PHOTOINHIBITION AND RECOVERY OF PHOTOSYNTHESIS IN COFFEA-ARABICA AND C-CANEPHORA

Photosynthetic parameters were determined in disks from leaves of C. a rabica cv. Red Catuai and C. canephora cv. Kouillou grown in the field . Kouillou showed a relatively higher irradiance requirement for satur ating photosynthesis, lower chlorophyll (Chl) content, and higher Chl a/b ratio than Catuai. Photoinhibition of photosynthesis under bright irradiance was manifested by decreases in maximum photochemical effici ency (evaluated by the variable to maximum fluorescence ratio, F-v/F-m ), as a consequence of an increased initial and a quenched maximum flu orescence. Restoration of F-v/F-m following photoinhibition in low irr adiance was faster in Kouillou than in Catuai. Chloramphenicol both ac celerated photoinhibition (mainly in Kouillou) and blocked its recover y for at least 190 min in either cultivar. Photosynthetic oxygen evolu tion under photoinhibitory conditions was decreased by chloramphenicol ; in control leaf disks this decrease was only observed in C. arabica, but with a rapid recovery within 90 min of low irradiance exposure. I n both coffee cultivars, the depressed photochemical efficiency of pho tosystem 2 was not accompanied by a concomitant lowering in oxygen evo lution during reversal from photoinhibition.