Phytochromes are light receptors in plants that absorb mainly red light and regulates plant response to light such as flowering. Describe the physiological mechanism in long-day and short-day plants that could induce flowering. In your opinion, how root cells able to respond to light?
Short-day plants form flowers only when day length is less than about 12 hours. If these are exposed to more than 12 hours of light per day, bloom formation does not occur. Other plants require only a short night to flower. These are termed "long day" plants.
Darwin (1879) has discovered negative phototropism of plant roots. This directional growth response to incoming light is called phototropism. Positive phototropism, observed in shoots, is growth toward a light source; whereas negative phototropism, seen in roots, is bending away from the light source.