Most plants are neither extreme shade avoiders or tolerators, but possess a combination of the two strategies; this helps adapt them to their environment.
If PR is present above a species-specific threshold, shade avoidance signal transduction pathways will be activated.
In the model organism Arabidopsis thaliana, the shade avoidance response varies at different points in the life cycle.
Water-imbibed seeds display hypocotyl elongation; if the shade were caused by excessive soil depth, this would help the seedling grow vertically very quickly and push up and out of the ground.
[4] Studies using Brassica rapa indicate that the light quality and ratio available to seedlings is sensed in the cotyledons, which upregulates the production of auxin.
Arabidopsis was used to demonstrate PIF (Phytochrome Interacting Factor) involvement in auxin production.
[6] Where the auxin lay, the plant grows on that side which causes it to bend in the opposite direction.
Shaded adults have elongated petioles at the rosette, smaller leaf blades, and suppressed axillary bud growth.
The leaves can also bend upwards towards potential light sources as a result of higher growth on the underside of the petiole than the top, a process called hyponasty.
Plants may flower early, as it is unlikely that growing more structures will result in profitable nutrient gain in the short term.