natural-products-in-plant-pest-management

Proteinaceous and Polyketide Compounds in Plant Protection 117E. carotovora subsp. carotovora (During et al., 1993). However, lysozyme excretioncan have adverse effect on soil microbiota. Thus, the growth of B. subtilishas been observed to be suppressed in rhizosphere transgenic T4 lysozymeproducingpotato plants (Ahrenholtz et al., 2000).LectinsPlant lectins are a heterogeneous collective of proteins that specifically bindcarbohydrates in a reversible way and take part in phytopathogen recognition.Interacting with like components, lectins can attach to the cell surface. Thestructure and functions of these compounds are discussed in detail (e.g.Chrispeels and Raikhel, 1991). Lectins are well known naturally occurringinsecticides of widespread effect. Some free lectins strongly affect microbegrowth in plants and probably contribute to inhibiting pathogenesis. There arechitin-specific lectins synthesized in the phloem and translocated via vessels.These findings suggest that lectins are potential antifungal agents.Proteinase (protease) inhibitors of plant originPlant inhibitors of proteinases are a large group of peptides or small proteinsable to bind proteolytic enzymes of different organisms with competitiveinhibition of their activity. In plants, they are abundant in seeds and storageorgans, where their content can be up to 10% of water-soluble proteins. Thesecompounds are considered as reserve proteins and regulators of protein statusor enzyme activity in plants. The proteinase inhibitors differ in substratespecificity, have various isoforms, and their oligomers can combine ordissociate with an influence on the inhibitor properties.A defensive function of proteinase inhibitors towards insects was initiallyrevealed when insects, after feeding, became inactive as a result of trypsininactivation. Protease inhibitors of plant origin were also shown to be activeagainst plant pathogenic nematodes. Since many phytopathogenic fungi andbacteria secrete extracellular proteolytic enzymes, which play an importantrole in pathogenesis (Valuyeva and Mosolov, 2004), plants use inhibition ofsuch enzymes as a defence strategy towards these microorganisms (Ryan,1990; Habib and Khalid, 2007).There are now ample data on protease inhibitors effective against phytopathogensin vitro and in vivo. For instance, inhibitors from potato inactivateproteinases secreted by F. solani or F. sambucinum into cultural liquid. Inhibitorsfrom buckwheat and pearl millet suppress spore germination and thegrowth of many fungi including Aspergillus flavus, Aspergillus parasiticus,F. moniliforme, F. oxysporum, A. alternata and Trichoderma reesei. Inhibitors ofproteinases are accumulated in response to pathogen invasion and preventdisease development (e.g. in tomato inoculated with P. infestans). In somecases, correlation between disease resistance and the constitutive inhibitorsis found (e.g. between wheat resistance to smut, or lupine and soybean tofusarial wilt). Cells of potato tubers treated with elicitors, such as salicylic orarachidonic acids, are able to excrete potatin and three chymotrypsininhibitors (Habib and Khalid, 2007).