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:Furthermore, Klepek et al. (2005) and Reinders et al. (2005) have shown that the promoter of the polyol transporter AtPLT5 from A. thaliana directs GUS and GFP expression along the vascular tissue of leaves and in sink tissues such as growing roots, developing siliques and anthers.
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