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Updated: Jun 19, 2026

Observation of Photobehavior in Chlamydomonas reinhardtii
Published on: May 6, 2022
ON "REVERSAL" OF PHOTOTROPISM IN PHYCOMYCES.
1Laboratory of General Physiology, Harvard University, Cambridge.
High light intensity does not reverse Phycomyces sporangiophore phototropism when infrared radiation is excluded. Instead, equal light on both sides causes indifference, while heat causes negative thermotropic bending.
Area of Science:
- Plant biology
- Photobiology
- Mycology
Background:
- Phototropism is a key growth response in plants and fungi.
- High light intensities have been anecdotally reported to reverse phototropism in Phycomyces.
- Understanding light responses is crucial for plant development studies.
Purpose of the Study:
- To investigate the effect of high light intensity on Phycomyces sporangiophore phototropism.
- To determine the role of infrared radiation in light-induced responses.
- To clarify the mechanisms underlying phototropic behavior under varying light conditions.
Main Methods:
- Controlled light exposure experiments on Phycomyces sporangiophores.
- Exclusion and inclusion of infrared radiation during high-intensity light treatments.
- Observation and measurement of sporangiophore bending responses.
Main Results:
- Reversal of phototropism was not observed when infrared radiation was excluded.
- High light intensities resulted in phototropic indifference due to balanced light stimulation.
- Unscreened heat radiation induced a distinct negative thermotropic bending.
Conclusions:
- The alleged reversal of phototropism by high light is an artifact of heat radiation.
- Proper exclusion of infrared radiation is essential for accurate phototropism studies.
- Phycomyces exhibits complex responses to light and heat, necessitating careful experimental design.
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