The seeds of plants are rich stores of proteins, carbohydrates, and lipids and are therefore used by heterotrophs as valuable food sources. Humans use seeds as a major food source and have learned, through agricultural practice, how to increase the levels and the quality of their components. They have also learned how to deal with the multiplicity of toxic or antinutritional compounds present in seeds. It is believed that these seeds, most of which are not essential for the establishment of the new plant following germination, contribute to the protection and defense of seeds against pathogens and predators. However, insects, fungi, and bacteria have also learned how to cope with detrimental compounds in order to take advantage of the high nutritional value of seeds.Coleopteran insects of the family Bruchidae, the seed weevils, have been associated with the seeds of leguminous plants through co-evolutionary processes. These processes have permitted the weevils to thrive on seeds full of toxic compounds, in contrast to the majority of the other potential aggressors, which are incapable of dealing with them. The association between bruchids and legume seeds is highly specific with only seeds of a very few species being attacked by any one insect species.Among our food sources, plants of the legume family contribute some of the most important protein-rich seeds. The common bean (Phaseolus vulgaris), native of the New World and the cowpea (Vigna unguiculata), which originated in Africa, are heavily attacked by bruchids, both in the field and in storage. Infestations are commonly so heavy that the seeds are unsuitable for use as food, feed, or planting.Control of bruchid infestation is done by treating stored seeds with methyl bromide, carbon disulfide, and several other chemicals. These are considered environmentally undesirable and are too expensive for subsistence farmers. To increase the insect resistance of cultivated varieties plant breeders are interested in understanding resistance mechanisms that operate in wild varieties or why certain bruchids attack one cultivated species but not another.Both the common bean and cowpea are endowed with compounds called general defensive compounds that protect their seeds against widely different herbivores. Among these are the tannins, cyanogenic glucosides, non-protein amino acids, and proteins such as protease and amylase inhibitors, lectins, chitinases, ␤-1,3-glucanases. These defensive compounds are ineffective against the host-specific bruchids, Callosobruchus maculatus and Zabrotes subfasciatus, which attack cowpea and common bean, respectively. Host-specific defenses are rare and are generally found in populations in the centers of dispersion of the particular plant species. Landraces of cowpea and common bean that produce seeds resistant to their associated bruchids have been discovered respectively in West Africa and Mexico. The biochemical basis of the resistance of cowpea and common bean seeds to C. maculatus and Z. subfasciatus, respectively, is the focus of t...

Vicilins (7S storage proteins) isolated from the seeds of the legumes Vigna unguiculata (cowpea), Vigna angularis (adzuki bean), Canavalia ensiformis (jack bean), Glycine max (soybean), Phaseolus vulgaris (common bean) and Phaseolus lunatus (lima bean) were shown to be immunologically related and to bind to a chitin matrix. The effect of the isolated vicilins on the development of the cowpea weevil Callosobruchus maculatus was examined. Vicilins from all non‐host seeds, including those of the C maculatus‐resistant cowpea line IT81D‐1045, strongly inhibited larval development (ED50 of 1·07±0·32% to 2·22±0·64%). Vicilins from the C maculatus‐susceptible cowpea CE‐31 and adzuki bean seeds were the exception with ED50 of 6·25±0·75% and 5·40±1·54%, respectively. These results correlate well with the host range of C maculatus and are possibly a reflection of the low digestibility of vicilins by insect midgut proteinases in addition to the ability they show in binding to chitin‐containing structures like the ones found in the bruchid midguts. © 1998 SCI.

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CvL, a lectin from the marine sponge Cliona varians was purified by acetone fractionation followed by Sepharose CL 4B affinity chromatography. CvL agglutinated papainized treated human erythrocytes with preference for type A erythrocytes. The lectin was strongly inhibited by monosaccharide d-galactose and disaccharide sucrose. CvL is a tetrameric glycoprotein of 28 kDa subunits linked by disulphide bridges with a molecular mass of 106 kDa by SDS-PAGE and 114 kDa by Sephacryl S300 gel filtration. The lectin was Ca2+ dependent, stable up to 60 degrees C for 60 min, with optimum pH of 7.5. CvL displays a cytotoxic effect on gram positive bacteria, such as Bacillus subtilis and Staphylococcus aureus. However, CvL did not affect gram negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa. Leishmania chagasi promastigotes were agglutinated by CvL up to 2(8) titer. These findings are indicative of the physiological defense roles of CvL and its possible use in the antibiosis of bacteria and protozoa pathogenic.

The presence of chitin in midgut structures of Callosobruchus maculatus larvae was shown by chemical and immunocytochemical methods. Detection by Western blotting of cowpea (Vigna unguiculata) seed vicilins (7S storage proteins) bound to these structures suggested that C. maculatus-susceptible vicilins presented less staining when compared to C. maculatus-resistant vicilins. Storage proteins present in the microvilli in the larval midgut of the bruchid were recognized by immunolabeling of vicilins in the appropriate sections with immunogold conjugates. These labeling sites coincided with the sites labeled by an anti-chitin antibody. These results, taken together with those previously published showing that the lower rates of hydrolysis of variant vicilins from C. maculatus-resistant seeds by the insects midgut proteinases and those showing that vicilins bind to chitin matrices, may explain the detrimental effects of variant vicilins on the development of C. maculatus larvae.

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Vicilin storage proteins (7S globulins) isolated from Vigna unguiculata (cowpea) seeds were shown to interfere with the germination of spores or conidia of the fungi Fusarium solani, Fusarium oxysporum, Colletotrichum musae, Phytophtora capsici, Neurospora crassa, and Ustilago maydis sporidia. Cowpea vicilins have been shown to bind to fungal structures, possibly chitin-containing structures of the cell wall, and can be desorbed by strong acid. The results presented in this paper are in agreement with data previously obtained on the chitin-binding properties of cowpea vicilins and the effect they exert on the development and survival of the storage pest insect Callosobruchus maculatus (Coleoptera:  Bruchidae). Keywords: 7S storage globulins; cowpea seeds; Vigna unguiculata; chitin-binding proteins; fungi; spore germination

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