Induction and characterization of some of the pathogenesis-related proteins in sugar beet

Analysis of the intercellular leaf proteins of tobacco necrosis virus (TNV)-infected sugar beet revealed 12 protein bands (B.v. D1–D12) in polyacrylamide gels (Davis system) normally used to separate acidic proteins, and eight protein bands (B.v. R1–R8) in gels (Reisfeld system) used to separate basic proteins. These proteins were either absent from healthy leaves or present in much smaller amounts. Both qualitative and quantitative differences were found in the proteins induced in cv. Sharpes Klein E and in a subline of a Maribo diploid multigerm family. All of these proteins are resistant to degradation by trypsin and chymotrypsin. All but D1, D6 and D7 were soluble at pH 2·8, and all but D1, D3, D4, D9 and D11 were induced by salicylic acid. There were no differences in the number and quantity of intercellular proteins from leaves of healthy plants and those from uninoculated uninfected leaves of TNV-infected plants. Purification of two of the acidic proteins (D2 and D3) was achieved by blotting them onto, and eluting them from, Immobilon. Subsequent analysis in a SDS polyacrylamide gel showed that both D2 and D3 had an apparent molecular weight of 28 kD. Amino acid analysis and partial sequencing of their N-termini showed an 80% homology to induced chitinases from cucumber and Arabidopsis thaliana and a lysozyme from Parthenocissus quinquifolia.