Etiolated Plant

a plant that has been raised in insufficient light, even total darkness.

Etiolated plants have a white or yellowish coloration that is due to the absence of chlorophyll, the green plant pigment. The stem becomes greatly elongated, and there is poor development of leaves, mechanical tissue, and stomata. The tissue of etiolated sprouts contains large quantities of hormones, especially auxins, which encourage cell elongation. If etiolated plants are given adequate light, they turn green rapidly.

Usually etiolation is avoided through the action of phytochrome, which absorbs light. Phytochrome activates photomorphogenesis (inhibiting cell elongation), the opening of the sectionally constructed first leaf, and the formation of conducting bundles. In tissue that is turning green there is active synthesis of chlorophyll, water-soluble pigments (flavonoids, anthocyanins), and growth inhibitors.

In nature, etiolation is frequently expedient. With inadequate lighting resulting from accelerated growth, shoots grow rapidly in the direction of light or, sometimes, horizontally underground (rhizomes, stolons). Long, weak stems and other features of etiolation characterize most lianas in tropical rain forests, where the dense crowns of trees create the conditions for etiolation. Some scientists believe that the climbing form of plant life developed as a result of etiolation: in an attempt to reach the light, the plants developed a weak stem that needed support.

The etiolated organs of many vegetable plants are used as food, for example, the internal leaves of cabbage, the bulbs of many bulbous plants, and the underground shoots of asparagus.