抄録
The xanthophyll cycle is known to play a key photoprotective role in plants. While it has been demonstrated that the pool size of xanthophyll cycle pigments (VAZ) increases during acclimation to high light (HL) intensity, the associated regulatory mechanism remains largely unknown. Since the redox state of Plastoquinone (PQ) is thought to influence the expression of photosynthesis-related genes, we addressed the possibility that the redox state of PQ affects the regulation of carotenoid synthesis. To do this, we used a photoautotrophic cell culture of Arabidopsis, that can grow stably in sugar-free medium, and regulated the redox state by adding the electron transport inhibitors, DCMU or 2,5-dibromo-3-methyl-6-isopropyl benzoquinone (DBMIB) to the cells. We then analyzed their effects on VAZ accumulation and the expression of genes encoding carotenoid biosynthesis enzymes. The VAZ pool size and the transcript levels of β-carotene hydroxylase genes (Chy1, Chy2, CYP97A3 [Lut5]) were higher under HL than under normal conditions; however, DCMU treatment partially blocked these effects. In contrast, DBMIB treatment increased VAZ accumulation and transcription of these genes without HL irradiation to a certain extent. Based on these results, we propose that the redox state of PQ is one of the regulator of the pool size of VAZ. The expression of LcyB encoding lycopene β-cyclase was also clearly up-regulated by HL, but not affected by PQ redox. In addition, using mutants of the β-carotene hydroxylase genes, we identified Chy1 as the gene that contributed most to the increase in VAZ pool size by HL.
