How does the sunflower turn, following the suns path?
P.N.M. Raghavendran, Raichur, Karnataka ANSWER: The turning of sunflower bud towards the sun is termed solar tracking or heliotropism. There are other species of plants whose leaves or flower buds follow the sun’s path as well. This response is a result of the direction of sunlight. The leaves or flower buds usually follow with a lag of 12 degrees behind the sun’s azimuth. The actual movement is triggered by the enlargement or shrinking of motor cells in the pulvinus. Pulvinus is the bulged region at the junction of the leaf or flower to the stem. The motor cells enlarge or shrink by absorbing or losing water respectively. This process is regulated by the influx or efflux of potassium ions, which is in turn regulated by receptors that sense the direction of sunlight. The coordinated bulging or shirking of appropriate motor cells leads to change in direction of the flower bud or leaf. Solar tracking of leaves obviously will increase the amount of light harvested for photosynthesis. In t
