1. Auxin Distribution:
* Auxin is a plant hormone that plays a crucial role in growth and development.
* When light shines on one side of a stem, auxin accumulates on the shaded side. This uneven distribution of auxin causes the cells on the shaded side to grow longer than the cells on the illuminated side.
* The elongation of cells on the shaded side causes the stem to bend towards the light source.
2. Light Receptors:
* Plant stems have photoreceptors that detect light.
* The most important photoreceptor involved in phototropism is phototropin.
* Phototropin absorbs blue light, which triggers a signal transduction pathway leading to auxin redistribution.
3. Other Factors:
* Gravity: While phototropism is the primary response, gravity also influences stem growth. This is called gravitropism.
* Internal factors: The internal state of the plant, including its age, nutritional status, and previous light exposure, can also influence phototropic responses.
In summary:
Plant stems exhibit a positive response to light due to the unequal distribution of auxin, triggered by light detection through photoreceptors like phototropin. This uneven growth leads to bending towards the light source, maximizing the plant's ability to capture sunlight for photosynthesis.
