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 elevated CO2 levels. To investigate the role of photosynthetic feedback in this phenomenon, photosynthetic parameters and growth were measured for lines of Flaveria linearis with low, intermediate or high cytosolic fructose-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 plants with low cytFBPase activity were less responsive to elevated CO2, and these plants had a reduced maximum potential for photosynthesis and growth. Plants with intermediate cytFBPase activity also showed a lower relative growth enhancement when grown at 65 Pa CO2. There was a significant 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 size effect for line 84-9 (low cytFBPase), and this could be partly attributed to the reduced CO2 sensitivity of this line. It is proposed that the capacity for sucrose synthesis in C-3 plants is partly responsible for their wide variation in CO2 responsiveness.