Four 9‐kDa proteins excreted by somatic embryos of grapevine are isoforms of lipid‐transfer proteins

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Abstract
Four 9‐kDa small extracellular proteins produced by embryogenic cultures in the absence of auxin have been purified from the extracellular medium of grapevine somatic embryo cultures through cation‐exchange chromatography and hydrophobic‐interaction chromatography. The partial amino‐acid sequences reflect high similarities between the four proteins as well as with the sequences established for carrot, spinach, millet and maize nonspecific lipid‐transfer proteins. All these sequences show conservation of three cysteines at positions 4, 14 and 30–32, as well as glycine, valine, tyrosine and lysine residues at positions 5, 7, 17 and 37, respectively. In‐vitro lipid‐transfer assays reveal that the four proteins catalyze the transfer of phosphatidylcholine from liposomes towards motochondria with an efficiency similar or higher than that of a purified maize lipid‐transfer protein.