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Phototropic solar tracking in sunflower plants: an integrative perspective
Ulrich Kutschera1, Winslow R Briggs2
1Department of Plant Biology, Carnegie Institution for Science, Stanford, CA 94305, USA kut@uni-kassel.de.
Annals of Botany
|October 1, 2015
Summary
Sunflower solar tracking movements in growing plants are driven by shade avoidance, not solely photosynthesis optimization. This behavior maximizes light capture in competitive environments.
Area of Science:
- Plant biology
- Plant physiology
- Phototropism
Background:
- Phototropic solar tracking in sunflower (Helianthus annuus) is a well-known but not fully understood plant movement.
- Debate exists on whether its adaptive significance is solely for photosynthesis optimization or if shade avoidance plays a role.
Purpose of the Study:
- To investigate the adaptive significance of phototropic solar tracking in sunflower.
- To determine the roles of photosynthesis optimization and shade avoidance in this behavior.
Main Methods:
- Documented diurnal East-West oscillations of growing sunflower stems and leaves in relation to the sun's position.
- Measured photon fluence rates and CO2 assimilation on upper leaves under various light conditions.
- Summarized evidence for shade-avoidance responses in growing sunflower plants.
Main Results:
- Phototropic solar tracking is performed only by elongating, vegetative sunflower shoots and upper leaves.
- Photon fluence response and CO2 assimilation data challenge the 'photosynthesis-optimization hypothesis' as the sole driver.
- Evidence suggests shade avoidance significantly contributes to solar tracking.
Conclusions:
- Shade avoidance, maximizing light-driven CO2 assimilation, is a major factor in sunflower solar tracking, especially in competitive settings.
- An integrative scheme for these growth movements in sunflowers is proposed.
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