Table IV. Comparison of the rates of protein synthesis and degradation in Col-0 and the starchless pgm mutant

Col-0 was grown for 21 d in an 8-h photoperiod. pgm was sown out 7 d earlier than Col-0 and initially grown in a 12-h photoperiod to allow the acquisition of biomass, before transfer to an 8-h photoperiod 3 d before the start of the pulse. Both genotypes were pulsed with 13CO2 for 24 h, followed by a 4-d chase. Plants were harvested at dawn before the start of the pulse, at dusk, 4 h into the night, at dawn at the end of the pulse, and at dawn after a 4-d chase. The experiment was repeated three times with separately grown batches of plants; in each experiment, one sample of five plants was harvested at each time point. Rates of synthesis were estimated for two time intervals in the night: between dusk and 4 h of darkness (T8–T12) and between 4 h of darkness and the end of the night (T12–T24). The data are provided in Supplemental Data Set S5, calculated enrichments in Supplemental Table S4, and plots of changes in the enrichment of selected amino acids in Figure 4. The rate of protein synthesis was calculated by correcting enrichment in Ala in protein by the enrichment in free Ala at dusk. Results are estimated from the average of three biological replicates.

PlantRGRProtein SynthesisProtein DegradationHalf-Life
Average per 24-h CycleLight (T0–T8) per HourDark (T8–T12) per HourDark (T12–T24) per HourPulseChasePulseChase
mg mg−1 d−1% total protein d−1d
Col-00.22125.292.110.680.73.184.843.382.48
pgm0.13718.021.810.540.294.336.092.672.17
Ratio pgm:Col-00.620.710.860.80.421.361.26