Heliotropism
Under heliotropism (of give a wiki. Ἥλιος hélios "sun" and τροπή Trope "twist" to German "turning to the sun") is the property of plants and animals , growth and movement of the sun align. In contrast to this, phototropism describes the property of growing in the direction of the light .
Under negative heliotropism refers to the movement of the plant / the animal away from the light.
Heliotropism in plants
Heliotropic plants track the movement of the sun from east to west . It can be the movement of flowers or leaves, or both. During the night the plants can take a random course, while at dawn they reorient themselves to the east, where the sun rises. This behavior shows, for example, the alpine buttercup species Ranunculus adoneus and the still unopened flowers of the sunflower ( Helianthus annuus ).
The movement is carried out by motor cells in a flexible segment called the pulvinus , which is just below the flower or leaf. The motor cells specialize in pumping potassium ions into nearby tissues, which changes the wall pressure of the cells . The segment bends because the motor cells on the shadow side become longer due to an increase in the turgor. Heliotropism responds to blue light. If a heliotropic species is provided with a red cover at night that blocks blue light, the plant will not face the sun the next morning. However, when covered with a blue translucent material, it follows the sun.
An important difference to phototropism is the reversibility of heliotropism, since the elongated motor cells can return to their original size at night.
The orientation of leaves to the sun is called leaf heliotropism. A vertical alignment to the sun is called diaheliotropism and a more or less parallel alignment is called paraheliotropism. In some plants, the diaheliotropic orientation can change into a paraheliotropic orientation at unfavorable times (e.g. in drought, high temperatures; usually around noon).
Flower heliotropism does not necessarily occur in the same plants as leaf heliotropism.
literature
- Hans Lambers, F. Stuart Chapin, Francis Stuart Chapin (III.), Thijs L. Pons: Plant Physiological Ecology . Springer, 2008, ISBN 978-0-387-78340-6 , doi : 10.1007 / 978-0-387-78341-3 ( [1] ).
- Donat-Peter Häder, Michael Lebert: Photomovement (= Comprehensive Series in Photosciences . Volume 1). Elsevier Science BV, 2001, ISBN 0-444-50706-X , ISSN 1568-461X ( [2] ).