Abstract
Phytochromes (phys), which absorb red (R) and far-red (FR) light, are expressed in almost all the organs throughout the life cycle of plants. Hence, the light stimuli perceived in different parts of a plant should be properly integrated to trigger the ultimate response at the whole plant level. To fully understand this phenomenon, we treated Arabidopsis seedlings with micro-beam LED light. The seedlings were grown under day/night cycles and treated with a micro-beam FR pulse at the end of the day to induce hypocotyl elongation, which is one of the typical shade avoidance responses. Consequently, we demonstrated that phys in cotyledons almost exclusively regulated the hypocotyl elongation, indicating the inter-organ signaling from cotyledons to the stem. In addition, we found that Pr formation during the first 4 hr of the dark period efficiently promoted the elongation, whereas the actual elongation took place in a much later phase of the dark period. The RT-PCR analysis is now in progress to search for key genes underlying the above inter-organ communication.
