This is the photo of the mint plant that I took during the hailstorm a few weeks ago. Have I "psychologically" damaged my poor little plant by using the flash?
Some species of plants use the length of the dark period [i.e. night] to sense the photoperiod, and hence, the proper season to flower, be it spring or fall. Not so much in highly seasonal places, though, where obviously temperature is a better cue.
In a phenomenon summarized by Bernier et al, (in The Physiology of Flowering) a short flash of red light (same effect as white light) during the night was sufficient to "confuse" the plants [read delayed or interfered with flowering]. Using a far-red light after this was sufficient to "undo" the effect.
Does this mean that we mess plants up with our houselights, headlights, flashlights, etc? I guess it would depend on the species, and the location of the plants involved... and it would have to happen over and over again. It would be like telling the plant "no wait it's still summer... no reason to flower and set fruit!"
Intricacies aside, basically, this effect is mediated by a light receiver called phytochrome, which has two forms, absorbing red and far-red respectively, and uses differences in absorption between the two as a signal for various things in the plant (including whether an obstacle is a plant or an opaque object such as a giant rock, how deep a seed is buried under leaf litter, etc.). Incredible!
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