Characterization and Role of Glucose-6-phosphate Dehydrogenase of Populus suaveolens in Induction of Freezing Resistance

Glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) was purified from the leaves of 8-week-old Populus suaveolens cuttings. The enzyme activity in the absence and presence of reduced dithiothreitol (DTTred) was determined. The results show that the G6PDH activity is not inactivated by pre-incubation with DTTred, indicating that the purified enzyme probably presented in cytosol of P suaveolens. The catalytic characteristics and kinetic parameters of cytosolic G6PDH purified from P.suaveolens cuttings were also studied. The results show that G6PDH is characterized by Km value of 360/amol.L^-1 for G6P and 16μmol.L^-1 for NADP, a pH range of 7.3-8.9, and the maximum activity around pH 8.2. The enzyme activity is inhibited by various metabolites such as NADPH, NADH, GTP, UTP, ATP, AMP, ADP, CoA, acetyl CoA, fructose-6-phosphate (F6P), erythrose-4-phosphate (E4P), ribose-5-phosphate (R5P) and 3-phosphoglycerate (3-PG) (all at 1 mmol‘L i except for NADPH and NADH)to different extents. NADPH is the most effective inhibitor of enzyme activity, with an inhibition of 72.0%. The addition of metal ions such as MgC12, CaC12 and KC1 (all 1.0 mmol.L^-1) to the standard reaction mixture has no remarkable influence on the cytosolic G6PDH activity. However, CdCl2 (1.0 mmol.L-1) causes high inhibitory effect on the enzyme activity. To explore the role of G6PDH on the enhancement of freezing resistance induced by freezing acclimation, the changes in the cytosolic G6PDH activity and freezing resistance (expressed as LTs0) of P. suaveolens cuttings during freezing acclimation at -20℃ were investigated. The results reveal that freezing acclimation decreases LTs0 of cuttings, and increases the activity of cytosolic G6PDH compared with control ones,while 2 d of de-acclimation at 25 ~C result in a decrease in cytosolic G6PDH activity, and caused an increase in LT50. Furthermore,the change in cytosolic G6PDH activity is found to be closely correlated to the degree of freezing resistance of cuttings during freezing acclimation. It is suggested that cytosolic G6PDH may be involved in the induction of freezing resistance of cuttings.     

Recent Progresses in the Studies of Genetic Engineering for Cold Resistance in Plants

Low temperature is one of abiotic stresses limiting the geographical location suitable for growing corps and periodically account for significant losses in plant productivity, so it's important for agriculture to improve the cold resistance of corps. Many plants can acquire increased frost tolerance after a period of exposure to low, non-freezing temperature through a complex adaptive process called cold acclimation. In the past ten years, with the great advance in the researches of molecular mechanism of cold acclimation, the studies of genetic engineering for cold resistance in plants have also been carried out extensively. Currently, there are two kinds of genes used in plant cold-resistant genetic engineering, Which are protective genes and regulating genes. Many studies indicate both kinds of genes have good prospect for improving the cold resistance of plants. However, there are also many problems in this field to be solved immediately.     

温度逆境锻炼对低温胁迫下番茄幼苗细胞膜脂质过氧化产物及抗氧化酶活性的影响

为了探索番茄植物交叉适应现象及其生理机制,以番茄品种东农704为材料,研究了低温和高温锻炼后番茄幼苗在2℃低温下叶片中丙二醛(MDA)和抗氧化酶活性的变化。结果显示,番茄幼苗经过适宜的低温和高温锻炼均可提高幼苗的抗冷性,并且高温锻炼在提高番茄幼苗抗冷性方面明显优于低温锻炼。2℃低温胁迫1d,未经锻炼幼苗与锻炼幼苗相比,其MDA含量明显升高,超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性大幅度下降,即使在恢复生长2d后,MDA仍维持在较高的水平,SOD、POD和CAT活性水平也较低。番茄幼苗在低温和高温锻炼后、低温胁迫后和恢复2d后,MDA含量和酶保护系统变化各有异同。上述研究结果表明番茄植物具温度逆境交叉适应性,低温和高温锻炼诱导的番茄抗寒机制存在着差异性。     

Comparison of G6PDH Activity and LT50 Between P.tomentosa and P.suaveolens During Freezing Acclimation

The differences of glucose-6P dehydrogenase(G6PDH) activity and freezing resistance induced by freezing acclima-tion between cuttings of freezing-sensitive P.tomentosa and freezing-resistant P.suaveolens were compared for exploring the role of G6PDH on the enhancement of freezing resistance induced by freezing acclimation.After 5d of freezing acclimation at -3℃ ,the LT50 of P.tomentosa has deereased from -6.2℃ incontrol cuttings to -14.3℃ in freezing acclimated ones,and the increase of LT50 of P.tomentosa has decreased from -6.2℃ in control cutting to -14.3℃ in freezing acclimated ones,and the increase of G6PDH activity was observed in freezing acclimated cuttings as compared with control ones.Whereas,when P.suaveolens was freezing acclimated at -20℃ for 5d,the LT50 has decreased from -27.1℃ in control cuttings to -43.5℃ in freezing acclimated ones,and the activity of G6PDH increased considerably.In addition,the increase of LT50 and the decrease of G6PDH activity resulting from 2d of deacclimation at 25℃ were found in two kinds of freezing acclimated cuttings.It is concluded that the increase in the activity of G6PDH may associate with the inherited freezing resistance of species and the enhancemen of freezing resistance of cuttings,and may play an important role in the antifreeze process under freezing temperature,which would provide the basis for the study on the molecular mechanism of freezing resistance in P.suaveolens and the cloning of gene associated with freezing resistance.     

11个南竹北移竹种抗寒性差异

利用半致死温度(LT₅₀)探讨不同竹种间抗寒性及冷驯化能力,筛选抗寒能力强、冷驯化能力佳的竹种,为我国“南竹北移”竹种选择、抗寒竹种引种等工作提供科学依据。以从江苏扬州引种至山东的11个竹种为试验材料,采用电导法配合Logistic方程推算各竹种的低温半致死温度。结果表明：11个竹种在来源地江苏的抗寒性强弱排序依次是：金镶玉竹>早园竹>毛金竹>黄纹竹>四季竹>阔叶箬竹>茶秆竹>乌哺鸡竹>大明竹>斑苦竹>紫竹;在引种地山东的抗寒性排序是：金镶玉竹>茶秆竹>大明竹>早园竹>黄纹竹>四季竹>乌哺鸡竹>毛金竹>斑苦竹>阔叶箬竹>紫竹。11个供试竹种中抗寒能力最强的是金镶玉竹,经引种地的低温驯化后,冷驯化能力最强的是大明竹,其次是茶秆竹和斑苦竹;最弱的是毛金竹和阔叶箬竹,未表现出冷驯化能力。     

低温锻炼对冷胁迫下黄瓜幼苗保护性酶的影响

以山农5号(耐寒品种)、津优1号(较耐寒品种)和津春4号(冷敏感品种)为试材,研究了不同低温锻炼对冷胁迫下黄瓜幼苗几种保护性酶和几种逆境物质的影响。结果表明,经过4℃、6℃和8℃低温锻炼的黄瓜幼苗,能明显提高冷胁迫下黄瓜幼苗SOD、POD、CAT酶活性,其中,6℃和8℃处理的效果要好于4℃处理。冷胁迫下,经过4℃、6℃和8℃低温锻炼的黄瓜幼苗,其可溶性糖和脯氨酸含量均高于对照。     

Low-temperature preservation (at 4 °C) of marine rotifer Brachionus

Mass production of rotifers is essential as live food during the larval rearing season, but a major problem of rotifer culture is unpredictable culture collapse. If mass‐produced rotifers could be kept alive at low temperature for an extended period of time, they could be supplied as live food to cultured marine fish larvae without interruption. Four experiments were performed to test this possibility in six strains of Brachionus plicatilis O. F. Müller and eight strains of Brachionus rotundiformis Tschugunoff. The results showed that: (1) B. rotundiformis strains were less tolerant to 4 °C than B. plicatilis strains. Among the B. rotundiformis strains, the strains known as SS type were the most susceptible and showed the lowest survival. (2) Exchange of culture media during the incubation at 4 °C in B. plicatilis and B. rotundiformis resulted in higher survival than not changing the culture media, but there were no differences in the regression slope with or without changing the culture media. (3) Acclimation at 15 °C for 96 h for B. plicatilis and B. rotundiformis before transfer to 4 °C resulted in higher survival rates than acclimation at 10 °C. (4) The combination of frequent exchange of culture media and acclimation significantly improved the survival of B. plicatilis and B. rotundiformis compared with controls that were maintained at 4 °C without exchange of the culture media. Large‐scale trials using B. plicatilis (Kamiura strain) cultured in 30‐L tanks were conducted in a hatchery at a density of 2000–20 000 individuals mL^?1. Rotifers were transferred directly from 25 °C to 4 °C. About 50% of the rotifers at 20 000 individuals mL^?1 survived after 14 days at 4 °C. These preserved rotifers could be cultured at 20 °C, recovering within 4 days.     

Temperature preference and oxygen consumption of the largemouth bass Micropterus salmoides (Lacépède) acclimated to different temperatures

The behavioural and metabolic responses of the largemouth bass Micropterus salmoides (Lacépède) to temperature were determined to define optimal thermal conditions. The final preferendum of largemouth bass juveniles determined with acute and gravitation methods was independent of the method (29.0–28.1 °C). The displacement velocity in the horizontal thermal gradient of bass juveniles was 22.4 cm h⁻¹ in the light phase and 22.6 cm h⁻¹ in the dark phase. Oxygen consumption rates in the largemouth bass increased significantly (P<0.05) from 48.8 to 69.4 mg O₂ Kg⁻¹ h⁻¹ with an increase in the acclimation temperature from 20 to 33 °C. The temperature quotient (Q₁₀) in the juveniles was 1.37–2.00 in the range of acclimation temperatures of 26–29 and 29–32 °C. The optimum temperature range for growth calculated using Jobling's equation was 28.1–28.6 °C and for Q₁₀ values 26–29 °C. The results are discussed in relation to the use of this information in aquaculture.     

Protein synthesis in tissues of fed and starved carp,acclimated to different temperatures

The temperature dependence of the rates of protein synthesis in the red and white skeletal muscle of the carp (Cyprinus carpio) was measured using a method which involved a single injection of tritiated phenylalanine. Plasma and muscle-free phenylalanine quickly reached a plateau level at all temperatures. During the plateau phase the incorporation of label into protein was liner. Muscle from fish previously acclimated to either a low temperature (8°C) or a high temperature (28°C), showed marked differences in the rates of protein synthesis. The results show that cold acclimation is associated with significantly higher rates of protein synthesis (p<0.001) in both red and white muscle. Arrhenius activation energies, derived from the rates of protein synthesis at the different experimental temperatures, were similar for both red and white muscle in fish acclimated to warm or cold temperatures. Measurements for both acclimated groups over the temperature range 8–34°C showed that the activation energy for the process of protein synthesis was 86.7 kJ/mol and 78.7 kJ/mol for the red and white muscle respectively.     

黄地老虎耐寒机理初探

黄地老虎个体发育期间各虫态的过冷却点,以卵期和蛹期最低,分别为-21.79和-19.2℃;成虫期最高为-5.75℃;幼虫期1～4龄随虫龄增大,其过冷却点升高,分别为-17.45,-16.29,-8.41和-6.51℃;5～6龄时又下降,分别为-12.72和-8.82℃.6龄幼虫在25,15,5和0℃4级降温锻炼下,抗寒力提高。主要表现为:①虫体过冷却点下降(从-7.58℃降到-17.41℃);②体内多种生化含量明显积累,0℃下处理的幼虫,其血糖、血脂、丙氨酸、丝氨酸、脯氨酸和蛋白质分别北25℃下处理时增加3.28,1.67,5.72,1.27,0.6和0.8倍。没有发现甘油和多元醇积累。