5. Other Growth Regulators and Seasonal Responses

Fall colors

Some tree leaves are noted for their spectacular fall color display. The changing fall colors are caused primarily by a photoperiodic response but also by a temperature response. As nights become longer in the fall, leaves stop producing chlorophyll. As the chlorophyll chemically degrades, it is not replaced. Other leaf pigments, the carotenoids, become visible and the green/orange splotches become more visible as the green chlorophyll turns orange. Carotenoids include the orange carotenes and the yellow xanthophylls. Anthocyanins produce the deep red and purplish-red colors in the fall display.

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