Question

What are bulliform cells? What are their functions?

Answer 1

Hint: The first mention of bulliform cells was in a revised and expanded version of botanist Eugenius Warming's Planet Samfund (Oncology of Plants) written for an English audience in 1909. One of the things he looked into was the phenomenon of leaf rolling in the Poaceae and Cyperaceae families, and how he discovered the bulliform cells, which he called "hinge-cells," on the epidermal layer of the leaf tissue, but deeper than the epidermal cells themselves and capable of folding distortion along with the leaf.

Complete answer:
Bulliform cells, also known as motor cells, are large, bubble-shaped epidermal cells found on the upper surface of leaves in groups of several monocots. These cells are found on the adaxial (upper) leaf surface. They are typically found near the midvein portion of the leaf and are large, white, and colorless.

During water stress, bulliform cells in the upper epidermis of monocot leaves cause the leaves to curl. When there is plenty of water, the water and bulge are absorbed; when there isn't enough water, the leaf curls, which helps to reduce water loss due to evaporation.

Folded leaves receive less sunlight, so they are heated less, reducing evaporation and conserving the plant's remaining water. Bulliform cells can be found on the leaves of a wide range of monocotyledon families, but are most commonly associated with grasses.

Note: The mesophyll is a layer of chlorophyll-containing parenchymatous cells found between the leaf's epidermal layers. In monocot leaves, the vascular bundles are collateral and closed, and each one is surrounded by a bundle sheath, which is a layer of thin-walled parenchymatous cells.