in QT5.2.0 and QT5.1.1 QSystemTrayIcon doesn't appear on linux(ubuntu 12.04)

QSystemTrayIcon doesn't appear on linux(ubuntu 12.04)
The code that is given below, I compiled both qt 5.1.1 and qt 4.8.5 and there isnt any problem with 4.8.5 but on 5.1.1 icon doesnt appear.

code:
QSystemTrayIcon* trayIcon = new QSystemTrayIcon;
trayIcon->setIcon(QIcon(":/new/prefix1/cart512x512.png"));
trayIcon->setToolTip(QString("Hello there..."));
trayIcon->show();