<p>Plants normally grow on substrates that are extremely rich in microorganisms, but infection remains a rare event. During evolution, plants have developed a variety of defence systems to protect themselves from potential pathogens. Proteins including thionins, plant defensins and chitinases have been shown to play active roles against pathogen infections. Plants produce a wide array of antimicrobial compounds for escaping from microorganisms, which have antibacterial, anti-fungal activity, etc. Antimicrobial peptides extracted from plants inhibit the growth of a variety of fungi, oomycetes, Gram-positive bacterial phytopathogenes and <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> (Baker's yeast). Many antimicrobial peptides (AMPs) which contain cysteine residues abundantly have been isolated from plants, and these are classified into the plant defensin family. Plant defensins can be classified broadly into three types (hevein type, C6 type, and C8 type) according to the number and the position of cysteine residues in the molecules. The C6 type of plant defensins are highly basic proteins that contain 6 cysteine residues and a continuous sequence of cysteines (-CC-). All the 6 cysteines are involved in disulphide bond formation for stabilising protein tertiary structure [<cite idref="PUB00017015"/>, <cite idref="PUB00017016"/>, <cite idref="PUB00017017"/>, <cite idref="PUB00017018"/>]. </p> Antimicrobial peptide, C6 type, conserved site