Changes in the antigen composition of the upper leaves of cucumber plants after inducing systemic acquired resistance by inoculation with Colletotrichum lagenarium

Systemic resistance was induced in cucumber plants by inoculating the first true leaves with Colletotrichum lagenarium. Changes in the antigen composition of the upper leaves were analysed quantitatively by immunoelectrophoresis. Eleven days after inoculation a “new” antigen appeared in the protected upper leaves, increased in concentration for a further two days and then decreased. This antigen appeared in the unprotected leaves of uninoculated plants only when plants started to flower. Several common antigens present in both protected and unhigher amounts in the leaves of protected plants than in the leaves of unprotected plants but decreased in both with the onset of flowering. The significance of these qualitative and quantitative changes is discussed.