Am J Bot (Review). Auxin activity: Past, present and future (2015)

Nice Open Access overview of auxin history and signaling, good for teaching.
Enders, T.A. and Strader, L.C. (2015). Auxin activity: Past, present, and future. American Journal of Botany. 102: 180-196.
“Long before its chemical identity was known, the phytohormone auxin was postulated to regulate plant growth. In the late 1800s, Sachs hypothesized that plant growth regulators, present in small amounts, move differentially throughout the plant to regulate growth. Concurrently, Charles Darwin and Francis Darwin were discovering that light and gravity were perceived by the tips of shoots and roots and that the stimulus was transmitted to other tissues, which underwent a growth response. These ideas were improved upon by Boysen-Jensen and Paál and were later developed into the Cholodny–Went hypothesis that tropisms were caused by the asymmetric distribution of a growth-promoting substance.”

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