ACCLIMATION OF TOMATO TO DIFFERENT CARBON-DIOXIDE CONCENTRATIONS - RELATIONSHIPS BETWEEN BIOCHEMISTRY AND GAS-EXCHANGE DURING LEAF DEVELOPMENT

Tomato plants were transferred to different CO2 mole fractions (350, 7 00, 1050 and 1400 mu mol CO2 mol(-1)) 31 d after sowing (2% of full ex pansion) and the light saturated rate of photosynthesis (P-max) of the unshaded 5th leaf was measured at either an ambient CO2 mole fraction , C-a of 350 mu mol CO2 mol(-1) [P-max (350)] or at the mole fraction of CO2 at which the plants were grown. At 60% and 95% leaf expansion, P-max of high CO2 grown plants measured at growth CO2, was greater tha n the P-max (350) of the ambient CO2 grown plants. However, by leaf ma turity, P-max (growth CO2) declined linearly as growth CO2 concentrati on increased. P-max (350) of plants exposed to elevated CO2 up to 60% leaf expansion had not acclimated to high CO2. At 95% leaf expansion, P-max (350) was smaller in the high CO2 grown plants. P-max (350) was predicted from Rubisco in vitro carboxylation capacity using tomato Ru bisco kinetic constants. By 95% leaf expansion, high CO2 grown plants showed similarities to the response of plants to low nitrogen supply, in terms of Rubisco and chlorophyll content. The observed and theoreti cal relationships between the initial slopes of the P-max/C-i response s and Rubisco activity were statistically equivalent. Both short-term and long-term effects of elevated CO2 on dark respiration (R(n)) were also investigated at two stages of leaf development (50 and 100% expan sion). R(a) (growth CO2) was smaller for the high CO2 grown plants com pared with the control plants, whereas R(n) (350) was either equal or greater for the plants grown in high CO2.