A sycamore cell wall polysaccharide and a chemically related tomato leaf polysaccharide possess similar proteinase inhibitor-inducing activities.
A large pectic polysaccharide, called rhamnogalacturonan I, that is solubilized by a fungal endo-alpha-1,4-polygalacturonase from the purified walls of suspension-cultured sycamore cells possesses proteinase inhibitor-inducing activity similar to that of the proteinase inhibitor-inducing factor, a pectic-like oligosaccharide fraction isolated from tomato leaves. This suggests that the proteinase inhibitor-inducing activity resides in particular polysaccharide fragments which can be released when plant cell walls are exposed to appropriate enzyme degradation as a result of either wounding or pest attack.
Ryan
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Institute of Biological Chemistry and Program in Biochemistry and Biophysics, Washington State University, Pullman, Washington 99164.
Bishop
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Pearce
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