Populus tomentosa seedlings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 1?mmol·L -1 of Ca 2+ ...Populus tomentosa seedlings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3,and 0 05?mmol·L -1 of CaM antagonist CPZ. The changes in the contents of total soluble protein and CaM, and freezing resistance in all pretreated seedlings in various periods ( viz: following cold acclimation, chilling stress and recovery) were investigated. Results showed that cold acclimation increased the contents of total soluble protein and CaM, and freezing resistance of seedlings, which could be strongly reduced by the pretreatments of EGTA CPZ and LaCl 3 Cold acclimation combined with CaCl 2 pretreatment enhanced the effect of cold acclimation on freezing resistance, and obviously increased the contents of total soluble protein and CaM, reduced the declining degree of the contents of total soluble protein and CaM caused by chilling stress as compared with cold acclimation, augmented the increase in the level of total soluble protein and CaM during the recovery periods. Further analysis found that an increase in total soluble protein content during cold acclimation with or without CaCl 2 pretreatment mainly resulted from the increase in content of heat stable protein in total soluble protein. It is suggested that Ca 2+ calmodulin may be involved in the synthesis of total soluble protein, and the induction of freezing resistance of seedlings.展开更多
In Arabidopsis, three lipase-like regulators, SAG101, EDS1, and PAD4, act downstream of resistance protein-associated defense signaling. Although the roles of SAG101, EDS1, and PAD4 in biotic stress have been extensiv...In Arabidopsis, three lipase-like regulators, SAG101, EDS1, and PAD4, act downstream of resistance protein-associated defense signaling. Although the roles of SAG101, EDS1, and PAD4 in biotic stress have been extensively studied, little is known about their functions in plant responses to abiotic stresses. Here, we show that SAG101, EDS1, and PAD4 are involved in the regulation of freezing tolerance in Arabidopsis. With or without cold acclimation, the sag101, edsl, and pad4 single mutants, as well as their double mutants, exhibited similarly enhanced tolerance to freezing temperatures. Upon cold exposure, the sag101, edsl, and pad4 mutants showed increased transcript levels of C-REPEAT/DRE BINDING FACTORs and their regulons compared with the wild type. Moreover, freezing-induced cell death and accumulation of hydrogen peroxide were ameliorated in sag101, edsl, and pad4 mutants. The sag101, edsl, and pad4 mutants had much lower salicylic acid （SA） and diacylglycerol （DAG） contents than the wild type, and exogenous application of SA and DAG compromised the freezing tolerance of the mutants. Furthermore, SA suppressed the cold-induced expression of DGATs and DGKs in the wild-type leaves. These findings indicate that SAG101, EDS1, and PAD4 are involved in the freezing response in Arabidopsis, at least in part, by modulating the homeostasis of SA and DAG.展开更多
As one of the most severe environmental stresses, freezing stress can determine native flora in nature and severely reduce crop production. Many mechanisms have been proposed to explain the damage induced by freezing-...As one of the most severe environmental stresses, freezing stress can determine native flora in nature and severely reduce crop production. Many mechanisms have been proposed to explain the damage induced by freezing-thawing cycle, and oxidative stress caused by uncontrollable production of harmful reactive oxygen species (ROS) are partially contributed to causing the injury. Plants in temperate regions have evolved a unique but effective metabolism of protecting themselves called cold acclimation. Cold-acclimating plants undergo a complex but orchestrated metabolic process to increase cold hardness triggered by exposure to low temperature and shortened photoperiod and achieve the maximum freezing tolerance by a concerted regulation and expression of a number of cold responsive genes. A complicated enzymatic system have been evolved in plants to scavenge the ROS to protect themselves from oxidative stress, therefore, cold-acclimating plants are expected to increase the de novo synthesis of the genes of antioxidant genes. Indeed, many antioxidant genes increase the expression levels in response to low temperature. Furthermore, the higher expression of many antioxidant enzymes are positively correlated to inducing higher tolerance levels against freezing. All the information summarized here can be applied for developing crop and horticultural plants to have more freezing tolerance for higher production with better quality. There have been extensive studies on the activities of antioxidant enzymes and the gene regulation, however, more researches will be required in near future to elucidate the most effective antioxidant enzymes to induce highest freezing tolerance in a crop plant in a transformation process or a breeding program.展开更多
The differences of glucose-6P dehydrogenase (G6PDH) activity and freezing resistance induced by freezing acclimation between cuttings of freezing-sensitive P. tomentosa and freezing-resistant P. suaveolens were compar...The differences of glucose-6P dehydrogenase (G6PDH) activity and freezing resistance induced by freezing acclimation 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 5 d of freezing acclimation at -3 ℃, the LT50 of P. tomentosa has decreased from -6.2 ℃ in control cuttings 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 5 d, 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 2 d 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 enhancement 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.展开更多
Cold acclimation is associated with many metabolic changes that lead to an increase of freezing tolerance. In order to investigate the biochemical process of cold acclimation in Ammopiptanthus mongolicus, seedlings we...Cold acclimation is associated with many metabolic changes that lead to an increase of freezing tolerance. In order to investigate the biochemical process of cold acclimation in Ammopiptanthus mongolicus, seedlings were acclimated at 2℃ under 16-h photoperiod （150 μmol·m^-2·s^-1 photosynthetically active radiation） for 14 d. Freezing tolerance in seedlings increased after 14 d of cold-hardening. Contents of protein, proline and solute carbohydrate in cotyledon increased after cold acclimation. Patterns of isozymes of superoxide dismutase （SOD）, peroxidase, catalase and polyphenol oxidase （PPO） were investigated. The activities of SOD, peroxidase and PPO in cold acclimated plants were increased during cold-hardening. We deduced that compatible solutes and antioxidant enzymes play important roles in development of freezing tolerance during cold acclimation in this evergreen woody plant.展开更多
The changes in the contents of total soluble protein and RNA, the activity of RNase in leaves and branches of Populus tomentosa cuttings at various periods (viz: cold acclimation, deacclimation, chilling stress an...The changes in the contents of total soluble protein and RNA, the activity of RNase in leaves and branches of Populus tomentosa cuttings at various periods (viz: cold acclimation, deacclimation, chilling stress and the recovery after chilling stress), and the survival rate and the freezing resistance of cuttings during cold acclimation at -3℃ were investigated. Results showed that cold acclimation not only increased the contents of total soluble protein and RNA, the survival rates and the freezing resistance of cuttings, decreased the activity of RNase, but also reduced the declining degree of total soluble protein and RNA contents, and the increasing level of RNase caused by chilling stress as compared with the controls. In addition, cold acclimation augmented the increase in the level of total soluble protein and RNA, and facilitated the decrease of RNase during the recovery periods. Further analysis found that the DNA content of all treatments kept relative stability at various periods. The changes in total soluble protein, RNA and RNase were closely related to the freezing resistance of cuttings. It appears that the increase of RNA content caused by cold acclimation induced decrease of RNase activity may be involved in the accumulation of total soluble protein and the induction of freezing resistance of cuttings.展开更多
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 det...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 pre- sented 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 Kmvalue of 360 μmol·L–1 for G6P and 16 μmol·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), eryth- rose-4-phosphate (E4P), ribose-5-phosphate (R5P) and 3-phosphoglycerate (3-PG) (all at 1 mmol·L–1 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 MgCl2, CaCl2and KCl (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 LT50) of P. suaveolens cuttings during freezing acclimation at –20 °C were investigated. The results reveal that freezing acclimation decreases LT50 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 fr展开更多
Populus euphratica Olive is the only tree species that can grow in the saline land and also survive cold winters in northwest China, and it plays a very important role in stabilizing the vulnerable ecosystem there. A ...Populus euphratica Olive is the only tree species that can grow in the saline land and also survive cold winters in northwest China, and it plays a very important role in stabilizing the vulnerable ecosystem there. A cell suspension culture was initiated from callus derived from plantlets of Populus euphratica. Cold acclimation was induced (LT50 of 17.5 ℃) in cell suspension at 45 ℃ in the dark for 30 days and the freezing tolerance increased from LT50 of 12.5 ℃ in nonacclimated cells to LT50 of 17.5 ℃ in cold-acclimated cells. Microvacuolation, cytoplasmic augmentation and accumulation of starch granules were observed in cells that were cold-acclimated by exposure to low temperatures. Several qualitative and quantitative changes in proteins were noted during cold acclimation. Antibodies to carrot extracellular (apoplastic) 36 kD antifreeze protein did not cross react on immunoelectroblots with extracellular proteins in cell suspension culture medium of Populus euphratica, indicating no common epitopes in the carrot 36 kD antifreeze protein and P. euphratica extracellular proteins. The relationship of these changes to cold acclimation in Populus euphratica cell cultures was discussed.展开更多
Populus tomentosa seedlings for cold-acclimating were pretreated wit h or without 20% saccharose. Changes in the concentrations of total soluble sugar , the survival rates, and freezing tolerance of seedlings during ...Populus tomentosa seedlings for cold-acclimating were pretreated wit h or without 20% saccharose. Changes in the concentrations of total soluble sugar , the survival rates, and freezing tolerance of seedlings during cold acclimatio n were investigated. The results showed that cold acclimation increased the conc entrations of total soluble sugar, the survival rates and freezing tolerance. Co ld acclimation, combined with the saccharose-pretreatment, enhanced the above- ment ioned effect of cold acclimation, and obviously increased the concentrations of total soluble sugar, the survival rates and freezing tolerance of seedlings. Fur ther analysis found that the concentrations of total soluble sugar in branches i ncreased greater than that in leaves during both cold acclimation with or withou t the pretreatment of saccharose. Moreover, an increase of the concentrations of total soluble sugar in branches and leaves was closely related to the freezing tolerance of seedlings. The results indicate the accumulation of soluble sugar i n seedlings induced by cold acclimation may be involved in the induction of free zing tolerance .展开更多
Populus tomentosa cuttings were treated with 1mmol·L -1 , 5mmol·L -1 , 10mmol·L -1 or 15mmol·L -1 of CaCl 2 for 1\|7 d, respectively, for studying the effects of different conc...Populus tomentosa cuttings were treated with 1mmol·L -1 , 5mmol·L -1 , 10mmol·L -1 or 15mmol·L -1 of CaCl 2 for 1\|7 d, respectively, for studying the effects of different concentrations of CaCl 2 on freezing resistance. Results indicated that 10?mmol·L -1 of CaCl 2 has greater effect than other concentrations on the enhancement of freezing resistance, and the optimum time of pretreatment was 5?d. In addition, cuttings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 of CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 05?mmol·L -1 of CaM antagonist CPZ or 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3 The changes in CaM and freezing resistance of all cuttings were investigated. The results showed that cold acclimation at -3℃ increased CaM content and decreased the minimum temperature for 100% survival. The CaCl 2 pretreatment enhanced the effect of cold acclimation and obviously increased CaM content and decreased the minimum temperature for 100% survival, but this effect was strongly inhibited by the EGTA, CPZ or LaCl 3 It is concluded that the effect of CaCl 2 on freezing resistance is associated with its concentration and time of pretreatment, Ca 2+ CaM may be involved in the induction of freezing resistance of the cuttings.展开更多
We investigated the changes in the contents of H202, malonaldehyde （MDA） and endogenous antioxidants, the activities of protective enzymes and some critical enzymes involved in the ascorbate-glutathione （ASA-GSH） ...We investigated the changes in the contents of H202, malonaldehyde （MDA） and endogenous antioxidants, the activities of protective enzymes and some critical enzymes involved in the ascorbate-glutathione （ASA-GSH） cycle as well as freezing resistance （expressed as LT50） and correlations mentioned above, in detail using Populus suaveolens cuttings. The purpose was to explore the physiological mechanism of the enhancement of freezing resistance induced by freezing acclimation at -20℃, and to elucidate the physiological mechanisms by which trees adapt to freezing. The results showed that freezing acclimation enhanced the activities of superoxide dismutase （SOD）, peroxidase （POD）, catalase （CAT）, monodehydroascorbate reductase （MDAR）, ascorbate peroxidase （APX）, dehydroascorbate reductase （DHAR） and glutathione reductase （GR）. And it increased the contents of reduced ascorbate （ASA）, reduced glutathione （GSH）, dehydroascorbate （DHA） and oxidized glutathione （GSSG）. However, H202 and MDA contents and LT50 of cuttings were decreased. LTs0 in cuttings was found to be closely correlated to the levels of SOD, POD, CAT, APX, DHAR, MDAR, GR, H202, MDA, ASA, GSH, DHA and GSSG during freezing acclimation. This suggested that the enhancement of freezing resistance of cuttings induced by freezing acclimation may relate to the distinct increase for the levels of SOD, POD, CAT, APX, DHAR, MDAR, GR, ASA, GSH, DHA, and GSSG. In addition, the observed levels of APX, DHAR, MDAR, GR, ASA, DHA, GSH and GSSG were higher than those of SOD, POD and CAT during freezing acclimation. It indicated that a higher capacity of the ASA-GSH cycle is required for H202 detoxification, and growth and development of cuttings. Based on the obtained results, it can be concluded that the ASA-GSH cycle plays an important role in enhancement of freezing resistance of P. suaveolens cuttings during freezing acclimation.展开更多
文摘Populus tomentosa seedlings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3,and 0 05?mmol·L -1 of CaM antagonist CPZ. The changes in the contents of total soluble protein and CaM, and freezing resistance in all pretreated seedlings in various periods ( viz: following cold acclimation, chilling stress and recovery) were investigated. Results showed that cold acclimation increased the contents of total soluble protein and CaM, and freezing resistance of seedlings, which could be strongly reduced by the pretreatments of EGTA CPZ and LaCl 3 Cold acclimation combined with CaCl 2 pretreatment enhanced the effect of cold acclimation on freezing resistance, and obviously increased the contents of total soluble protein and CaM, reduced the declining degree of the contents of total soluble protein and CaM caused by chilling stress as compared with cold acclimation, augmented the increase in the level of total soluble protein and CaM during the recovery periods. Further analysis found that an increase in total soluble protein content during cold acclimation with or without CaCl 2 pretreatment mainly resulted from the increase in content of heat stable protein in total soluble protein. It is suggested that Ca 2+ calmodulin may be involved in the synthesis of total soluble protein, and the induction of freezing resistance of seedlings.
文摘In Arabidopsis, three lipase-like regulators, SAG101, EDS1, and PAD4, act downstream of resistance protein-associated defense signaling. Although the roles of SAG101, EDS1, and PAD4 in biotic stress have been extensively studied, little is known about their functions in plant responses to abiotic stresses. Here, we show that SAG101, EDS1, and PAD4 are involved in the regulation of freezing tolerance in Arabidopsis. With or without cold acclimation, the sag101, edsl, and pad4 single mutants, as well as their double mutants, exhibited similarly enhanced tolerance to freezing temperatures. Upon cold exposure, the sag101, edsl, and pad4 mutants showed increased transcript levels of C-REPEAT/DRE BINDING FACTORs and their regulons compared with the wild type. Moreover, freezing-induced cell death and accumulation of hydrogen peroxide were ameliorated in sag101, edsl, and pad4 mutants. The sag101, edsl, and pad4 mutants had much lower salicylic acid （SA） and diacylglycerol （DAG） contents than the wild type, and exogenous application of SA and DAG compromised the freezing tolerance of the mutants. Furthermore, SA suppressed the cold-induced expression of DGATs and DGKs in the wild-type leaves. These findings indicate that SAG101, EDS1, and PAD4 are involved in the freezing response in Arabidopsis, at least in part, by modulating the homeostasis of SA and DAG.
文摘As one of the most severe environmental stresses, freezing stress can determine native flora in nature and severely reduce crop production. Many mechanisms have been proposed to explain the damage induced by freezing-thawing cycle, and oxidative stress caused by uncontrollable production of harmful reactive oxygen species (ROS) are partially contributed to causing the injury. Plants in temperate regions have evolved a unique but effective metabolism of protecting themselves called cold acclimation. Cold-acclimating plants undergo a complex but orchestrated metabolic process to increase cold hardness triggered by exposure to low temperature and shortened photoperiod and achieve the maximum freezing tolerance by a concerted regulation and expression of a number of cold responsive genes. A complicated enzymatic system have been evolved in plants to scavenge the ROS to protect themselves from oxidative stress, therefore, cold-acclimating plants are expected to increase the de novo synthesis of the genes of antioxidant genes. Indeed, many antioxidant genes increase the expression levels in response to low temperature. Furthermore, the higher expression of many antioxidant enzymes are positively correlated to inducing higher tolerance levels against freezing. All the information summarized here can be applied for developing crop and horticultural plants to have more freezing tolerance for higher production with better quality. There have been extensive studies on the activities of antioxidant enzymes and the gene regulation, however, more researches will be required in near future to elucidate the most effective antioxidant enzymes to induce highest freezing tolerance in a crop plant in a transformation process or a breeding program.
基金National Natural Science Foundation of China(Grant No.30271093)
文摘The differences of glucose-6P dehydrogenase (G6PDH) activity and freezing resistance induced by freezing acclimation 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 5 d of freezing acclimation at -3 ℃, the LT50 of P. tomentosa has decreased from -6.2 ℃ in control cuttings 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 5 d, 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 2 d 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 enhancement 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.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.30671476 and 30271067).
文摘Cold acclimation is associated with many metabolic changes that lead to an increase of freezing tolerance. In order to investigate the biochemical process of cold acclimation in Ammopiptanthus mongolicus, seedlings were acclimated at 2℃ under 16-h photoperiod （150 μmol·m^-2·s^-1 photosynthetically active radiation） for 14 d. Freezing tolerance in seedlings increased after 14 d of cold-hardening. Contents of protein, proline and solute carbohydrate in cotyledon increased after cold acclimation. Patterns of isozymes of superoxide dismutase （SOD）, peroxidase, catalase and polyphenol oxidase （PPO） were investigated. The activities of SOD, peroxidase and PPO in cold acclimated plants were increased during cold-hardening. We deduced that compatible solutes and antioxidant enzymes play important roles in development of freezing tolerance during cold acclimation in this evergreen woody plant.
文摘The changes in the contents of total soluble protein and RNA, the activity of RNase in leaves and branches of Populus tomentosa cuttings at various periods (viz: cold acclimation, deacclimation, chilling stress and the recovery after chilling stress), and the survival rate and the freezing resistance of cuttings during cold acclimation at -3℃ were investigated. Results showed that cold acclimation not only increased the contents of total soluble protein and RNA, the survival rates and the freezing resistance of cuttings, decreased the activity of RNase, but also reduced the declining degree of total soluble protein and RNA contents, and the increasing level of RNase caused by chilling stress as compared with the controls. In addition, cold acclimation augmented the increase in the level of total soluble protein and RNA, and facilitated the decrease of RNase during the recovery periods. Further analysis found that the DNA content of all treatments kept relative stability at various periods. The changes in total soluble protein, RNA and RNase were closely related to the freezing resistance of cuttings. It appears that the increase of RNA content caused by cold acclimation induced decrease of RNase activity may be involved in the accumulation of total soluble protein and the induction of freezing resistance of cuttings.
基金the Foundation ofState-designated Base for Biology Researching and Teaching in Beijing Forestry University
文摘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 pre- sented 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 Kmvalue of 360 μmol·L–1 for G6P and 16 μmol·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), eryth- rose-4-phosphate (E4P), ribose-5-phosphate (R5P) and 3-phosphoglycerate (3-PG) (all at 1 mmol·L–1 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 MgCl2, CaCl2and KCl (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 LT50) of P. suaveolens cuttings during freezing acclimation at –20 °C were investigated. The results reveal that freezing acclimation decreases LT50 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 fr
基金the National Natural Science Foundation of China (Grant No. 30271067)Fok Ying Tung Education Foundation (71030)+1 种基金 Key Teachers Foundation of the Educational Ministry of China and the State Key Basic Research and Development Plan of China (G199901600
文摘Populus euphratica Olive is the only tree species that can grow in the saline land and also survive cold winters in northwest China, and it plays a very important role in stabilizing the vulnerable ecosystem there. A cell suspension culture was initiated from callus derived from plantlets of Populus euphratica. Cold acclimation was induced (LT50 of 17.5 ℃) in cell suspension at 45 ℃ in the dark for 30 days and the freezing tolerance increased from LT50 of 12.5 ℃ in nonacclimated cells to LT50 of 17.5 ℃ in cold-acclimated cells. Microvacuolation, cytoplasmic augmentation and accumulation of starch granules were observed in cells that were cold-acclimated by exposure to low temperatures. Several qualitative and quantitative changes in proteins were noted during cold acclimation. Antibodies to carrot extracellular (apoplastic) 36 kD antifreeze protein did not cross react on immunoelectroblots with extracellular proteins in cell suspension culture medium of Populus euphratica, indicating no common epitopes in the carrot 36 kD antifreeze protein and P. euphratica extracellular proteins. The relationship of these changes to cold acclimation in Populus euphratica cell cultures was discussed.
文摘Populus tomentosa seedlings for cold-acclimating were pretreated wit h or without 20% saccharose. Changes in the concentrations of total soluble sugar , the survival rates, and freezing tolerance of seedlings during cold acclimatio n were investigated. The results showed that cold acclimation increased the conc entrations of total soluble sugar, the survival rates and freezing tolerance. Co ld acclimation, combined with the saccharose-pretreatment, enhanced the above- ment ioned effect of cold acclimation, and obviously increased the concentrations of total soluble sugar, the survival rates and freezing tolerance of seedlings. Fur ther analysis found that the concentrations of total soluble sugar in branches i ncreased greater than that in leaves during both cold acclimation with or withou t the pretreatment of saccharose. Moreover, an increase of the concentrations of total soluble sugar in branches and leaves was closely related to the freezing tolerance of seedlings. The results indicate the accumulation of soluble sugar i n seedlings induced by cold acclimation may be involved in the induction of free zing tolerance .
文摘Populus tomentosa cuttings were treated with 1mmol·L -1 , 5mmol·L -1 , 10mmol·L -1 or 15mmol·L -1 of CaCl 2 for 1\|7 d, respectively, for studying the effects of different concentrations of CaCl 2 on freezing resistance. Results indicated that 10?mmol·L -1 of CaCl 2 has greater effect than other concentrations on the enhancement of freezing resistance, and the optimum time of pretreatment was 5?d. In addition, cuttings used for cold acclimation at -3℃ were pretreated with or without 10?mmol·L -1 of CaCl 2, 3?mmol·L -1 of Ca 2+ chelator EGTA, 0 05?mmol·L -1 of CaM antagonist CPZ or 0 1?mmol·L -1 of Ca 2+ channel inhibitor LaCl 3 The changes in CaM and freezing resistance of all cuttings were investigated. The results showed that cold acclimation at -3℃ increased CaM content and decreased the minimum temperature for 100% survival. The CaCl 2 pretreatment enhanced the effect of cold acclimation and obviously increased CaM content and decreased the minimum temperature for 100% survival, but this effect was strongly inhibited by the EGTA, CPZ or LaCl 3 It is concluded that the effect of CaCl 2 on freezing resistance is associated with its concentration and time of pretreatment, Ca 2+ CaM may be involved in the induction of freezing resistance of the cuttings.
文摘We investigated the changes in the contents of H202, malonaldehyde （MDA） and endogenous antioxidants, the activities of protective enzymes and some critical enzymes involved in the ascorbate-glutathione （ASA-GSH） cycle as well as freezing resistance （expressed as LT50） and correlations mentioned above, in detail using Populus suaveolens cuttings. The purpose was to explore the physiological mechanism of the enhancement of freezing resistance induced by freezing acclimation at -20℃, and to elucidate the physiological mechanisms by which trees adapt to freezing. The results showed that freezing acclimation enhanced the activities of superoxide dismutase （SOD）, peroxidase （POD）, catalase （CAT）, monodehydroascorbate reductase （MDAR）, ascorbate peroxidase （APX）, dehydroascorbate reductase （DHAR） and glutathione reductase （GR）. And it increased the contents of reduced ascorbate （ASA）, reduced glutathione （GSH）, dehydroascorbate （DHA） and oxidized glutathione （GSSG）. However, H202 and MDA contents and LT50 of cuttings were decreased. LTs0 in cuttings was found to be closely correlated to the levels of SOD, POD, CAT, APX, DHAR, MDAR, GR, H202, MDA, ASA, GSH, DHA and GSSG during freezing acclimation. This suggested that the enhancement of freezing resistance of cuttings induced by freezing acclimation may relate to the distinct increase for the levels of SOD, POD, CAT, APX, DHAR, MDAR, GR, ASA, GSH, DHA, and GSSG. In addition, the observed levels of APX, DHAR, MDAR, GR, ASA, DHA, GSH and GSSG were higher than those of SOD, POD and CAT during freezing acclimation. It indicated that a higher capacity of the ASA-GSH cycle is required for H202 detoxification, and growth and development of cuttings. Based on the obtained results, it can be concluded that the ASA-GSH cycle plays an important role in enhancement of freezing resistance of P. suaveolens cuttings during freezing acclimation.
