Photoperiodism is regulated by which of the following substances? Naim 08:29 AP Biology Photoperiodism is regulated by which of the following substances? A. Anthocyanin B. Chlorophyll C. Gibberellins D. Phytochrome E. Xanthophyll Answer: D. Phytochrome Learn More : Share this Share on FacebookTweet on TwitterPlus on Google+