An antimicrobial protein of about 1 O kD, called AceAMPl, was isolated from onion (Allium cepa L.) seeds. Based on the nearcomplete amino acid sequence of this protein, oligonucleotides were designed for polymerase chain reaction-based cloning of the corresponding cDNA. l h e mature protein is homologous t o plant nonspecific lipid transfer proteins (nsLTPs), but it shares only 76% of the residues that are conserved among all known plant nsLTPs and is unusually rich in arginine. AceAMP1 inhibits all 12 tested plant pathogenic fungi at concentrations below 10 pg mL-'. Its antifungal activity is either not at all or is weakly affected by the presence of different cations at concentrations approximating physiological ionic strength conditions. AceAMP1 is also active on two Cram-positive bacteria but is apparently not toxic for Cram-negative bacteria and cultured human cells. In contrast t o nsLTPs such as those isolated from radish or maize seeds, AceAMPI was unable t o transfer phospholipids from liposomes to mitochondria. On the other hand, lipid transfer proteins from wheat and maize seeds showed little or no antimicrobial activity, whereas the radish lipid transfer protein displayed antifungal activity only in media with low cation concentrations. l h e relevance of these findings with regard to the function of nsLTPs is discussed.Although plant seeds are usually sown on a substrate that is extremely rich in microorganisms, infection of seeds or seedling tissues normally occurs at relatively low frequency. It is believed that seed proteins that exhibit antimicrobial activity may participate in the protection of seeds against potential microbial invaders. Different types of antimicrobial proteins have been purified from plant seeds '

Maize lipid-transfer protein (LTP) is a small soluble protein which is able to transfer in vitro phospholipids between membranes and to bind fatty acids or lysoderivatives. In the studies reported here, fluorescent-labelled fatty acids were used to characterise the nature of the binding site on LTP. A fluorescent analogue of 12 carbons with a pyrene moiety attached at the end, alone or in conjunction with an anthroyloxy analogue, indicated that LTP could bind two fatty acids although with a marked difference in affinity. The binding capacity was strongly affected after reduction of the protein by dithiothreitol, showing that the four S-S bonds of LTP are essential for its lipid binding property. Other analogues used were 16-carbon or 18-carbon fatty acids with an anthracene moiety attached at different points of the hydrocarbon chain. Emission maxima of these molecules varied with the analogue and suggested a motional constraint for the bound fatty acid which is more important around the middle of the chain than at its extremities. Binding displacement studies were carried out with a wide range of fatty acids or fatty acyl derivatives. Fatty acids of 16 to 19 carbons were found to be the preferred ligands. The presence of one double bond did not change appreciably the affinity of LTP, although the presence of two or three double bonds or of a hydroxyl moiety significantly reduced the affinity. Fatty acyl-CoA or lysoderivatives bound as well as the corresponding fatty acid.

We studied the temporal and spatial pattern of lipid transfer protein (LTP) gene expression, as well as the localization of this protein, in maize. Using an LTP gene, we observed an accumulation of LTP mRNA in embryos and endosperms during seed maturation. LTP gene expression was also investigated in young seedlings. After germination, the leve1 of LTP mRNA in the coleoptile increased, with a maximum at 7 days, whereas LTP mRNA levels were low in the scutellum and negligible in roots. The high levels of LTP mRNA found in coleoptiles and embryos were confirmed by in situ hybridization. Moreover, LTP gene expression appeared to be localized in the externa1 cellular layers and around the leaf veins. Using immunogold methods, we also observed that LTP was distributed heterogeneously in the different cells of coleoptiles and leaves. The highest concentrations of LTP were found in the outer epidermis of the coleoptiles as well as in the leaf veins. Together, our observations indicate that LTP gene expression is not only organ specific and time specific but also cell specific.