The time course of acclimation to the stress of triose phosphate use limitation

Triose-phosphate utilization (TPU) limits the maximum rate at which plants can photosynthesize. However, TPU is almost never found to be limiting photosynthesis under ambient conditions for plants. This, along with previous results showing adaptability of TPU at low temperature, suggest that TPU capacity is regulated to be just above the photosynthetic rate achievable under the prevailing conditions. A set of experiments were performed to study the adaptability of TPU capacity when plants are acclimated to elevated CO2 concentrations. Plants held at 1500 ppm CO2 were initially TPU-limited. After 30 hours, they no longer exhibited TPU limitations, but they did not elevate their TPU capacity. Instead, the maximum rates of carboxylation and electron transport declined. A time course of regulatory responses was established. A step increase of CO2 first caused PSI to be oxidized, but after 40 s, both PSI and PSII had excess electrons as a result of acceptor-side limitations. Electron flow to...