EFFECTS OF SUCROSE ON PHOTOSYNTHESIS AND PHOSPHOENOLPYRUVATE CARBOXYLASE ACTIVITY OF IN-VITRO CULTURED STRAWBERRY PLANTLETS

Photosynthesis and phosphoenolpyruvate carboxylase activity were inves tigated in 5, 10 and 28 day-old micropropagated strawberry plantlets ( Fragaria x ananassa Duch. cv Kent) rooted in vitro with different leve ls of sucrose (0, 1, 3 and 5%) on cellulose plugs (Sorbarods). The pho tosynthetic capability was influenced by the level of sucrose in the c ulture medium with the largest rates of photosynthesis corresponding t o the cultures with 0 and 1% sucrose. The apparent quantum yield and t he ratio of variable fluorescence to maximum fluorescence were also re duced in plantlets cultured with 3 or 5% sucrose as compared to those with 0 or 1%. Phosphoenolpyruvate carboxylase activity was largest 5 a nd 10 days after the onset of culture and decreased in the absence of sucrose in the culture medium. At 28 days after the onset of culture, the activity of this carboxylating enzyme was lower than at the beginn ing of culture and independent of the concentration of sucrose in the culture medium. Phosphoenolpyruvate carboxylase appears to be an impor tant carboxylating enzyme in micropropagated plantlets.