Background Polygalacturonase inhibiting proteins(PGIPs)play a pivotal role in plant defense against plant patho-gens by inhibiting polygalacturonase(PG),an enzyme produced by pathogens to degrade plant cell wall pecti...Background Polygalacturonase inhibiting proteins(PGIPs)play a pivotal role in plant defense against plant patho-gens by inhibiting polygalacturonase(PG),an enzyme produced by pathogens to degrade plant cell wall pectin.PGIPs,also known as leucine-rich repeat pathogenesis-related(PR)proteins,activate the host’s defense response upon interaction with PG,thereby reinforcing the host defense against plant pathogens attacks.In Egyptian or extra-long staple cotton(Gossypium barbadense),the interaction between PGIP and PG is one of the crucial steps in the defense mechanism against major pathogens such as Xanthomonas citri pv.malvacearum and Alternaria mac-rospora,which are responsible for bacterial leaf blight and leaf spot diseases,respectively.Results To unravel the molecular mechanisms underlying these PR proteins,we conducted a comprehensive study involving molecular modeling,protein-protein docking,site-specific double mutation(E169G and F242K),and molec-ular dynamics simulations.Both wild-type and mutated cotton PGIPs were examined in the interaction with the PG enzyme of a bacterial and fungal pathogen.Our findings revealed that changes in conformations of double-mutated residues in the active site of PGIP lead to the inhibition of PG binding.The molecular dynamics simulation studies provide insights into the dynamic behaviour and stability of the PGIP-PG complexes,shedding light on the intricate details of the inhibitory and exhibitory mechanism against the major fungal and bacterial pathogens of G.barbadense,respectively.Conclusions The findings of this study not only enhance our understanding of the molecular interactions between PGs of Xanthomonas citri pv.malvacearum and Alternaria macrospora and PGIP of G.barbadense but also pre-sent a potential strategy for developing the disease-resistant cotton varieties.By variations in the binding affinities of PGs through specific mutations in PGIP,this research offers promising avenues for the development of enhanced resistance to cotton plants against bacterial leaf blight and leaf spot diseases.展开更多
Polygalacturonase (PG,EC3.2.1.15) is the key cell wall hydrolase in fruit ripening. The identification and characterization of a full length cDNA (pMT18) encoding for PG from Feicheng peach (Prunus persica (L.) Bat...Polygalacturonase (PG,EC3.2.1.15) is the key cell wall hydrolase in fruit ripening. The identification and characterization of a full length cDNA (pMT18) encoding for PG from Feicheng peach (Prunus persica (L.) Batsch cv. Feicheng) is described. The pMT18 clone is 1188 bp in length, with an open reading frame of 393 amino acids. The homology and phylogenetic analyses indicate a remarkable similarity between peach PG and other ripening related PG. And seven consensus sequences have revealed in peach PG compared to the PG from other plants. However, the profound divergence with other PG and the unique structure features suggest that peach PG probably belongs to a new evolutionary class. In RT PCR analysis, pMT18 related RNA was undetectable in leaves, and was much abundant in ripe fruits. The ripening specific expression pattern of this cDNA will be useful in investigating the roles of PG in fruit ripening and developing a transgenic peach with the improved post harvesting quality in the future.展开更多
Fruit ripening is a complex process and is regulated by many factors. Ethylene and polygalacturonase （PG）, lipoxygenase （LOX）, expansin （EXP） are all critical regulating factors in fruit ripening and softening p...Fruit ripening is a complex process and is regulated by many factors. Ethylene and polygalacturonase （PG）, lipoxygenase （LOX）, expansin （EXP） are all critical regulating factors in fruit ripening and softening process. With antisense ACS tomato, Nr mutant tomato and cultivated tomato as materials, Northern blot hybridization showed that PG, LeEXP1 and LOXexpressed differently in different parts of cultivated tomato fruit during ripening, which was related to fruit ripening. The ripening process of columella and radial pericarp was faster than pericarp. In both Nr mutant and antisense ACS transgenic tomato fruit, expression levels ofPG, LeEXPI and LOXwere generally lower than those in cultivated fruit but still related to fruit ripening. The expression levels ofPG, LeEXP1 and LOX increased in the mature green tomato fruits after 0.5 h treatment with ethylene （100 μL/L）. These results indicate that gene expression ofPG, LeEXP1 and LOXwere positively regulated by ethylene. The time and cumulative effect of the concentration exists in the expression of PG regulated by ethylene. The regulation of LOX expression mainly depended on the fruit development after great amount of ethylene was produced. PG played a major role in ripening and softening of tomato fruit, and cooperated with the regulation of EXP and LOX.展开更多
In this study, 1 500 bp PG gene promoter was amplified from leaves of tomato cultivar ＇ Zhongshu No. 4＇. The bioinformatic analysis of PG promoter sequences was conducted. PG promoter elements were predicted and ana...In this study, 1 500 bp PG gene promoter was amplified from leaves of tomato cultivar ＇ Zhongshu No. 4＇. The bioinformatic analysis of PG promoter sequences was conducted. PG promoter elements were predicted and analyzed by PLANTCARE and PLACE. The results showed that tomato PG promoter contained multiple c/s-acting regulatory elements such as typical basic elements TATA-Box and CAAT-Box, light responsive elements 3-AF1 binding site, ATl-motif, ATCT- motif, Box 4, Box I, GA-motif, GTl-motif, Spl and MRE, heat stress-responsive element HSE, ethylene-responsive element ERE, meristem-specifie regulatory element CCGTCC-box, endosperm expression-related regulatory elements GCN4_motif and Skn-l_motif, defense and stress responsiveness element TC-rich repeats, and circadian control-related element circadian, indicating that the expression of tomato PG gene is related to light, temperature, hormone, stress and other factors. This study laid the foundation for subsequent research about regulation of PG gene expression in plants.展开更多
The present study aimed to purify and characterize one polygalacturonase from L. gongylophorus (PGaseLg), the symbiotic fungus of Atta sexdens. The enzyme was isolated by salting out of crude extract followed by two c...The present study aimed to purify and characterize one polygalacturonase from L. gongylophorus (PGaseLg), the symbiotic fungus of Atta sexdens. The enzyme was isolated by salting out of crude extract followed by two chromatographic steps. PGaseLG was identified with MS analysis and molecular exclusion chromatography revealed the monomeric nature of a protein with an estimated molecular weight of about 39 kDa. PGaseLg has an optimum temperature of 60°C and optimum pH activity at 5.0. Using polygalacturonate as a substrate, the calculations of K<sub>M</sub>, V<sub>max</sub> and k<sub>cat</sub> were 0.65 mg·mL<sup>-1</sup>, 1800 μmol·min<sup>-1</sup>·mg<sup>-1</sup> and 35.97 s<sup>-1</sup>, respectively. The enzyme was stable for more than 3 h at 50°C at pH 5.0;otherwise, at lower or higher pH values, the PGaseLg was less stable. The influence of several metals, EDTA and β-mercaptoethanol on enzyme activity was also determined. Thin layer chromatography (TLC) analyses indicated that PGaseLg is an exopolygalacturonase.展开更多
Penicillium expansum 3.5425 was applied in solid-state fermentation(SSF)of agricultural wastes for polygalacturonase biosynthesis.Among various carbon additives,apple pomace was most suitable for the biosynthesis of p...Penicillium expansum 3.5425 was applied in solid-state fermentation(SSF)of agricultural wastes for polygalacturonase biosynthesis.Among various carbon additives,apple pomace was most suitable for the biosynthesis of polygalacturonase(1440.57 U/g).Optimization of medium parameters using rotational orthogonal design(ROD)experiment combined with optimal fermentation conditions resulted in a 2.72-fold increase in the polygalacturonase production.By using ammonium sulphate precipitation,ion-exchange and gel-permeation chromatography,the polygalacturonase produced by P.expansum 3.5425 was finally purified which had specific activity of 19269 U/mg and molecular weight of 30 kDa.The enzyme was remarkably active in the pH range of 3-5 and at 50℃,which makes it more acceptable in the industrial application.Besides,partially purified polygalacturonase(875.15 U/mL)was used for apple juice clarification and the clarity at 0.4 mL/kg was maximum,which reveals a great potential of polygalacturonase in food industry.展开更多
The aim of this study was to continuously hydrolyze mango peel pectin,an agricultural waste,into pectic oligosaccharides(POS)with antibacterial activity.A packed-bed reactor(PBR)with immobilized polygalacturonase was ...The aim of this study was to continuously hydrolyze mango peel pectin,an agricultural waste,into pectic oligosaccharides(POS)with antibacterial activity.A packed-bed reactor(PBR)with immobilized polygalacturonase was designed,and the effects of the process conditions(flow rate,substrate concentration,and enzyme amount)were evaluated.The optimal conditions were obtained using response surface analysis,and a stable POS production with a yield of 94.56%was achieved.The PBR retained 82%of its initial activity after continuous operation for 72 h.The POS products exhibited good antibacterial activity against E.coli,S.aureus,B.subtilis,and S.typhimurium.The destructive effects of POS on the membrane system integrity were observed via scanning electron microscopy and the leakage of intracellular nucleic acids.Thus,the PBR is a powerful tool for continuous POS production,and hence,it can be applied as an alternative to chemical preservatives in the food industry.展开更多
In this study, a total of 85 apple polygalacturonase genes were characterized and clustered into seven groups based on the Malus × domestica whole-genome sequence. These genes coded for proteins containing 176–1...In this study, a total of 85 apple polygalacturonase genes were characterized and clustered into seven groups based on the Malus × domestica whole-genome sequence. These genes coded for proteins containing 176–1 125 amino acids with isoelectric points ranging from 4.68 to 9.58.The predicted Md PG genes were distributed on all chromosomes except the 14 th. We then systematically analyzed conserved Md PG protein motifs and the structures of Md PG genes. We identified Md PG proteins containing four conserved motifs that are widely found in different PG proteins.Additionally, we found that Md PG75 was the largest gene, encompassing 18 exons. Finally, we systematically analyzed the functional connection network of Md PG proteins and predicted the functions of related Md PG genes before undertaking a preliminary validation. Overall, we have described the genome-wide identification and analysis of the apple PG gene family.展开更多
Artemisia sphaerocephaia is a sand-fixing shrub oc-curring in the deserts of Northwest China.The polysac-charide pellicle that surrounds the achene forms during seed development and becomes a thick mucilaginous layer ...Artemisia sphaerocephaia is a sand-fixing shrub oc-curring in the deserts of Northwest China.The polysac-charide pellicle that surrounds the achene forms during seed development and becomes a thick mucilaginous layer when the dry seed is wetted.In natural habitals,the ach-enes start to mature from September to Octaber1.The mature achenes,enclosed in their dry polysaccharide pel-licles,are dispersed by wind and adhere to sand grains by the mucilaginous layer that develops from the pellicle when the achene surface is wetted.A major component of the mucilage on the exterior of the pericarp is pectin.The thick pellicle of these species serves as a means of water catchment as well as helping the seed adhere to sand par-ticles.Strong adherence to the sand surface once the mu-cilage is dry prevents further dispersion by rain and wind and deters collection by ants and other seed preda-torg[2.3].展开更多
Combinatorial chemistry has been a focus of research activity in modern drug discovery and biotechnology. It is a concept by which a vast library of molecular diversity is synthesized and screened for target propertie...Combinatorial chemistry has been a focus of research activity in modern drug discovery and biotechnology. It is a concept by which a vast library of molecular diversity is synthesized and screened for target properties. This report is to illustrate the application of enzyme technology using the concept of combinatorial chemistry as a novel approach for the bioconversion of plant fibers. Citrus pectin was subjected to combinatorial enzyme digestion to create libraries of pectic oligosaccharides with diverse structural variants. Repeated cycles of fractionation and screening resulted in the isolation and identification of an active oligoGalA species with antimicrobial activity.展开更多
This study aimed at the physical, chemical and biochemical changes during ripening of Sweetsop （Annona squamosa L.） and Golden Apple （Spondias citherea Sonner） fruits during ripening as important features to bette...This study aimed at the physical, chemical and biochemical changes during ripening of Sweetsop （Annona squamosa L.） and Golden Apple （Spondias citherea Sonner） fruits during ripening as important features to better understand their postharvest handling. It was carried out physical analysis such as firmness and chemical analysis such as total chlorophyll, total carotenoids, soluble solids, pectins and titrable acidity and biochemical analysis such as pectin methyl esterase, polygalacturonase, cellulase, and peroxidase and polyphenoloxidase activities in crude extract. Fruits were harvested at different stages of ripening. Experimental design was completely randomized and was carried out analysis of variance and Tukey tests, Total chlorophyll was decreasing in later stages of ripening, total soluble solid contents increased as the fruits ripen, while the acidity expressed percentage of citric acid decreased during fruits ripening. The loss of firmness and soluble solids content increased as the fruit get ripped stage, while the content of pectin decreased. Activity was observed for pectin methyl esterase and polygalacturonase enzymes during all stages of maturation, presenting the highest activity for both enzymes in the mature state. No cellulase activity detected at any stage during the ripening of these fruits. Activity of the enzyme polyphenoloxidase and peroxidase, associated with pulp browning was higher in the last stages of ripening of these fruits. Physical, chemical and biochemical patterns during ripening were different according to fruit species suggesting differential postharvest handling requirements.展开更多
This review is concerned with the mechanisms controlling fruit softening.Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream,with separate controls for distinct qu...This review is concerned with the mechanisms controlling fruit softening.Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream,with separate controls for distinct quality attributes such as colour,flavour,texture,and aroma.Ethylene plays a critical role as a ripening hormone and is implicated in controlling different facets of ripening,including texture change,acting through a range of transcriptional regulators,and this signalling can be blocked using 1-methylcyclopropene.A battery of at least seven cell-wall-modifying enzymes,most of which are synthesized de novo during ripening,cause major alterations in the structure and composition of the cell wall components and contribute to the softening process.Significant differences between fruits may be related to the precise structure and composition of their cell walls and the enzymes recruited to the ripening programme during evolution.Attempts to slow texture change and reduce fruit spoilage by delaying the entire ripening process can often affect negatively other aspects of quality,and low temperatures,in particular,can have deleterious effects on texture change.Gene silencing has been used to probe the function of individual genes involved in different aspects of ripening,including colour,flavour,ethylene synthesis,and particularly texture change.The picture that emerges is that softening is a multi-genic trait,with some genes making a more important contribution than others.In future,it may be possible to control texture genetically to produce fruits more suitable for our needs.展开更多
基金CABin grant(F.no.Agril.Edn.4-1/2013-A&P)Indian Council of Agricul-tural Research,Ministry of Agriculture and Farmers’Welfare,Govt.of India and Department of Biotechnology,Govt.of India for BIC project grant(BT/PR40161/BTIS/137/32/2021)。
文摘Background Polygalacturonase inhibiting proteins(PGIPs)play a pivotal role in plant defense against plant patho-gens by inhibiting polygalacturonase(PG),an enzyme produced by pathogens to degrade plant cell wall pectin.PGIPs,also known as leucine-rich repeat pathogenesis-related(PR)proteins,activate the host’s defense response upon interaction with PG,thereby reinforcing the host defense against plant pathogens attacks.In Egyptian or extra-long staple cotton(Gossypium barbadense),the interaction between PGIP and PG is one of the crucial steps in the defense mechanism against major pathogens such as Xanthomonas citri pv.malvacearum and Alternaria mac-rospora,which are responsible for bacterial leaf blight and leaf spot diseases,respectively.Results To unravel the molecular mechanisms underlying these PR proteins,we conducted a comprehensive study involving molecular modeling,protein-protein docking,site-specific double mutation(E169G and F242K),and molec-ular dynamics simulations.Both wild-type and mutated cotton PGIPs were examined in the interaction with the PG enzyme of a bacterial and fungal pathogen.Our findings revealed that changes in conformations of double-mutated residues in the active site of PGIP lead to the inhibition of PG binding.The molecular dynamics simulation studies provide insights into the dynamic behaviour and stability of the PGIP-PG complexes,shedding light on the intricate details of the inhibitory and exhibitory mechanism against the major fungal and bacterial pathogens of G.barbadense,respectively.Conclusions The findings of this study not only enhance our understanding of the molecular interactions between PGs of Xanthomonas citri pv.malvacearum and Alternaria macrospora and PGIP of G.barbadense but also pre-sent a potential strategy for developing the disease-resistant cotton varieties.By variations in the binding affinities of PGs through specific mutations in PGIP,this research offers promising avenues for the development of enhanced resistance to cotton plants against bacterial leaf blight and leaf spot diseases.
文摘Polygalacturonase (PG,EC3.2.1.15) is the key cell wall hydrolase in fruit ripening. The identification and characterization of a full length cDNA (pMT18) encoding for PG from Feicheng peach (Prunus persica (L.) Batsch cv. Feicheng) is described. The pMT18 clone is 1188 bp in length, with an open reading frame of 393 amino acids. The homology and phylogenetic analyses indicate a remarkable similarity between peach PG and other ripening related PG. And seven consensus sequences have revealed in peach PG compared to the PG from other plants. However, the profound divergence with other PG and the unique structure features suggest that peach PG probably belongs to a new evolutionary class. In RT PCR analysis, pMT18 related RNA was undetectable in leaves, and was much abundant in ripe fruits. The ripening specific expression pattern of this cDNA will be useful in investigating the roles of PG in fruit ripening and developing a transgenic peach with the improved post harvesting quality in the future.
基金Supported by National Project of Scientific and Technical Supporting Programs Funded by Ministry of Science and Technology of China (No.2006BAD22B01)National Natural Science Foundation of China (No.30800767)Postdoctoral Fund of China (No.20080430725)
文摘Fruit ripening is a complex process and is regulated by many factors. Ethylene and polygalacturonase （PG）, lipoxygenase （LOX）, expansin （EXP） are all critical regulating factors in fruit ripening and softening process. With antisense ACS tomato, Nr mutant tomato and cultivated tomato as materials, Northern blot hybridization showed that PG, LeEXP1 and LOXexpressed differently in different parts of cultivated tomato fruit during ripening, which was related to fruit ripening. The ripening process of columella and radial pericarp was faster than pericarp. In both Nr mutant and antisense ACS transgenic tomato fruit, expression levels ofPG, LeEXPI and LOXwere generally lower than those in cultivated fruit but still related to fruit ripening. The expression levels ofPG, LeEXP1 and LOX increased in the mature green tomato fruits after 0.5 h treatment with ethylene （100 μL/L）. These results indicate that gene expression ofPG, LeEXP1 and LOXwere positively regulated by ethylene. The time and cumulative effect of the concentration exists in the expression of PG regulated by ethylene. The regulation of LOX expression mainly depended on the fruit development after great amount of ethylene was produced. PG played a major role in ripening and softening of tomato fruit, and cooperated with the regulation of EXP and LOX.
基金Supported by Natural Science Foundation of Yunnan Province(2011FB049)National Natural Science Foundation of China(31260481,31460516)+1 种基金Fund of Yunnan Education Department(2013Y251)Development Fund of the Department of Life Science and Technology,Kunming University(GXKM201505)
文摘In this study, 1 500 bp PG gene promoter was amplified from leaves of tomato cultivar ＇ Zhongshu No. 4＇. The bioinformatic analysis of PG promoter sequences was conducted. PG promoter elements were predicted and analyzed by PLANTCARE and PLACE. The results showed that tomato PG promoter contained multiple c/s-acting regulatory elements such as typical basic elements TATA-Box and CAAT-Box, light responsive elements 3-AF1 binding site, ATl-motif, ATCT- motif, Box 4, Box I, GA-motif, GTl-motif, Spl and MRE, heat stress-responsive element HSE, ethylene-responsive element ERE, meristem-specifie regulatory element CCGTCC-box, endosperm expression-related regulatory elements GCN4_motif and Skn-l_motif, defense and stress responsiveness element TC-rich repeats, and circadian control-related element circadian, indicating that the expression of tomato PG gene is related to light, temperature, hormone, stress and other factors. This study laid the foundation for subsequent research about regulation of PG gene expression in plants.
文摘The present study aimed to purify and characterize one polygalacturonase from L. gongylophorus (PGaseLg), the symbiotic fungus of Atta sexdens. The enzyme was isolated by salting out of crude extract followed by two chromatographic steps. PGaseLG was identified with MS analysis and molecular exclusion chromatography revealed the monomeric nature of a protein with an estimated molecular weight of about 39 kDa. PGaseLg has an optimum temperature of 60°C and optimum pH activity at 5.0. Using polygalacturonate as a substrate, the calculations of K<sub>M</sub>, V<sub>max</sub> and k<sub>cat</sub> were 0.65 mg·mL<sup>-1</sup>, 1800 μmol·min<sup>-1</sup>·mg<sup>-1</sup> and 35.97 s<sup>-1</sup>, respectively. The enzyme was stable for more than 3 h at 50°C at pH 5.0;otherwise, at lower or higher pH values, the PGaseLg was less stable. The influence of several metals, EDTA and β-mercaptoethanol on enzyme activity was also determined. Thin layer chromatography (TLC) analyses indicated that PGaseLg is an exopolygalacturonase.
基金The authors would like to thank the High-Level Talent Scientific Research Staring Foundation(No.2015015)provided by Henan Institute of Science&TechnologyKey Scientific Research Project(17A550001)supported by Education Department of Henan Province+1 种基金Program for Innovative Research Talents(in Science and Technology)of Henan Provincial University(16HASTIT015)Excellent Youth Foundation of Henan Scientific Committee(174100510003).
文摘Penicillium expansum 3.5425 was applied in solid-state fermentation(SSF)of agricultural wastes for polygalacturonase biosynthesis.Among various carbon additives,apple pomace was most suitable for the biosynthesis of polygalacturonase(1440.57 U/g).Optimization of medium parameters using rotational orthogonal design(ROD)experiment combined with optimal fermentation conditions resulted in a 2.72-fold increase in the polygalacturonase production.By using ammonium sulphate precipitation,ion-exchange and gel-permeation chromatography,the polygalacturonase produced by P.expansum 3.5425 was finally purified which had specific activity of 19269 U/mg and molecular weight of 30 kDa.The enzyme was remarkably active in the pH range of 3-5 and at 50℃,which makes it more acceptable in the industrial application.Besides,partially purified polygalacturonase(875.15 U/mL)was used for apple juice clarification and the clarity at 0.4 mL/kg was maximum,which reveals a great potential of polygalacturonase in food industry.
基金supported by the National Natural Science Foundation of China(No.32072164)Natural Science Foundation of Jiangsu Province(No.BK20210458)+1 种基金the National Key Research and Development Program of China(No.2020YFC1606804)the Postdoctoral Research Funding Plan of China(No.2019M651710).
文摘The aim of this study was to continuously hydrolyze mango peel pectin,an agricultural waste,into pectic oligosaccharides(POS)with antibacterial activity.A packed-bed reactor(PBR)with immobilized polygalacturonase was designed,and the effects of the process conditions(flow rate,substrate concentration,and enzyme amount)were evaluated.The optimal conditions were obtained using response surface analysis,and a stable POS production with a yield of 94.56%was achieved.The PBR retained 82%of its initial activity after continuous operation for 72 h.The POS products exhibited good antibacterial activity against E.coli,S.aureus,B.subtilis,and S.typhimurium.The destructive effects of POS on the membrane system integrity were observed via scanning electron microscopy and the leakage of intracellular nucleic acids.Thus,the PBR is a powerful tool for continuous POS production,and hence,it can be applied as an alternative to chemical preservatives in the food industry.
基金financially supported by the National Science and Technology Supporting Project (2013BAD20B03)China Agriculture Research System (CARS-28), National Spark Plan Program (2014GA850002)+1 种基金Science and Technology Innovative Engineering Project in Shaanxi Province, China (2015NY114)Collaborative Innovation of the Center for Shaanxi Fruit Industry Development
文摘In this study, a total of 85 apple polygalacturonase genes were characterized and clustered into seven groups based on the Malus × domestica whole-genome sequence. These genes coded for proteins containing 176–1 125 amino acids with isoelectric points ranging from 4.68 to 9.58.The predicted Md PG genes were distributed on all chromosomes except the 14 th. We then systematically analyzed conserved Md PG protein motifs and the structures of Md PG genes. We identified Md PG proteins containing four conserved motifs that are widely found in different PG proteins.Additionally, we found that Md PG75 was the largest gene, encompassing 18 exons. Finally, we systematically analyzed the functional connection network of Md PG proteins and predicted the functions of related Md PG genes before undertaking a preliminary validation. Overall, we have described the genome-wide identification and analysis of the apple PG gene family.
文摘Artemisia sphaerocephaia is a sand-fixing shrub oc-curring in the deserts of Northwest China.The polysac-charide pellicle that surrounds the achene forms during seed development and becomes a thick mucilaginous layer when the dry seed is wetted.In natural habitals,the ach-enes start to mature from September to Octaber1.The mature achenes,enclosed in their dry polysaccharide pel-licles,are dispersed by wind and adhere to sand grains by the mucilaginous layer that develops from the pellicle when the achene surface is wetted.A major component of the mucilage on the exterior of the pericarp is pectin.The thick pellicle of these species serves as a means of water catchment as well as helping the seed adhere to sand par-ticles.Strong adherence to the sand surface once the mu-cilage is dry prevents further dispersion by rain and wind and deters collection by ants and other seed preda-torg[2.3].
文摘Combinatorial chemistry has been a focus of research activity in modern drug discovery and biotechnology. It is a concept by which a vast library of molecular diversity is synthesized and screened for target properties. This report is to illustrate the application of enzyme technology using the concept of combinatorial chemistry as a novel approach for the bioconversion of plant fibers. Citrus pectin was subjected to combinatorial enzyme digestion to create libraries of pectic oligosaccharides with diverse structural variants. Repeated cycles of fractionation and screening resulted in the isolation and identification of an active oligoGalA species with antimicrobial activity.
文摘This study aimed at the physical, chemical and biochemical changes during ripening of Sweetsop （Annona squamosa L.） and Golden Apple （Spondias citherea Sonner） fruits during ripening as important features to better understand their postharvest handling. It was carried out physical analysis such as firmness and chemical analysis such as total chlorophyll, total carotenoids, soluble solids, pectins and titrable acidity and biochemical analysis such as pectin methyl esterase, polygalacturonase, cellulase, and peroxidase and polyphenoloxidase activities in crude extract. Fruits were harvested at different stages of ripening. Experimental design was completely randomized and was carried out analysis of variance and Tukey tests, Total chlorophyll was decreasing in later stages of ripening, total soluble solid contents increased as the fruits ripen, while the acidity expressed percentage of citric acid decreased during fruits ripening. The loss of firmness and soluble solids content increased as the fruit get ripped stage, while the content of pectin decreased. Activity was observed for pectin methyl esterase and polygalacturonase enzymes during all stages of maturation, presenting the highest activity for both enzymes in the mature state. No cellulase activity detected at any stage during the ripening of these fruits. Activity of the enzyme polyphenoloxidase and peroxidase, associated with pulp browning was higher in the last stages of ripening of these fruits. Physical, chemical and biochemical patterns during ripening were different according to fruit species suggesting differential postharvest handling requirements.
文摘This review is concerned with the mechanisms controlling fruit softening.Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream,with separate controls for distinct quality attributes such as colour,flavour,texture,and aroma.Ethylene plays a critical role as a ripening hormone and is implicated in controlling different facets of ripening,including texture change,acting through a range of transcriptional regulators,and this signalling can be blocked using 1-methylcyclopropene.A battery of at least seven cell-wall-modifying enzymes,most of which are synthesized de novo during ripening,cause major alterations in the structure and composition of the cell wall components and contribute to the softening process.Significant differences between fruits may be related to the precise structure and composition of their cell walls and the enzymes recruited to the ripening programme during evolution.Attempts to slow texture change and reduce fruit spoilage by delaying the entire ripening process can often affect negatively other aspects of quality,and low temperatures,in particular,can have deleterious effects on texture change.Gene silencing has been used to probe the function of individual genes involved in different aspects of ripening,including colour,flavour,ethylene synthesis,and particularly texture change.The picture that emerges is that softening is a multi-genic trait,with some genes making a more important contribution than others.In future,it may be possible to control texture genetically to produce fruits more suitable for our needs.
