Polling for the crucial bypoll to Dr Radhakrishnan Nagar constituency, from where Tamil Nadu Chief Minister and AIADMK supremo Jayalalithaa is seeking re-election, began today at 8 AM amid tight security. Twenty eight candidates, including social activist "Traffic" Ramaswamy are in the fray. However, the main contest is between Jayalalithaa and CPI nominee C Mahendran. Jayalalithaa has to fulfil a constitutional requirement of getting elected as MLA within six months of becoming CM.