Changes in antioxidative enzymes in cucumber cotyledons during natural senescence: comparison with those during dark-induced senescence

Changes in 7 antioxidative enzymes in naturally senescent cotyledons of cucumber ( Cucumis sativus ) were investigated. The activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) gradually decreased during the progression of senescence, while those of ascorbate peroxidase (APX; EC 1.11.1.11) and guaiacol peroxidase (GPX; EC 1.11.1.7) gradually increased. The activity of monodehydroascorbate reductase (MDAR; EC 1.6.5.4) was not significantly changed. Western blot analysis showed that the protein level of mitochondrial SOD gradually declined. The protein level of catalase transiently decreased and then increased in the later stages of senescence, despite the decrease in its activity. The overall behavior was markedly different from that found in cotyledons of artificially senescing seedlings transferred into darkness; the activities of SOD, catalase, APX, GPX and GR gradually increased.     

Exogenous treatment with salicylic acid leads to increased antioxidant capacity in leaves of barley plants exposed to paraquat

Our previous study suggests that salicylic acid mediates tolerance in barley plants to paraquat (Ananieva et al. 2002). To further define the role of SA in paraquat induced responses, we analysed the capacity of the antioxidative defence system by measuring the activities of several antioxidative enzymes: superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), catalase (CAT, EC 1.11.1.6), and guaiacol peroxidase (POX, EC 1.11.1.7). Twelve-day-old barley seedlings were supplied with 500 micromol/L SA or 10 micromol/L Pq via the transpiration stream and kept in the dark for 24 h. Then they were exposed to 100 micromol m(-2) s(-1) PAR and samples were taken 6 h after the light exposure. Treatment of seedlings with 10 micromol/L Pq reduced the activity of APX and GR, did not affect the activity of POX and DHAR but caused over a 40% increase in the activity of CAT. Pre-treatment with 500 micromol/L SA for 24 h in the dark before Pq application increased the activities of the studied enzymes in both the chloroplasts (SOD activity) and the other compartments of the cell (POX, CAT activity). The effect of SA pre-treatment was highly expressed on DHAR and POX activity. The data suggest that SA antagonizes Pq effects, via elicitation of an antioxidative response in barley plants.     

Effect of lanthanum ions (La3+) on the reactive oxygen species scavenging enzymes in wheat leaves

Physiological effects of lanthanum ions on the activities of the enzymes in the reactive oxygen species (ROS) scavenging system in leaves of wheat (Triticum aestivum L.) seedlings were studied. Wheat leaves treated in Hogland solution with 0.1 mM LaCl₃ for 48 h showed increased levels of superoxide dismutase (SOD), catalase (CAT), ascorbate-specific peroxidase (AsA-POD), and dehydroascorbate reductase (DHAR). However, a minor effect was observed on the levels of monodehydroascorbate reductase (MDAR) and glutathione reductase (GR), which regulate the release of energy required by the ROS scavenging system. The whole system was linked up by H⁺ transmission. Our results indicated that the activities of the enzymes that function directly to remove ROS were elevated by La³⁺ treatment, which is consistent with the observations that La³⁺-treated plants had increased tolerance to environmental stresses. The remaining levels of MDAR and GR suggested that these two enzymes might be regulated differently from that of the other four enzymes studied.     

Different responses of tobacco antioxidant enzymes to light and chilling stress

The effect of elevated light treatment (25 degrees C, PPFD 360 mumol m-2 sec-1) or chilling temperatures combined with elevated light (5 degrees C, PPFD 360 mumol m-2 sec-1) on the activity of six antioxidant enzymes, guaiacol peroxidases, and glutathione peroxidase (GPx, EC 1.11.1.9) protein accumulation were studied in tobacco Nicotiana tabacum cv. Petit Havana SR1. Both treatments caused no photooxidative damage, but chilling caused a transient wilting. The light treatment increased the activities of ascorbate peroxidase (APx, EC 1.11.1.11) and guaiacol peroxidases while catalase (EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were unchanged. In contrast, chilling treatment did not increase any of the antioxidant enzyme activities, but decreased catalase and to a lesser extent DHAR activities. Glutathione peroxidase protein levels increased sporadically under light treatment and constantly under chilling. Both chilling and light stress caused induction of glutathione synthesis and accumulation of oxidised glutathione, although the predominant part of the glutathione pool remained in the reduced form. Antioxidant enzymes from the chilling treated plants were measured at both 25 degrees C and 5 degrees C. Measurements at 5 degrees C revealed a 3-fold reduction in catalase activity, compared with that measured at 25 degrees C, indicating that the overall reduction in catalase after four days of chilling was approximately 10-fold. The overall reduction in activity for the other antioxidant enzymes after four days of chilling was 2-fold for GR and APx, 1.5-fold for MDHAR, 3.5-fold for DHAR. The activity of SOD was the same at 25 and 5 degrees C. These results indicate that catalase and DHAR are most strongly affected by the chilling treatment and may be the rate-limiting factor of the antioxidant system at low temperatures.     

The oxidative stress caused by salinity in two barley cultivars is mitigated by elevated CO2

Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 m M NaCl) on protective enzyme activities under ambient (350 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ concentrations were investigated in two barley cultivars ( Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO₂, upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO₂ alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO₂ and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO₂ mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.     

Changes in the antioxidative systems in mitochondria during ripening of pepper fruits

The presence of enzymes of the ascorbate–glutathione cycle was studied in mitochondria purified from green and red pepper (Capsicum annuum L.) fruits. All four enzymes, ascorbate peroxidase (APX; EC 1.11.1.11), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) were present in the isolated mitochondria of both fruit ripening stages. The activity of the reductive ascorbate–glutathione cycle enzymes (MDHAR, GR and DHAR) was higher in mitochondria isolated from green than from red fruits, while APX and the antioxidative enzyme superoxide dismutase (SOD; EC 1.15.1.1) were higher in the red fruits. The levels of ascorbate and L-galactono-γ-lactone dehydrogenase (GLDH; EC 1.3.2.3) activity were found to be similar in the mitochondria of both fruits. The higher APX and Mn-SOD specific activities in mitochondria from red fruits might play a role in avoiding the accumulation of any activated oxygen species generated in these mitochondria, and suggests an active role for these enzymes during ripening.     

Effect of hypoxia on the antioxidative enzymes in aerobically grown rice (Oryza sativa) seedlings

The development of the antioxidative system is repressed in rice ( Oryza sativa L. cv. Yamabiko) seedlings germinated under water, but the system is synthesized within 24 h after exposure of the seedlings to air. In order to see whether this regulation of the antioxidative system is reversible, the changes were investigated after submergence of aerobically grown seedlings under water. Low survivability, no morphological change and a slight increase in activity of alcohol dehydrogenase (ADH; EC 1.1.1.1) were observed 24 h after the submergence. Activities of some antioxidative enzymes were decreased, but they were still higher than those in seedlings germinated under water. Superoxide dismutase (SOD; EC 1.15.1.1) in mitochondria, in addition to cytosolic forms of SOD, showed no significant changes, whereas plastidic SOD decreased drastically, which reflected the changes in the development of the corresponding organelles. Thus, the regulation of the antioxidative system was, in part, reversible. In contrast, catalase (EC 1.11.1.6) activity alone was increased by the shift from air to submergence.     

Dehydroascorbate reductase and glutathione reductase play an important role in scavenging hydrogen peroxide during natural and artificial dehydration of Jatropha curcas seeds

Changes in H₂O₂ and the main antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), in endospermic and embryonic tissues were studied in developing and artificially dried Jatropha curcas seeds. Immature seeds were desiccation-tolerant at 80 days after flowering, as they were able to germinate fully after artificial drying on silica gel had reduced their water content to 10–12% of fresh weight. In both endospermic and embryonic tissues, H₂O₂ level and, consequently, lipid peroxide content, decreased during seed development as well as after artificial dehydration of developing seeds. All examined antioxidant enzymes except DHAR showed a decrease in total activity in mature stages as compared with early stages. Expression analysis of SOD genes revealed that the decrease in total SOD activities was related to the decrease in Cu/Zn-SOD expression, while the continuous activity of SOD during maturation was related to an increase in Mn-SOD expression. Artificial drying resulted in increased SOD and DHAR activity, irrespective of the developmental stage. Our results revealed weak participation of CAT and APX in H₂O₂ scavenging, as well as no significant alterations in GR activities either during maturation or after artificial drying. Changes in SOD and GR isoenzyme patterns occurred during maturation-related drying, but not after artificial drying. These results highlight the role of ascorbate-glutathione cycle enzymes (DHAR and GR) in H₂O₂ scavenging during maturation or after artificial drying of developing J. curcas seeds.     

Activities of SOD and the ascorbate-glutathione cycle enzymes in subcellular compartments in leaves and roots of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii

The activities of the ascorbate-glutathione cycle enzymes ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) and SOD were studied in cell organelles of the cultivated tomato Lycopersicon esculentum (M82) and its wild salt-tolerant related species Lycopersicon pennellii (Lpa). All four enzymes of the ascorbate-glutathione cycle were present in chloroplasts/plastids, mitochondria and peroxisomes of leaf and root cells of both tomato species. In all leaf and root organelles of both species, the activity of MDHAR was similar to, or higher than, that of APX, while the activity of DHAR was one order of magnitude lower than that of MDHAR. Based on these results, it is suggested that in the organelles of both tomato species, ascorbate is regenerated mainly by MDHAR. In both tomato species, GR activity, and to a lesser extent DHAR activity, was found to reside in the soluble fraction of all leaf and root cell organelles, while APX and MDHAR activities were distributed between the membrane and soluble fractions. A higher SOD to APX activity ratio in all Lpa organelles was the major difference between the two tomato species. It is possible that this higher ratio contributes to the inherently better protection of Lpa from salt stress, as was previously reported.     

Antioxidative responses to different altitudes in leaves of alpine plant Polygonum viviparum in summer

Mountain environmental stresses result in increased formation of hydrogen peroxide (H₂O₂) and accumulation of malondialdehyde (MDA) in leaves of Polygonum viviparum. The activities of several antioxidative system enzymes such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), glutathione reductase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the contents of several non-enzymatic antioxidants such as reduced form of ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) were investigated in leaves of P. viviparum, which were collected from three altitudes (2,200, 3,200, and 3,900 m) of Tianshan Mountain in China. The activities of these four antioxidative enzymes were accompanied by increases of H₂O₂ levels from 2,200 to 3,200 m. However, the activities of CAT and POD were decreased, whereas the activities of SOD and GR continually increased at 3,900 m. Analyses of isoforms of SOD, CAT, POD, and GR showed that the leaves of P. viviparum exposed different altitude conditions are capable of differentially altering the intensity. Additionally, two new isoforms of SOD were detected at 3900 m. A continual increase in the ASC, ASC to DHA ratio, GSH and GSH/[GSH + GSSG] ratio, and the activity of DHAR were observed in leaves of P. viviparum with the elevation of altitude. These results suggest that the higher contents of ASC, GSH as well as an increase in reduced redox state may be essential to antioxidation processes in the leaves of P. viviparum, whereas antioxidant enzymes system is a cofactor in the processes.     

Constitutively Elevated Levels of Putrescine and Putrescine-Generating Enzymes Correlated with Oxidant Stress Resistance in Conyza bonariensis and Wheat

Changes in ascorbate and glutathione levels and in activities of ascorbate peroxidase, catalase, dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and superoxide dismutase (SOD) were investigated in tobacco mosaic virus (TMV)-inoculated lower leaves and in non-inoculated upper leaves of Nicotiana tabacum L. cv Xanthi-nc. In separate experiments the effects of exogenous salicylic acid (SA) were also studied. Symptom appearance after TMV inoculation was preceded by a slight, transient decline of ascorbate peroxidase, GR, GST, and SOD activities in the inoculated lower leaves, but after the onset of necrosis these activities and the glutathione level substantially increased. Ascorbic acid level and DHAR activity declined and dehydroascorbate accumulated in the inoculated leaves. In upper leaves, the glutathione level and the activities of GR, GST, and SOD increased 10 to 14 d after TMV inoculation of the lower leaves, concomitantly with the development of systemic acquired resistance. From the six distinct SOD isoenzymes found in tobacco leaves, only the activities of Cu,Zn-SOD isoenzymes were affected by TMV. SA injection induced DHAR, GR, GST, and SOD activities. Catalase activities were not modified by TMV infection or SA treatment. It is supposed that stimulated antioxidative processes contribute to the suppression of necrotic symptom development in leaves with systemic acquired resistance.     

Differential Responses in Activity of Antioxidant Enzymes to Different Environmental Stresses in Arabidopsis thaliana

Arabidopsis thaliana . Three-week-old plants were exposed to a high temperature (30 C), an enhanced light intensity (200 μE/m²/sec), water deficiency (water deprivation for 2 days), a chilling temperature (5 C), or ultraviolet-B (UV-B) radiation (0.25 or 0.094 W/m²) for 1 week (except for water deficiency). The high temperature and enhanced light treatments increased only dehydroascorbate reductase (DHAR) activity. Water deficiency enhanced the activities of DHAR and guaiacol peroxidase (PER). Chilling temperature increased the activities of ascorbate peroxidase (APX) and glutathione reductase (GR), whereas it decreased catalase (CAT) activity. UV-B at an intensity of 0.25 W/m² elevated the activities of APX, monodehydroascorbate reductase (MDHAR), GR, PER and superoxide dismutase (SOD). It was suggested that the amounts of phenylpropanoid compounds increased during treatments of plants with enhanced light intensity, chilling temperature, and UV-B. These results suggest that some differences exist among the oxidative stress conditions caused by the different treatments, although all of these treatments seem to be related to active oxygen production. We propose that in A. thaliana, environmental stresses may be classified into those which induce DHAR activity and those which induce APX activity. Received 11 January 1999/ Accepted in revised form 22 April 1999     

Red 'Anjou' pear has a higher photoprotective capacity than green 'Anjou'

Photoprotective function of anthocyanins along with xanthophyll cycle and antioxidant system in fruit peel was investigated in red 'Anjou' vs green 'Anjou' pear (Pyrus communis) during fruit development and in response to short-term exposure to high light. The sun-exposed peel of red 'Anjou' had higher maximum quantum yield of photosystem II (F(V)/F(M)) than that of green 'Anjou' and both the sun-exposed peel and the shaded peel of red 'Anjou' had smaller decreases in F(V)/F(M) after 2-h high light (photon flux density of 1500 mumol m(-2) s(-1)) treatment than those of green 'Anjou'. At the middle and late developmental stages, the xanthophyll cycle pool size on a chlorophyll basis, the activity of superoxide dismutase, ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) and the level of reduced ascorbate and total ascorbate pool in the sun-exposed peel were either the same or lower in red 'Anjou' than in green 'Anjou', whereas the xanthophyll cycle pool size on a chlorophyll basis and the activity of APX, catalase, MDAR, DHAR and GR in the shaded peel were higher in red 'Anjou' than in green 'Anjou'. It is concluded that red 'Anjou' has a higher photoprotective capacity in both the sun-exposed peel and the shaded peel than green 'Anjou'. While the higher anthocyanin concentration along with the larger xanthophyll cycle pool size and the higher activity of some antioxidant enzymes may collectively contribute to the higher photoprotective capacity in the shaded peel of red 'Anjou', the higher photoprotective capacity in the sun-exposed peel of red 'Anjou' is mainly attributed to its higher anthocyanin concentration.     

Changes in organelle superoxide dismutase isoenzymes during air adaptation of submerged rice seedlings: Differential behaviour of isoenzymes in plastids and mitochondria

Changes in activities and levels of superoxide dismutase (SOD, EC 1.15.1.1) isoenzymes were studied during air adaptation of submerged rice (Oryza sativa L.) seedlings. Seeds were germinated for 6 d in the dark under water (submerged), and then for another day in air (air-adapted). For a control, seeds were germinated for 6 d throughout in air (aerobic). Staining for activity of SOD of shoot extracts showed a total of five major distinct forms of SOD: one mitochondrial Mn enzyme (mtSOD) and four CuZn enzymes, one of which was plastidic (plSOD) and the other three cytosolic (cytSOD). Activity of plSOD was much lower in submerged seedlings than in aerobic controls and increased after exposure to air. In contrast, mtSOD activity in submerged seedlings was as high as that found in aerobic controls, and did not increase upon exposure to air. One of the cytSODs showed responses similar to those of plSOD. The activities of another two cytSODs were slightly lower in submerged seedlings than those in aerobic controls, but decreased after 24 h of air adaptation. Western blot analysis revealed that these changes in activities of SODs are due to changes in the levels of their enzyme proteins. We also followed changes in the levels of cytochrome c and ferredoxin-NADP⁺ reductase (EC 1.6.99.4) as indices of the development of mitochondria and plastids, respectively. Organelle SODs were always present at higher levels than would be expected in view of the development of the electron-transport systems of the corresponding organelles during submergence and the subsequent air-adaptation period.Abbreviations cytSOD cytosolic CuZn-superoxide dismutase - FNR ferredoxin-NADP⁺ reductase - mtSOD mitochondrial Mn-superoxide dismutase - plSOD plastidic CuZn-superoxide dismutase - SOD superoxide dismutase We gratefully acknowledge Dr. A. Wada, Kyoto University, for the use of a densitometer for this work, and also would like to thank Y. Maki, Kyoto University, for help with the densitometry of the photographs.     

环境胁迫和抗坏血酸的氧化还原状态

为了解环境胁迫对植物体中抗坏血酸含量及氧化还原状态的影响,以不同强度的冰冻和干旱两种胁迫为例,研究了它们对沈阳几种针叶树离体叶抗坏血酸、脱氢抗坏血酸含量以及抗坏血酸-谷胱甘肽循环中4种酶活性的影响.结果表明,两种胁迫达到一定强度后,都能使还原态抗坏血酸含量下降而使脱氢抗坏血酸含量上升.冰冻使抗坏血酸过氧化酶和单脱氢抗坏血酸还原酶活性下降.轻度失水使这两种酶活性上升,失水加重后转而趋于下降.脱氢抗坏血酸还原酶和谷胱甘肽还原酶活性对两种胁迫反应均不如前两种酶敏感.结合以前的研究结果,认为这一H2O2清除系统在导致驯化(acclimation)的轻度胁迫作用下可以得到加强,而当胁迫强度过大时则其清除能力下降并使组织受到伤害.文中还报告了沈阳几种针叶树抗寒性和针叶中抗坏血酸含量及上述4种酶活性之间的相关关系.     

Antioxidative responses of Calendula officinalis under salinity conditions.

To gain a better insight into long-term salt-induced oxidative stress, some physiological parameters in marigold (Calendula officinalis L.) under 0, 50 and 100 mM NaCl were investigated. Salinity affected most of the considered parameters. High salinity caused reduction in growth parameters, lipid peroxidation and hydrogen peroxide accumulation. Under high salinity stress, a decrease in total glutathione and an increase in total ascorbate (AsA + DHA), accompanied with enhanced glutathione reductase (GR, EC 1.6.4.2) and ascorbate peroxidase (APX, EC 1.11.1.11) activities, were observed in leaves. In addition, salinity induced a decrease in superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POX, EC 1.11.1.7) activities. The decrease in dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities suggests that other mechanisms play a major role in the regeneration of reduced ascorbate. The changes in catalase (CAT, EC 1.11.1.6) activities, both in roots and in leaves, may be important in H2O2 homeostasis.     

Changes in extreme high-temperature tolerance and activities of antioxidant enzymes of sacred lotus seeds

Sacred lotus (Nelumbo nucifera Gaertn. ‘Tielian’) seed is long-lived and extremely tolerant of high temperature. Water content of lotus and maize seeds was 0.103 and 0.129 g H2O [g DW] ?1, respectively. Water content, germination percentage and fresh weight of seedlings produced by surviving seeds gradually decreased with increasing treatment time at 100℃. Germination percentage of maize (Zea mays L. ‘Huangbaogu’) seeds was zero after they were treated at 100℃ for 15 min and that of lotus seeds was 13.5% following the treatment at 100℃ for 24 h. The time in which 50% of lotus and maize seeds were killed by 100℃ was about 14.5 h and 6 min, respectively. With increasing treatment time at 100℃, relative electrolyte leakage of lotus axes increased significantly, and total chlorophyll content of lotus axes markedly decreased. When treatment time at 100℃ was less than 12 h, subcellular structure of lotus hypocotyls remained fully intact. When treatment time at 100℃ was more than 12 h, plasmoly-sis gradually occurred, endoplasmic reticulum became unclear, nuclei and nucleoli broke down, most of mitochondria swelled, lipid granules accumulated at the cell periphery, and organelles and plas-molemma collapsed. Malondialdehyde (MDA) content of lotus axes and cotyledons decreased during 0-12 h of the treatment at 100℃ and then increased. By contrast, the MDA content of maize embryos and endosperms increased during 5-10 min of the treatment at 100℃ and then decreased slightly. For lotus seeds: (1) activities of superoxide dismutase (SOD) and glutathione reductase (GR) of axes and cotyledons and of catalase (CAT) of axes increased during the early phase of treatment at 100℃ and then decreased; and (2) activities of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) of axes and cotyledons and of CAT of cotyledons gradually decreased with increasing treat-ment time at 100℃. For maize seeds: (1) activities of SOD and DHAR of embryos and endosperms and of GR of embryos increased during the early phase of the treatment at 100℃ and then decreased; and (2) activities of APX and CAT of embryos and endosperms and of GR of endosperms rapidly decreased with increasing treatment time at 100℃. With decrease in seed germination, activities of SOD, APX, CAT, GR and DHAR of axes and cotyledons of lotus seeds decreased slowly, and those of embryos and endosperms of maize seeds decreased rapidly.     

环境胁迫和抗坏血酸的氧化还原状态

为了解环境胁迫对植物体中抗坏血酸含量及氧化还原状态的影响，以不同强度的冰冻和干旱两种胁迫为例，研究了它们对沈阳几种针叶树离体叶抗坏血酸、脱氢抗坏血酸含量以及抗坏血酸-谷胱甘肽循环中4种酶活性的影响。结果表明，两种胁迫达到一定强度后，都能使还原态抗坏血酸含量下降而使脱氢抗坏血酸含量上升。冰冻使抗坏血酸过氧化酶和单脱氢抗坏血酸还原酶活性下降。轻度失水使这两种酶活性上升，失水加重后转而趋于下降。脱氢抗坏血酸还原酶和谷胱甘肽还原酶活性对两种胁迫反应均不如前两种酶敏感。结合以前的研究结果，认为这一H2O2清除系统在导致驯化(acclimation)的轻度胁迫作用下可以得到加强，而当胁迫强度过大时则其清除能力下降并使组织受到伤害。文中还报告了沈阳几种针叶树抗寒性和针叶中抗坏血酸含量及上述4种酶活性之间的相关关系。