etiolation: a standalone construct

In plant physiology, etiolation is the developmental syndrome of a plant grown in darkness: the stem or hypocotyl elongates rapidly, leaves stay small and unexpanded, chlorophyll fails to form so the tissue is pale yellow, and a protective apical hook is retained, all tactics that help a buried seedling reach light before its reserves run out. Downs' 1955 study of dark-grown bean seedlings showed that even brief red light reverses this elongation, and that the reversal is itself undone by far-red light, an early demonstration of phytochrome control over the shift from dark to light growth. The referent is the dark-grown growth pattern, measured by elongation, pigmentation, and leaf expansion, which light converts into normal green (de-etiolated) development.[1]

Unit

The degree of stem elongation, chlorophyll loss, and suppressed leaf expansion under darkness

Recovery means

On exposure to light the seedling de-etiolates: elongation slows, the hook opens, leaves expand, and chlorophyll accumulates

Measured by

Measured by hypocotyl or stem length, chlorophyll content, and leaf expansion in dark-grown versus light-grown plants