Figure 10.

A model explaining the role of porphyrins in plant responses to drought. Both drought and porphyrins trigger the accumulation of ROS, which activates plant responses to drought stress, while suppressing porphyrin levels. ROS initiate signaling cascades that stimulate gene activation. The possible association of drought responses with the SA signaling pathway is shown with dotted arrows, and the negative influence on porphyrin and ROS accumulation is shown with T-bars. The drought-mediated suppression of porphyrin biosynthetic pathway transcripts and intermediates is proposed as a mechanism leading to reduced damage during dehydration. Unbound hemes are used to supplement the level of ROS scavengers inside and outside of the plastids.