Chitosan from Mushroom Improves Drought Stress Tolerance in Tomatoes.

Chitosan is a derivative of chitin that is one of the most abundant biopolymers in nature, found in crustacean shells as well as in fungi cell walls. Most of the commercially available chitosans are produced from the exoskeletons of crustaceans. The extraction process involves harsh chemicals, has limited potential due to the seasonal and limited supply and could cause allergic reactions. However, chitosan has been shown to alleviate the negative effect of environmental stressors in plants, but there is sparse evidence of how chitosan source affects this bioactivity. The aim of this study was to investigate the ability of chitosan from mushroom in comparison to crustacean chitosan in enhancing drought stress tolerance in tomato plants (cv. MicroTom). Chitosan treatment was applied through foliar application and plants were exposed to two 14-day drought stress periods at vegetative and fruit set growth stages. Phenotypic (e.g., fruit number and weight), physiological (RWC) and biochemical-stress-related markers (osmolytes, photosynthetic pigments and malondialdehyde) were analyzed at different time points during the crop growth cycle. Our hypothesis was that this drought stress model will negatively impact tomato plants while the foliar application of chitosan extracted from either crustacean or mushroom will alleviate this effect. Our findings indicate that drought stress markedly decreased the leaf relative water content (RWC) and chlorophyll content, increased lipid peroxidation, and significantly reduced the average fruit number. Chitosan application, regardless of the source, improved these parameters and enhanced plant tolerance to drought stress. It provides a comparative study of the biostimulant activity of chitosan from diverse sources and suggests that chitosan sourced from fungi could serve as a more sustainable and environmentally friendly alternative to the current chitosan from crustaceans.

Effects of an Extract of the Brown Seaweed Ascophylum nodosum on Postprandial Glycaemic Control in Healthy Subjects: A Randomized Controlled Study.

The effects of the consumption of an extract of the brown seaweed Ascophyllum nodosum (BSW) on postprandial glucose and insulin responses to white bread were investigated in an acute, randomized, double-blind, three-arm, crossover, controlled trial in healthy, normoglycemic subjects. Sixteen subjects were administered either control white bread (50 g total digestible carbohydrates) or white bread with 500 mg or 1000 mg of BSW extract. Biochemical parameters were measured in venous blood over 3 h. Significant inter-individual variation in the glycaemic response to white bread was observed. Analysis of the responses of all subjects to either 500 mg or 1000 mg of BSW extract versus control revealed no significant effects of treatments. The variation in response to the control was used to classify individuals into glycaemic responders and non-responders. In the sub-cohort of 10 subjects with peak glucose levels after white bread above 1 mmol/L, we observed a significant decrease in maximum levels of plasma glucose after the intervention meal with 1000 mg of extract compared with the control. No adverse effects were reported. Further work is warranted to define all factors that determine "responders" to the effects of brown seaweed extracts and identify the cohort that would benefit the most from their consumption.

Comparison of edible brown algae extracts for the inhibition of intestinal carbohydrate digestive enzymes involved in glucose release from the diet.

Type II diabetes is considered the most common metabolic disorder in the developed world and currently affects about one in ten globally. A therapeutic target for the management of type II diabetes is the inhibition of α- glucosidase, an essential enzyme located at the brush border of the small intestinal epithelium. The inhibition of α-glucosidase results in reduced digestion of carbohydrates and a decrease in postprandial blood glucose. Although pharmaceutical synthetic inhibitors are available, these are usually associated with significant gastrointestinal side effects. In the present study, the impact of inhibitors derived from edible brown algae is being investigated and compared for their effect on glycaemic control. Carbohydrate- and polyphenolic-enriched extracts derived from Ascophyllum nodosum, Fucus vesiculosus and Undaria pinnatifida were characterised and screened for their inhibitory effects on maltase and sucrase enzymes. Furthermore, enzyme kinetics and the mechanism of inhibition of maltase and sucrase were determined using linear and nonlinear regression methods. All tested extracts showed a dose-dependent inhibitory effect of α-glucosidase with IC50 values ranging from 0⋅26 to 0⋅47 mg/ml for maltase; however, the only extract that was able to inhibit sucrase activity was A. nodosum, with an IC50 value of 0⋅83 mg/ml. The present study demonstrates the mechanisms in which different brown seaweed extracts with varying composition and molecular weight distribution differentially inhibit α-glucosidase activities. The data highlight that all brown seaweed extracts are not equal in the inhibition of carbohydrate digestive enzymes involved in postprandial glycaemia.

Synergistic Antimicrobial Effect of Chitosan Polymers and Oligomers.

This study evaluated the efficacy of the combined application of well-characterized chitosan polymer (degree of acetylation = 10%, degree of polymerization [DPn] = 90, and dispersity [ÐDP] = 2.8) and oligomers (partially acetylated chitosan polymers and oligosaccharides [paCOS]) (DP = 2 to 17) on conidia germination and mycelial growth of Fusarium graminearum, the major causal agent of Fusarium head blight in wheat. The polymer alone showed a higher inhibitory effect than the paCOS mixture alone, with half-maximal inhibitory concentrations of less than 50 µg ml-1 and more than 100 µg ml-1, respectively. Using time-lapse microscopy, we also showed that paCOS did not affect conidia germination at 50 µg ml-1, whereas chitosan polymer at the same concentration led to a delay in germination and in elongation of germ tubes. Scanning electron microscopy was used to observe the chitosan-induced changes in hyphal morphology. Surprisingly, the combination of chitosan polymer and paCOS led to strong synergistic effects in inhibiting conidia germination and fungal growth, as quantified by both the Abbot and Wadley equations. To our knowledge, this is the first report on a synergistic effect of a combination of chitosan polymers and oligomers, also highlighting for the first time the importance of ÐDP when studying structure-function relationships of functional biopolymers such as chitosan. The consequences of this finding for the improvement of chitosan-based antimicrobial or plant protective products are discussed. Given the economic importance of F. graminearum, this study suggests that the combination of chitosan polymer and oligomers can be used to support an efficient, sustainable plant protection strategy.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

New series of metal complexes by amphiphilic biopolymeric Schiff bases from modified chitosans: Preparation, characterization and effect of molecular weight on its biological applications.

To improve biological activity of chitosans, new Zn(II), Pd(II) and Pt(II) complexes with biopolymeric amphiphilic Schiff bases anchored in different molecular weight chitosans matrices modified with salicylaldehyde and glycidol were prepared. Salicylaldehyde was introduced to generate complexing Schiff base sites in the chitosans matrix while glycidol is intended to increase the water solubility of the resulting biopolymeric complexes. These novel complexes were characterized using various techniques and assayed for antimicrobial and antitumor activity. The effectiveness of modification was evaluated using FTIR spectroscopy, and thermal behavior of the complexes by TG/DTG-DTA. XPRD showed that the crystallinity of the ligand diminished after the metal complexation. Surface morphologies, investigated by SEM, revealed that the complexes are rougher than chitosan matrix, and the presence of metallic ions was confirmed by EDX. Electronic spectra suggested square planar geometry for Pd(II) and Pt(II) complexes. Concerning antimicrobial activity, the novel complexes exhibited higher antibacterial efficiency against Pseudomonas syringae than against the Fusarium graminearum fungi regarding the free ligand. Complexes also exhibited high antitumor effects against the MCF-7 breast cancer cells, with certain selectivity regarding non-tumor cells (Balb/C 3T3 clone A31) depending on concentration and molar mass, indicating that they could potentially be used for antitumor applications.

Characterization, solubility and biological activity of amphihilic biopolymeric Schiff bases synthesized using chitosans.

Chitosans are versatile biopolymers recognized for their wide range of biological activities. However, the low solubility in neutral and basic solutions restricts the applications. Thus amphiphilic biopolymeric Schiff bases from chitosans, salicylaldehyde and glycidol were successfully synthesized and characterized using 1H-NMR, UV/Vis, FTIR, TG/DTG-DTA and tested for their antimicrobial activities against plant pathogenic microorganisms and human breast cancer cells (MCF-7). Overall, functionalization of chitosans with salicylaldehyde and glycidol with different molecular weight (Mw¯) was performed to improve the biological actives of chitosans. Thus the biological activity of the new amphiphilic compounds prepared in this work were evaluated regarding microorganisms with agricultural relevance and tumor cells. The biopolymeric amphiphilic Schiff bases showed significant effects against Pseudomonas syringae (IC50 < 5 µg mL-1) compared to the natural chitosans with medium Mw¯ (CHM 223 kDa) and low Mw¯ (CHL 64 kDa), which had IC50 values of 42 and 37 µg mL-1, respectively. In addition, they improved antitumor activity against tumor cells compared to the natural chitosan.

Synthesis, Characterization and Biological Activities of Biopolymeric Schiff Bases Prepared with Chitosan and Salicylaldehydes and Their Pd(II) and Pt(II) Complexes.

In an attempt to enhance chitosan biological activities, biopolymeric Schiff bases of chitosan and different salicylaldehydes and their palladium(II) and platinum(II) complexes were synthesized and tested. The chemical structures of these derivatives were characterized using ¹H-NMR, FTIR spectroscopy and XPRD. Thermal analysis was done through TGA/DTG-DTA. Electronic absorption spectra and surface morphologies were analyzed by SEM-EDAX. Chitosan and its derivatives were evaluated for their in vitro antimicrobial activity against two common bacterial and fungal plant pathogens Pseudomonas syringae pv. tomato and Fusarium graminearum, respectively, and for their antitumor activity against a human breast cancer cell line (MCF-7). It was found that, compared to the nonmodified chitosan, chitosan modified with Schiff bases and their complexes was highly toxic against the MCF-7 cell line and had antibacterial effects against P. syringea. However, the modified chitosan derivatives had less pronounced antifungal effects against F. graminearum compared to the nonmodified chitosan, suggesting different modes of action.