In which table of Purchase Order tables the Purchase Requisition Number will be stored

Hi Guru's

I want to know in which table the Purchase requisition number will reside once it is used to autocreate a Purchase Order.

From the front-end I can able to view the Purchase requisition number under Purchase Order Distributions-More tab. But from backend i.e. through select command I find no value for the REQ_HEADER_REFERENCE_NUM(as it shows as blank) in the PO_DISTRIBUTIONS_ALL table.

Please advice

Thanks in Advance

SG