Reversal of etiolation effect by light is called

The correct option is Photomorphogenesis.

To understand why this is the correct answer, let us break down the botanical concepts step-by-step:

1. What is Etiolation?
When plants are grown in complete darkness or under extremely low light conditions, they exhibit a developmental pattern called etiolation. Etiolated plants typically show characteristics such as long, weak stems (due to rapid elongation), small and undeveloped leaves, a pale yellow color due to the absence of chlorophyll, and lack of structural support.

2. Reversal of Etiolation (De-etiolation)
When an etiolated plant is exposed to light, it undergoes a dramatic transition to normal, healthy growth. This reversal process is also known as de-etiolation or greening. The stem elongation rate slows down, leaves expand, chloroplasts develop, and chlorophyll synthesis begins, turning the plant green.

3. The Role of Photomorphogenesis
The term photomorphogenesis refers to the growth and development of plants directly controlled by light (where light acts as a developmental signal rather than just an energy source for photosynthesis). The transition from etiolated growth (skotomorphogenesis) to green, healthy vegetative growth (photomorphogenesis) is triggered by light photoreceptors (such as phytochromes and cryptochromes). Therefore, the light-induced reversal of the etiolation effect is a classic example of photomorphogenesis.

4. Analysis of Other Options:
• Red-far red light interaction: This refers to the mechanism by which phytochrome photoreceptors switch between active and inactive forms in response to different wavelengths, which acts as the trigger but is not the name of the developmental response itself.
• Anisotropic wall expansion: This is a biophysical process where cell walls expand preferentially in one direction, determining cell shape, but is not the specific term for light-induced etiolation reversal.
• Richmond Lang effect: This is the delay of senescence (aging/leaf yellowing) in detached leaves by cytokinins, which is unrelated to light reversal of etiolation.