Effect of glutamate on Pyricularia oryzae infection of rice monitored by changes in photosynthetic parameters and antioxidant metabolism.

Considering the importance of blast caused by Pyricularia oryzae in the decrease of rice yield worldwide, this study aimed to assess the photosynthetic performance [leaf gas exchange and chlorophyll (Chl) a fluorescence parameters as well as the photosynthetic pigments concentration], the activities of antioxidant enzymes [ascorbate peroxidase, catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase] and concentrations of hydrogen peroxide (H2 O2 ) and malondialdehyde (MDA) in the leaves of rice plants non-supplied (-Glu) or supplied (+Glu) with glutamate (Glu) and non-infected or infected by P. oryzae. Blast severity was reduced in the leaves of +Glu plants. On the infected leaves of +Glu plants, the values for internal CO2 concentration were lower while the values for net carbon assimilation rate, stomatal conductance as well as for the concentrations of Chl a, Chl b and carotenoids were higher in comparison to infected leaves of -Glu plants. The functionality of the photosynthetic apparatus was preserved in the infected leaves of +Glu plants. The activities of CAT, GPX, GR, POX and SOD increased in the infected leaves of both -Glu and +Glu plants compared to their non-inoculated counterparts, but their activities were lower for +Glu plants. The lower activity of these antioxidative enzymes was triggered by the reduced hydrogen peroxide concentration in the infected leaves of +Glu plants resulting in lower MDA concentration. It can be concluded that photosynthesis was less impaired in infected plants supplied with glutamate due to the lower biochemical constraints for CO2 fixation. Moreover, there was a need for lower activity of reactive oxygen species scavenging enzymes in infected leaves of plants supplied with glutamate due to the lower oxidative stress imposed by P. oryzae infection.

Fungal rock phosphate solubilization using sugarcane bagasse.

The effects of different doses of rock phosphate (RP), sucrose, and (NH(4))(2)SO(4) on the solubilization of RP from Araxá and Catalão (Brazil) by Aspergillus niger, Penicillium canescens, Eupenicillium ludwigii, and Penicillium islandicum were evaluated in a solid-state fermentation (SSF) system with sugarcane bagasse. The factors evaluated were combined following a 2(3) + 1 factorial design to determine their optimum concentrations. The fitted response surfaces showed that higher doses of RP promoted higher phosphorus (P) solubilization. The addition of sucrose did not have effects on P solubilization in most treatments due to the presence of soluble sugars in the bagasse. Except for A. niger, all the fungi required high (NH(4))(2)SO(4) doses to achieve the highest level of P solubilization. Inversely, addition of (NH(4))(2)SO(4) was inhibitory to P solubilization by A. niger. Among the fungi tested, A. niger stood out, showing the highest solubilization capacity and for not requiring sucrose or (NH(4))(2)SO(4) supplementation. An additional experiment with A. niger showed that the content of soluble P can be increased by adding higher RP doses in the medium. However, P yield decreases with increasing RP doses. In this experiment, the maximal P yield (approximately 60 %) was achieved with the lower RP dose (3 g L(-1)). Our results show that SSF can be used to obtain a low cost biofertilizer rich in P combining RP, sugarcane bagasse, and A. niger. Moreover, sugarcane bagasse is a suitable substrate for SSF aiming at RP solubilization, since this residue can supply the C and N necessary for the metabolism of A. niger within a range that favors RP solubilization.

Antimicrobial susceptibility of Aeromonas spp. isolated from pig ileum segments to natural isothiocyanates.

With this study we intend to evaluate the effects of 8 different glucosinolate hydrolysis products including isothiocyanates as antibacterial compounds against Aeromonadaceae, isolated from intestinal segments of pigs collected directly from slaughter-houses in the North of Portugal. Four Aeromonas species, A. allosaccharophila, A. hydrophila, A. media and A. veronii were identified. Using disc-diffusion bioassay all compounds were tested at 6 different doses (0.015, 0.15, 0.75, 1.5 and 3.0 µmoles) in dimethyl-sulfoxide (DMSO). Antibiotic standard (gentamicin) and DMSO (negative control) were included in all experiments. Minimum and maximum dose inhibitions (in µmoles) were assessed. To our knowledge, this is the first study of antimicrobial activity of glucosinolate hydrolysis products against Aeromonas species. The results showed that glucosinolate hydrolysis products and particularly the isothiocyanates have antimicrobial activity, which was proportional to the concentration used. However, not all revealed the same tendency, which means that the chemical structure of each compound is fundamental to understand their effectiveness. Among the different isothiocyanates the benzylisothiocyanate, sulforaphane and 2-phenylethylisothiocyanate were the most effective in vitro inhibitors of bacterial growth. This in vitro study provides enough data to demonstrate the potential use of these natural dietary chemicals for treating infectious diseases caused by Aeromonas spp.

Antibacterial effects of glucosinolate-derived hydrolysis products against enterobacteriaceae and enterococci isolated from pig ileum segments.

The aim of this study was to evaluate the effects of various glucosinolate-derived hydrolysis products (HP) as antibacterial compounds against Enterobacteriaceae and Enterococcaceae isolated from intestinal segments of healthy pigs collected directly from slaughter-houses in the North of Portugal. Using a previously described disk-diffusion bioassay, all HP were tested at six different doses (0.015, 0.15, 0.75, 1.5, 3.0, and 15.0 µmoles) in dimethyl-sulfoxide (DMSO), with the exception of sulforaphane (SFN), which was not tested at 15.0 µmoles. Positive (antibiotic standard) and negative controls (DMSO) were included in all experiments. All the experiments were conducted in triplicate. In vitro inhibition of the bacterial growth by the HP was proportional to the concentration used and in many cases was even higher than for the gentamycin, the antibiotic control. The results clearly showed that the glucosinolates-derived HPs were very effective in vitro inhibitors of bacterial growth. The natural products, and specifically the isothiocyanates, should be evaluated as potential alternative control agents for potentially pathogenic bacteria (e.g., dietary amendment of pig foods with glucosinolate-containing plants).