Through which process is liquid exuded from the uninjured part of a leaf tip?

The stomatal apparatus consists of:

Transpiration is mainly a process of

$A$ : During stomatal opening there is relative change in $TP$ of guard cell and subsidiary cell.
$R$ : $TP$ of subsidiary cell decreases during opening and that of guard cells increase.

Which process are the guard cells associated with?

What will be the effect of accumulation of potassium ions in guard cells?