Thank you all for your reply. I could solve this problem by dropping to the root prompt from the recovery mode.
At the root prompt, the file system was readonly, but I could change it by command "mount -o remount,rw /" and revert the change I made to the /etc/network/interfaces file.
After this, the system came up again! I do not know the implications of this command, but it solved my problem. Comments from here also helped.
How to change "read-only" file at root prompt - Ask Ubuntu
Thanks once again for all the clues.