Cellular Polysaccharides Research Articles

Antifungal screening of selenium nanoparticles biosynthesized by microcystin-producing Desmonostoc alborizicum

Metal nanoparticles exhibit excellent antifungal abilities and are seen as a good substitute for controlling different kinds of fungi. Of all known taxa, cyanobacteria have received significant consideration as nanobiofactories, as a result of the cellular assimilation of heavy metals from the environment. The cellular bioactive enzymes, polysaccharides and pigments can be used as reducers and coatings during biosynthesis. The probability of the antifungal activity of selenium nanoparticles (SeNPs) to prevent plant fungi that can affect humans was evaluated and a toxic Iranian cyanobacterial strain of Desmonostoc alborizicum was used to study the biotechnology of SeNP synthesis for the first time. Characterization of nanoparticles with a UV-Vis spectrophotometer showed the formation of SeNPs in the range of 271–275 nm with the appearance of an orange color. Morphological examination of nanoparticles with Transmission Electron Microscopy (TEM), revealed the spherical shape of nanoparticles. The results of X-Ray Diffraction (XRD) showed 7 peaks and a hexagonal structure of average crystal size equal to 58.8 nm. The dispersion index of SeNPs was reported as 0.635, which indicated the homogeneity of the nanoparticle droplet size. The zeta potential of the nanoparticles was + 22.7. Fourier-transform infrared spectroscopy (FTIR) analysis exhibited a sharp and intense peak located at the wave number of 404 cm− 1, related to the SeNPs synthesized in this research. The results of the antifungal activity of SeNPs showed among the investigated fungi, Pythium ultimum had the highest resistance to SeNPs (14.66 ± 0.52 µg/ml), while Alternaria alternata showed the highest sensitivity (9.66 ± 0.51 µg/ml) (p < 0.05). To the best of our knowledge this is the first report concerning the characterization and antifungal screening of SeNPs biosynthesized by Iranian cyanobacteria, which could be used as effective candidates in medical applications.

Exploring the cellular surface polysaccharide and root nodule symbiosis characteristics of the rpoN mutants of Bradyrhizobium sp. DOA9 using synchrotron-based Fourier transform infrared microspectroscopy in conjunction with X-ray absorption spectroscopy.

The functional significance of rpoN genes that encode two sigma factors in the Bradyrhizobium sp. strain DOA9 has been reported to affect colony formation, root nodulation characteristics, and symbiotic interactions with Aeschynomene americana. rpoN mutant strains are defective in cellular surface polysaccharide (CSP) production compared with the wild-type (WT) strain, and they accordingly exhibit smaller colonies and diminished symbiotic effectiveness. To gain deeper insights into the changes in CSP composition and the nodules of rpoN mutants, we employed synchrotron-based Fourier transform infrared (SR-FTIR) microspectroscopy and X-ray absorption spectroscopy. FTIR analysis of the CSP revealed the absence of specific components in the rpoN mutants, including lipids, carboxylic groups, polysaccharide-pyranose rings, and β-galactopyranosyl residues. Nodules formed by DOA9WT exhibited a uniform distribution of lipids, proteins, and carbohydrates; mutant strains, particularly DOA9∆rpoNp:ΩrpoNc, exhibited decreased distribution uniformity and a lower concentration of C=O groups. Furthermore, Fe K-edge X-ray absorption near-edge structure and extended X-ray absorption fine structure analyses revealed deficiencies in the nitrogenase enzyme in the nodules of DOA9∆rpoNc and DOA9∆rpoNp:ΩrpoNc mutants; nodules from DOA9WT and DOA9∆rpoNp exhibited both leghemoglobin and the nitrogenase enzyme. IMPORTANCE This work provides valuable insights into how two rpoN genes affect the composition of cellular surface polysaccharides (CSPs) in Bradyrhizobium sp., which subsequently dictates root nodule chemical characteristics and nitrogenase production. We used advanced synchrotron methods, including synchrotron-based Fourier transform infrared (SR-FTIR) microspectroscopy and X-ray absorption spectroscopy (XAS), for the first time in this field to analyze CSP components and reveal the biochemical changes occurring within nodules. These cutting-edge techniques confer significant advantages by providing detailed molecular information, enabling the identification of specific functional groups, chemical bonds, and biomolecule changes. This research not only contributes to our understanding of plant-microbe interactions but also establishes a foundation for future investigations and potential applications in this field. The combined use of the synchrotron-based FTIR and XAS techniques represents a significant advancement in facilitating a comprehensive exploration of bacterial CSPs and their implications in plant-microbe interactions.

Dissecting the metal resistance genes contributed by virome from mining-affected metal contaminated soils

Virus-borne auxiliary genes have been demonstrated to influence their hosts’ characteristics and flexibility, resulting in an elevated ability to withstand diverse conditions and competition. However, the research on the soil viral community and its influencing factors is not extensive. The effects of bacterium-phage co-evolution in the metal contaminated environment have yet to be fully understood. In our research, numerous viral genes with conserved functional residues/motifs working on detoxifying heavy metals were pinpointed in the virome recovered from 58 contaminated soil metagenomic samples of mineral area, including tellurite resistance genes (e.g., terC, terD), copper resistance genes (e.g., copC, copA), and arsenate resistance genes (e.g., arsC). Moreover, viral proteins involved in key processes of nutrient uptake and metabolism, cellular function, polysaccharides production and biomineralization were also detected, which may also contribute to the response of microbial community to heavy metal stress. Our research showed that viruses have helped their hosts to acquire novel metal-resistance abilities through horizontal gene transfer (HGT) during the adaptation to challenging metal-rich environments. This was also evidenced by the high Codon adaption index (CAI) values across metal-resistance-related genes. This study has advanced our understanding on virus-host interplay within heavy metal contaminated soils.

Biomedical Applications of Biosynthesized Gold Nanoparticles from Cyanobacteria: an Overview.

Recently there had been a great interest in biologically synthesized nanoparticles (NPs) as potential therapeutic agents. The shortcomings of conventional non-biological synthesis methods such as generation of toxic byproducts, energy consumptions, and involved cost have shifted the attention towards green syntheses of NPs. Among noble metal NPs, gold nanoparticles (AuNPs) are the most extensively used ones, owing to the unique physicochemical properties. AuNPs have potential therapeutic applications, as those are synthesized with biomolecules as reducing and stabilizing agent(s). The green method of AuNP synthesis is simple, eco-friendly, non-toxic, and cost-effective with the use of renewable energy sources. Among all taxa, cyanobacteria have attracted considerable attention as nano-biofactories, due to cellular uptake of heavy metals from the environment. The cellular bioactive pigments, enzymes, and polysaccharides acted as reducing and coating agents during the process of biosynthesis. However, cyanobacteria-mediated AuNPs have potential biomedical applications, namely, targeted drug delivery, cancer treatment, gene therapy, antimicrobial agent, biosensors, and imaging.

Acceleration of Aril Cracking by Ethylene in Torreya grandis During Nut Maturation.

Torreya grandis ‘Merrillii’ is a famous nut with great nutritional value and high medicinal value. Aril cracking is an important process for seed dispersal, which is also an indicator of seed maturation. However, the cracking mechanism of T. grandis aril during the maturation stage remains largely unknown. Here, we provided a comprehensive view of the physiological and molecular levels of aril cracking in T. grandis by systematically analyzing its anatomical structure, physiological parameters, and transcriptomic response during the cracking process. These results showed that the length of both epidermal and parenchymatous cell layers significantly increased from 133 to 144 days after seed protrusion (DASP), followed by a clear separation between parenchymatous cell layers and kernel, which was accompanied by a breakage between epidermal and parenchymatous cell layers. Moreover, analyses of cell wall composition showed that a significant degradation of cellular wall polysaccharides occurred during aril cracking. To examine the global gene expression changes in arils during the cracking process, the transcriptomes (96 and 141 DASP) were analyzed. KEGG pathway analysis of DEGs revealed that 4 of the top 10 enriched pathways were involved in cell wall modification and 2 pathways were related to ethylene biosynthesis and ethylene signal transduction. Furthermore, combining the analysis results of co-expression networks between different transcription factors, cell wall modification genes, and exogenous ethylene treatments suggested that the ethylene signal transcription factors (ERF11 and ERF1A) were involved in aril cracking of T. grandis by regulation of EXP and PME. Our findings provided new insights into the aril cracking trait in T. grandis.

Effective Inhibition of SARS-CoV-2 Entry by Heparin and Enoxaparin Derivatives.

Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has caused a pandemic of historic proportions and continues to spread globally, with enormous consequences to human health. Currently there is no vaccine, effective therapeutic, or prophylactic. As with other betacoronaviruses, attachment and entry of SARS-CoV-2 are mediated by the spike glycoprotein (SGP). In addition to its well-documented interaction with its receptor, human angiotensin-converting enzyme 2 (hACE2), SGP has been found to bind to glycosaminoglycans like heparan sulfate, which is found on the surface of virtually all mammalian cells. Here, we pseudotyped SARS-CoV-2 SGP on a third-generation lentiviral (pLV) vector and tested the impact of various sulfated polysaccharides on transduction efficiency in mammalian cells. The pLV vector pseudotyped SGP efficiently and produced high titers on HEK293T cells. Various sulfated polysaccharides potently neutralized pLV-S pseudotyped virus with clear structure-based differences in antiviral activity and affinity to SGP. Concentration-response curves showed that pLV-S particles were efficiently neutralized by a range of concentrations of unfractionated heparin (UFH), enoxaparin, 6-O-desulfated UFH, and 6-O-desulfated enoxaparin with 50% inhibitory concentrations (IC50s) of 5.99 μg/liter, 1.08 mg/liter, 1.77 μg/liter, and 5.86 mg/liter, respectively. In summary, several sulfated polysaccharides show potent anti-SARS-CoV-2 activity and can be developed for prophylactic as well as therapeutic purposes.IMPORTANCE The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV-2) in Wuhan, China, in late 2019 and its subsequent spread to the rest of the world has created a pandemic situation unprecedented in modern history. While ACE2 has been identified as the viral receptor, cellular polysaccharides have also been implicated in virus entry. The SARS-CoV-2 spike glycoprotein (SGP) binds to glycosaminoglycans like heparan sulfate, which is found on the surface of virtually all mammalian cells. Here, we report structure-based differences in antiviral activity and affinity to SGP for several sulfated polysaccharides, including both well-characterized FDA-approved drugs and novel marine sulfated polysaccharides, which can be developed for prophylactic as well as therapeutic purposes.

Characterization of structural properties of fungal-bacterial biofilms by Fourier Transform Infrared Spectroscopy

Investigating the structural properties of biofilms is important as they undergo profound changes in their genetic and cellular make up once planktonic cells are converted to biofilm communities. Present study focused on examining the structural attributes of fungal-bacterial biofilms (FBBs), a novel introduction to biotechnological applications, in comparison to bacterial (BBs) and fungal (FBs) biofilms. Enterobacter sp. and Aspergillus sp. were used as the bacterial and fungal counterparts in biofilms. FBB, BB and FB were developed in vitro in a prescribed Biofilm Formation Medium. The biofilm formation was observed under the light microscope. The biofilms were pelletized and Infra-Red spectra were recorded using Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis clearly showed the presence of Amide I (~1635 cm-1) and II (~1544 cm-1), C-O and P=O stretching, and CH2 scissoring in FBB and BB. FB showed only the Amide I band. The absorbance values of above functional groups, cellular polysaccharides, amides and fatty acids gradually increased in the first three days of biofilm maturation and then leveled off. FBB showed higher accumulation of all macro molecules recorded at each sampling time, thus demonstrating its increased metabolic activity compared to BB and FB.

Storage lipid and polysaccharide metabolism in Yarrowia lipolytica and Umbelopsis isabellina

Complex biochemical mechanisms are being involved in oleaginous microorganisms during storage lipid and polysaccharide metabolism. Detailed biochemical analyses and monitoring of key enzymes involved in carbon metabolism were performed in Yarrowia lipolytica and Umbelopsis isabellina, which are often used as model oleaginous microorganisms. It was found that during the early oleaginous phase, the carbon source (glucose) was channeled to lipid accumulation, but also to polysaccharide biosynthesis. However, during transition from the early to the late oleaginous phase, glucose was exclusively converted to lipids, while in U. isabellina, but not in Y. lipolytica, an additional conversion of cellular polysaccharides into lipids was observed. After glucose depletion in the growth medium, cellular storage material was degraded either for generating maintenance energy or for supporting further microbial growth, depending on the availability of essential nutrients in the growth medium. We demonstrated that in both microorganisms, reserve lipids were exclusively used as an intra-cellular carbon source in order to generate energy for maintenance purpose. When cellular storage material degradation was related to new cell mass production, a bioconversion of lipids into new lipid-free material, consisting of polysaccharides and proteins, was observed in Y. lipolytica, while new lipid-free material in U. isabellina was richer in proteins. Lipid and polysaccharide remodeling may occur in some cases in both microorganisms. This study revealed some new biochemical features of oleaginous microorganisms that may be crucial for the design of new biotechnological processes, such as the production of bio-molecules of industrial, technological, and medical interest.

Hydroxyl radical is involved in cell wall disassembly and aril breakdown in mulberry fruit during storage

The effect on hydroxyl radical (OH) on cellular wall disassembly and aril breakdown in mulberry fruit was investigated in vitro and in vivo. The in vitro experiment showed OH induced total sugar and uronic acid released from the cell wall material of mulberries in a dose-dependent manner. Then the harvested mulberries were treated with 5mM OH to find out its effect in vivo. The results suggested that the application of exogenous OH induced degradation of cellular wall polysaccharides, especially water soluble pectin (WSP) and hemicellulose, which was associated with the higher incidence of aril breakdown in OH-treated mulberries. Meanwhile, the results of gel permeation chromatography analysis further demonstrated that OH enhanced depolymerization and structural modifications of polysaccharides of mulberries during storage as experienced by the downshift in molecular mass of WSP and hemicellulose fractions. These results indicated that as a consequence of the enhanced degradation of cell wall polysaccharides, OH could increase the incidence of aril breakdown in harvested mulberry fruit during storage.

Enzymatic synthesis of lactosylated and sialylated derivatives of epothilone A.

Epothilone A is a derivative of 16-membered polyketide natural product, which has comparable chemotherapeutic effect like taxol. Introduction of sialic acids to these chemotherapeutic agents could generate interesting therapeutic glycoconjugates with significant effects in clinical studies. Since, most of the organisms biosynthesize sialic acids in their cell surface, they are key mediators in cellular events (cell-cell recognition, cell-matrix interactions). Interaction between such therapeutic sugar parts and cellular polysaccharides could generate interesting result in drugs like epothilone A. Based on this hypothesis, epothilone A glucoside (epothilone A 6-O-β-D-glucoside) was further decorated by conjugating enzymatically galactose followed by sialic acids to generate epothilone A 7-O-β-D-glucopyranosyl, 4'-O-α-D-galactoside i.e., lactosyl epothilone A (lac epoA) and two sialosides of epothilone A namely epothilone A 7-O-β-D-glucopyranosyl, 4'-O-α-D-galactopyranosyl 3″-O-α-N-acetyl neuraminic acid and epothilone A 7-O-β-D-glucopyranosyl, 4'-O-α-D-galactopyranosyl 6″-O-α-N-acetylneuraminic acid i.e., 3'sialyllactosyl epothilone A: 3'SL-epoA, and 6'sialyllactosyl epothilone A: 6'SL-epoA, respectively. These synthesized analogs were spectroscopically analyzed and elucidated, and biologically validated using HUVEC and HCT116 cancer cell lines.

Lipid Flippases for Bacterial Peptidoglycan Biosynthesis.

The biosynthesis of cellular polysaccharides and glycoconjugates often involves lipid-linked intermediates that need to be translocated across membranes. Essential pathways such as N-glycosylation in eukaryotes and biogenesis of the peptidoglycan (PG) cell wall in bacteria share a common strategy where nucleotide-sugars are used to build a membrane-bound oligosaccharide precursor that is linked to a phosphorylated isoprenoid lipid. Once made, these lipid-linked intermediates must be translocated across a membrane so that they can serve as substrates in a different cellular compartment. How translocation occurs is poorly understood, although it clearly requires a transporter or flippase. Identification of these transporters is notoriously difficult, and, in particular, the identity of the flippase of lipid II, an intermediate required for PG biogenesis, has been the subject of much debate. Here, I will review the body of work that has recently fueled this controversy, centered on proposed flippase candidates FtsW, MurJ, and AmJ.

Spectroscopic studies of vanadium biosorption on different types of carbohydrate biomass

The biosorption potential of different types of carbohydrate biomass is investigated to evaluate their application to purify water contaminated by vanadium in environmentally relevant oxidation states (VIV and VV). Spectroscopic studies were done by electron paramagnetic resonance (EPR), vanadium nuclear magnetic resonance (51V NMR), circular dichroism (CD), and electronic absorption in the visible range (vis). Both d-galacturonic and d-glucuronic acids are major components of plant cellular wall polysaccharides. The interaction of VIV with the model ligands d-galacturonic and d-glucuronic acids showed that complexation starts at low pH values (pH 3) and that carboxylate and sugar–OH groups, as well as water molecules, are involved in the coordination. At pH &gt; 4.5, coordination promotes the sugar–OH deprotonation and new species form with the ligand chelating the metal ion via oxygen atoms of carboxylate and of adjacent sugar–O− donors. The studies with pectin and citric acid show the ability of both compounds to partially reduce VV to VIV in solution and the EPR parameters suggest coordination of carboxylate, sugar–OH, and water molecules. The interaction of VV with biomass from different sources shows that grapefruit, orange peel, and plane tree fruit are the most suitable candidates for the biosorption of vanadium. Studies with VV and grapefruit (or the grainless stalk of corn) indicate that the reduction takes place at the “surface” of the solid. EPR studies on the interaction of VIV with different carbohydrate biomass show their ability to complex high amounts of VIV. We propose that the biosorption mechanism, when the biomass is in contact with VV species, involves sorption, reduction, and retention at the surface level of VIV coordinated by oxygen donors of the biomass. When the interaction starts with VIV, the main process just involves the uptake of the metal ion at the surface level.

Mushroom Polysaccharides and Lipids Synthesized in Liquid Agitated and Static Cultures. Part II: Study of Volvariella volvacea

Volvariella volvacea strains were studied in relation with their ability to produce biomass, lipids and polysaccharides. Firstly, screening of four strains (AMLR 188, 190, 191 and 192) was performed in agar cultures, where the mycelial growth rate of the strains was measured, and in static liquid cultures, where the production of biomass, the biosynthesis of total cellular lipids and the consumption of glucose were monitored. For all strains, biomass production was significant (13-15 g l(-1)) and total lipid in dry weight (%, w/w) ranged from 3 to 12 %. Afterwards, a detailed kinetic analysis of mycelial biomass, extra- and intra- cellular polysaccharides (EPS, IPS, respectively) as well as lipid production by a V. volvacea selected strain was conducted in submerged static and agitated cultures. Maximum values of 15 g l(-1) biomass, ~1.0 g l(-1) EPS and 5.5 g l(-1) IPS were recorded. Agitation did not have severe impact on biomass, EPS and IPS production, but it increased total lipid in dry weight quantities. EPS, IPS and lipid in dry weight values decreased with time. Glucose was the major cellular carbohydrate detected. Total fatty acid analysis of cellular lipids was performed for all V. volvacea strains and linoleic acid (Δ9,12)C18:2 was predominant. Neutral lipids constituted the major fraction of cellular lipids, but their quantity decreased as fermentation proceeded. Phospholipids were the most saturated lipid fraction.

Eficiência fotoquímica em folhas do mamoeiro (Carica papaya L.) cv. Golden durante o estádio reprodutivo e caracterização da ontogenia dos frutos

Considerando que a fisiologia do amadurecimento dos frutos do mamoeiro envolve desde a produção de fotoassimilados, para a sua formação e desenvolvimento, até as enzimas que degradarão a parede celular, promovendo o amolecimento da polpa, o objetivo deste trabalho foi avaliar a cinética da emissão da fluorescência da clorofila a em folhas do mamoeiro (Carica papaya L.) cv. Golden durante o período reprodutivo e avaliar os teores de sólidos solúveis (SS), acidez titulável (AT) e atividade da pectinametilesterase (PME) durante a ontogenia dos frutos. Os maiores índices de desempenho fotoquímico (PItotal) foram verificados nos estádios de formação e crescimento dos frutos, devido ao melhor desempenho das reações de oxirredução do fotossistema I [δR0/(1-δR0)]. Maior eficiência fotoquímica das plantas neste período possibilita maior demanda pelo carbono fixado para a síntese de compostos para o metabolismo celular. Em geral, os fotoassimilados são direcionados para os drenos fortes mais próximos, entretanto as sementes têm prioridade, portanto os teores de SS, AT e a atividade da PME na polpa dos frutos permaneceram constantes durante o desenvolvimento dos mesmos, sendo verificadas alterações nestas características somente no estádio de colheita. Estes resultados confirmam a participação da PME como enzima que prepara o substrato para que as demais enzimas pectinolíticas atuem, disponibilizando os ácidos orgânicos desmetilados e o início da degradação dos polissacarídeos da parece celular antes mesmo da colheita.

The Enhanced Cu&lt;sup&gt;2+&lt;/sup&gt;- Stress Resistance of Microcystis Aeruginosa Induced by Exogenous Abscisic Acid

Previous studies showed that abscisic acid (ABA) play a role in oxidative and osmotic stress response of cyanobacteria cells. Whether it has function in metal stress response remains unclear. The effect of exogenous Abscisic Acid on Cu2+-Stress resistance of bloom-forming cyanobacteria Microcystis aeruginosa was studied in this paper. The results showed that 20 mg. l-1 exogenous ABA can effectively enhance the resistance ability of Microcystis aeruginosa cells to Cu2+-stress at the concentration of 0.25 mg.l-1. Exogenous ABA can restore the growth inhibition by elevating chlorophyll a, phycocyanin and allophycocyanin protein content in Cu2+-stressed cells. ABA helps absorbing more metal ions to decrease its toxicity by inducing solvable protein and cellular polysaccharides biosynthesis. By promoting the Superoxide Dismutase and Glutathione Peroxidase activities, exogenous ABA can effectively help scavenge the excess superoxide radicals in the cells caused by Cu2+-Stress. These results indicated that ABA might also play important role in metal-stress response and resistance.

Structural characterization of the uncommon polysaccharides obtained from Peltigera canina photobiont Nostoc muscorum

Cellular and extracellular polysaccharides of the lichenized fungus Peltigera canina photobiont Nostoc muscorum (UTEX-2493) were evaluated. From EPS a linear (1 → 4)-linked β- d-xylan was chemically characterized, and because of this and other findings involving lichenized fungi it could be proposed that this polymer may be typical of photobionts isolated from lichen thalli. From cellular biomass extracts a complex polysaccharide formed mainly of l-arabinose (2,3- O-Me 2-, 24.8%) and d-xylose (2,3- O-Me 2-, 10.6%) both units (1 → 4)-linked was described. A smaller part of this structure has β- l-Ara p and β- d-Xyl p units branched at O-3 by α- d-Man p units, which in turn presents O-3 or O-2 single-unit substitution by α- d-Man p or α- l-Fuc p as non-reducing ends. Arabinosyl residues were found to be in the β- l-arabinopyranosyl form, different from the most common form described in plant cell wall polysaccharides, α- l-arabinofuranosyl (Ara f). Both polymers characterized in this work were not previously described when analyzing Nostoc sp. or cyanobacteria in general.

The MAGi RNA extraction method: a highly efficient and simple procedure for fresh and dry plant tissues

AbstractBACKGROUND: Samples from different plant species, different organs or tissues at different times of the year, usually show great differences in their cell compositions, pH, and the endogenous RNase activities, decreasing the RNA yield and quality.RESULTS: In this study we describe a reagent and a simple total RNA isolation method for plant organs, tissues and dry seeds. The RNA extraction reagent (MAGi) is non‐toxic and can be stored at room temperature for several months to years. The principle of the total RNA extraction is that tissues are lysed in extraction solution with the aid of mortar homogenization–maceration, and cellular proteins, polysaccharides and DNA are removed from the RNA. We tested the reported method on more than 16 different types of plant seed and 15 different tissues and organs of pepper.CONCLUSION: The RNA extraction procedure reported in the present study greatly reduces the time required to isolate dry seed total RNA and other tissues by more than half as compared with the previously reported methods. The range of typical RNA yield and quality represents a significant improvement over existing protocols. The quality is high enough to be considered as suitable method for RT‐PCR, cDNA library construction and microarray gene expression studies. Copyright © 2008 Society of Chemical Industry

Effects of reactive oxygen species on cellular wall disassembly of banana fruit during ripening

Fruit softening is generally attributed to cell wall disassembly. Experiments were conducted to investigate effects of various reactive oxygen species (ROS) on in vitro cellular wall disassembly of harvested banana fruit. The alcohol-extracted insoluble residue (AEIR) was obtained from the pulp tissues of banana fruit at various ripening stages and then used to examine the disassembly of cellular wall polysaccharides in the presence of superoxide anion (O2-), hydrogen peroxide (H2O2) or hydroxyl radical (OH) and their scavengers. The presence of OH accelerated significantly disassembly of cellular wall polysaccharides in terms of the increase in contents of total sugars released and uronic acid, and the decrease in molecular mass of soluble polysaccharides, using gel permeation chromatography. However, the treatment with H2O2 or O2- showed no significant effect on the disassembly of cellular wall polysaccharides. Furthermore, the degradation of the de-esterified AEIR was more susceptible to OH attack than the esterified AEIR. In addition, the effect of OH could be inhibited in the presence of OH scavenger. This study suggests that disassembly of cellular wall polysaccharides could be initiated by OH as the solublisation of the polysaccharides increased, which, in turn, accelerated fruit softening.

Effect of hydroxyl radical on the scission of cellular wall polysaccharides in vitro of banana fruit at various ripening stages

Fruit ripening is generally attributed to disassembly of cellular wall, particularly due to solubilisation and depolymerisation of pectin and hemicellulose. Experiments were conducted to test effects of hydroxyl radicals (·OH) on the scission of cellular wall polysaccharides from pulp tissues of banana fruit at different ripening stage. Cellular wall materials were isolated from pulp tissues of banana fruit at different ripening stages. Two pectic fractions, water soluble pectin (WSP) and acid soluble pectin (ASP), and two hemicellulosic fractions, 1 M KOH soluble hemicellulose (HC1) and 4 M KOH soluble hemicellulos (HC2), were obtained from the cellular wall materials from pulp tissues, respectively. Effects of ·OH induced by the Fenton reaction on the scission of pectin and hemicellulose in vitro were investigated. As fruit ripening progressed, the sugar components of the WSP, HC1 and HC2 attacked by ·OH showed obvious molecular-mass downshifts. Thus, ·OH caused the disassembly of polysaccharides (WSP, ASP, HC1 and HC2) from cellular walls of pulp tissues of banana fruit, demonstrated by the reduced molecular mass distribution. Moreover, ·OH production in pulp tissues increased significantly as banana fruit ripened, which further help account for the role of ·OH in accelerated fruit ripening.

Identification and quantification of indole-3-acetic acid in the kelp Laminaria japonica Areschoug and its effect on growth of marine microalgae

A method was established for the identification and quantification of indole-3-acetic acid (IAA) in extracts of the kelp Laminaria japonica. An IAA content of 90–95 μg kg−1 fresh weight in kelp extract was determined by high performance liquid chromatography (HPLC). IAA identification was based on a combination of co-chromatography and comparative chromatography with a standard, analysis of UV spectra, and atmospheric pressure electrospray mass spectrometry (APESI-MS). IAA was isolated by silica gel chromatography and HPLC. The effect on the growth of four marine microalgae of the pure IAA isolated from kelp extract was investigated. Exogenously added IAA from kelp enhanced the growth of Chlorella sp., Dunaliella salina and Porphyridium cruentum, but not that of Chaetoceros muelleri. IAA from kelp significantly inhibited the accumulation of soluble cellular proteins in Chlorella sp. and P. cruentum, and had a very significant effect on chlorophyll biosynthesis in Chlorella sp. However, there was no obvious effect of IAA on the regulation of biosynthesis of cellular polysaccharides in these four marine microalgae.