DIURNAL TIME COURSES OF CO2 GAS-EXCHANGE IN CLOSED AND OPEN GAS SYSTEMS FOR COFFEE (COFFEA-ARABICA L), POMEGRANATE (PUNICA-GRANATUM L), CITRUS (CITRUS-LIMONIA OSB), GRAPE (VITIS-VINIFERA L), AND BANANA (MUSA XPARADISIACA L) IN-VITRO PLANTLETS UNDER DIFFERENT ENVIRONMENT CONDITIONS

Continuous measurements were made of CO2 gas exchange over a period of three days on ill vitro plantlets of coffee (Coffea arabica L.), pome granate (Punica granatum L.), citrus (Citrus limonia Osb.), grape (Vit is vinifera L.), and banana (Musa x paradisiaca L.). The gas used for measurements contained CO2 concentrations of 350, 600, 1000 or 2000 mu l l(-1). Measurements in the closed system for coffee plantlets grown in medium containing different sucrose concentrations showed a strong decrease of the CO2 concentration in the cuvette atmosphere during th e light period almost reaching the CO2 compensation point (70 mu l l(- 1) CO2). During the dark period a continuous increase was observed. Me asured in the open system diurnal time courses of in vitro pomegranate and citrus plantlets showed that CO2 assimilation rates were strongly influenced by light intensity and temperature. A positive balance of CO2 gas exchange was found for pomegranate plantlets only with light i ntensities beyond 100 mu mol m(-2) s(-1) photosynthetic photon flux de nsity (PPFD). Citrus plantlets were independent of the sucrose concent ration in the medium and showed a positive CO2 balance at 350 mu l l(- 1) CO2 gas concentration. Banana plantlets revealed negative balances under all conditions examined.