ABRUPT AND IRREVERSIBLE REDUCTION OF CHLOROPHYLL FLUORESCENCE ASSOCIATED WITH LEAF-SPOT IN SAINTPAULIA (AFRICAN VIOLET)

The change in chlorophyll fluorescence was investigated using fluoresc ence microscopy at the initial stage of leaf spot occurrence in Saintp aulia ionantha H. Wendl. (African violet), When Saintpaulia leaf was e xposed to a rapid temperature drop, florescence intensity declined ver y quickly within a very short time (20 s) and did not recover after re warming. This abrupt reduction of chlorophyll fluorescence was caused even by 20 degrees C water for just 2 s, when leaf temperature prior t o treatment was 35 degrees C, This change of chlorophyll fluorescence was observed only in the palisade cells in a leaf. In addition, ultras tructural study of the chloroplast cf the palisade cells showed an abr upt disruption in the photosynthetic apparatus. These results indicate that the initial stage of leaf spot occurrence is developed very quic kly within a very short time and that it might be caused by a differen t mechanism to conventional chilling injury. (C) 1998 Elsevier Science B.V.