Bulliform cells are responsible for

The correct option is Inward curling of leaves in monocots.

Explanation of Bulliform Cells and Their Function:
1. Definition and Location: Bulliform cells, also known as motor cells, are large, bubble-shaped, empty epidermal cells. They occur in groups, primarily on the adaxial (upper) surface of leaves in many monocot plants, such as grasses.
2. Role in Water Regulation: These cells play a critical role in regulating leaf movement based on water availability. When water is abundant, bulliform cells absorb moisture, become turgid (swollen), and cause the leaf blade to open and expand.
3. Response to Drought Stress: When the plant experiences water stress or dry weather, these cells lose water and become flaccid (limp). The loss of turgor pressure within the bulliform cells causes the leaves to roll or curl inward.
4. Significance: This inward curling reduces the surface area of the leaf exposed to sunlight and wind, which minimizes water loss through transpiration, helping the plant conserve water during dry periods.