Internodal elongation is the process by which the stem of a plant grows in length between the nodes. It is an essential process for plant growth and development. Among the various plant hormones, gibberellin is primarily responsible for stimulating internodal elongation.

Gibberellins are a group of plant hormones that regulate various aspects of plant growth and development, including stem elongation. They are synthesized in the shoot apex, young leaves, and developing seeds. Gibberellins promote internodal elongation by affecting cell division, cell expansion, and cell wall loosening in the stem.

Gibberellins and Cell Division:
Gibberellins stimulate cell division in the cambium, which is the region of actively dividing cells in the stem. This leads to an increase in the number of cells, resulting in the elongation of the stem.

Gibberellins and Cell Expansion:
Gibberellins also promote cell expansion, which is the process by which cells increase in size. They stimulate the synthesis of enzymes that break down the cell wall components, allowing the cells to expand. This leads to the elongation of the stem.

Gibberellins and Cell Wall Loosening:
Gibberellins induce the synthesis of enzymes called expansins, which are responsible for loosening the cell wall. Expansins break the bonds between cellulose fibers in the cell wall, allowing the cells to expand and elongate.

In addition to gibberellins, other plant hormones such as auxin, cytokinin, and ABA also play a role in stem elongation. However, among these hormones, gibberellin is the primary regulator of internodal elongation.

Conclusion:
In conclusion, internodal elongation is stimulated by gibberellin, a plant hormone that promotes cell division, cell expansion, and cell wall loosening in the stem. Gibberellins are synthesized in specific regions of the plant and regulate various aspects of plant growth and development. While other hormones also play a role in stem elongation, gibberellin is the key hormone responsible for stimulating internodal elongation.