Notes on shade avoidance in plants
Phytochromes.
Pr: 650-670 nm; Pfr: 705-740 nm.
Activated (Pr to Pfr) by:
1) Absorption of red light
Deactivated (Pfr to Pr) by:
1) Absorption of far-red light
2) Some nono-photoinduced reaction, slowly (Li et al., 2011)
3) Warmer temperatures (Halliday & Davis, 2016)
Shade avoidance syndrome (SAS)
Includes:
1) Upward bending of leaf petiole (the branch connecting leaf to stem (leaf hyponasty)
2) Stem (internode) elongation
Detection of neighboring foliage
Includes:
1) Physical touching of leaf tips
2) Volatile chemicals
3) Variation in light quality
These include:
A) High in green and far-red
B) Low in blue and red
C) In other words, low (R:FR) and (B:G) ratio
Horizontally propagated FR light from nearing plants lowers R:FR
Actual shading lowers it further
(But note that the former acts by increasing FR but no change to R. This might be important)
Also:
a) B:G ratio decreases
b) UV-B levels depleted
c) R/FR, blue, and UV-B photoreceptors converge on shared signaling network (what?) to control shade avoidance.