Plants adapt through chemical signals
The three key pigments in photosynthesis: chlorophyll a, chlorophyll b, and β-carotene, to absorb darker frequencies of light a plant may produce more pigments that absorb dimmer light and become darker or appear red.
Auxin hormones help plants detect light, however, auxins are toxic to plants in large concentrations; they are most toxic to dicots and less so to monocots.
Auxins are used to produce seedless fruit.
Synthetic auxin herbicides, including 2,4-D and 2,4,5-T, have been developed and used for weed control, 2,4-D is a synthetic auxin.
The defoliant Agent Orange, used extensively by British forces in the Malayan Emergency and American forces in the Vietnam War, was a mix of 2,4-D and 2,4,5-T. The compound 2,4-D is still in use and is thought to be safe, but 2,4,5-T was more or less banned by the U.S. Environmental Protection Agency in 1979. The dioxin TCDD is an unavoidable contaminant produced in the manufacture of 2,4,5-T. As a result of the integral dioxin contamination, 2,4,5-T has been implicated in leukemia, miscarriages, birth defects, liver damage, and other diseases.
Talking to Plants