Question

Name the chemical wch helps the pollen grain exbiting chemotropism during its movement towards the ovary.

Answer 1

The stigma of the pistil secretes some sugary exudates which retain pollen falling on the stigma. As the pollen grain falls on the stigma, secretions of stigma lyse the exine of the pollen and initiate the growth of pollen tube.
*Pollen tube grows under the influence of PME ( Pectin methylesterases).
*Pollen tube also exhibits chemotactic movement under the influence of  calcium concentration gradient. 
*Unfertilised ovules secrete some substances to direct the entry of pollen into the ovule. After entering the ovule, some cells of the integument dissolve themselves and form a mucilaginous substance which make the movement of the pollen tube easier inside the ovule. 

Answer 2

Answer:

Chemical is PME. The growth of a plant part due to chemical stimulus is known as chemotropism or Chemotropism is the movement of a part of the plant in response to a chemical stimulus. The growth of pollen tube towards the ovule induced by a sugary substance as stimulus. This is an example of positive chemotropism.