Photoinhibition and recovery of photosynthesis in Coffea arabica and C. canephora

Photosynthetic parameters were determined in disks from leaves of C. arabica cv. Red Catuaí and C. canephora cv. Kouillou grown in the field. Kouillou showed a relatively higher irradiance requirement for saturating photosynthesis, lower chlorophyll (Chl) content, and higher Chl a/b ratio than Catuaí. Photoinhibition of photosynthesis under bright irradiance was manifested by decreases in maximum photochemical efficiency (evaluated by the variable to maximum fluorescence ratio, Fv/Fm), as a consequence of an increased initial and a quenched maximum fluorescence. Restoration of Fv/Fm following photoinhibition in low irradiance was faster in Kouillou than in Catuaí. Chloramphenicol both accelerated photoinhibition (mainly in Kouillou) and blocked its recovery for at least 190 min in either cultivar. Photosynthetic oxygen evolution 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. In both coffee cultivars, the depressed photochemical efficiency of photosystem 2 was not accompanied by a concomitant lowering in oxygen evolution during reversal from photoinhibition.