Figure 9.

Proposed model of −Mg-triggered chlorophyll degradation and Mg remobilization. A, Simplified model. B, Detailed model. Mg depletion impairs the phloem export of Suc in the early stages of Mg deprivation. This leads to high accumulations of carbohydrates in source leaves, which inhibits photosynthetic CO₂ fixation. As a result, more photosynthetic electron transfer to O₂ occurs, which increases the generation of ROS. ROS levels, particularly H₂O₂, positively regulate OsSGR expression through chloroplast-to-nucleus signaling and thereby accelerate chlorophyll degradation to release Mg for remobilization. Thus, chlorophyll breakdown not only facilitates Mg remobilization but also slows down photosynthetic electron generation, protecting leaves from further photodamage.