CHARACTERISTICS OF SLOW CHLOROPHYLL FLUORESCENCE EMISSION IN 4 COFFEA-ARABICA GENOTYPES SUBMITTED TO WATER-STRESS

The characteristics of slow chlorophyll (Chi) fluorescence emission we re studied in fully developed leaves of coffee (Coffea arabica) cultiv ars Red Catuai, Catimor, H-421 (a Timer Hybrid with Yellow Catuai), an d H-430 (a Timer Hybrid with Red Catuai). Fluorescence measurements we re made with a Hansatech system, using leaf discs (1000 mm(2)), under continuous red irradiation (660 mn peak, photon flux density ca. 300 m u mol m(-2) s(-1)) at 35 degrees C. During dehydration, there was nea apparent Chi loss from the leaves of all genotypes, but the electron n ow between the two photosystems decreased. The hybrid H-421 was the le ast affected. On the other hand, the light reactions of photosystem 2 and its capacity to reduce the primary photosynthetic electron accepto r were mot affected by water stress.