Fungi are far more complex organisms than viruses or bacteria and can develop numerous diseases in plants that cause loss of a substantial portion of the crop every year. Plants have developed various mechanisms to defend themselves against these fungi which include the production of low-molecular-weight secondary metabolites and proteins and peptides with antifungal activity. In this review, families of plant antifungal proteins (AFPs) including defensins, lectins, and several others will be summarized. Moreover, the application of AFPs in agriculture will also be analyzed.

A 11 kDa antifungal protein FEAP was purified from buckwheat (Fagopyrum esculentum) seed extract with a procedure involving (NH 4 ) 2 SO 4 precipitation and chromatography on SP-Sepharose, Affi-gel blue gel, Mono S, and Superdex peptide. Its N-terminal sequence was AQXGAQGGGAT, resembling those of buckwheat peptides Fα-AMP1 and Fα-AMP2. FEAP exhibited thermostability (20−100 °C) and acid resistance (pH 1−5). Its antifungal activity was retained in the presence of 10−150 mmol/L of K + , Mn 2+ , or Fe 3+ ions, 10−50 mmol/L of Ca 2+ or Mg 2+ ions, and 50% methanol, 50% ethanol, 50% isopropanol, or 50% chloroform. Its half-maximal inhibitory concentrations toward spore germination and mycelial growth in Botrytis cinerea were 79.9 and 236.7 μg/mL, respectively. Its antifungal activity was superior to the fungicide cymoxanil mancozeb (248.1 μg/mL). FEAP prevented B. cinerea from infecting excised leaves, intact leaves, and isolated fruits of cherry tomato. Its mechanism involved induction of an increase in cell membrane permeability and a decrease in mitochondrial membrane potential.

In this study, a 8.5-kDa antifungal peptide designated as BGAP was purified from the crude extract of the seeds of Brassica oleracea var. gongylodes by employing a protocol that comprised cation exchange chromatography on SP-Sepharose, cation exchange chromatography on Mono S and gel filtration chromatography on Superdex peptide. BGAP showed the highest amino acid sequence similarity to defensin peptides by mass spectrometric analysis. BGAP showed a broad spectrum of antifungal activity with a half maximal inhibitory concentration at 17.33 μg/mL, 12.37 μg/mL, 16.81 μg/mL, and 5.60 μg/mL toward Colletotrichum higginsianum, Exserohilum turcicum, Magnaporthe oryzae and Mycosphaerella arachidicola, respectively. The antifungal activity of BGAP remained stable (i) after heat treatment at 40–100 °C for 15 min; (ii) after exposure to solutions of pH 1–3 and 11–13 for 15 min; (iii) after incubation with solutions containing K+, Ca2+, Mg2+, Mn2+ or Fe3+ ions at the concentrations of 20–150 mmol/L for 2 h; and (iv) following treatment with 10% methyl alcohol, 10% ethanol, 10% isopropanol or 10% chloroform for 2 h. Fluorescence staining experiments showed that BGAP brought about an increase in cell membrane permeability, a rise in reactive oxygen species production, a decrease in mitochondrial membrane potential, and an accumulation of chitin at the hyphal tips of Mycosphaerella arachidicola.

A ribonuclease, with a molecular mass of 22.5 kDa and an N-terminal sequence exhibiting resemblance to previously isolated buckwheat storage proteins and allergens, was isolated from Japanese large brown buckwheat seeds. The ribonuclease was purified using a simple protocol that comprised ion exchange chromatography on Q-Sepharose and DEAE-cellulose and gel filtration on Superdex 75. The ribonuclease exhibited low activity toward poly U, lower activity toward poly C, and very low activity toward poly A and poly G. The enzyme was activated upon exposure to 10 mM of Fe(2+) and Zn(2+) ions but was inhibited by Ca(2+), Mg(2+), and Mn(2+) ions at the same concentration. The optimum pH and optimum temperature for the enzyme were pH 9 and 60 °C, respectively. It inhibited proliferation of HepG2 hepatoma and MCF 7 breast cancer cells, with an IC50 value of 79.2 and 63.8 μM, respectively. It potently inhibited HIV-1 reverse transcriptase activity with an IC50 of 48 μM. However, there were no antifungal and mitogenic activities.