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Plant defensins are a prominent family of cationic peptides in the plant kingdom. They are structurally and functionally related to defensins that have been previously characterized in mammals and insects. They present molecular masses between 5 and 7kDa and possess a pattern of eight conserved Cys residues. The three-dimensional structure of plant defensins is small and globular. It has three anti-parallel beta-sheets and one alpha-helix that is stabilized by a structural motif composed of disulfide bridges. This motif is found in other peptides with biological activity and is called the Cys stabilized alphabeta motif (CSalphabeta). Based on the growing knowledge on defensin structure, gene expression and regulation, and also their in vitro biological activity, it has become clear that plant defensins are complex and sophisticated peptides whose function extends beyond their role in defense of plants against microbial infection. This review discusses recent data and will present comprehensive information regarding the study of defensins.

Oil bodies were removed from mature sunflower through wet grinding followed by filtration then centrifugation and recovered as the buoyant fraction. Washing this fraction with buffer (water-washed oil bodies, WWOB) or 9 M urea (ureawashed oil bodies, UWOB) resulted in the removal of extraneous proteins. SDS-PAGE of the proteins still associated with the oil body fraction after washing indicated that this effect was particularly dramatic with urea washing. Thirty-eight percent of the total seed tocopherol was recovered in WWOB after only one cycle of oil body recovery. The total phenolic content (TPC) of differentially washed sunflower seed oil bodies was used as a marker for the nonspecific association of phenolic compounds to oil bodies. This value decreased with increased removal of proteins from oil bodies, whereas the converse was true for tocopherol values, which increased from 214 mg total tocopherol kg −1 WWOB [dry wt basis (dwb)] to 392 mg total tocopherol kg −1 UWOB (dwb). The ratio of the four tocopherol isomers remained constant in the seed and oil body preparations (α:β:γ:δ approximately 94:5:0.5:0.5). This work provides evidence that an intrinsic population of tocopherol molecules exists in the oil bodies of mature sunflower seeds. d Water-washed oil bodies (WWOB) for this study were recovered from one cycle of the extraction protocol from 47.5g seed.

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Plant defensins are cationic peptides that are ubiquitous within the plant kingdom and belong to a large superfamily of antimicrobial peptides found in several organisms collectively called defensins. The primary structure of these peptides includes 45 to 54 amino acid residues with considerable sequence variation. At the level of three-dimensional structure, they are small and globular, composed of three anti-parallel β-sheets and one α-helix, which is highly conserved among these peptides. The three-dimensional structure is stabilized by four disulfide bridges formed by eight strictly conserved Cys residues. Two of these bridges compose the Cys-stabilized α-helix β-strand motif, which is found in other peptides with biological activities. Plant defensins present numerous biological activities, such as inhibiting protein synthesis, ion channel function and α-amylase and trypsin activity; impairing microbial, root hair and parasitic plant growth; mediating abiotic stress and Zn tolerance; altering ascorbic acid redox state; stimulating sweet taste sensation; serving as epigenetic factors; affecting self-incompatibility; and promoting male reproductive development. Some of these biological activities, such as microbial growth inhibition and sweet taste induction, coupled with a scaffold that provides these peptides with incredible physicochemical resistance to harsh environments and the potential for simple amino acid substitution, raise the opportunity to improve the function of defensins or introduce new activities, endowing these peptides with great biotechnological and medical significance. This review will cover the biological activities and roles of plant defensins and will focus on their application in the field of biotechnology.

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