PHOTOSYNTHETIC OXYGEN EVOLUTION BY 4 COFFEA-ARABICA GENOTYPES SUBJECTED TO A DEHYDRATION REHYDRATION CYCLE/

Photosynthetic oxygen evolution by eight month old plants of the Coffe a arabica hybrids H-421 (cv. Yellow Catuai x cv. Timer Hybrid) and H-4 30 (cv. Red Catuai x cv. Timer Hybrid), a Catimor progeny, and one lin e of cv. Red Catuai was followed polarographically during a dehydratio n/rehydration cycle. Fully hydrated plants showed a maximum photosynth etic rate (A(max)) in the range of 20.6 to 34.6 mu mol m(-2) s(-1) and an apparent quantum yield of 0.074 to 0.086. During dehydration A(max ) steadily decreased as the water potential declined. Changes were not found among the slope and the intercept values, with the exception of the slope Value of hybrid H-421. The recovery was regained 96.0, 96.5 , 85.0 and 78.0 h after rehydration for the genotypes Catimor, H-430, Catuai and H-421, respectively. In response to stress, the mesophyll r esistance restricts carbon dioxide fixation, with after-effects of var iable duration.