The rate of dark CO2 efflux from mature wheat (Triium aestivum cv
Gabo) leaves at the end of the night is less than that found after a period
of photosynthesis. After photosynthesis, the dark CO2 efflux shows complex
dependence on time and temperature. For about 30 minutes after
darkening, CO2 efflux includes a large component which can be abolished
by transferring Muminated leaves to 3% 0 and 330 microbar CO2 before
darkening. After 30 minutes of darkness, a relatively steady rate of CO2
efflux was obtained. The temperature dependence of steady-state dark
CO2 efflux at the end of the night differs from that after a period of
photosynthesis. The higher rate of dark CO2 effiux followin photosynthesis
is correlated with accumulated net CO2 assimilation and with an
increase in several carbohydrate fractions in the leaf. It is also correlated
with an increase in the CO2 co_msation point in 21% 02, and an increase
in the light compensation point. The interactions between CO2 efflux from
carbohydrate oxidation and photorespiration are discussed. It is concluded
that the rate of CO2 efflux by respiration Is comparable in darkened and
illuminated wheat leaves