In Turkey, the Minimum Obstacle Clearance (MOC) in primary areas is 300m; what about other countries and region?
The MOC value you are referring to is related to the en-route phase of an IFR flight, so your statement that it is the lowest altitude a plane can descend to when approaching the runway is wrong. That value depends on the type of approach, aircraft equipment and various other factors. It is not a fixed value shared among different airports. You probably have MOC confused with Minimum Descend Altitude (non-precision approaches) or Decision Altitude (precision approaches).
However, to answer your actual question, 300 metres is an ICAO standard for MOCA (Minimum Obstacle Clearance Altitude) in the primary area for the en-route phase of an IFR flight. So other countries use the same value, unless they have special local rules specifying a different value.
Note than, in mountainous areas, the minimum obstacle clearance applied, depending on terrain elevation, is 450 metres for terrain between 3000 ft and 5000 ft, and 600 metres for terrain higher than 5000 ft.
In the US the MOCA—Minimum Obstruction Clearance Altitude is 1000' in non-mountainous areas and 2,000' in designated mountainous areas. A map of the areas is contained in 14 CFR PART 95—IFR ALTITUDES. In addition to obstacle clearance the MOCA also ensures reception of VOR signals. Pilots flying off-route e.g GPS direct, are responsible for determining the MOCA for their route.
e) The MOCA assures obstruction clearance on an ATS route, ATS route segment, or other direct route, and adequate reception of VOR navigation signals within 22 nautical miles of a VOR station used to define the route.