INFLUENCE OF CO2 CONCENTRATION, LIGHT-INT ENSITY, AND SUCROSE CONCENTRATION ON NET PHOTOSYNTHESIS OF CITRUS PLANTLETS DURING IN-VITRO PROPAGATION

Light curves of the CO2 gas exchange of irt vitro plantlets of citrus (Citrus limonia Osb. (Rutaceae)) were measured continuously in an open system using different CO2 concentrations (350, 1000, and 2000 mu l l (-1) CO2). The plantlets were grown in media with sucrose concentratio ns from 0 to 5% under light intensities of 60, 100, and 260 mu mol m(- 2) l(-1). Before starting the measurements the plantlets were pretreat ed with 1000 mu l l(-1) CO2 for several weeks. Control plantlets were grown for the same period in gas tight vessels. CO2 concentration of t he gas atmosphere inside the plant vessels had a stronger influence on CO2 gas exchange of citrus plantlets than sucrose concentration of th e medium. Net photosynthesis of plantlets grown under various light in tensities differed only little when using the same CO2 concentration f or measurement as used for growing. After pretreatment with 1000 mu l l(-1) CO2 during growth, net photosynthesis of plantlets measured unde r 350 Cll l(-1) CO2 was higher compared to control plantlets.