Research Notes Changes in the Activity and the Polypeptide Composition of the Oxygen-Evolving Complex in Photosystem II of Tobacco Leaves Infected with Cucumber Mosaic Virus Strain Y. Hideki Takahashi. Faculty of Agriculture, Tohoku University, 1-1, Tsutsumidori Amamiyamachi, Aoba-ku, Sendai 981, Japan. Yoshio Ehara. Faculty of Agriculture, Tohoku University, 1-1, Tsutsumidori Amamiyamachi, Aoba-ku, Sendai 981, Japan.. MPMI 5:269-272. Accepted 27 January 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992.

The amount of 22- and 23-kDa polypeptides in a 23-kDa protein family, which plays a regulatory role in photosynthetic oxygen evolution, decreased significantly during the progress of appearance of chlorotic spots in cucumber mosaic virus strain Y (CMV[Y])-inoculated tobacco (Nicotiana tabacum ‘Ky57’) leaves (Plant Mol. Biol. 16:689-698, 1991). The present study was conducted to determine if the amount of other polypeptides of the oxygen-evolving complex and the oxygen-evolving activity also decreased in CMV(Y)-inoculated tobacco leaves. The amount of a 33-kDa polypeptide, which is essential to oxygen evolution, did not decrease in CMV(Y)-inoculated leaves showing early symptoms, although the amount of 22- and 23-kDa polypeptides began to decrease. However, comparative analysis of electron transport in thylakoid membranes indicated that the oxygen-evolving activity in CMV(Y)-inoculated tobacco leaves was only partly reduced, compared with the activity in CMV(O)-inoculated tobacco leaves which did not show clear symptoms. Partial inhibition of the oxygen-evolving activity, by a differential decrease in the amount of polypeptides of the oxygen-evolving complex, seems to be associated with the primary molecular process of symptom expression in CMV(Y)-inoculated tobacco leaves.