The plus sign above the staff indicates left hand pizzicato. In the Table 24(b) of the Code, this is illustrated as an X, but the plus sign is more commonly used (and is shown in Example 25.5.1-2.) We use dots 456, 345 (left hand sign) before a note that has a plus above it. (Usual octave indicator and dot 3 rules apply.)
The x1 in measure 43 indicates a backward fingering extension for the cello. (It doesn't go with the arco.) As to how best to braille it - this is tricky. You may have to create a sign and explain it in a TN before the piece. I've run across "HI2" and "LO2" fingerings in string methods. I added dots 12 after the finger number to indicate LO and a dot 1 to indicate HI. You could do something like that. Or you could simply braille it as a word-sign expression before the note - but again, I'd add a TN to give the cellist a heads-up to look out for it, especially since they usually look for fingerings after a note.
Hope this helps a little!