Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Their observations led to hypothesis that CRT represents a universal mediator of fast plasmodesmata closure that plays a key role in cell-to-cell transport, as it was originally
suggested (Baluška et al. 1999, 2003).
Category: