Abstract
In plants grown in a low R/FR ratio, rapid stem and petiole elongation, which enables the plant to receive enough sunlight, is observed. This response is referred to as the shade avoidance response. The end-of-day FR (EOD-FR) treatment also causes similar responses. In addition to the growth response, rapid induction of genes such as AtHB2 and HFR1 is observed. Many auxin-inducible genes are also up-regulated. However, it remains unknown how different parts of the plant communicate in the process of those responses. In the present study, we irradiated petiole and blade separately with FR in Arabidopsis to locate the photo-perceptive site for the response. The results clearly demonstrated that phyB in blades almost exclusively regulated both the elongation and gene expression responses in petioles. Hence, a signal appears to be transduced from the blade to petiole after the light perception. Similar experiments are now in progress for seedlings.
