 h-1. Three culture conditions, which differed in supply of glucose and oxygen, were chosen so as to change catabolic fluxes in the central metabolism, while keeping anabolic fluxes constant. In the three steady-state situations, the ratio between specific rates of glucose and glutamine consumption differed by more than twentyfold. The specific rates of glucose consumption and lactate production were highest at low oxygen supply, whereas the specific rate of glutamine consumption was highest in the culture fed with low amounts of glucose. Under low oxygen conditions, the specific production of ammonia increased and the consumption pattern of amino acids showed large changes compared with the other two cultures. For the three steady states, activities of key enzymes in glycolysis, the pentose phosphate pathway, glutaminolysis, and the TCA cycle were measured. The differences in the in vivo fluxes were only partially reflected in changes in enzyme levels. The largest differences were observed in the levels of glycolytic enzymes, which were elevated under conditions of low oxygen supply. High activities of phosphoenolpyruvate carboxykinase (E.C. 4.1.1.32) in all cultures suggest an important role for this enzyme as a link between glutaminolysis and glycolysis. For all enzymes, in vitro activities were found that could accommodate the estimated maximum in vivo fluxes. These results show that the regulation of fluxes in central metabolism of mammalian cells occurs mainly through modulation of enzyme activity and, to a much lesser extent, by enzyme synthesis.     

Metabolic and physiological responses in tissues of the long-lived bivalve Arctica islandica to oxygen deficiency

In Arctica islandica, a long lifespan is associated with low metabolic activity, and with a pronounced tolerance to low environmental oxygen. In order to study metabolic and physiological responses to low oxygen conditions vs. no oxygen in mantle, gill, adductor muscle and hemocytes of the ocean quahog, specimens from the German Bight were maintained for 3.5 days under normoxia (21 kPa=controls), hypoxia (2 kPa) or anoxia (0 kPa). Tissue levels of anaerobic metabolites octopine, lactate and succinate as well as specific activities of octopine dehydrogenase (ODH) and lactate dehydrogenase (LDH) were unaffected by hypoxic incubation, suggesting that the metabolism of A. islandica remains fully aerobic down to environmental oxygen levels of 2 kPa. PO(2)-dependent respiration rates of isolated gills indicated the onset of metabolic rate depression (MRD) below 5 kPa in A. islandica, while anaerobiosis was switched on in bivalve tissues only at anoxia. Tissue-specific levels of glutathione (GSH), a scavenger of reactive oxygen species (ROS), indicate no anticipatory antioxidant response takes place under experimental hypoxia and anoxia exposure. Highest specific ODH activity and a mean ODH/LDH ratio of 95 in the adductor muscle contrasted with maximal specific LDH activity and a mean ODH/LDH ratio of 0.3 in hemocytes. These differences in anaerobic enzyme activity patterns indicate that LDH and ODH play specific roles in different tissues of A. islandica which are likely to economize metabolism during anoxia and reoxygenation.     

Red muscle proportions and enzyme activities in deep‐sea demersal fishes

Owing to the paucity of data on the red muscle of deep‐sea fishes, the goal of this study was to determine the proportions of red muscle in demersal fishes and its enzymatic activities to characterize how routine swimming abilities change with depths of occurrence. Cross sectional analysis of the trunk musculature was used to evaluate the proportion of red muscle in 38 species of Californian demersal fishes living at depths between 100 and 3000 m. The activity of metabolic enzymes was also assayed in a sub‐set of 18 species. Benthic fishes had lower proportions of red muscle and lower metabolic enzyme activities than benthopelagic species. Mean proportion of red muscle declined significantly with depth with the greatest range of values in shallow waters and species with low proportions found at all depths. This suggested that while sedentary species occur at all depths, the most active species occur in shallow waters. Citrate synthase activity declined significantly with depth across all species, indicating that the mass‐specific metabolic capacity of red muscle is lower in deep‐sea species. These patterns may be explained by coupling of red and white muscle physiologies, a decrease in physical energy of the environment with depth or by the prevalence of anguilliform body forms and swimming modes in deep‐living species.     

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression

Summary The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O₂. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O₂]<1.5 ppm (4kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% V _max value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia. It is assumed that the occurrence of haemoglobin in this species is essential for its capacity to survive long periods of hypoxia.Abbreviations ATP adenosine triphosphate - I₅₀ inhibitor concentration at 50% V _max - PFK phosphofructokinase - P _c critical PO₂ - SEM standard error of mean - VO₂ oxygen consumption rate - ww wet weight     

Respiratory adaptations to running-water microhabitats in mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis, Ephemeroptera

The mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis inhabit either fast-flowing or, for the latter species, calm zones of running water. We studied (1) mechanisms and limitations of oxygen transport in single individuals (oxygen consumption rate, occurrence and rate of gill movements, and heartbeats) in running water of different oxygen concentrations and (2) capacities for anaerobiosis (L-lactate production). Our aim was to look for specific adaptations in the two species to slightly different microhabitats. Epeorus sylvicola, whose immovable gills are not able to generate ventilatory convection, proved to be an oxyconformer at both test temperatures (11 degrees and 15 degrees C). Ecdyonurus torrentis showed a progressively stronger oxyregulatory behavior at higher temperatures. In this species an onset of gill beating was found at moderate hypoxia (below 16 kPa). Ventilating individuals reached maximum rates (300 min-1) of 5-14 kPa. In the case of a further reduction of oxygen partial pressure, the ventilatory rate started to decrease. Ventilatory activity, however, was maintained down to very low oxygen concentrations. Neither in E. sylvicola nor in E. torrentis was experimental evidence found to confirm the hypothesis of a respiratory function of hindgut movements. During hypoxia, the heart rate was constant in both species (E. sylvicola: 80 min-1; E. torrentis: 60 min-1): bradycardia occurred either below 1.5 kPa or below 4 kPa. Anaerobiosis, that is, lactate production, was not detected in either species.     

Muscle enzyme activities in a deep-sea squaloid shark, Centroscyllium fabricii, compared with its shallow-living relative, Squalus acanthias

The activities of several enzymes of energy metabolism were measured in the heart, red muscle, and white muscle of a deep and a shallow living squaloid shark, Centroscyllium fabricii and Squalus acanthias, respectively. The phylogenetic closeness of these species, combined with their active predatory nature, similar body form, and size makes them well matched for comparison. This is the first time such a comparison has been made involving a deep-sea elasmobranch. Enzyme activities were similar in the heart, but generally lower in the red muscle of C. fabricii. Paralleling the trend seen in deep-sea teleosts, the white muscle of C. fabricii had substantially lower activities of key glycolytic enzymes, pyruvate kinase and lactate dehydrogenase, relative to S. acanthias or other shallow living elasmobranchs. Unexpectedly, between the squaloid sharks examined, creatine phosphokinase activity was higher in all tissues of the deep living C. fabricii. Low white muscle glycolytic enzyme activities in the deep-sea species coupled with high creatine phosphokinase activity suggests that the capacity for short burst swimming is likely limited once creatine phosphate supplies have been exhausted.     

Oxygen‐mediated plasticity confers hypoxia tolerance in a corallivorous polychaete

There is mounting evidence that the deoxygenation of coastal marine ecosystems has been underestimated, particularly in the tropics. These physical conditions appear to have far‐reaching consequences for marine communities and have been associated with mass mortalities. Yet little is known about hypoxia in tropical habitats or about the effects it has on reef‐associated benthic organisms. We explored patterns of dissolved oxygen (DO) throughout Almirante Bay, Panama and found a hypoxic gradient, with areas closest to the mainland having the largest diel variation in DO, as well as more frequent persistent hypoxia. We then designed a laboratory experiment replicating the most extreme in situ DO regime found on shallow patch reefs (3 m) to assess the response of the corallivorous fireworm, Hermodice carnaculata to hypoxia. Worms were exposed to hypoxic conditions (8 hr ~ 1 mg/L or 3.2 kPa) 16 times over an 8‐week period, and at 4 and 8 weeks, their oxygen consumption (respiration rates) was measured upon reoxygenation, along with regrowth of severed gills. Exposure to low DO resulted in worms regenerating significantly larger gills compared to worms under normoxia. This response to low DO was coupled with an ability to maintain elevated oxygen consumption/respiration rates after low DO exposure. In contrast, worms from the normoxic treatment had significantly depressed respiration rates after being exposed to low DO (week 8). This indicates that oxygen‐mediated plasticity in both gill morphology and physiology may confer tolerance to increasingly frequent and severe hypoxia in one important coral predator associated with reef decline.     

Experimental studies on the light sense in the hagfish,Eptatretus burgeri andParamyxine atami (Cyclostomata)

Photo-reception and sensitivity to light were studied in two Japanese hagfishes,Eptatretus burgeri living in shallow water andParamyxine atami living in water of about 100m depth. Both species responded to general illumination by first moving the tail or head and then by swimming. Local illumination revealed that regions most sensitive to light were the skin of the tail in both species and a line of unpigmented skin running down the back ofE. burgeri. The light sensitivity of the lensless eyes, which are situated below the skin, was very weak in both species.P. atami showed shorter reaction time to light thanE. burgeri. No change in skin colour was induced either by almost complete hypophysectomy or by continuous illumination against a white background. Under-water observations with SCUBA revealed that free movingE. burgeri responded well to illumination uncovered during the night, but the ones buried in mud, with only the heads uncovered did not.     

Oxidative stress in growth hormone transgenic coho salmon with compressed lifespan - a model for addressing aging

Abstract Growth hormone (GH) transgenic fish have dramatically enhanced growth rates, increased oxygen demands and reactive oxygen species production. GH-transgenic coho salmon provide an opportunity to address effects of increased metabolism on physiological aging. The objective of this study was to compare oxidative stress in wild-type (WT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch) of different ages (1 and 2 years). Antioxidant enzyme activity, protein carbonyls (PC) and glutathione (GSH, GSSG) were measured. PC correlated to growth rates in individual fish. T fish exhibited lower antioxidant enzyme activities and GSH levels compared to the WT, while levels of PC and GSSG were higher. Age affects were observed in both WT and T fish; enzyme activities and GSH decreased while PC and GSSG increased. Our results support the metabolic rate theory of aging. This study aims to be a platform for continued studies of the theories of aging using fish as model organisms.     

Impaired cardiac mitochondrial membrane potential and respiration in copper-deficient rats

Cardiac mitochondrial respiration, ATP synthase activity, and membrane potential and intactness were evaluated in copper-deficient rats. In the presence of NADH, both copper-deficient and copper-adequate mitochondria had very low oxygen consumption rates, indicating membrane intactness. However copper-deficient mitochondria had significantly lower oxygen consumption rates with NADH than did copper-adequate mitochondria. Copper-deficient mitochondria had significantly lower membrane potential than did copper-adequate mitochondria using fluorescent dyes. Copper-deficient mitochondria had significantly lower state 3 oxygen consumption rates and were less sensitive to inhibition by oligomycin, an ATP synthase inhibitor. Copper-deficient and copper-adequate mitochondria responded similiarly to CCCP. No difference was observed in mitochondrial ATPase activity between copper-deficient and copper-adequate rats using submitochondrial particles. We conclude that cardiac mitochondrial respiration is compromised in copper-deficient rats, and may be related to an altered ATP synthase complex and/or a decreased mitochondrial membrane potential.     

Effects of Se, Cu and Se + vitamin E deficiency on the activities of CuZnSOD, GSH-Px, CAT and LPO levels in chicken erythrocytes

Antioxidant enzymes and vitamins provide a defence against the damage of cells by reactive oxygen species in living systems. The effect of Cu, Se and vitamin E deficiencies on the antioxidant enzyme activities and lipid peroxide levels of chicken erythrocytes were investigated during 6 weeks of a depletion diet. CuZnSOD activity and the plasma Cu level of the Cu-deficient group which was fed a diet containing 0.2 mg Cu x kg(-1) were reduced to 62 and 71% respectively. GSH-Px activity of the Se-deficient group was decreased by 46% but by 21% in the Cu-deficient group. CAT activity values of Se- and Cu-deficient groups were increased by 28 and 10% respectively. The maximum increase of LPO levels in erythrocyte membranes was observed as 32% for the Se+E-deficient group. The LPO level of the Cu-deficient group which had decreased CuZnSOD and GSH-Px activity, was also observed to be significantly increased when compared with the controls (p < 0.05).     

The effect of light on oxygen consumption in two amphipod crustaceans-the hypogean Niphargus stygius and the epigean Gammarus fossarum

The effects of light on the metabolic rates of the hypogean amphipod Niphargus stygius and the epigean amphipod Gammarus fossarum were compared by measuring oxygen consumption and respiratory electron transport system (ETS) activity. They were exposed to light intensities of 720 and 4700 lx at 10°C. Oxygen consumption increased significantly in N. stygius exposed to both low and high intensities of light, but no significant increase was observed in G. fossarum at either intensity. The increase of oxygen consumption in N. stygius was significantly greater at the higher light intensity. This indicates a stress response in which exploitation of half the metabolic potential for energy production in N. stygius during exposure to high light intensity constitutes an adverse effect on its metabolism, since this species usually uses less than 25% of its total metabolic potential for standard metabolic demands.     

Comparative red blood cell metabolism in three wallaby species, Macropus eugenii, Macropus parma and Thylogale thetis (Macropodidae: Marsupialia)

Aspects of red blood cell metabolism were compared among three species of small macropodid marsupials from different habitats. Packed cell volume (PCV), erythrocyte reduced glutathione (GSH) concentration and GSH regeneration rates were similar in all three species. The Parma wallaby had very low red cell potassium levels compared to the other species studied. The Tammar wallaby had higher rates of glucose consumption and lactate production in vitro at both pH 7.4 and 8.2 than did the Parma and significantly lower adenosine triphosphate (ATP) levels than the other species. These findings are consistent with preliminary reports published previously. The differences noted cannot be directly related to differences in the habitats of the species.     

Effect of toxins of the 'red-tide' dinoflagellate Alexandrium spp. on the oxygen consumption of marine copepods

Toxic algal species produce a variety of responses in copepodconsumers ranging from avoidance to retching behavior to highmortality. Toxic algae have also been observed to induce rapidheartbeat in copepods, but little is known of other specificphysiological effects. The following experiment tested the effectof exposure to a toxic diet on the oxygen consumption ratesand citrate synthase activities of five copepod species thatco-occur with the toxic dinoflagellate Alexandrium tamarensein the Gulf of Maine. Experimental animals were presented withdiets of toxic and non-toxic Alexandrium isolates, as well asambient food, for 24 h before measuring oxygen consumption rates.In addition, citrate synthase activities were determined ontwo copepod species exposed to toxic and non-toxic isolatesof A. tamarense over a 3 to 4 day period. Calanus finmarchicus,Pseudocalanus spp. and Acartia hudsonica consumed Alexandriumand showed no response of oxygen consumption rates to the experimentaltreatments. Citrate synthase activities of A. hudsonica andTemora longicornis were also unaffected by Alexandrium toxincontent. Finally, Metridia lucens had lower rates after exposureto both Alexandrium isolates. However, Metridia fed little oneither Alexandrium isolate, and in a subsequent experiment short-termstarvation produced a similar decline in oxygen consumption,which is likely to account for the declines observed in theprior experiment. Thus, it appears that the toxin content ofAlexandrium has little if any short-term effect on the respirationrates of these copepods.     

Intensity of mineralization processes in mountain lakes in NW Slovenia

The potential and actual intensity of mineralization in sediments of fourteen mountain lakes and one subalpine lake in NW Slovenia have been measured. Potential mineralization was measured as the intensity of the electron transport system (ETS) activity of microzoobenthos and microbial communities and the actual mineralization as the oxygen consumption of respiration processes, both measured at a standard temperature of 20°C. The lakes are of different trophic levels and some exhibit seasonal anoxia. All but one are hardwater lakes. Two layers of sediment cores from the deepest point of the lakes were analysed: a surface layer and one below 15 cm. Significant differences among different lakes in their ETS activity and oxygen consumption in the surface and lower layers of sediment were observed. ETS activities and oxygen consumption rates were higher in the surface layers of all the lakes. From the three investigated deterministic factors (temperature, lake depth and total phosphorus in the water column) on sedimentary metabolism ETS activity in the surface layer correlated significantly with total phosphorus and lake depth, but oxygen consumption rate showed a significant correlation only with total phosphorus. The relationship between oxygen consumption and ETS activity was also investigated. ETS activities correlated with oxygen consumption rates according to the equation of logR = 0.421^* logETS + 0.898 (r=0.82; n=30; p<0.001). The R/ETS ratio was lower at the sediment surface than in the layers deeper than 15 cm. It is concluded that ETS activity and oxygen consumption are good indicators of the intensity of the metabolic activity and mineralization in lake sediments. As the characteristics of lakes and some environmental factors influence the ETS activity and the oxygen consumption differently, the same R/ETS ratio should not be used as conversion factor in calculations for different lakes.     

Adaptations to life in the sulfide system: a comparison of oxygen detoxifying enzymes in thiobiotic and oxybiotic meiofauna (and freshwater planarians)

Summary Although thiobiotic meiofauna live under anoxia, they have higher levels of the oxygen-detoxifying enzymes catalase and superoxide dismutase (SOD) than oxybiotic species. Microoxyphilic oxybios have lower enzyme activities than other oxybiotic species. All meiofauna have lower activities than oxybiotic macrofauna. Catalase and SOD activities increased in direct proportion to sulfide tolerance in thiobios and to ambient oxygen concentration in oxybios. All meiofaunal species studied, including oxybios, are usually exposed to lower O₂ concentrations than burrow-dwelling macrofauna and so have lower catalase and SOD activities. Enzyme activities in thiobios must be related to sulfide concentration and sulfide metabolism because simple oxygen exposure is an unlikely explanation. Thiobiotic catalase is insensitive to both azide and 3-amino-1,2,4-triazole, similar to a sulfide-insensitive bacterial enzyme called pseudocatalase. Catalase and SOD activities are inversely proportional to light sensitivity in three planarian species, suggesting a photo-protective role for these enzymes in these species.     

The heart as a working model to explore themes and strategies for anoxic survival in ectothermic vertebrates

Most vertebrates die within minutes when deprived of molecular oxygen (anoxia), in part because of cardiac failure, which can be traced to an inadequate matching of cardiac ATP supply to ATP demand. Cardiac power output (PO; estimated from the product of cardiac output and central arterial pressure and an indirect measure of cardiac ATP demand) is directly related to cardiac ATP supply up to some maximal level during both normoxia (ATP supply estimated from myocardial O(2) consumption) and anoxia (ATP supply estimated from lactate production rates). Thus, steady state PO provides an excellent means to examine anoxia tolerance strategies among ectothermic vertebrates by indicating a matching of cardiac glycolytic ATP supply and demand. Here, we summarize in vitro measurements of PO data from rainbow trout, freshwater turtles and hagfishes to provide a reasonable benchmark PO of 0.7 mW g(-1) for maximum glycolytic potential of ectothermic hearts at 15 degrees C, which corresponds to a glycolytic ATP turnover rate of about 70 nmol ATP g(-1) s(-1). Using this benchmark to evaluate in vivo PO data for hagfishes, carps and turtles, we identify two cardiac survival strategies, which in conjunction with creative waste management techniques to reduce waste accumulation, allow for long-term cardiac survival during anoxia in these anoxia-tolerant species. Hagfish and crucian carp exemplify a strategy of evolving such a low routine PO that routine cardiac ATP demand lies within the range of the maximum cardiac glycolytic potential. Common carp and freshwater turtles exemplify an active strategy of temporarily and substantially decreasing cardiac and whole body metabolism so that PO is below maximum cardiac glycolytic potential during chronic anoxia despite being quite close to this potential under normoxia.     

外源钙和茉莉酸甲酯诱导番茄植株抗灰霉病研究

以‘辽园多丽’番茄幼苗为材料,研究了经钙(Ca)、钙螯合剂(EGTA)和茉莉酸甲酯(MeJA)处理后接种番茄灰霉病幼苗叶片的病情指数、活性氧(H2O2、O2.-)含量和过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、过氧化物酶(POD)活性的变化。结果显示:(1)Ca、MeJA、MeJA+Ca处理番茄幼苗的灰霉病发病率分别比对照显著降低32.5%、38.0%和54.5%,而MeJA+Ca处理又显著低于Ca、MeJA处理32.6%和15.3%;MeJA+EGTA处理高于MeJA处理30.3%,但低于EGTA处理13.1%;Ca处理低于EGTA处理34.2%。(2)Ca、MeJA及MeJA+Ca处理番茄幼苗叶片中活性氧积累量高于对照,MeJA+Ca处理又高于Ca、MeJA处理;但MeJA+EGTA处理活性氧积累量低于MeJA处理,而高于EGTA处理;Ca处理的活性氧含量高于EGTA处理。(3)Ca、MeJA及MeJA+Ca处理幼苗叶片的SOD、CAT、POD的活性均比对照提高,且以MeJA+Ca处理最高;而MeJA+EGTA处理抗氧化酶活性低于MeJA处理,但高于EGTA处理;Ca处理抗氧化酶活性高于EGTA处理。研究表明,钙在茉莉酸甲酯诱导番茄抗灰霉病过程中具有重要调节作用,这种作用与钙促进茉莉酸甲酯诱导番茄活性氧积累和抗氧化酶活性有关。     

The Olfactory System in the Pacific Hagfishes Eptatretus stoutii,Eptatretus deani,and Myxine circifrons

In front of the olfactory organ in the northeastern Pacific hagfishes Eptatretus stoutii, E. deani, and Myxine circifrons there is a valve that may function to direct water in between the olfactory laminae. In Myxine circifrons the well developed valve is supposed to act alone, whereas the smaller valve in the two species of Eptatretus studied is supposed to act together with the horizontal extensions of the median olfactory lamina. No significant differences were found between the investigated species by ultrastructural examination. In the olfactory epithelium the supporting cells are provided with microvilli and generally contain a great amount of light secretory granules. Both ciliated olfactory receptor cells and microvillous olfactory receptor cells are present. The cilia show a 9 + 0 arrangement of the microtubules with a tendency for a dislocation of one pair of the microtubules toward the center of the cilium. These remarkable features of the olfactory receptor cells, not yet seen in other vertebrates, appear to be a character common to the myxinoid cyclostomes.     

低钾胁迫对番茄叶片活性氧及抗氧化酶系的影响

以2种不同低钾耐性大果番茄(钾敏感型番茄081018和耐低钾型番茄081034)为材料,比较低钾处理下2种番茄叶片中活性氧产生及抗氧化酶系活性和相关基因表达差异,明确植物叶片对低钾胁迫的响应机制.结果显示:(1)钾敏感型番茄在低钾胁迫时,叶片中各种保护酶(SOD及其同工酶、POD、CAT、APX)活性随处理时间延长呈下降趋势,同时活性氧(O2-、H2O2)和MDA含量急剧增加;耐低钾型番茄在低钾胁迫条件下,其各类保护酶活性均比对照水平有所升高,而且O2-、H2O2和MDA的含量增加也较少.(2)钾敏感型番茄在低钾胁迫时叶片内Cu/Zn-SOD、CAT和APX基因的相对表达量均有下降趋势,而同期耐低钾型番茄在低钾胁迫时Cu/Zn-SOD、CAT和APX的表达却明显增加,这与其对应的酶活性变化趋势同步.研究表明,低钾胁迫使耐低钾型番茄具有较高保护酶基因表达量,产生较高的保护酶活性,可降低活性氧的破坏作用,防止膜渗透性增加,使之对低钾的适应性较强,而钾敏感番茄品系则相反.