Movements of sunflower and shade avoidance (Viewpoint)

The shade avoidance response, which may optimize CO2-assimilation, appears to be the ‘driving force’ behind these conspicuous plant movements.

One of the best-known plant movements, phototropic solar tracking in sunflower (Helianthus annuus), has not yet been fully characterized. Two questions are still a matter of debate.

  1. Is the adaptive significance solely an optimization of photosynthesis via the exposure of the leaves to the sun?
  2. Is shade avoidance involved in this process?
Sunflower
Photo: Kate Ter Haar / Flickr.

Kutschera and Briggs examine reports from the literature together with observations from 10-week-old sunflower plants made on rainy, cloudy and clear days in California and find that movements occur only under open-sky conditions, and they are confined to the upper third of the stem and cease at anthesis, leaving the sunflower heads facing east. Based on photon-fluence and photosynthesis measurements on the upper leaves, and published data, they conclude that, in populations of competing sunflower plants, the shade avoidance response, which may optimize CO2-assimilation, appears to be the ‘driving force’ behind these conspicuous plant movements.

Reference List

Kutschera, U., & Briggs, W. R. (2015). Phototropic solar tracking in sunflower plants: an integrative perspective. Annals of Botany, 117(1), 1–8. https://doi.org/10.1093/aob/mcv141