The effects of supplementary ultraviolet-B (UV-B) radiation on the changes in synthesis and degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and light-harvesting chlorophyll a/b binding protein of PSII (LHCII) were examined, as well as mRNA levels for small and large subunits of Rubisco (rbcS and rbcL, respectively) and LHCII (cab) with leaf age in UV-sensitive rice (Norin 1) and UV-resistant rice (Sasanishiki). Both Rubisco and LHCII were actively synthesized until the leaf had fully expanded, and then decreased with increasing leaf age. Synthesis of Rubisco, but not LHCII, was significantly suppressed by UV-B in Norin 1. The degradation of Rubisco was enhanced by UV-B around the time of leaf maturation in the two cultivars. The levels of rbcS and rbcL were reduced by UV-B at the early stages after leaf emergence in both cultivars. Cab transcripts were first present at high levels in the two cultivars, but drastically decreased due to UV-B treatment immediately after leaf emergence in Norin 1. It was shown that synthesis and degradation of Rubisco and LHCII greatly changed with leaf age: Rubisco synthesis was significantly suppressed by supplementary UV-B radiation at the transcription step during the early leaf stages. It was also suggested that the difference in UV-B sensitivity in Rubisco synthesis between the two rice cultivars might be due to specific suppression both transcriptionally and post-transcriptionally.
- Leaf age
- Light-harvesting chlorophyll a/b binding protein of PSII
- Oryza sativa L.
- Protein synthesis and degradation
- Ribulose-1,5-bisphosphate carboxylase/oxigenase
- Transcription regulation
- Ultraviolet-B radiation