int
main ()
{
        write (1, "MOMMA", 5);
        return 0;
}
"MOMMA" string is stored in .rodata section, let's disassemble (objdump -D):
Disassembly of section .text:
...
080483b0 <main>:
...
 80483c1:       c7 44 24 08 05 00 00    movl   $0x5,0x8(%esp)
 80483c8:       00 
 80483c9:       c7 44 24 04 bc 84 04    movl   $0x80484bc,0x4(%esp)
 80483d0:       08 
 80483d1:       c7 04 24 01 00 00 00    movl   $0x1,(%esp)
 80483d8:       e8 13 ff ff ff          call   80482f0 <write@plt>
...
(items are push()'d in reverse order $0x5, $0x80484bc, $0x1)
Anyway, let's search for 0x80484bc :

Disassembly of section .rodata:
...
080484b8 <_IO_stdin_used>:
 80484b8:       01 00                   add    %eax,(%eax)
 80484ba:       02 00                   add    (%eax),%al
 80484bc:       4d                      dec    %ebp
 80484bd:       4f                      dec    %edi
 80484be:       4d                      dec    %ebp
 80484bf:       4d                      dec    %ebp
 80484c0:       41                      inc    %ecx
"\x4d\x4f\x4d\x4d\x41" = "MOMMA"

Thus demonstrating that despite "MOMMA" is used in main() (.text section), it is retrieved from .rodata section

Now, let's store "MOMMA" in a const var and call it from write():
# objdump -s test|grep -A 1 rodata
Contents of section .rodata:
 80484c4 03000000 01000200 4d4f4d4d 4100      ........MOMMA. 

So, the string is used in the .text section from .rodata section in both cases.