Cholodny–Went model
In the 1920s, Cholodny and Went proposed a simple idea to explain plant bending. They said that directional growth—toward light in shoots and downward in roots—comes from an uneven distribution of a plant hormone called auxin.
How it works: Auxin is made at the tip of the growing shoot. When light or gravity changes, auxin moves to the shaded or lower side of the plant. In shoots, more auxin on the shaded side makes cells grow faster there, so the stem bends toward the light. In roots, more auxin on the lower side slows growth there, causing the root to bend downward.
The idea was supported by early experiments and became a foundational explanation for tropisms. Over time, some scientists questioned it, arguing that other hormones might be involved, that exact auxin gradients aren’t always clear, or that bending can occur without a strong gradient. Subsequent work in corn, tomato, maize, and Arabidopsis showed mixed results, with evidence for both auxin gradients and local auxin movement.
Today, auxin remains central to how plants respond to light and gravity, but researchers recognize a more complex picture. Other hormones, such as cytokinin and ethylene, also influence these responses, and tropisms may involve multiple signals and local movement rather than a single, global gradient. The Cholodny–Went model still provides a key starting point for understanding how plants steer their growth.
This page was last edited on 2 February 2026, at 14:26 (CET).