The system modulating ROS content in germinating seeds of two Brazilian savanna tree species exposed to As and Zn

The effects of increasing arsenic (0, 10, 50, 100 mg L^?1) and zinc (0, 50, 80, 120, 200 mg L^?1) doses on germination and oxidative stress markers (H₂O₂, MDA, SOD, CAT, APX, and GR) were examined in two Brazilian savanna tree species (Anadenanthera peregrina and Myracrodruon urundeuva) commonly used to remediate contaminated soils. The deleterious effects of As and Zn on seed germination were due to As- and Zn-induced H₂O₂ accumulation and inhibition of APX and GR activities, which lead to oxidative damage by lipid peroxidation. SOD and CAT did not show any As- and Zn-induced inhibition of their activities as was seen with APX and GR. We investigated the close relationships between seed germination success under As and Zn stress in terms of GR and, especially, APX activities. Increased germination of A. peregrina seeds exposed to 50 mg L^?1 of Zn was related to increased APX activity, and germination in the presence of As (10 mg L^?1) was observed only in M. urundeuva seeds that demonstrated increased APX activity. All the treatments for both species in which germination decreased or was inhibited showed decreases in APX activity. A. peregrina seeds showed higher Zn-tolerance than M. urundeuva, while the reverse was observed with arsenic up to exposures of 10 mg L^?1.     

Physiological responses and antioxidant enzyme changes in <Emphasis Type="Italic">Sulla coronaria</Emphasis> inoculated by cadmium resistant bacteria

Plant growth promoting bacteria (PGPB) may help to reduce the toxicity of heavy metals on plants growing in polluted soils. In this work, Sulla coronaria inoculated with four Cd resistant bacteria (two Pseudomonas spp. and two Rhizobium sullae) were cultivated in hydroponic conditions treated by Cd; long time treatment 50 µM CdCl₂ for 30 days and short time treatment; 100 µM CdCl₂ for 7 days. Results showed that inoculation with Cd resistant PGPB enhanced plant biomass, thus shoot and root dry weights of control plants were enhanced by 148 and 35% respectively after 7 days. Co-inoculation of plants treated with 50 and 100 µM Cd increased plant biomasses as compared to Cd-treated and uninoculated plants. Cadmium treatment induced lipid peroxidation in plant tissues measured through MDA content in short 7 days 100 µM treatment. Antioxidant enzyme studies showed that inoculation of control plants enhanced APX, SOD and CAT activities after 30 days in shoots and SOD, APX, SOD, GPOX in roots. Application of 50 µM CdCl₂ stimulated all enzymes in shoots and decreased SOD and CAT activities in roots. Moreover, 100 µM of CdCl₂ increased SOD, APX, CAT and GPOX activities in shoots and increased significantly CAT activity in roots. Metal accumulation depended on Cd concentration, plant organ and time of treatment. Furthermore, the inoculation enhanced Cd uptake in roots by 20% in all treatments. The cultivation of this symbiosis in Cd contaminated soil or in heavy metal hydroponically treated medium, showed that inoculation improved plant biomass and increased Cd uptake especially in roots. Therefore, the present study established that co-inoculation of S. coronaria by a specific consortium of heavy metal resistant PGPB formed a symbiotic system useful for soil phytostabilization.     

脱水速率对黄皮胚轴脱水敏感性及膜脂过氧化的影响

以黄皮种子离体胚轴为材料,研究了不同干燥速率对胚轴脱水反应和膜脂过氧化的影响.在脱水过程中,胚轴的萌发率、活力指数、电解质渗漏速率,超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性逐渐降低,膜脂过氧化产物MDA的含量不断增加.脱水速率愈快,胚轴的半致死含水量就愈低.快速干燥的胚轴能在较低的含水量下存活是因为缩短了在中间含水量下发生的膜脂过氧化作用的时间,以及保持较高的SOD、POD和CAT活性;缓慢干燥的胚轴当与周围环境达到水分平衡后,生活力的丧失将与保持在水分平衡后的时间有关.因此,脱水速率是一种影响顽拗性种子或者胚轴脱水敏感性的重要因子.     

Desiccation-induced ROS accumulation and lipid catabolism in recalcitrant <Emphasis Type="Italic">Madhuca latifolia</Emphasis> seeds

Loss of viability in desiccation-sensitive seeds of Madhuca latifolia (Roxb.) J. F. Macbr., an important multipurpose tropical tree, was correlated with seed water content (WC). WC declined from 0.59 to 0.19 g g^?1 fresh mass, 35 days after harvest from mother plant, at ambient conditions (temperature 25 ± 2 °C, relative humidity 50 ± 2%). The desiccation-induced reduction in viability was related with an accumulation of reactive oxygen species (ROS) that promoted lipid peroxidation associated loss of membrane integrity. Conducted study revealed 1.6–19 folds rise in lipid peroxidized products in desiccated M. latifolia seeds, and was found to be linked inversely with WC and germination percentage. Additionally, increased activities (7 and 13 folds) of lipid hydrolyzing enzymes; lipase (EC 3.1.1.3) and lipoxygenase (EC 1.13.11.12) respectively, were discernible in desiccating M. latifolia seeds. In summary, increased ROS, lipid oxidation, lipase and lipoxygenase were strongly correlated with viability loss in desiccating M. latifolia seeds.     

Free radical scavenging as affected by accelerated ageing and subsequent priming in sunflower seeds

Lipid peroxidation resulting from loss of free radical scavenging is thought to be involved in deterioration of sunflower (Helianthus annuus L.) seeds during accelerated ageing. In other respects, presoaking of seeds in a solution of low water potential (osmopriming) has been demonstrated to reinvigorate aged seeds. The aim of the present work was to study the effect of osmopriming on the germination of aged sunflower seeds and to investigate whether this effect was associated with the restoration of antioxidant defence systems. Seeds were aged for 5 days at 45°C and 100% relative humidity and then primed for various durations up to 7 days at 15°C in a solution of polyethylene glycol 6000 at ?2 MPa. Lipid peroxidation was estimated by measuring malondialdehyde (MDA) and conjugated diene contents, and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were measured throughout the treatments. Accelerated ageing resulted in a marked decrease in the germination rate, and was associated with an increase in the levels of MDA and conjugated dienes, thus indicating lipid peroxidation. Ageing was also characterized by a decrease in the activities of CAT and GR. The activities of SOD and DHAR were much less altered. No APX activity was detected whatever the seed treatment. Priming of aged seeds progressively restored the initial germinative ability and resulted in a marked decrease in the levels of MDA and conjugated dienes, indicating a fall in lipid peroxidation processes. These effects of priming were also well correlated to the recovery of SOD, CAT and GR activities. Priming treatment for 7 days led to full restoration of the cell detoxifying mechanisms which were strongly altered during ageing. Glutathione content showed the same changes as GR activity. There existed a clear-cut relationship between seed germinative energy, expressed as the germination rate, and the efficiency of free radical scavenging systems, in particular CAT and GR activities and glutathione content. The results suggest that the antioxidant defence systems might play a key role in seed vigour.     

Morphological and Physiological Responses of Cotton (Gossypium hirsutum L.) Plants to Salinity

Salinization usually plays a primary role in soil degradation, which consequently reduces agricultural productivity. In this study, the effects of salinity on growth parameters, ion, chlorophyll, and proline content, photosynthesis, antioxidant enzyme activities, and lipid peroxidation of two cotton cultivars, [CCRI-79 (salt tolerant) and Simian 3 (salt sensitive)], were evaluated. Salinity was investigated at 0 mM, 80 mM, 160 mM, and 240 mM NaCl for 7 days. Salinity induced morphological and physiological changes, including a reduction in the dry weight of leaves and roots, root length, root volume, average root diameter, chlorophyll and proline contents, net photosynthesis and stomatal conductance. In addition, salinity caused ion imbalance in plants as shown by higher Na⁺ and Cl⁻ contents and lower K⁺, Ca²⁺, and Mg²⁺ concentrations. Ion imbalance was more pronounced in CCRI-79 than in Simian3. In the leaves and roots of the salt-tolerant cultivar CCRI-79, increasing levels of salinity increased the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), but reduced catalase (CAT) activity. The activities of SOD, CAT, APX, and GR in the leaves and roots of CCRI-79 were higher than those in Simian 3. CAT and APX showed the greatest H₂O₂ scavenging activity in both leaves and roots. Moreover, CAT and APX activities in conjunction with SOD seem to play an essential protective role in the scavenging process. These results indicate that CCRI-79 has a more effective protection mechanism and mitigated oxidative stress and lipid peroxidation by maintaining higher antioxidant activities than those in Simian 3. Overall, the chlorophyll a, chlorophyll b, and Chl (a+b) contents, net photosynthetic rate and stomatal conductance, SOD, CAT, APX, and GR activities showed the most significant variation between the two cotton cultivars.     

Proteomic profiling and redox status alteration of recalcitrant tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis>) seed in response to desiccation

Tea seed is believed to be recalcitrant based on its sensitivity to chilling or drying stress. Reactive oxygen species (ROS) and alterations in cytosolic redox status have been implicated in intolerance to desiccation by recalcitrant seed, but there is little information available regarding how ROS are regulated in seeds susceptible to drying stress. We investigated changes in protein expression and activity in tea embryo in response to desiccation using physiological and proteomic methods. Results showed that desiccation treatment dramatically induced the accumulation of H₂O₂ in tea embryos, accompanied by increased activities of antioxidant enzymes like ascorbate peroxidase (APX) and superoxide dismutase (SOD). Proteomic analyses also demonstrated that 23 proteins associated with defense response, metabolism and redox status were up-regulated following desiccation. Increase in antioxidants, ascorbic acid (AsA) and catalase (CAT) (H₂O₂ scavengers) partially assuaged desiccation damage to tea seed, resulting in improved germination rates. Higher accumulation of H₂O₂ aggravated desiccation damage to seeds leading to lower germination activity. We propose that desiccation causes an over-accumulation of ROS that are not efficiently scavenged by increased levels of antioxidant enzymes. High levels of ROS alter the redox status and are detrimental to seed viability. Reducing ROS to appropriate concentrations is an efficient way to reduce desiccation damage and improve germination rates of recalcitrant seeds.     

Active oxygen species metabolism in neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) seeds exposed to natural ageing and controlled deterioration

Success of ex situ storage of germplasm for trade and conservation essentially depends upon the precision of the protocol employed for the assessment of germination potential. Active oxygen species and antioxidative enzymes during natural ageing (NA) and controlled deterioration (CD) was monitored during the loss of seed vigour and germination potential in neem seeds showing intermediate seed storage behaviour. Higher levels of SOD, CAT and APX were strongly and positively associated with germination and vigour. The loss of CAT and APX activity estimated quantitatively and number of isoenzymes were closely accompanied with the simultaneous increase in the amounts of H₂O₂ and OH-radical. The decline in germination and vigour was negatively related with the levels of H₂O₂ and OH-radical and enhanced electrolyte leakage. The amounts of OH-radical were positively correlated with the decline in DNA content and DNA damage. The levels of SOD isoenzymes initially increased as the germination index of seeds declined from 5250 to 762 and 882 under NA and CD conditions, respectively. Increasing activity of SOD in the ageing seeds were associated with the accumulation of H₂O₂. The role of antioxidative enzymes in maintaining signalling and damaging amounts of AOS as well as revelations of different pathways of ageing during NA and CD in the ageing neem seeds were discussed.     

Induced anti-oxidant activity in soybean alleviates oxidative stress under moderate boron toxicity

The effect of B toxicity on antioxidant responses of soybean (Glycine max) cv. Athow was investigated by growing plants for 43 days at 0.2 (control), 2 and 12 mg B kg^?1. At the end of the treatment period, shoot growth, lipid peroxidation level, the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), and their isoenzymes in leaves were measured. Boron concentration in leaves was significantly increased by the increasing levels of B treatment from 43 to 522 mg kg^?1, and shoot dry matter was depressed at 12 mg B kg^?1. Significant increases in SOD, CAT, and APX activities were determined in leaves under 12 mg B kg^?1; however, GR activities were decreased while POX activity was unchanged. Increased enzymic antioxidant activity arose from a combination of newly formed isoenzymes and activation of existing isoenzymes. By contrast, SOD and GR activities were decreased by 2 mg B kg^?1 concentration as compared to the control groups while POX activity was increased and the activity of CAT did not change. Malondialdehyde content increased under 2 mg B kg^?1 but decreased under 12 mg B kg^?1. These results suggest that higher antioxidant activity observed under 12 than at 2 mg B kg^?1 provided higher free radical-scavenging capacity, and thus a lower level of lipid peroxidation in Athow. While the induction of increased antioxidant activity was related to internal boron levels, the signaling and coordination of responses remain unclear.     

Compatible solutes improve regrowth,ameliorate enzymatic antioxidant systems,and reduce lipid peroxidation of cryopreserved <Emphasis Type="Italic">Hancornia speciosa</Emphasis> Gomes lateral buds

Hancornia speciosa is a native fruit species from Brazil with important economic applications. However, the use of this species has been challenged by difficulties in its storage. Cryopreservation is a safe and efficient tool for long-term storage. Nevertheless, cryopreservation may promote reactive oxygen species (ROS) formation with subsequent lipid peroxidation, which causes membrane damage. The use of in vitro antioxidant compounds could help eliminate ROS and consequently improve explant survival. In the current study, the lateral buds of H. speciosa were precultivated in proline or glycine betaine (GB)-containing solutions, and the effect of these compounds on the enzymatic activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) and on lipid peroxidation was measured after sample warming. The present findings indicated that oxidative stress induced by cryopreservation was significantly reduced by the precultivation of lateral buds with proline and GB. SOD activity increased, and subsequently, hydrogen peroxide (H₂O₂) production increased followed by the immediate activation of CAT and APX. The enzyme activity increased for 7 following rewarming, indicating that precultivation with 0.1 M proline was fundamental to achieving high levels of shoot regeneration from H. speciosa lateral buds.     

Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H₂O₂) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H₂O₂, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H₂O₂ content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.     

The deterioration of <Emphasis Type="Italic">Moringa oleifera</Emphasis> Lam. seeds in the course of storage involves reserve degradation

Seed deterioration in the course of storage may involve hydrolytic reactions. Hence, we aimed to evaluate viability, vigour, contents of reserves and metabolites, and activities of hydrolytic enzymes in Moringa oleifera Lam. seeds during storage under controlled conditions. Seeds were packaged in semipermeable plastic and maintained in a growth chamber (27 ± 2 °C and RH 60–65%) and under refrigeration (4 ± 2 °C and RH 20–25%) for 18 months. Samples were taken at the start of the experiment and every 3 months. During the first 12 months, water content, viability, and vigour remained almost unaffected, while the content of neutral lipids, starch, soluble sugars and free amino acids did not reduce in the seeds kept under refrigeration. After this period, the loss of viability and vigour was accompanied by the degradation of storage lipids, storage proteins, and non-reducing sugars associated with the increase of lipase and acid protease activity in both environmental conditions. As the seed water content remained below 8% in the course of the experiment, we suggest that non-enzymatic hydrolysis might play a role in the deterioration of M. oleifera seeds during storage. At least for planting, we recommend that M. oleifera seeds be kept at low relative humidity under refrigeration for up to 12 months.     

Kinetin-Mediated Prolongation of Viability in Recalcitrant Sal (Shorea robusta Gaertn. f.) Seeds at Low Temperature: Role of Kinetin in Delaying Membrane Deterioration during Desiccation-Induced Injury

The effects of kinetin (6-furfurylaminopurine) on viability during storage of recalcitrant sal (Shorea robusta Gaertn. f.) seeds at low temperature (15°C) were investigated. The freshly mature sal seeds showed an absolute loss of viability within 6–7 dah (days after harvest) when stored at ambient or at 15°C (control). Storage of these seeds at 15°C after kinetin (10 ppm) treatment prolonged the viability period up to 35 days with 20% germination. The kinetin-treated seeds exhibited 100% germination up to 10 days compared with 3 days in controls. Measurements of leachate conductivity, ·O⁻ ₂ and lipid peroxidation registered gradual increases from 0 dah onward to 35 dah with significantly low levels compared with controls. On the other hand, an enormous increase in superoxide dismutase activity was discernible for a longer duration (0–35 dah) in kinetin-treated seeds than in control seeds where it remained for 3 dah. The role of kinetin in prolonging seed viability by reducing the loss of leachates, lipid peroxidation, ·O⁻ ₂, and enhancing of superoxide dismutase is discussed. Received October 7, 1997; accepted January 27, 1998     

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.     

Arsenic-induced root growth inhibition in mung bean (<Emphasis Type="Italic">Phaseolus aureus</Emphasis> Roxb.) is due to oxidative stress resulting from enhanced lipid peroxidation

Arsenic (As) toxicity and its biochemical effects have been mostly evaluated in ferns and a few higher plants. In this study, we investigated the effect of As (10.0 and 50.0 μM) on seedling growth, root anatomy, lipid peroxidation (malondialdehyde and conjugated dienes), electrolyte leakage, H₂O₂ content, root oxidizability and the activities of antioxidant enzymes in mung bean (Phaseolus aureus Roxb.). Arsenic significantly enhanced lipid peroxidation (by 52% at 50.0 μM As), electrolyte leakage and oxidizability in roots. However, there was no significant change in H₂O₂ content. Arsenic toxicity was associated with an increase in the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR). In response to 50.0 μM As, the activities of SOD and GR increased by over 60% and 90%, respectively. At 10.0 μM As, the activity of ascorbate peroxidase (APX) increased by 83%, whereas at 50.0 μM it declined significantly. The catalase (CAT) activity, on the other hand, decreased in response to As exposure, and it corresponded to the observed decrease in H₂O₂ content. We conclude that As causes a reduction in root elongation by inducing an oxidative stress that is related to enhanced lipid peroxidation, but not to H₂O₂ accumulation.     

Accelerated ageing and subsequent imbibition affect seed viability and the efficiency of antioxidant system in macaw palm seeds

Accelerated ageing is an accurate test indicator of seed vigor and storability that helps to understand the mechanisms of cellular and biochemical deterioration that occur during seed ageing. This study was carried out to elucidate the mechanisms of ageing in macaw palm embryos. Seeds were artificially aged during 4, 8 and 12 days at 45 °C and 100% relative humidity. After ageing, seeds were tested for viability (tetrazolium), electrical conductivity, lipid peroxidation (MDA) and hydrogen peroxide (H₂O₂) content. Part of the aged seeds was imbibed for 8 days and then determined the hydrogen peroxide content and the activity of antioxidant system enzymes (superoxide dismutase, catalase and glutathione reductase). Ageing reduced the embryo viability from 8 days of treatment and increased malondialdehyde content (MDA) and solute leakage. Hence, membrane permeability correlated with both loss of viability and lipid peroxidation. Imbibition after ageing significantly increased H₂O₂ content along with superoxide dismutase activity. Catalase activity was significantly higher than control in embryos aged from 8 days and imbibed, and glutathione reductase activity did not change. Our results suggest that macaw palm seed deterioration during accelerated ageing is closely related to lipid peroxidation, and that enzymatic antioxidant system is not completely efficient in reducing reactive oxygen species after imbibition, a critical phase to germination. Moreover, accelerated ageing test can be used as a reliable model to understand the mechanisms involved in palm seeds deterioration.     

The relations between antioxidant enzymes and chlorophyll fluorescence parameters in common bean cultivars differing in sensitivity to drought stress

Effects of the antioxidant system and chlorophyll fluorescence on drought tolerance of four common bean (Phaseolus vulgaris L.) cultivars were studied. The cultivars were positioned in the order of a decrease in their drought tolerance: Yakutiye, Pinto Villa, Ozayse, and Zulbiye on the basis of changes in the water potential, stomatal conductance, photosynthetic pigment content, and lipid peroxidation. Under drought conditions, the level of H₂O₂ was not changed in cv. Pinto Villa but decreased in other cultivars. Antioxidant enzymes (superothide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)) were generally activated in all cultivars. Interestingly, CAT, APX, and GR activities were not changed in cv. Pinto Villa, APX activity decreased in cv. Yakutiye, and CAT activity was not changed in cv. Zulbiye. The increases in SOD and GPX activities in cv. Ozayse were higher than in other cultivars. Drought stress reduced the effective quantum yield of PS2 (Φ_PS2) and the photochemical quenching (q_p), while it increased nonphotochemical quenching (NPQ) in all cultivars. The reduction or increase was more pronounced in cv. Zulbiye. There were generally significant correlations between q_p, NPQ, and ROS scavenging by SOD and APX. Also, there were significant correlations between SOD and q_p in tolerant cultivars and APX and q_p in sensitive ones. The results indicate that activation of SOD and APX was closely related to the efficiency of PS2 in common bean cultivars. This interaction was essential for protection of photosystems and plant survival under drought.     

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°C. Germination percentage of maize (Zea mays L. ‘Huangbaogu’) seeds was zero after they were treated at 100°Cfor 15 min and that of lotus seeds was 13.5% following the treatment at 100°C for 24 h. The time in which 50% of lotus and maize seeds were killed by 100°C was about 14.5 h and 6 min, respectively. With increasing treatment time at 100°C, relative electrolyte leakage of lotus axes increased significantly, and total chlorophyll content of lotus axes markedly decreased. When treatment time at 100°C was less than 12 h, subcellular structure of lotus hypocotyls remained fully intact. When treatment time at 100°C was more than 12 h, plasmolysis 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 plasmolemma collapsed. Malondialdehyde (MDA) content of lotus axes and cotyledons decreased during 0 −12 h of the treatment at 100°C and then increased. By contrast, the MDA content of maize embryos and endosperms increased during 5–10 min of the treatment at 100°C 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°C 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 treatment time at 100°C. 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°C 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°C. 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.     

Exogenous salicylic acid alleviates NaCl toxicity and increases antioxidative enzyme activity in <Emphasis Type="Italic">Lycopersicon esculentum</Emphasis>

Effects of exogenous salicylic acid (SA) on plant growth, contents of Na, K, Ca and Mg, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and contents of ascorbate and glutathione were investigated in tomato (Lycopersicon esculentum L.) plants treated with 100 mM NaCl. NaCl treatment significantly increased H₂O₂ content and lipid peroxidation indicated by accumulation of thiobarbituric acid reactive substances (TBARS). A foliar spray of 1 mM SA significantly decreased lipid peroxidation caused by NaCl and improved the plant growth. This alleviation of NaCl toxicity by SA was related to decreases in Na contents, increases in K and Mg contents in shoots and roots, and increases in the activities of SOD, CAT, GPX and DHAR and the contents of ascorbate and glutathione.     

ROS production and antioxidative system activity in embryonic axes of <Emphasis Type="Italic">Quercus robur</Emphasis> seeds under different desiccation rate conditions

The seeds of pedunculate oak (Quercus robur L.) were subjected to slow (S) and rapid (R) desiccation at desiccation rates of 0.16 and 0.39% H₂O per hour, respectively. Till ca. 40% water content (WC) the germination capacity of seeds in the S and R variants was high (ca. 100%). Between 40 and 28% WC, germination capacity declined to 20 and 50% in S and R variants, respectively. The decrease in seed viability was accompanied by a significant increase of electrolyte leakage from embryonic axes (28% for S and 15% for R variants). In the embryonic axes of seeds subjected to slow desiccation, malondialdehyde (MDA) and free fatty acid (FFA) contents were significantly higher than those in R variants, indicating greater membrane damage due to lipid peroxidation. The production of ROS (H₂O₂ and O₂^·−) was significantly higher in S than in R variants. The low molecular weight antioxidants α-tocopherol, ascorbic acid (ASA), and phenolic compounds indicated different reactions in response to desiccation stress. ASA levels decreased during desiccation to a similar degree in both the S and R variants. A significant decrease of total phenols was observed in R variant, which coincided with a significant increase of guaiacol peroxidase (POX) activity. α-Tocopherol content was significantly higher in the embryonic axes of seeds subjected to rapid drying. The activities of the enzymatic scavengers APX and GR had similar runs and were slightly higher in R variant. The activities of POX and SOD were significantly higher in the embryonic axes of seeds subjected to rapid drying. These results show that rapid dehydration of Q. robur seeds leads to the greater mobilization of antioxidant system in embryonic axes, particularly increased levels of α-tocopherol and POX and SOD activities, in the first stages of water loss. This mobilization has a greater impact on maintenance of higher viability of seeds after drying to lower level of WC.