In plants rhythmic changes of various environmental cues such as light or temperature are anticipated and synchronized with biochemical processes through the intrinsic timing mechanisms of circadian clocks (1). In this study, we employ polysome analysis to explore the changes in global translation levels during both diel (light/dark) and circadian (light/light) cycles in 14-day-old Arabidopsis thaliana seedlings. We detected gradual changes in the global translational level over the diel cycle. Polysome loading was upregulated during the day and was downregulated during the night. Furthermore, our data also revealed gradual changes in the global translation level over the circadian cycle. We found that polysome loading increased and decreased in the ‘subjective’ day and night phases, respectively. Thus, our data suggest that the global translation level might be governed by the circadian clock. We next plan to directly monitor diel and circadian dynamics of protein synthesis rates by puromycin labeling. During our study, we also identified novel regulatory elements (upstream open reading frames (uORFs)) that are potentially involved in the translational regulation of circadian and daily rhythms. Using site-directed mutagenesis, luciferase reporter assay system and transient transformation in Arabidopsis thaliana we further aim to verify functions of predicted regulatory elements and, therefore, shed more light on the translational regulation of circadian and daily rhythms.