Gibberellins primarily promote:

Gibberellins are a class of plant hormones (phytohormones) that play a critical role in regulating various developmental processes. Their primary and most well-known function is promoting **stem elongation** by stimulating both cell division and cell elongation between the nodes (internodal growth). ### Breaking down the options: 1. **Stem elongation:** Gibberellins ($GA$) trigger the expression of genes that loosen cell walls, allowing the stem to stretch. This is famously seen in 'bolting' (rapid stem growth) in rosette plants. 2. **Leaf fall (Abscission):** This is primarily controlled by **Ethylene** and **Abscisic Acid ($ABA$)**. 3. **Cell death (Senescence):** This is associated with **Ethylene** and sometimes nutrient stress, whereas Gibberellins usually delay senescence in some tissues. 4. **Stomatal closure:** This is the hallmark function of **Abscisic Acid ($ABA$)**, which acts as a stress hormone during drought. Therefore, the primary function of gibberellins is promoting stem growth.