maybe you can have a look to this "not so bad" paper :

Developmental and Environmental Regulation of Aquaporin Gene Expression across Populus Species: Divergence or Redundancy?

:-)

As far as I know, there is no database for tissue-specific aquaporin expression.

But some aqp were shown to be expressed in flowers/pollen (TIP5s, and NIP4 in arabidopsis and poplar)

TIP3s exhibit a seedling/seeds preferential expression

In poplar, some TIPs also exhibit a preferential expression in root

Thanks for the hint, it is an interesting paper. Unfortunately I do not work with Populus, so this is only of limited use to me. Nevertheless, every bit helps.

Try the most recent FANTOM5 database of digital gene expression in different cell types. 

http://www.nature.com/nature/journal/v507/n7493/abs/nature13182.html

Maybe I should have made it more clear that I am working with Arabidospsis, but thanks for the input  :)