Two homogeneous proteins active in vitro against the bacterial pathogen Clavibacter michiganensis subsp. sepedonicus were obtained from a crude cell-wall preparation from the leaves of Columbia wild-type Arabidopsis. The N-terminal amino acid sequences of these proteins allowed their identification as lipid transfer proteins (LTP-a1, LTP-a2); the LTP1-a1 sequence was identical to that deduced from a previously described cDNA (EMBL M80566) and LTP-a2 was quite divergent (44% identical positions). These proteins were not detected in the cytoplasmic fraction by Western-blot analysis. Proteins LTP-s1 and LTP-s2 were similarly obtained from spinach leaves; LTP-s1 was 91% identical to a previously purified spinach LTP (Swiss Prot P10976), and LTP-s2 was moderately divergent (71% identical positions). About 1/3 of the total LTPs were detected in the cytoplasmic fraction from spinach by Westem-blot analysis. Concentrations of these proteins causing 50% inhibition (EC-50) were in the 0.1–1 μM range for the bacterial pathogens C. michiganensis and Pseudomonas solanacearum and close to 10 μM for the fungal pathogen Fusarium solani.
