Optimization of Production and Preliminary Characterization of New Exopolysaccharides from <i>Gluconacetobacter hansenii</i>LMG1524

The influence of different carbon and nitrogen sources, of ethanol concentration, the optimal pH, temperature and medium composition were evaluated on extracellular polysaccharides (EPS) synthesis and bacterial growth of Gluconacetobacter hansenii LMG1524, and preliminary characterization of EPS was investigated. The highest EPS yields were obtained using glycerol and ammonium sulphate as carbon and nitrogen sources, respectively. The increase of ethanol concentration in the medium did not influence the EPS synthesis but reduced the bacterial growth. The optimum temperature and pH for polysaccharides production were respectively 25℃ and 5;whereas for cell growth were respectively 30℃ and 4. The optimal culture medium composition was determined as follows: 10 g/L sucrose, 0.892 g/L (NH4)2SO4, 0.34 g/L NaNO3, 3 mL acetic acid, 1.5 g/L KH2PO4, 1.5 g/L K2HPO4 and 0.6 g/L MgSO4. The polysaccharides produced were of 14 and 10 polymerization degrees (DP) and constituted mainly of glucose, galactose and mannose, in relative percent of 36.36, 33.94 and 22.42, respectively.

Systemic Activation of Defensive Enzymes and Protection in Tobacco Plantlets against <i>Phytophthora nicotianae</i>Induced by Oligosaccharins

Oligosaccharins are potent biomolecules which activate defense responses and resistance in tobacco plants. However, it is not known the systemic behavior of defensive enzymes activated by these elicitors. In this work, the dynamic behavior of key defensive enzymes was evaluated in tobacco plant leaves previously treated through the roots with chitosan polymer (CH), chitosan (COS) and pectic (OGAS) oligosaccharides and Spermine (Sp). All macromolecules tested activated protein levels and defense enzymatic activity in tobacco leaves but with different response dynamics among them and depending on the biochemical variable evaluated. Defense response above control levels were detected since 12 hours after treatments and it consisted in a biphasic behavior with two peaks for PAL (EC 4.3.1.5) and β 1 - 3 glucanase (EC 3.2.1.6) enzymatic activities. The highest enzymatic levels for these enzymes were achieved at 48 hours in plantlets elicited with COS and at 72 hours for those plants treated with chitosan polymer, while the highest POD (EC 1.11.1.6) activity was detected with CH between 48 and 72 hours. These results demonstrated systemic defense activation by oligosaccharins in tobacco whose dynamic of defense response is affected by the kind of oligosaccharins tested. When applying OGAS by foliar spray on tobacco, systemic resistance against Phytoththora nicotianae was induced and plantlets were protected with the low concentration tested by 46% under the bioassays conditions performed. Moreover, enzymatic determinations on roots and leaves previous to plant-pathogen interaction showed increments above 30% of control levels for PAL and POD activities. It means that oligosaccharins activate local and systemic defense responses in plants in the absent of pathogen infection.

Effect of Chitosaccharides in Nodulation and Growth in Vitro of Inoculated Soybean

The influence of chitosaccharides on the symbiotic interaction between Bradyrhizobium and soybean was examined. The results show that chitosaccharides either positively or negatively affect soybean nodulation or plant growth depending on their molecular weight, concentration and the application methods. When directly added to the in vitro culture media, chitosan of high molecular weight inhibit Bradyrhizobium viability in a dose dependent manner while chitooligosaccharides reduce slightly the bacteria viability only at concentration equal or higher than 50 mg·L-1. Chitooligosaccharides significantly enhance nodule formation and dry mass in soybean roots at doses between 10 and 100 mg·L-1. Both types of chitosaccharides, at the highest doses (>500 mg·L-1), negatively affect plant height and root size, whereas medium doses (50 to 100 mg·L-1) increase slightly leave number. Under field conditions, foliar application of both chitosaccharides enhances growth and nodulation of soybean plants. Nevertheless, using this application method, chitosan remains more effective than chitooligosaccharides.

Unique two-way free-standing thermo-and photo-responsive shape memory azobenzene-containing polyurethane liquid crystal network

In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects.Based on the step-growth nature of hydroxyls and isocyanates,the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials.A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond.Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation.In addition,taking advantage of the trans-cis photoisomerization of azobenzene,the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at450 and 550 nm,respectively.Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.