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Hyponastic ResponseThe hyponastic response is an upward bending of leaves or other plant parts, resulting from growth of the lower side. This can be observed in many terrestial plants and is thought to be linked to the plant hormone ethylene. Submerged plants often show the hyponastic reponse, where the upward bending of the leaves and the stretching of the petioles might help the plant to restore normal gas exchange with the atmosphere. Plants produce ethylene, and normally this disolves in the air quite easily. But when the plant is submerged ethylene is trapped in the plant. Plants that are exposed to elevated ethylene levels in experimental set-ups also show the hyponstic response.
2003, Utrecht University, NL Image shows a typical example of the hyponastic growth of a submerged Rumex palustris plant. After 6 hours (plant marked B) of submergence the leaves showed a more upright position compared with the start of submergence.
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