EVALUATION OF THE PHOTOAUTOTROPHIC ABILIT Y OF VITIS PLANTLETS (ROOTSTOCK VAR GRAVESAC) - SET-UP OF A SPECIAL OPEN FLOW GAS-EXCHANGE SYSTEM

The photosynthetic ability of Vitis rootstock plantlets (var. Gravesac ) was estimated in vitro with an open flow system specially designed f or in vitro culture. CO2 response curves were established and respirat ion was also measured. The maximum net photosynthetic rate, reached at 500 mu l l(-1) of CO2, is 2 mu mol m(-2) s(-1). At 350 mu l l(-1) CO2 the photosynthetic activity is 1.6 mu mol m(-2) s(-1). The dark respi ration rate is 0.018 mu mol s(-1) g(-1) of total dry weight. The total amount of soluble carbohydrates in the medium remains the same whethe r plantlets were present or not. In the medium with plantlets, the suc rose is entirely hydrolysed in glucose and fructose within two months. No carbohydrate uptake from the medium was recorded indicating an aut otrophic behaviour. Measurements of CO2 exchange were also performed a t leaves of plants cultivated in a greenhouse. The photosynthetic acti vity of in vitro plants accounts only for 20% of the level of greenhou se-grown plants.