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.     

黄皮种子发育过程中脱水敏感性与细胞膜透性的关系

黄皮（Ｃｌａｕｓｅｎａ ｌａｎｓｉｕｍ （Ｌｏｕｒ．） Ｓｋｅｅｌｓ）胚轴与完整种子的发育模式以及发育中电解质渗漏率变化有些不同． 种子生理成熟前、后的胚轴对脱水的反应也不同,前者经轻微脱水可提高萌发率和活力指数,后者不耐任何程度的脱水．活力指数的急剧下降伴随着电解质渗漏率的迅速上升．实验表明,黄皮种子在发育过程中没有形成耐脱水性． 细胞膜透性变化可反映脱水对种子的伤害程度     

Relation Between Desiccation Sensitivity and Membrane Permeability of Developing Clausena lansium Seeds

Desiccation sensitivity and its relation to membrane permeability of the embryonic axes of the developing wampee (Clausena lansium (Lour.) Skeels) seeds were studied by measuring the changes in electrolyte leakage, germination and vigor index after the embryonic axes were rapidly air-dried to various water contents. During development, the fresh and dry weight per seed reached nearly maximum value at 72 d after anthesis, but the dry weight per embryonic axis continuously increased until 85 d after anthesis. The embryonic axes acquired the full capacity for germination at 58 d after anthesis and their vigor index continuously rose up from 51 to 92 d after anthesis. The electrolyte leakage of the developing the embryonic axes linearly declined to the minimum value at 72 d after anthesis and then went up again. The electrolyte leakage of the embryonic axes was higher than that of the whole seeds at the same time. The immature embryonic axes did not germinate completely, while mild desiccation could improve their viability. Any degree of desiccation decreased the vigor index of the embryonic axes which have reached physiological maturation and the decline of vigor index was corresponded to the increase of electrolyte leakage. According to this experiment, the authors concluded that wampee seeds did not gain desiccation-tolerance which was a characteristic of orthodox seeds during development. High water content was essential for maintaining membrane integrity and stabiligy of matured wampee seeds. The injury of seed viability during dehydration could be estimated by using the electro-conductivity method.     

State and Phase Transition Behaviors ofQuercus rubraSeed Axes and Cotyledonary Tissues: Relevance to the Desiccation Sensitivity and Cryopreservation of Recalcitrant Seeds

Freezing and melting transitions of cellular water in embryonic axes and cotyledonary tissues of recalcitrantQuercus rubra(red oak) seeds were compared under slow and rapid cooling conditions. The relevance of desiccation sensitivity (critical water content) and state/phase transition behaviors to cryopreservation was examined. Under a slow to intermediate cooling condition (≤10°C min⁻¹), unfrozen water content in the tissues decreased to less than the critical water content, resulting in a dehydration damage. Under a rapid cooling condition (>100°C min⁻¹) using liquid nitrogen (LN₂), freeze-induced dehydration damage could be avoided if the initial water content was >0.50 g g⁻¹dry wt. However, at water content >0.50 g g⁻¹dry wt, the vitrified cellular matrix was highly unstable upon warming at 10°C min⁻¹. These results offered a theoretical explanation on the difficulty for successful cryopreservation of recalcitrant red oak embryonic axes. A complete state/phase transition diagram for red oak axes was constructed, and a vitrification-based cryopreservation protocol that employed predehydration and rapid cooling was examined. State/phase transition behaviors of cellular water are important parameters for cryopreservation; however, vitrification alone was not sufficient for seed tissues to survive the cryopreservation condition.     

Ascorbic acid metabolism in ageing recalcitrant sal (Shorea robusta Gaertn. f.) seeds

Changes in ascorbate content and its enzymatic utilization pattern were studied in embryonic axes and cotyledons of sal seeds undergoing rapid loss of viability, at ambient conditions. Ascorbate levels were significantly higher initially in the embryonic axes (0.32 mg/g fresh weight) and cotyledons (0.21 mg/g fresh weight) of freshly mature, relatively hydrated (42.2% moisture content) and 100% viable sal seeds. It declined sharply as the tissues; embryonic axes and cotyledons, desiccated with absolutely no detectable amount in non-viable seeds (21% moisture content). Significantly strong correlation was obtained between desiccation of embryonic axes (r = 0.96) and cotyledon (r = 0.97) with loss of ascorbate levels and loss of germinability. Higher rates of ascorbic acid utilization (AAU) recorded in the embryonic axes of 100% viable seed declined sharply as the seed viability reduced due to desiccation below 36.8% moisture content. AAU was not detected in the cotyledons.     

Rate of dehydration and cumulative desiccation stress interacted to modulate desiccation tolerance of recalcitrant cocoa and ginkgo embryonic tissues

Rate of dehydration greatly affects desiccation tolerance of recalcitrant seeds. This effect is presumably related to two different stress vectors: direct mechanical or physical stress because of the loss of water and physicochemical damage of tissues as a result of metabolic alterations during drying. The present study proposed a new theoretic approach to represent these two types of stresses and investigated how seed tissues responded differently to two stress vectors, using the models of isolated cocoa (Theobroma cacao) and ginkgo (Ginkgo biloba) embryonic tissues dehydrated under various drying conditions. This approach used the differential change in axis water potential (DeltaPsi/Deltat) to quantify rate of dehydration and the intensity of direct physical stress experienced by embryonic tissues during desiccation. Physicochemical effect of drying was expressed by cumulative desiccation stress [integralf(psi,t)], a function of both the rate and time of dehydration. Rapid dehydration increased the sensitivity of embryonic tissues to desiccation as indicated by high critical water contents, below which desiccation damage occurred. Cumulative desiccation stress increased sharply under slow drying conditions, which was also detrimental to embryonic tissues. This quantitative analysis of the stress-time-response relationship helps to understand the physiological basis for the existence of an optimal dehydration rate, with which maximum desiccation tolerance could be achieved. The established numerical analysis model will prove valuable for the design of experiments that aim to elucidate biochemical and physiological mechanisms of desiccation tolerance.     

Differential drying rates of recalcitrant Trichilia dregeana embryonic axes: a study of survival and oxidative stress metabolism

Studies to elucidate the biochemical basis of survival of excised embryonic axes (EAs) of recalcitrant seeds of Trichilia dregeana at different drying rates revealed significant differences between slow and rapid drying. Rapid drying allowed these EAs to survive dehydration to much lower water contents (WCs; ca. 0.31 g g^?1 dry mass basis with 73% germination) compared with slow drying, where 90% of the EAs lost viability at a WC of ca. 0.79 g g^?1. In EAs slowly dried within seeds, the levels of hydroxyl radical (three‐ to fivefold at WCs >0.5 g g^?1) and lipid peroxidation (50% at similar WC) were significantly higher compared with those dried rapidly to comparable WCs. When EAs were dried slowly, enzymic antioxidant levels were not sustained and declined significantly with prolonged storage. In contrast, sustained activity of enzymic antioxidants was detected in rapidly dried EAs even at relatively low WCs. Furthermore, the greater decline in glutathione (GSH)/GSH disulphide ratio in EAs slowly dried within seeds compared with rapidly dried EAs and a shift in GSH redox potential to relatively more positive values in the EAs slowly dried within seeds was correlated with considerable viability loss. It is apparent from this study that greater retention of viability to lower WCs in rapidly dried EAs from recalcitrant seeds may at least be partly explained by the retention of functional antioxidant status. It is also suggested that the reduction of viability in rapidly dried EAs at very low WCs appears to be a non‐oxidative process.     

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.     

A comparison of partial dehydration and hydrated storage-induced changes in viability,reactive oxygen species production,and glutathione metabolism in two contrasting recalcitrant-seeded species

This study compared the responses of Avicennia marina and Trichilia dregeana seeds, both of which are recalcitrant, to partial dehydration and storage. Seeds of A. marina exhibited a faster rate of water and viability loss (± 50% viability loss in 4 days) during partial dehydration, compared with T. dregeana (± 50% viability loss in 14 days). In A. marina embryonic axes, reactive oxygen species (ROS) production peaked on 4 days of dehydration and was accompanied by an increase in the GSH:GSSG ratio; it appears that the glutathione system alone could not overcome dehydration-induced oxidative stress in this species. In A. marina, ROS and axis water content levels increased during hydrated storage and were accompanied by a decline in the GSH:GSSG ratio and rapid viability loss. In T. dregeana embryonic axes, ROS production (particularly hydrogen peroxide) initially increased and thereafter decreased during both partial dehydration and hydrated storage. Unlike in A. marina embryonic axes, this reduced ROS production was accompanied by a decline in the GSH:GSSG ratio. While T. dregeana seeds may have incurred some oxidative stress during storage, a delay in and/or suppression of the ROS-based trigger for germination may account for their significantly longer storage longevity compared with A. marina. Mechanisms of desiccation-induced seed viability loss may differ across recalcitrant-seeded species based on the rate and extent to which they lose water during partial drying and storage. While recalcitrant seed desiccation sensitivity and, by implication, storage longevity are modulated by redox metabolism, the specific ROS and antioxidants that contribute to this control may differ across species.     

Embryo Water Status and Survival in the Recalcitrant Species Quercus robur L: Evidence for a Critical Moisture Content

The responses of Q. robur L. fruits, seeds and embryonic axesto desiccation are characterized and discussed in relation tocurrent knowledge of recalcitrant seed behaviour. A relationshipbetween viability and seed moisture content is described. Thisrelationship was unaffected by rate of drying, year of harvestor presence of the pericarp. Desiccation sensitivity did notincrease with storage. Excised embryonic axes survived to lower moisture contents thanintact seeds. However, in the intact seed, loss of viabilityappeared to be determined by a critical moisture content inthe cotyledons. Consequently, the level of desiccation tolerancewithin the axis attached to cotyledons was not determined byaxis drying rate. A link is drawn between the difference in the desiccation toleranceof embryonic axes and of cotyledons, and estimates of theirdifferent levels of matrix-bound water. The results presentedare consistent with a critical moisture content for survivalwhich is determined by the loss of all free cellular water.This hypothesis takes account of the differential desiccationsensitivity of seed tissues and differences in desiccation tolerancebetween species.     

Sugar effects on membrane damage during desiccation of pea embryo protoplasts

Desiccation tolerance of protoplasts isolated from germinating pea (Pisum sativum L. cv. 'Alaska') embryonic axes depends, in part, on the osmotic strength and composition of the suspending medium. To determine the reason for this dependence and whether treatment with different solutions results in different types of damage, protoplast recovery and survival were assessed after dehydration to a range of water contents. Protoplasts were derived from germinating axes that had intermediate desiccation tolerance. Protoplasts were isolated and resuspended in buffers containing sucrose/raffinose (85:15, w/w) or sorbitol, which were isotonic or hypertonic to the cells of the embryonic axis, then were flash-dried to a range of water contents. Protoplasts were rehydrated and stained with fluorescein diacetate (FDA) to assess survival and to estimate two types of membrane injury: lysis and the loss of semipermeability. In all treatments, protoplast survival dropped sharply during the initial phase of dehydration due to lysis. Protoplast survival was greater in hypertonic sucrose/raffinose buffer than in isotonic sucrose/raffinose buffer, or in the latter made hypertonic by the addition of sorbitol. When sorbitol was substituted for sucrose/raffinose in either the isolation or desiccation buffer, or both, protoplast survival at intermediate and low hydrations decreased due to a loss of membrane semipermeability. The results indicate that additional sucrose/raffinose is beneficial for the desiccation tolerance of protoplasts, the benefit is not due to a simple osmotic effect, and the benefit is greatest at water contents less than 0.5 g g(-1) DW, where the presence of the sugars appears to protect membrane semipermeability.     

Interactions among water content, rapid (nonequilibrium) cooling to -196 degrees C, and survival of embryonic axes of Aesculus hippocastanum L. seeds

This study investigated the interactions among water content, rapid (nonequilibrium) cooling to -196 degrees C using isopentane or subcooled nitrogen, and survival of embryonic axes of Aesculus hippocastanum. Average cooling rates in either cryogen did not exceed 60 degrees C s(-1) for axes containing more than 1.0 g H(2)O g(-1)dw (g g(-1)). Partial dehydration below 0.5 g gg(-1) facilitated faster cooling, averaging about 200 and 580 degrees C s(-1) in subcooled nitrogen and isopentane, respectively. The combination of partial drying and rapid cooling led to increased survival and reduced cellular damage in axes. Electrolyte leakage was 10-fold higher from fully hydrated axes cooled in either cryogen than from control axes that were not cooled. Drying of axes to 0.5 g g(-1), reduced electrolyte leakage of cryopreserved axes to levels similar to those of control material. Axis survival was assayed by germination in vitro. Axes with water contents greater than 1.0 g g(-1), did not survive cryogenic cooling. Between 1.0 and 0.75 g g(-1), axes survived cryogenic exposure but developed abnormally. The proportion of axes developing normally after being cooled in isopentane increased with increasing dehydration below 0.75 g g(-1), reaching a maximum between 0.5 and 0.25 g g(-1) after being cooled at > or =300 degrees C s(-1). Cooling rates attained in subcooled nitrogen did not exceed 250 degrees C s(-1), and normal development of axes was observed only at < or =0.4 g g(-1). These results support the hypothesis that rapid cooling enhances the feasibility of cryopreservation of desiccation-sensitive embryonic axes by increasing the upper limit of allowable water contents and overall survival.     

Ultrastructural Evidence for the Effects of Freezing in Embryonic Axes of Pisum sativum L. at Various Water Contents

This study investigated the effects of rapid drying (in an airstream) and rapid freezing (in sub-cooled liquid nitrogen) onthe survival and ultrastructural preservation of pea embryonicaxes that had been imbibed for 4 h (desiccation tolerant) and24 h (desiccation sensitive). Maximum survival of all axes inthe absence of freezing was attained. Similarly, 100% survivalwas obtained if freezing was preceded by rapid drying. Axesimbibed for 24 h and not dried were more sensitive to freezingthan undried, 4 h imbibed axes. Ultrastructural examinationshowed no organellar or cytomatrical deformations in axes fromany of the treatments. Some cells of the 24 h imbibed axes showedlocalized plasmalemma abnormalities after railed dehydration.Subsequent to freezing, irregular nuclei were observed and plasmalemmavesiculation occurred. If these axes were not dried prior tofreezing, plasmalemma vesiculation became prominent, clumpingof the cytoskeleton occurred and some wall abnormalities becameapparent. Rapid drying probably increases intercellular soluteconcentrations, and sub-cooled liquid nitrogen will increasethe rate of heat exchange between tissue and cryogen. A combinationof rapid drying and rapid freezing may obviate, or reduce, therequirement for cryoprotectants on freezing of desiccation sensitivetissue.Copyright 1995, 1999 Academic Press Pisum sativum L., pea, embryonic axis, ultrastructure, transmission electron microscopy, cryopreservation, rapid freezing     

Viability Loss Pattern under Rapid Dehydration of Antiaris toxicaria Axes and its Relation to Oxidative Damage

The relation between oxidative damage and viability loss of excised embryonic axes of Antiaris toxicaria subjected to rapid drying with silica gel at 15 °C was studied.Changes of survival rate,accumulation of thiobarbituric acid-reactive substances (TBARs),activities of superoxide dismutase (SOD),catalase (CAT),ascorbate peroxidase (APX),glutathione reductase (GR) and the permeability of cell membrane that was determined as relative electrolyte leakage (REL) were measured.The half-life moisture content (MCL50) was 0.41 g H2O/g DW (dry weight basis).During drying,the activities of SOD,CAT and APX increased until MCL50,and declined thereafter.The generation speed of ·O2-,and content of H2O2 and TBARs remained steadily or even decreased at MC levels higher than MCL50,demonstrating a low oxidative level in these axes.There was no significant correlation between viability loss and accumulation of reactive oxygen species or lipid peroxidation within the dehydration process until MCL50.Whereas the increase in REL from the beginning of the drying process indicated that the cell membrane was damaged.In conclusion,under rapid drying with silica gel the viability loss of excised recalcitrant A.toxicaria axes seemed to be triggered by mechanical or physical damage,rather than metabolic damage.     

玉米胚发育过程中脱水耐性的变化

对离体玉米胚脱水耐性的变化以及不同脱水速率对其脱水耐性的影响进行了研究。授粉后16d的玉米胚能耐轻微脱水,含水量从1.45降低到0.28gH2Og-1DW时胚的萌发率为100%,但含水量低于0.1gH2Og-1DW时胚死亡。胚的脱水耐性随着发育逐渐加强,表现为电解质渗漏速率逐渐降低,萌发率和幼苗干重逐渐增加。授粉后20d胚内超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性较高,过氧化氢酶(CAT)活性较低;授粉后24d,这些酶的活性与授粉后20d的正好相反。脂质过氧化产物丙二醛(MDA)在种子发育过程中呈下降趋势。不同脱水速率明显地影响胚的脱水耐性:在慢速脱水到含水量0.1~0.18gH2Og-1DW时,胚的萌发率和幼苗干重比快速脱水高,电解质渗漏速率比快速脱水低;在快速脱水条件下胚中的SOD、APX活性和MDA含量也比慢速脱水高;CAT活性的变化不明显。     

Fourier Transform Infrared Microspectroscopy Detects Changes in Protein Secondary Structure Associated with Desiccation Tolerance in Developing Maize Embryos

Isolated immature maize (Zea mays L.) embryos have been shown to acquire tolerance to rapid drying between 22 and 25 d after pollination (DAP) and to slow drying from 18 DAP onward. To investigate adaptations in protein profile in association with the acquisition of desiccation tolerance in isolated, immature maize embryos, we applied in situ Fourier transform infrared microspectroscopy. In fresh, viable, 20- and 25-DAP embryo axes, the shapes of the different amide-I bands were identical, and this was maintained after flash drying. On rapid drying, the 20-DAP axes had a reduced relative proportion of α-helical protein structure and lost viability. Rapidly dried 25-DAP embryos germinated (74%) and had a protein profile similar to the fresh control axes. On slow drying, the α-helical contribution in both the 20- and 25-DAP embryo axes increased compared with that in the fresh control axes, and survival of desiccation was high. The protein profile in dry, mature axes resembled that after slow drying of the immature axes. Rapid drying resulted in an almost complete loss of membrane integrity in the 20-DAP embryo axes and much less so in the 25-DAP axes. After slow drying, low plasma membrane permeability ensued in both the 20- and 25-DAP axes. We conclude that slow drying of excised, immature embryos leads to an increased proportion of α-helical protein structures in their axes, which coincides with additional tolerance of desiccation stress.     

Changing desiccation tolerance of pea embryo protoplasts during germination

Protoplasts were isolated from pea (Pisum sativum L. cv. Alaska) embryonic axes during and after germination to determine whether the loss of desiccation tolerance in the embryos also occurs in the protoplasts. At all times studied, protoplast survival decreased as water content decreased; however, the sensitivity to dehydration was less when the protoplasts were isolated from embryos that were still desiccation-tolerant (12 h and 18 h of imbibition) than when protoplasts were derived from axes that were sensitive (24 h and 36 h of imbibition). The water content at which 50% of the population was killed (WC50) increased throughout germination and early seedling growth for both the intact tissue and the protoplasts derived from them. Prior to radicle emergence, protoplasts were less desiccation-tolerant than the intact axes; however, protoplasts isolated from radicles shortly after emergence had lower WC50s than the intact radicles. A comparison of protoplast survival after isolation and dehydration in either 500 mM sucrose/raffinose or 700 mM sucrose revealed no difference in tolerance except at 24 h of imbibition, when protoplasts treated in the more concentrated solution had improved tolerance of dehydration. Although intact epicotyls are generally more desiccation-tolerant than radicles, protoplasts isolated separately from epicotyls and radicles did not differ in tolerance. Collectively, these data suggest that protoplasts gradually lose desiccation tolerance during germination, as do the orthodox embryos from which they were derived. However, even prior to radicle emergence, protoplasts display a sensitivity to progressive dehydration that is similar to that shown by recalcitrant and ageing embryos.     

Increased rate of drying reduces metabolic inequity and critical water content in radicles of Cicer arietinum L.

Orthodox seed serves as easily accessible model to study desiccation-sensitivity in plant tissues because once they undergo germination, they become sensitive to desiccation imposed injuries. In the proposed study, effects of rate of drying on the viability, electrolyte leakage, superoxide accumulation, lipid-protein oxidation and antioxidant enzymes were explored in excised radicles of Cicer arietinum L. under dehydration and wet storage. For both the drying conditions, desiccation could be explained by exponential and inverse functions. Under rapid drying tissue viability as scored by germination efficiency and tetrazolium staining remained 100 % all through the analysis (24 h) but declined remarkably after 0.30 g g⁻¹ fresh mass water content (4 days) under slow drying. Moreover, precipitous fall in tissue viability was observed after 2 weeks of wet storage. Rapid drying was also accompanied with limited amounts of electrolyte leakage, superoxide radical, malondialdehyde and protein hydroperoxide, together with enhanced level of protein. Additionally, activities of both superoxide dismutase and ascorbate peroxidase were increased in rapidly dried radicles, but guaiacol peroxidase was declined. In contrary, above referred biomarkers were observed to perform either inversely or poorly during slow drying and wet storage suggesting that above documented alterations might be the resultant of ageing and not desiccation. Gathered data demonstrated that increased drying lowers the critical water content for tissue survival and also reduces the risk of damage resulting from aqueous-based deleterious reactions. Additionally, it also showed that growing radicles are a popular model to explore desiccation-sensitivity in plant tissues and/or seeds.     

Response of Chinese Wampee Axes and Maize Embryos to Dehydration at Different Rates

Survival of wampee (Clausena lansium Sksels) axes and maize (Zea mays L.) embryos decreased with rapid and slow dehydration. Damage of wampee axes by rapid dehydration was much less than by slow dehydration, and that was contrary to maize embryos. The malondialdehyde contents of wampee axes and maize embryos rapidly increased with dehydration, those of wampee axes were lower during rapid dehydration than during slow dehydration, and those of maize embryos were higher during rapid dehydration than during slow dehydration. Activities of superoxide dismutsse (SOD), ascorbate peroxidase (APX) and catalase (CAT) of wampee axes markedly increased during the sady phase of dehydration, and then rapidly decreased, and those of rapidly dehydrated axes were higher than those of slow dehydrated axes when they were dehydrated to low water contents. Activities of SOD and APX of maize embryos notable decreased with dehydration. There were higher SOD activities and lower APX activities of slowly dehydrated maize embryos compared with rapidly dehydrated maize embryos. CAT activities of maize embryos markedly increased during the eady phase of dehydration, and then decreased, and those of slowly dehydrated embryos were higher than those of rapidly dehydrated embryos during the late phase of dehydration.