Application Express :: Dynamic Action In Report Region In Master Detail Form

I have created a master detail form , in which many validation etc is done ,the MASTER is a FORM  and DETAIL is a REPORTNow I am stuck up with the detail region .i.e reportI have Line Detail where there are ITEMS such as SL NO:

,ITEM_ID , UOM ( Unit of measuremnt ) etcNow here is where

Using POP UP LOV i have managed to fetch in LOV for the item "ITEM_ID",---

i can select an item name using the pop up LOV ,Now all that I want is when I select an item name from the pop up lov , an Item Id is displayed or fetched in that particular place , now i want the corresponding UOM to be diaplayed  ( i.e the UOM for that particular Item Id which has been selected by me from the pop up lov ). 

In order to resolve this I created a Dynamic action where in I get the UOM . Bt the problem is that the ITEMS displayed for selecting in the WHEN section (DYNAMIC action-IDENTIFICATION section-WHEN section----- items (  here i am not listed with ITEMS of the REPORT region instead ITEMS of the MASTER is available )-TRUE ACTION section etc is only theITEMS of the MASTER region ..