Figure 9.

Working model depicting how light perception at the apex initiates an auxin- and redox-dependent systemic signaling pathway leading to enhanced rates of photosynthetic induction in distal leaves. In this model, R light perceived by phyB and FR light perceived by phyA function antagonistically to regulate IAA biosynthesis. As a result of light perception-driven PAT, IAA triggers systemic H₂O₂ production in distal leaves, which is able to accelerate CEF around PSI, leading to increased ATP production. In this way, light perception by the apex can enhance photosynthetic CO₂ assimilation and the resultant carbon gain in distal leaves.