Abstract
During photomorphogenesis, chloroplasts are differentiated with concomitant activation of chlorophyll biosynthesis. Previously, we showed that in Arabidopsis roots, the chlorophyll biosynthesis, as well as the chloroplast differentiation is positively and negatively regulated by cytokinin and auxin, respectively, showing that these phytohormones are involved in the coordinated control of chlorophyll biosynthesis via transcriptional regulation. Here, we analyzed the effects of these phytohormones on chlorophyll biosynthesis during photomorphogenesis in Arabidopsis etiolated seedlings. Mutant analyses revealed that during photomorphogenesis, chlorophyll accumulation in cotyledons increased in auxin-signaling mutants axr2, shy2 and slr, while decreased in a cytokinin receptor mutant ahk2ahk3 when compared with wild-type. Since these phytohormones also regulate photomorphogenic changes such as hypocotyl elongation, it is likely that auxin and cytokinin oppositely affect the regulation of chlorophyll biosynthesis in aerial tissues, which is highly correlated to the tissue development and the cell specificity.
