Morphology and Photosynthetic Efficiency of Tobacco Leaves That Received End-of-Day Red and Far Red Light during Development.

Shaded leaves in plant canopies receive a higher proportion of far red relative to red light than is received by unshaded leaves. Brief end-of-day irradiations with red or far red light, acting through the phytochrome system, reversibly control morphological development of tobacco plants. Leaves that received far red light for 5 minutes at the end of each day during development were longer and narrower than those that received end-of-day red light. The far red treated leaves weighed less, had fewer stomata, and had less chlorophyll per unit area of leaf. Net CO(2) assimilation rates did not differ significantly between red- and far red-treated leaves on an area basis; however, the far red-treated leaves assimilated significantly more CO(2) on a leaf weight basis.