A spinach plants will not flower unless it is exposed to ten hours of darkness for two weeks. Therefore, spinach is considered a short-day plant. Phytochrome is activated by blue light. In North America, a plant that flowers in June of each year would be considered a short-day plant. Abscisic acid is a type of auxin.
Cytokinins are responsible for circadian rhythms.
Food distributors expose fruit to ethylene in order to retard spoilage.