Seed sterilization is essential for preventing seed borne fungal diseases. Sterilization tools based on physical technologies have recently received much attention. However, available information is very limited in terms of efficiency, safety, and mode of action. In this study, we have examined antifungal activity of ozone and arc discharge plasma, potential tools for seed sterilization. In our results, ozone and arc discharge plasma have shown differential antifungal effects, depending on the environment associated with fungal spores (freely submerged in water or infected seeds). Ozone inactivates Fusarium fujikuroi (fungus causing rice bakanae disease) spores submerged in water more efficiently than arc discharge plasma. However, fungal spores associated with or infecting rice seeds are more effectively deactivated by arc discharge plasma. ROS generated in water by ozone may function as a powerful fungicidal factor. On the other hand, shockwave generated from arc discharge plasma may have greatly contributed to antifungal effects on fungus associated with rice seeds. In support of this notion, addition of ultrasonic wave in ozone generating water has greatly increased the efficiency of seed disinfection.

Lysozyme,ribonuclease A, ovalbumin and bovine serum albumin were reacted with reducing sugars under physiological conditions of 37°C and pH 7.4, and polymerization of proteins, changes in amino acid composition and carbonyl compounds formed during the reaction were investigated. Incubation of all the protein-sugar systems resulted in noticeable losses of arginine and lysine residues. Polymerization, as well as impairment of arginine residues of lysozyme, with fructose and aldopentose was higher than with aldohexoses. 3-Deoxyglucosone (3DG) was identified as one of the major carbonyl compoundsgenerated in the reaction systems of proteins with glucose and fructose. The formation of 3DGin protein-fructose systems was 1.3~2 times that in proteinglucose systems. Glucose alone did not polymerize succinylated lysozyme, but fructose did and it impaired only arginine residues. These results indicate that 3DGwas generated on the reaction between glucose and free amino groups in proteins, whereas it was generated from fructose alone with the modification of free amino groups. It is strongly suggested that 3DGwas the cross-linker responsible for the polymerization of proteins and the attacker of arginine residues.

We previously isolated the OsCBT gene, which encodes a calmodulin (CaM)-binding protein, from a rice expression library constructed from fungal elicitor-treated rice suspension cells. In order to understand the function of OsCBT in rice, we isolated and characterized a T-DNA insertion mutant allele named oscbt-1. The oscbt-1 mutant exhibits reduced levels of OsCBT transcripts and no significant morphological changes compared to wild-type plant although the growth of the mutant is stunted. However, oscbt-1 mutants showed significant resistance to two major rice pathogens. The growth of the rice blast fungus Magnaporthe grisea, as well as the bacterial pathogen Xanthomonas oryzae pv. oryzae was significantly suppressed in oscbt-1 plants. Histochemical analysis indicated that the hypersensitive-response was induced in the oscbt-1 mutant in response to compatible strains of fungal pathogens. OsCBT expression was induced upon challenge with fungal elicitor. We also observed significant increase in the level of pathogenesis-related genes in the oscbt-1 mutant even under pathogen-free condition. Taken together, the results support an idea that OsCBT might act as a negative regulator on plant defense.

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