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Wounding in higher plants leads to an increased synthesis of specific messenger RNAs. A cDNA clone complementary to a wound-induced message from potato tubers was used to isolate a lambda clone from a genomic library of Solanum tuberosum var. Maris Piper. DNA sequence analysis has shown that this single genomic clone contains two novel wound-induced genes, called win1 and win2, organised in close tandem array. The coding sequences of these two genes are highly homologous and are interrupted by a single intron. However, the sequences of the introns and flanking regions have diverged widely. Win1 and win2 encode cysteine-rich proteins of 200 and 211 amino-acids, respectively, which show striking homologies to several chitin-binding proteins. Southern analysis of genomic DNA has shown that win1 and win2 are members of a small multi-gene family which is estimated to have a minimum of five members per haploid genome of Maris Piper and appears to be conserved within the Solanaceae. We have shown by Northern analysis and S1 mapping that the two genes exhibit differential organ-specific expression after the wounding of a potato plant.

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1. The two major proteins from the phloem exudate of Cucurbita maxima (pumpkin), PP1 and PP2, were stable in the absence of reducing agents after modification of their accessible cysteine residues with iodoacetamide. This permitted their purification without precautions to prevent oxidation.2. PP2, a lectin specific for oligomers of N-acetyl-D-glucosamine, was shown by sedimentation-equilibrium ultracentrifugation to be a dimer of M, of 48000. Neither dithiothreitol nor tri-(N-acetyl-D-glucosamine) altered this value. The constituent polypeptides were linked by two buried disulphide bridges. PP2 behaved aberrantly on gel-filtration on both Sephadex and Bio-Gel unless tri-(N-acetyl-D-glucosamine) was added to the elution buffer; the M , was then measured as 46000. Other proteins which bind oligomers of N-acetyl-D-glucosamine are also retarded on gel-filtration.3. Soluble phloem filaments were prepared by collection of exudate into deaerated buffer containing iodoacetamide but no reducing agent. Oxidative gellation of the filaments was prevented by rapid modification of their many accessible cysteine residues, and is assumed to have maintained the degree of polymerisation found in vivo.Those disulphide bridges which were present allowed the incorporation of approximatically 60 % of the PP1 and 80 % of the PP2 into polymeric material. It is concluded that PP1 and PP2 are both structural proteins present in the filaments observable in vivo.4. PP2 had an elongated binding-site for oligomers of N-acetyl-D-glucosamine. It is suggested that this lectin immobilises bacteria and fungi to the cross-linked filaments which seal wounded phloem sieve-tubes, and thus maintains sterility.The sieve-tube cells of phloem tissue conduct organic nutrients around plants by intracellular mass-flow of the translocated material [l]. Protein filaments known as P-protein are the major structures microscopically observable in the sieve-tube lumen, but their function and positioning are disputed [2-41. Both the stream of translocates and the P-proteins are contained in a fluid exudate collected from mature sieve-tubes of certain plant species [5 -81.Phloem exudate from Cucurbita (pumpkin) forms a gel on exposure to air due to cross-linking of the filaments, and this can be prevented or reversed by agents which reduce disulphide bridges [9,10]. Reduction gives two proteins: phloem protein 1 (PPl), which reconstitutes filaments on oxidation [lo-121, and phloem protein 2 (PP2), which also precipitates on oxidation but does not form filaments [12], and which is a lectin specific for oligomers of N-acetylglucosamine [13 -151. Several different M , measurements have been given for these proteins: 88000-136000 for PP1 [4,10, 11,161 and 20000-60000 for PP2 [4,11,14,16].We show here that PP2 is a dimer of M , of 48000 held together by buried disulphide bridges, and that filaments from Cucurbita phloem contain both PP1 and PP2, which are therefore both structural proteins.Abbreviations. (GlcNAc),, (GlcNAc), and (Glc NAc),, di-, tri-, tetra-~-(1+4)-(2...