RESPONSES TO ELEVATED CO2 OF FLAVERIA-LINEARIS PLANTS HAVING A REDUCED ACTIVITY OF CYTOSOLIC FRUCTOSE-1,6-BISPHOSPHATASE

Wide variation exists in the growth responses of C-3 plants to elevate d CO2 levels. To investigate the role of photosynthetic feedback in th is phenomenon, photosynthetic parameters and growth were measured for lines of Flaveria linearis with low, intermediate or high cytosolic fr uctose-1,6-bisphosphatase (cytFBPase) activity when grown at either 35 or 65 Pa CO2. The effects of pot size on the responses of these lines to elevated CO2 were also examined. Photosynthesis and growth of plan ts with low cytFBPase activity were less responsive to elevated CO2, a nd these plants had a reduced maximum potential for photosynthesis and growth. Plants with intermediate cytFBPase activity also showed a low er relative growth enhancement when grown at 65 Pa CO2. There was a si gnificant pot size effect on photosynthesis and growth for line 85-1 ( high cytFBPase). This effect was greatest for Line 85-1 when grown at 35 Pa CO2, since these plants showed the greatest downward acclimation of photosynthesis when grown in small pots. There was a minimal pot s ize effect for line 84-9 (low cytFBPase), and this could be partly att ributed to the reduced CO2 sensitivity of this line. It is proposed th at the capacity for sucrose synthesis in C-3 plants is partly responsi ble for their wide variation in CO2 responsiveness.