what is the best way to merge the double vertices lines in a plane to sphere object without loosing the plane UV map setting? when i use the self created plane to sphere object , i still have to deal with the double lines from start to end borders from the original bent plane .
in the picture we can see the lines are double where they will touch eachother.

in the second picture we see the final result with the sphere using the plane uv map, 
now is that still available when the double start to end border lines are merged ?

or is this impossible ?

what is the best way to merge these double lines and still have the plane uv map working?
Use W>Remove doubles to join them. Next, use Ctrl-E>Mark seem along the verts to allow for separation, basically joined edges will always remain connected, messing up your UV map, unless you specify otherwise with mark seem. Finally select everything in the UV image editor and hit P for pin to lock 'em in place. When you UV unwrap again, everything will be in order.