A nondestructive method for peptide bond conjugation of antigenic haptens to a diphtheria toxoid carrier, exemplified by two antisera specific to acetolactate synthase

Partial characterization and localization of a novel type of antifungal protein (IWF6) isolated from sugar beet leaves

An antifungal protein was isolated from the intercellular washing fluid (IWF) of leaves of sugar beet (Beta vulgaris L., cv. Monova) and purified to homogeneity. The protein, IWF6, comprising 37 amino acids with six cysteines, was able to inhibit the growth of the pathogen Cercospora beticola (Sacc.) in vitro, by 75% after 120 h of growth at a concentration of 20 µg ml(-1). The amino acid sequence data were used to generate a polymerase chain reaction (PCR) clone, employed for the isolation of a corresponding cDNA clone. The cDNA encodes a precursor protein with an N-terminal putative signal sequence of 45 amino acids, followed by the mature protein of 37 amino acids. Antibodies raised against a synthetic peptide covering the complete sequence of IWF6 were used in immunolocalization studies. The protein was recognized by the antibody in nearly all leaf cell types except epidermal cells. In necrotic tissue, the protein was mainly recognized on C. beticola hyphae growing in a 'pellet' (ball-like) structure. The hyphal 'pellets' are primarily located beneath the stomata. IWF6 shows less than 26% identity to any previously described protein.

New antifungal proteins from sugar beet (Beta vulgaris L.) showing homology to non-specific lipid transfer proteins

Two novel, nearly identical antifungal proteins, IWF1 and IWF2, were isolated from the intercellular washing fluid (IWF) of sugar beet leaves. The proteins were purified to homogeneity and their amino acid sequences were determined. They are basic, monomeric proteins of 91 amino acid residues, 89 of which are identical. Both proteins show strong in vitro antifungal activity against Cercospora beticola, the casual agent of leaf spot disease in sugar beet. Based on primary sequence homology, including the presence of 8 conserved cysteine residues, IWF1 and IWF2 are related to the family of plant non-specific lipid transfer proteins (nsLTPs). Antibodies were raised against IWF2 after conjugation to diphtheria toxoid. The amino acid sequence data was used to generate a polymerase chain reaction (PCR) clone, employed for the isolation of a cDNA clone encoding a closely related isoform IWFA, which differs from IWF1 by two amino acid substitutions only. The induction and subcellular localization of these proteins were studied by western and northern blotting analyses after treatment with 2,6-dichloroisonicotinic acid (INA), a compound capable of inducing resistance against C. beticola, and after fungal infection. The following observations were made: (1) the proteins were present in leaves of non-INA-treated and uninfected control plants, (2) they were only slightly induced by INA treatment and during infection with C. beticola, and (3) they were present both intra- and extracellularly. However, their strong antifungal potentials together with immunohistological investigations, the proteins accumulating in contact with the fungus and in autolysing cells, suggested a role of these proteins in plant defence. Finally, immunohistology revealed a remarkable expression pattern of the IWF1 and IWF2 proteins, or serologically related proteins, in sugar beet styles, in that single or a few scattered papillae and a few cells in the lower transmitting tissue strongly and specifically reacted with the antibody.