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Shao-ling Zhang - One of the best experts on this subject based on the ideXlab platform.
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Distribution and metabolism of ascorbic acid in pear fruits (Pyrus pyrifolia Nakai cv. Aikansui)
African Journal of Biotechnology, 2013Co-Authors: Wenjiang Huang, Gaihua Qing, Huping Zhang, Shao-ling ZhangAbstract:Ascorbate accumulation levels, distribution and key enzyme activities involved in synthesizing via Smirnoff-Wheeler pathway and recycling in different pear fruit tissues during development were studied. Results show that the ascorbate contents increased with the fruit development, and reached the highest titers in 30 days after anthesis (DAA), then decreased and maintained a level. The higher contents of ascorbate in the peel of pear fruit were observed, which results from a combination of higher activities of L-galactose dehydrogenase (GalDH) and L-galactono-1,4-lactone (GalLDH) involving ascorbate biosynthesis and higher dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities used to recycle ascorbate. Exogenous feeding of ascorbate synthesis precursors demonstrated that the peel had stronger capability of de novo ascorbate biosynthesis via Smirnoff-Wheeler pathway and uronic acid pathway whereas the flesh and core had lower capability for ascorbate synthesis. These results suggest that the pear fruit is able to cause de novo ascorbate biosynthesis and the peel had higher capability for ascorbate biosynthesis than the flesh and core. Keywords : Pyrus pyrifolia , ascorbate, biosynthesis African Journal of Biotechnology Vol. 12(16), pp. 1952-1961
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cAMP activates hyperpolarization-activated Ca2+ channels in the pollen of Pyrus pyrifolia
Plant cell reports, 2011Co-Authors: Cong Jin, Zhongling Shang, Y. B. Gao, Shao-ling ZhangAbstract:Many signal-transduction processes in plant cells have been suggested to be triggered by signal-induced opening of calcium ion (Ca2+) channels in the plasma membrane. Cyclic nucleotides have been proposed to lead to an increase in cytosolic free Ca2+ in pollen. However, direct recordings of cyclic-nucleotide-induced Ca2+ currents in pollen have not yet been obtained. Here, we report that cyclic AMP (cAMP) activated a hyperpolarization-activated Ca2+ channel in the Pyrus pyrifolia pollen tube using the patch-clamp technique, which resulted in a significant increase in pollen tube protoplast cytosolic-Ca2+ concentration. Outside-out single channel configuration identified that cAMP directly increased the Ca2+ channel open-probability without affecting channel conductance. cAMP-induced currents were composed of both Ca2+ and K+. However, cGMP failed to mimic the cAMP effect. Higher cytosolic free-Ca2+ concentration significantly decreased the cAMP-induced currents. These results provide direct evidence for cAMP activation of hyperpolarization-activated Ca2+ channels in the plasma membrane of pollen tubes, which, in turn, modulate cellular responses in regulation of pollen tube growth.
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A cascade signal pathway occurs in self-incompatibility of Pyrus pyrifolia.
Plant signaling & behavior, 2011Co-Authors: Chun-lei Wang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) possesses an S-RNase-based gametophytic self-incompatibility (GSI) system and S-RNase, the self-incompatibility (SI) determinant in the pistil, has also been implicated in the rejection of self-pollen and genetically identical pollen. We have demonstrated that S-RNase depolymerises actin cytoskeleton, triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube, which indicates programmed cell death (PCD) may occur in SI response of Pyrus pyrifolia. Recently, we have identified that S-RNase specifically disrupted tip-localized reactive oxygen species (ROS) of incompatible pollen tube via arrest of ROS formation in mitochondria and cell walls in Pyrus pyrifolia. Furthermore, tip-localized ROS disruption not only decreased the Ca2+ current and depolymerised the actin cytoskeleton, but it also induced nuclear DNA degradation in the pollen tube. The results mentioned above indicate that a cascade signal pathway may occur in SI of Pyrus pyrifolia and PCD is used to terminate the incompatible pollen tubes growth. In this addendum, we review the cascade signal pathway of Pyrus pyrifolia SI.
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S-RNase disrupts tip-localized reactive oxygen species and induces nuclear DNA degradation in incompatible pollen tubes of Pyrus pyrifolia.
Journal of Cell Science, 2010Co-Authors: Chun-lei Wang, Yongbin Gao, Gong Chen, Shao-ling ZhangAbstract:Pear ( Pyrus pyrifolia L.) has an S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. However, RNA degradation might be only the beginning of the SI response, not the end. Recent in vitro studies suggest that S-RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia , and it seems that a relationship exists between self S-RNase, actin depolymerization and DNA degradation. To further uncover the SI response in pear, the relationship between self S-RNase and tip-localized reactive oxygen species (ROS) was evaluated. Our results show that S-RNase specifically disrupted tip-localized ROS of incompatible pollen tubes via arrest of ROS formation in mitochondria and cell walls. The mitochondrial ROS disruption was related to mitochondrial alteration, whereas cell wall ROS disruption was related to a decrease in NADPH. Tip-localized ROS disruption not only decreased the Ca 2+ current and depolymerized the actin cytoskeleton, but it also induced nuclear DNA degradation. These results indicate that tip-localized ROS disruption occurs in Pyrus pyrifolia SI. Importantly, we demonstrated nuclear DNA degradation in the incompatible pollen tube after pollination in vivo. This result validates our in vitro system in vivo.
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s rnase triggers mitochondrial alteration and dna degradation in the incompatible pollen tube of Pyrus pyrifolia in vitro
Plant Journal, 2009Co-Authors: Chun-lei Wang, Gong Chen, Xue-tin Jiang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.
Chun-lei Wang - One of the best experts on this subject based on the ideXlab platform.
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A cascade signal pathway occurs in self-incompatibility of Pyrus pyrifolia.
Plant signaling & behavior, 2011Co-Authors: Chun-lei Wang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) possesses an S-RNase-based gametophytic self-incompatibility (GSI) system and S-RNase, the self-incompatibility (SI) determinant in the pistil, has also been implicated in the rejection of self-pollen and genetically identical pollen. We have demonstrated that S-RNase depolymerises actin cytoskeleton, triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube, which indicates programmed cell death (PCD) may occur in SI response of Pyrus pyrifolia. Recently, we have identified that S-RNase specifically disrupted tip-localized reactive oxygen species (ROS) of incompatible pollen tube via arrest of ROS formation in mitochondria and cell walls in Pyrus pyrifolia. Furthermore, tip-localized ROS disruption not only decreased the Ca2+ current and depolymerised the actin cytoskeleton, but it also induced nuclear DNA degradation in the pollen tube. The results mentioned above indicate that a cascade signal pathway may occur in SI of Pyrus pyrifolia and PCD is used to terminate the incompatible pollen tubes growth. In this addendum, we review the cascade signal pathway of Pyrus pyrifolia SI.
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S-RNase disrupts tip-localized reactive oxygen species and induces nuclear DNA degradation in incompatible pollen tubes of Pyrus pyrifolia.
Journal of Cell Science, 2010Co-Authors: Chun-lei Wang, Yongbin Gao, Gong Chen, Shao-ling ZhangAbstract:Pear ( Pyrus pyrifolia L.) has an S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. However, RNA degradation might be only the beginning of the SI response, not the end. Recent in vitro studies suggest that S-RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia , and it seems that a relationship exists between self S-RNase, actin depolymerization and DNA degradation. To further uncover the SI response in pear, the relationship between self S-RNase and tip-localized reactive oxygen species (ROS) was evaluated. Our results show that S-RNase specifically disrupted tip-localized ROS of incompatible pollen tubes via arrest of ROS formation in mitochondria and cell walls. The mitochondrial ROS disruption was related to mitochondrial alteration, whereas cell wall ROS disruption was related to a decrease in NADPH. Tip-localized ROS disruption not only decreased the Ca 2+ current and depolymerized the actin cytoskeleton, but it also induced nuclear DNA degradation. These results indicate that tip-localized ROS disruption occurs in Pyrus pyrifolia SI. Importantly, we demonstrated nuclear DNA degradation in the incompatible pollen tube after pollination in vivo. This result validates our in vitro system in vivo.
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s rnase triggers mitochondrial alteration and dna degradation in the incompatible pollen tube of Pyrus pyrifolia in vitro
Plant Journal, 2009Co-Authors: Chun-lei Wang, Gong Chen, Xue-tin Jiang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.
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S‐RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia in vitro
The Plant journal : for cell and molecular biology, 2008Co-Authors: Chun-lei Wang, Gong Chen, Xue-tin Jiang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.
Minjie Qian - One of the best experts on this subject based on the ideXlab platform.
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Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai).
Frontiers in physiology, 2017Co-Authors: Minjie Qian, Qingfeng Niu, Songling Bai, Lu Bao, Yongwang Sun, Dong Zhang, Yuanwen TengAbstract:miR156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that two miR156 members (i.e., MIR156a and MIR156ba) were expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the MIR156a and MIR156ba precursors. We identified 19 miR156-targeted SPL genes using the ‘Suli’ pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba abundance increased after bags were removed. Yeast two-hybrid results revealed that the MYB10/bHLH/WD40 protein complex exists in pear, likely to regulate anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PyMYB10. We propose the following model for miRNA-mediated light-induced anthocyanin accumulation in pear fruits: miR156 positively regulates light-induced anthocyanin biosynthesis by cleaving PpSPL genes to stabilize the MYB10/bHLH/WD40 protein complex, which is essential for activating the expression of anthocyanin biosynthetic genes.
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Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai)
Frontiers Media S.A., 2017Co-Authors: Minjie Qian, Qingfeng Niu, Songling BaiAbstract:MicroRNA156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that miR156 was expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the miR156a and miR156ba precursors. We identified 19 SPL genes using the “Suli” pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were putative miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba/g/s/sa abundance increased after bags were removed. Yeast two-hybrid results suggested that PpMYB10, PpbHLH, and PpWD40 could form a protein complex, probably involved in anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PpMYB10. The results obtained in this study are helpful in understanding the possible role of miR156 and its target PpSPL genes in regulating light-induced red peel coloration and anthocyanin accumulation in pear
Yuanwen Teng - One of the best experts on this subject based on the ideXlab platform.
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Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai).
Frontiers in physiology, 2017Co-Authors: Minjie Qian, Qingfeng Niu, Songling Bai, Lu Bao, Yongwang Sun, Dong Zhang, Yuanwen TengAbstract:miR156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that two miR156 members (i.e., MIR156a and MIR156ba) were expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the MIR156a and MIR156ba precursors. We identified 19 miR156-targeted SPL genes using the ‘Suli’ pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba abundance increased after bags were removed. Yeast two-hybrid results revealed that the MYB10/bHLH/WD40 protein complex exists in pear, likely to regulate anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PyMYB10. We propose the following model for miRNA-mediated light-induced anthocyanin accumulation in pear fruits: miR156 positively regulates light-induced anthocyanin biosynthesis by cleaving PpSPL genes to stabilize the MYB10/bHLH/WD40 protein complex, which is essential for activating the expression of anthocyanin biosynthetic genes.
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Genetic Relationships among Pyrus pyrifolia Cultivars from Southeastern China and Japan
Acta Horticulturae, 2010Co-Authors: Danying Cai, Xiaoyan Zheng, Yuanwen Teng, David M. SpoonerAbstract:A total of 90 Pyrus pyrifolia cultivars from southeastern China and Japan were used to assess genetic diversity and overall similarity using eight Amplified Fragment Length Polymorphism (AFLP) primer combinations. Eighty-eight percent of the 429 bands produced were polymorphic. Unweighted Pair Group Method with Arithmetic Mean (UPGMA) cluster analysis of these data support two major groups, mostly consistent with their geographic distribution. Most of the P. pyrifolia cultivars from southeastern China formed one group and most of the Japanese cultivars were in the other group. However, some cultivars from southeastern China and Japan clustered together. These results support our previous studies which indicated that some Japanese pear cultivars are genetically similar to those from Zhejiang and Fujian Provinces of China. Nevertheless, most Japanese pears are genetically distant from Chinese sand pears.
Gong Chen - One of the best experts on this subject based on the ideXlab platform.
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S-RNase disrupts tip-localized reactive oxygen species and induces nuclear DNA degradation in incompatible pollen tubes of Pyrus pyrifolia.
Journal of Cell Science, 2010Co-Authors: Chun-lei Wang, Yongbin Gao, Gong Chen, Shao-ling ZhangAbstract:Pear ( Pyrus pyrifolia L.) has an S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. However, RNA degradation might be only the beginning of the SI response, not the end. Recent in vitro studies suggest that S-RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia , and it seems that a relationship exists between self S-RNase, actin depolymerization and DNA degradation. To further uncover the SI response in pear, the relationship between self S-RNase and tip-localized reactive oxygen species (ROS) was evaluated. Our results show that S-RNase specifically disrupted tip-localized ROS of incompatible pollen tubes via arrest of ROS formation in mitochondria and cell walls. The mitochondrial ROS disruption was related to mitochondrial alteration, whereas cell wall ROS disruption was related to a decrease in NADPH. Tip-localized ROS disruption not only decreased the Ca 2+ current and depolymerized the actin cytoskeleton, but it also induced nuclear DNA degradation. These results indicate that tip-localized ROS disruption occurs in Pyrus pyrifolia SI. Importantly, we demonstrated nuclear DNA degradation in the incompatible pollen tube after pollination in vivo. This result validates our in vitro system in vivo.
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s rnase triggers mitochondrial alteration and dna degradation in the incompatible pollen tube of Pyrus pyrifolia in vitro
Plant Journal, 2009Co-Authors: Chun-lei Wang, Gong Chen, Xue-tin Jiang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.
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S‐RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia in vitro
The Plant journal : for cell and molecular biology, 2008Co-Authors: Chun-lei Wang, Gong Chen, Xue-tin Jiang, Shao-ling ZhangAbstract:Pear (Pyrus pyrifolia L.) has a S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. No studies, however, have examined the extent of organelle alterations during the SI response in Pyrus pyrifolia. Consequently, this study focused on the alterations to mitochondria and nuclear DNA in incompatible pollen tubes of the pear. Methylthiazolyldiphenyl-tetrazolium bromide was used to evaluate the viability of pollen tubes under S-RNase challenge. The results showed that the viability of the control and compatible pollen tubes decreased slightly, but that of the incompatible pollen and pollen tubes began to decline at 30 min. The mitochondrial membrane potential (Delta psi(mit)) was also tested with rhodamine 123 30 min after SI challenge, and was shown to have collapsed in the incompatible pollen tubes after exposure to S-RNase. Western blotting 2 h after SI challenge confirmed that the Delta psi(mit) collapse induced leakage of cytochrome c into the cytosol. Swollen mitochondria were detected by transmission electron microscopy as early as 1 h after SI challenge and the degradation of nuclear DNA was observed by both 4,6-diamidino-2-phenylindole and transferase-mediated dUTP nick-end labeling. These diagnostic features of programmed cell death (PCD) suggested that PCD may specifically occur in incompatible pollen tubes.
