These three plant lines were also examined under elevated
CO2 conditions. In plants grown and assayed under high CO2
(1000 ppm), there is less stimulation of CO2 assimilation by low
O2, because photorespiration is suppressed by the high levels of
CO2. However, the trend of increased stimulation by low O2 was
the same as that observed under ambient CO2 conditions. TLUp1-9
showed greater O2 sensitivity than WT. In TL46 there was actually
reversed sensitivity to O2 as the rate of photosynthesis under 2% O2
was lower than at 21% (Fig. 3B) which has previously been observed
in this plant line and is characteristics of starch deficient genotypes
[12]. These results clearly show that increased capacity for starch
biosynthesis results not only in higher photosynthetic capacity but