Abstract
Neofusiccocum batangarum is the causal agent of scabby canker of cactus pear (Opuntia ficus-indica L.). The symptoms of this disease are characterized by crusty, perennial cankers, with a leathery, brown halo. Characteristically, a viscous polysaccharide exudate, caking on contact with air, leaks from cankers and forms strips or cerebriform masses on the surface of cactus pear cladodes. When this polysaccharide mass was partial purified, surprisingly, generated a gel. The TLC analysis and the HPLC profile of methyl 2-(polyhydroxyalkyl)-3-(o-tolylthiocarbomoyl)-thiazolidine-4R-carboxylates obtained from the mixture of monosaccharides produced by acid hydrolysis of the three EPSs examined in this research work [the polysaccharide component of the exudate (EPSC) and the EPSs extracted from asymptomatic (EPSH) and symptomatic (EPSD) cladodes] showed the presence of d-galactose, l-rhamnose, and d-glucose in a 1:1:0.5 ratio in EPSC while d-galactose, l-rhamnose, d-glucose, and d-xylose at the same ratio were observed in EPSH and EPSD. The presence of uronic acid residues in EPSC was also showed by solid state NMR and IR investigation. Furthermore, this manuscript reports the chemical-physical characterization of the gel produced by the infected cactus pear.
Highlights
The presence of galactose, rhamnose, and glucose was observed in EPSC
More complex mixtures showing the presence of galactose, rhamnose, glucose and xylose were evidenced in both EPSs present in the asymptomatic (EPSH)
The mixtures of monosaccharides obtained by acid hydrolysis of EPSC, EPSH, and EPSD were converted in the corresponding methyl 2-(polyhydroxyalkyl)-3-(o-tolylthiocarbomoyl)-thiazolidine-4R-carboxylates by reaction with L-cysteine methyl ester hydrochloride and phenyl isothiocyanate
Summary
Once under the attack of a pathogenic microorganism, the plant activates its defense mechanisms and only when the microorganism overcomes all the protectant barriers, either physical or of chemical nature, it establishes a consistent interaction with the plant, leading to a disease. Many plants are able to exude complex mixtures of bioactive molecules performing a variety of roles. An exudate produced by many plant species (Euforbiacee, Papaveracee, Moracee, Sapotacee, Composite Asteracee, etc.) is latex, a milky emulsion, usually whitish—rarely yellow, orange, brown, or red [6,7]—composed of small organic compounds suspended in a liquid dispersion medium. Latex acts as the first line of plant defense against herbivores and pathogens, and it plays a role in environmental stress conditions [6–8]
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