Figure 6.

Steady-state levels of protoporphyrinogen IX oxidase transcripts under diurnal and circadian growth conditions. Tobacco plants were grown for 4 weeks in a 12-h/12-h light/dark cycle. Plants were harvested every 4 h starting 1 h after the onset of the light phase. Another set of plants was subsequently transferred to continuous light or darkness for 48 h. Leaf material was collected for the same 4-h time intervals. Total RNA was isolated and used for Northern blot analysis as described in the legend of Fig. 5.