Investigations on the action of Phytophthora quercina, P. citricola and P. gonapodyides toxins on tobacco plants

Phytophthora quercina, P. citricola and P. gonapodyides isolated from declining oak roots and from soil rhizosphere in the field, released proteins into their culture medium. The proteins of P. quercina and P. gonapodyides caused severe chlorosis and necrosis on tobacco leaves. Only few symptoms were seen for the P. citricola protein. Surprisingly leaf chlorosis and necrosis were only visible in the light, whereas wilt symptoms were light-independent. The proteins were characterized on SDS gels as small peptides with basic and acidic isoelectric points. All proteins were heat stable. Even boiling for 15 min did not affect their activity. However, pronase treatment totally destroyed their activity. Transmission electron microscopy studies clearly showed that membrane structures especially of chloroplasts were damaged. The proteins of P. quercina and P. gonapodyides strongly crossreacted with the antibody raised against the P. cryptogea protein cryptogein. Therefore, these proteins might belong to the family of Phytophthora leaf necrotic proteins called elicitins.