ADP, AMP and Pi interactions with a (Na++ K++ Mg2+)-dependent ATPase in sugar beet roots

Continuous measurements of CO₂-release from intact roots of Lolium multiflorum growing in nutrient solution were carried out during 3–7 weeks. Periods of days with high level of irradiance and periods with low level alternated. Root respiration rate was found to depend on photosynthesis. The change in root respiration, induced by change in photosynthesis, was delayed. The root respiration rate showed diurnal fluctuations with two characteristic peaks occurring 4–6 and 14–16 hours after onset of the photoperiod. The amplitudes increased with increasing photosynthesis. The frequencies were independent of the length of photoperiod, when this varied between 8 and 16 hours. The fluctuations are discussed in relation to diurnal fluctuations in protein synthesis.