Inducible defense-related proteins have been described in many plant species upon infection with oomycetes, fungi, bacteria, or viruses, or insect attack. Several types of proteins are common and have been classified into 17 families of pathogenesis-related proteins (PRs). Others have so far been found to occur more specifically in some plant species. Most PRs and related proteins are induced through the action of the signaling compounds salicylic acid, jasmonic acid, or ethylene, and possess antimicrobial activities in vitro through hydrolytic activities on cell walls, contact toxicity, and perhaps an involvement in defense signaling. However, when expressed in transgenic plants, they reduce only a limited number of diseases, depending on the nature of the protein, plant species, and pathogen involved. As exemplified by the PR-1 proteins in Arabidopsis and rice, many homologous proteins belonging to the same family are regulated developmentally and may serve different functions in specific organs or tissues. Several defense-related proteins are induced during senescence, wounding or cold stress, and some possess antifreeze activity. Many defense-related proteins are present constitutively in floral tissues and a substantial number of PR-like proteins in pollen, fruits, and vegetables can provoke allergy in humans. The evolutionary conservation of similar defense-related proteins in monocots and dicots, but also their divergent occurrence in other conditions, suggest that these proteins serve essential functions in plant life, whether in defense or not.

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Significance of Inducible Defense-related Proteins in Infected Plants

Chitosan as Antimicrobial Agent: Applications and Mode of Action

Antimicrobial properties of chitosan and mode of action: A state of the art review

Response to cadmium in higher plants

Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

The fungicidal effect of chitosan on fungi of varying cell wall composition

Characterization of the smallest chitosan oligomer that is maximally antifungal to Fusarium solani and elicits pisatin formation in Pisum sativum

Chitosan, a polymer of β-1,4-linked glucosamine residues with a strong affinity for DNA, was implicated in the pea pod-Fusarium solani interaction as an elicitor of phytoalexin production, an inhibitor of fungal growth and a chemical which can protect pea tissue from infection by F. solani f. sp. pisi. Purified Fusarium fungal cell walls can elicit phytoalexin production in pea pod tissue. Enzymes from acetone powders of pea tissue release eliciting components from the F. solani f. sp. phaseoli cell walls. Hydrochloric acid-hydrolyzed F. solani cell walls are about 20% glucosamine. The actual chitosan content of F. solani cell walls is about 1%. However, chitosan assays and histochemical observations indicate that chitosan content of F. solani spores and adjacent pea cells increases following inoculation. Dormant F. solani spores also accumulate chitosan. Concentrations of nitrous acid-cleaved chitosan as low as 0.9 microgram per milliliter and 3 micrograms per milliliter elicit phytoalexin induction and inhibit germination of F. solani macroconidia, respectively. When chitosan is applied to pea pod tissue with or prior to F. solani f. sp. pisi, the tissue is protected from infection.

/pdf/chitosan-as-a-component-of-pea-fusarium-solani-interactions-44rjp9obib.pdf

Chitosan as a Component of Pea-Fusarium solani Interactions

Infection of immature pea pods with Fusarium solani f.sp. phaseoli (a non-pathogen of peas) or f.sp. pisi (a pea pathogen) resulted in induction of chitinase and beta-1,3-glucanase. Within 30 hours, activities of the two enzymes increased 9-fold and 4-fold, respectively. Chitinase and beta-1,3-glucanase were also induced by autoclaved spores of the two F. solani strains and by the known elicitors of phytoalexins in pea pods, cadmium ions, actinomycin D, and chitosan. Furthermore, exogenously applied ethylene caused an increase of chitinase and beta-1,3-glucanase in uninfected pods. Fungal infection or treatment with elicitors strongly increased ethylene production by immature pea pods. Infected or elicitor-treated pea pods were incubated with aminoethoxyvinylglycine, a specific inhibitor of ethylene biosynthesis. This lowered stress ethylene production to or below the level of uninfected controls; however, chitinase and beta-1,3-glucanase were still strongly induced. It is concluded that ethylene and fungal infection or elicitors are separate, independent signals for the induction of chitinase and beta-1,3-glucanase.

/pdf/ethylene-symptom-not-signal-for-the-induction-of-chitinase-4ssvfrcate.pdf

Ethylene: Symptom, Not Signal for the Induction of Chitinase and β-1,3-Glucanase in Pea Pods by Pathogens and Elicitors

Chitinase and β-1,-3-glucanase activities increased coordinately in pea (Pisum sativum L. cv “Dot”) pods during development and maturation and when immature pea pods were inoculated with compatible or incompatible strains of Fusarium solani or wounded or treated with chitosan or ethylene. Up to five major soluble, basic proteins accumulated in stressed immature pods and in maturing untreated pods. After separation of these proteins by chromatofocusing, an enzymic function could be assigned to four of them: two were chitinases and two were β-1,3-glucanases. The different molecular forms of chitinase and β-1,3-glucanase were differentially regulated. Chitinase Ch1 (mol wt 33,100) and β-1,3-glucanase G2 (mol wt 34,300) were strongly induced in immature tissue in response to the various stresses, while chitinase Ch2 (mol wt 36,200) and β-1,3-glucanase G1 (mol wt 33,500) accumulated during the course of maturation. With a simple, three-step procedure, both chitinases and both β-1,3-glucanases were purified to homogeneity from the same extract. The two chitinases were endochitinases. They differed in their pH optimum, in specific activity, in the pattern of products formed from [3H]chitin, as well as in their relative lysozyme activity. Similarly, the two β-1,3-glucanases were endoglucanases that showed differences in their pH optimum, specific activity, and pattern of products released from laminarin.

/pdf/antifungal-hydrolases-in-pea-tissue-i-purification-and-4uqgiafan9.pdf

Antifungal Hydrolases in Pea Tissue: I. Purification and Characterization of Two Chitinases and Two β-1,3-Glucanases Differentially Regulated during Development and in Response to Fungal Infection

Lee A. Hadwiger

Papers

The fungicidal effect of chitosan on fungi of varying cell wall composition

Characterization of the smallest chitosan oligomer that is maximally antifungal to Fusarium solani and elicits pisatin formation in Pisum sativum

Chitosan as a Component of Pea-Fusarium solani Interactions

Ethylene: Symptom, Not Signal for the Induction of Chitinase and β-1,3-Glucanase in Pea Pods by Pathogens and Elicitors

Antifungal Hydrolases in Pea Tissue: I. Purification and Characterization of Two Chitinases and Two β-1,3-Glucanases Differentially Regulated during Development and in Response to Fungal Infection