Think about this: plants see you.
In fact, plants monitor their visible environment all the time. Plants see if you come near them; they know when you stand over them. They even know if you’re wearing a blue or a red shirt. They know if you’ve painted your house or if you’ve moved their pots from one side of the living room to the other.
Of course plants don’t ‘see’ in pictures as you or I do. Plants can’t discern between a slightly balding middleaged man with glasses and a smiling little girl with brown curls. But they do see light in many ways and colours that we can only imagine. Plants see the same ultraviolet light that gives us sunburn and infrared light that heats us up.
Plants can tell when there’s very little light, like from a candle, or when it’s the middle of the day, or when the sun is about to set into the horizon. Plants know if the light is coming from the left, the right, or from above. They know if another plant has grown over them, blocking their light. And they know how long the lights have been on.
So, can this be considered ‘plant vision’? [.]
In nature, the last light any plant sees at the end of the day is far- red, and this signifi es to the plant that it should ‘turn off’. In the morning, it sees red light and it wakes up. In this way a plant measures how long ago it last saw red light and adjusts its growth accordingly. Exactly which part of the plant sees the red and far-red light to regulate flowering?
We know from Darwin’s studies of phototropism that the ‘eye’ of a plant is in its tip while the response to the light occurs in the stem. So we might conclude, then, that the ‘eye’ for photoperiodism is also in the tip of the plant.
Surprisingly, this isn’t the case. If in the middle of the night you shine a beam of light on different parts of the plant, you discover that it’s suffi cient to illuminate any single leaf in order to regulate flowering in the entire plant. On the other hand, if all the leaves are pruned, leaving only the stem and the apex, the plant is blind to any fl ashes of light, even if the entire plant is illuminated.
If the phytochrome in a single leaf sees red light in the middle of the night, it’s as if the entire plant were illuminated. Phytochrome in the leaves receives the light cues and initiates a mobile signal that propagates throughout the plant and induces fl owering.
What a Plant Knows
A FIELD GUIDE TO THE
SENSES OF YOUR GARDEN
– AND BEYOND [.]