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Evidently due to the process of photosynthesis, plants are able to "sense" light (as demonstrated by the phototropic response). My question is, how quickly are plants able to perceive changes in light intensity?

I.e. if there is a strong light shining on a plant, and at t=0 the light is switched off, is there some delay τd before the plant exhibits a response to the change in light intensity?

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  • $\begingroup$ Hi, welcome to StackExchange Biology. While this is an interesting question, it could benefit from a look at these points: 1. 'Evidently due to the process of photosynthesis, plants are able to "sense" light (as demonstrated by the phototropic response)' This statement needs modification as photosynthesis and phototropism are very different processes. (Though one could argue that phototropism evolved to increase the efficiency of photosynthesis.) 2. It would also be nice to include (in the question body) efforts you made to answer the question: what books/sites you read, what you found out. $\endgroup$
    – Adhish
    Jul 4 '20 at 3:47
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    $\begingroup$ Hi. As a preface let me apologize for my lack of clarity / background knowledge. Biology is not my field of study, but I have been curious about this question for a while. To address your concerns: 1) By this I mainly meant to indicate that plants evidently do have some pathway for sensing the intensity of light. Phototropism is evidence of this, as it shows that plants have some "awareness" of the location of a light source. 2) I have searched for research relating to the response times of photoreceptors in plants, but have only been able to find information such as absorption patterns. $\endgroup$ Jul 4 '20 at 4:04
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    $\begingroup$ I should add that some of my confusion comes from not understand the difference between animal and plant photoreceptors. If they are very similar, then it could be inferred that a plant's response time would be very similar to that of a human. However, I imagine there is very little evolutionary advantage for plants to have a fast response time to changes in light when compared to animals. $\endgroup$ Jul 4 '20 at 4:21
  • $\begingroup$ Thanks for the clarification. Please edit your question body and incorporate your comments into it (in a concise manner). This will improve your question and increase the chances of getting a useful answer. $\endgroup$
    – Adhish
    Jul 4 '20 at 5:55
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The delay for UVR8 photoactivation seems to be in the range of picoseconds depending on the wavelength:

Global analysis in terms of a model of parallel decaying components indicated four lifetimes of 14.7 ps, 370 ps, 1.9 ns, and 5.9 ns.

Time resolved fluorescence of the UVR8 dimer. (A)

The photodynamics of the Trp ensemble in UVR8 can be summarized as illustrated in Figure 5B. We observe excited state decay in the few-hundred- picoseconds to nanoseconds time domain to the triplet intermediate U460.

Tentative photocycle of UVR8
photoactivation as observed in vitro.

For a better understanding of photoactivation mechanism times, you can read the following article:

Proton-Coupled Electron Transfer Constitutes the Photoactivation Mechanism of the Plant Photoreceptor UVR8 Journal of the American Chemical Society 137(25) · May 2015

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