Detection of tomatinase from Fusarium oxysporum f.sp. lycopersici in infected tomato plants.

摘要

The antifungal glycoalkaloid alpha-tomatine of tomato is thought to protect the plant against phytopathogenic fungi. F. oxysporum f.sp. lycopersici, a vascular pathogen of tomato, produces a tomatinase enzyme which hydrolyses the glycoalkaloid intonon-fungitoxic compounds. Detoxification of alpha-tomatine may be how this fungus avoids the plant glycoalkaloid barrier. As an initial step to evaluate this possibility, the induction of tomatinase was studied: (i) in fungal cultures containing extractsfrom leaf, stem or root of tomato plants and (ii) in stems and roots of tomato (cv. Moneymaker) plants infected with the pathogen at different infection stages. The kinetics of tomatinase induction with leaf extract (0.6% dry weight) was similar to thatobserved with 20μg/ml of alpha-tomatine. In the presence of stem extract, tomatinase activity was less than 50% of that induced with leaf extract, whereas in the presence of root extract tomatinase activity was very low. In the stem of infected tomatoplants tomatinase activity was higher at the wilt stage than in previous infection stages and in roots, tomatinase activity appeared with the first symptoms and was maintained until wilting. TLC analysis showed that the tomatinase induced in culture medium with plant extracts and in infected tomato plants had the same mode of action as the enzyme induced with pure alpha-tomatine, hydrolysing the glycoalkaloid into its non-fungitoxic forms, tomatidine and beta-lycotetraose. The antisera raised against purified tomatinase recognized in extracts of roots and stems of infected tomato plants a protein of 50 000 (45 000 when proteins were deglycosylated), corresponding to the tomatinase enzyme. It is concluded that F. oxysporum f.sp. lycopersici expresses tomatinase in vivo following infection of a tomato plant.