Antimicrobial peptides target cytoplasmic membranes and intracellular macromolecules. As a general feature, most antimicrobial peptides are amphipathic and this property serves a key role in their antimicrobial activity by promoting microbial membrane interactions. However, microbial cell surfaces such as membranes or cell walls are composed of a variety of components, which generate significant differences between the surfaces of prokaryote and eukaryote cells [17], [18], [42] and [44]. Previous

studies have shown that the pleurocidin peptide presents a selective membrane-disruption effect in some fungi [22], but its mechanism of action remains to Smad inhibitor be determined. The antifungal activities of the short pleurocidin peptides were screened in vitro against Alternaria sp. and F. oxysporum. Table 3 shows the MIC and MFC values for the different fungi. The MIC and GKT137831 MFC values of pleurocidin ranged from 0.79 μg mL−1 to >25 μg mL−1 and 3.12 μg mL−1 to >50 μg mL−1, respectively. Whereas the MIC and MFC values of Plc-2 ranged from 3.12 μg mL−1 to >50 μg mL−1 and 6.25 μg mL−1 to >50 μg mL−1, respectively. These values illustrate the relative antifungal potency of the two peptides, with MIC values quite comparable to the conventional fungicide captan. The highest inhibitory activity of the two peptides was observed against Colletotrichum sp., and the lowest inhibition was noted against

A. ochraceus. Plc-2 was less

active than pleurocidin, except against F. oxysporum, for which the MIC and the MFC values were the same. Both peptides exhibited fungistatic and fungicidal activity for all Cyclooxygenase (COX) the ascomycete fungi tested. Significant morphological changes were observed when the phytopathogenic fungi were exposed to pleurocidin and Plc-2 at concentrations that partially inhibit growth (Fig. 2). Most of these fungi exhibited increased branching (hyper-branching) and swelling of the hyphae in the presence of the peptides. Condensed hyphal aggregates were commonly observed when fungi were treated with peptides followed by staining with CFW. The fluorescent probe SG was used to assess cell permeation of fungi treated with both peptides. All the fungi showed identical fluorescent staining. Cellular membranes were compromised and also disrupted if the fungal structures were incubated with pleurocidin or Plc-2 (Fig. 2). The fact that Plc-2 is reduced in size compared to pleurocidin might alter its structural properties. The Plc-2 peptide presented the smallest charge (+2) and highest pI (9.7). Its major molecular moment (0.16) was at the low end for all of the synthesized peptides ( Table 1). Comparing the primary structure of Plc-2 with the structure of antimicrobial peptides with similar activity (dermaseptin-1, ceratotoxin and PR39) together with the results presented here ( Fig.