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 decli ning oak roots and from soil rhizosphere in the field, released proteins in to their culture medium. The proteins of P. quercina and P. gonapodyides ca used severe chlorosis and necrosis on tobacco leaves. Only few symptoms wer e seen for the P. citricola protein. Surprisingly leaf chlorosis and necros is were only visible in the light, whereas wilt symptoms were light-indepen dent. The proteins were characterized on SDS gels as small peptides with ba sic and acidic isoelectric points. All proteins were heat stable. Even boil ing for 15 min did not affect their activity. However, pronase treatment to tally destroyed their activity. Transmission electron microscopy studies cl early showed that membrane structures especially of chloroplasts were damag ed. The proteins of P. quercina and P. gonapodyides ides strongly crossreac ted with the antibody raised against the P. cryptogea protein cryptogein. T herefore, these proteins might belong to the family of Phytophthora leaf ne crotic proteins called elicitins. (C) Elsevier. Paris.