Help needed with xhost

[Ambrogio De Lorenzo]

Hi all,
I use my laptop with a user (root in this case, but please don't say
"don't use root").
Sometimes I use to launch on terminal some commands with other users.
To permit to that commands to display on my screen I used "xhost +".
This worked well on my last laptop with fedra 14.

Now, on Fedora 20, if I use the same sequence, the command are unable to
open the display.

On root console the command xhost has this output
# xhost 
access control disabled, clients can connect from any host
SI:localuser:root

On the other terminal the command (amelu for example) returns
$ amule
Error: Unable to initialize gtk, is DISPLAY set properly?

I can't understand why but I would like to understand it.

Can someone explain to me this behaviour?

Tnx
 Ambrogio