Existence of chitinase activity in mature corn kernels (Zea mays L.)

Abstract

Reducing infection by Aspergillus flauus group species that produce aflatoxins in corn is an area of intense interest. One speculation is that chitinase could be a resistance factor involved in inhibiting or reducing fungal growth. Mature kernels of yellow corn (A. flauus resistant) and white corn (A. flauus susceptible) were assayed for chitinase activity. Results showed higher activity in germ tissue than in the endosperm with disparity between the two varieties. The highest activity per quantity of protein was observed in the germ of white corn and in salt fractions from whole kernel corn precipitated with 20% ammonium sulfate. From gel permeation chromatography, major chitinase activity occurred in the fractions with molecular size ranging from 14 to 25 kDa. Isoelectric focusing on acrylamide gels showed major chitinase activity in protein zones at pH 3-4. These data provide evidence that the catalytic components exist in several isozyme forms that are acidic and highly associated in the native state.Several studies have shown that seeds and vegetative tissues of higher plants contain chitinases (Grassman et al., 1934; Powning and Irzykliewicz, 1965;Wargo, 1975; Boller, 1985; Broekaert et al., 1988). Studies with various model systems have shown that chitinases are also induced by pathogen attacks and chemical treatments that impart stress on plants (Boller et al., 1983;Metraux and Boller, 1986). All of these studies provide circumstantial evidence that chitinases exist in different forms in plants and may be somehow involved in host defense against fungal pathogens (Payne et al., 1990). Our interest in chitinases in corn arises from the critical problem of aflatoxin contamination caused by the fungi Aspergillus flauus and A. parasiticus. The complex relationship between fungal infection and aflatoxin formation is an area of intense research worldwide. Currently, one of the objectives in solving the problem is the identification of resistance genes that could be transferred within the species through classical breeding or genetic engineering. Hence, if intrinsic chitinase is indeed a pertinent resistance factor in corn, then appropriate strategies could be coordinated to improve the health and safety of this major crop.In this preliminary study, our objective was to develop a similarity profile of chitinase activity in the endosperm and the germ of two varieties of mature corn kernels. We chose kernels from open-pollinated varieties with extremes in aflatoxin contamination due to A. flavus infection, namely Yellow Creole (highly resistant) and Huffman (highly susceptible white endosperm variety) in field studies reported earlier (Zuber et al., 1983). Certain protein fractions from these two varieties were shown to have antifungal properties in an earlier study (Neucere and Zeringue, 1987). MATERIALS AND METHODS Extraction of Corn Tissues and Protein Fractionation.For preliminary experiments, kernels of the two varieties were sectioned by cutting the lower third of whole kernels, which included most of the ge...

Relative Toxicity of the Maize Endosperm Ribosome-Inactivating Protein to Insects

“…For example, proteins of the same type/class known to have activity against insects have been isolated from maize. They include proteases (Mitsuhashi and Oaks, 1994), protease and amylase inhibitors (Swartz et al, 1977;Mahoney et al, 1984;Blaco-Labra et al, 1995) tritin-like proteins (Coleman and Roberts, 1982), and chitinases (Neucere et al, 1991;Zhe-fu et al, 1992). However, studies that relate naturally occurring concentrations to defensive activity have been limited.…”

A Study of Some Biochemical and Histopathological Responses of Wet-stored Recalcitrant Seeds of Avicennia marina Infected by Fusarium moniliforme

“…The antifungal properties of b-1,3-glucanases and chitinases have been discussed extensively (for reviews, see Bol and Linthorst, 1990;Stintzi et al, 1993;Van Loon, 1997;Fritig et al, 1998;Van Loon and Van Strien, 1999). Both enzymes have been reported from a variety of monocotyledonous and dicotyledonous plant species, in different tissues and life-cycle stages, including seeds of tobacco (Leubner-Metzger et al, 1995, 1996, tomato (Wu et al, 2001), pea ((Petruzzelli et al, 1999, barley (Jacobsen et al, 1990), maize (Neucere et al, 1991;Huynh et al, 1992) and cucumber (Majeau et al, 1990). However, their occurrence in recalcitrant seeds has not been investigated.…”