there is no specific inhibitor for PIP aquaporins in any plant. In the beginning of aquaporin research people used Hg++, but this is of course by far not a specific inhibitor. Basically the same is true with any pharmacological approach including pharmacy itself. Only antibodies could come close to a "specific" interaction, it always will be a question of the threshold you set for defining "specificity".
Since I do not know the reason for your question, you may want to think about other approaches.
It will be interesting to express the Aquaporins in a Xenopus oocyte and study their inhibitors through electrophysiology.However, it appears that a few ion channels are found in the Xenopus oocyte including at least one aquaporin, Still it is an attractive system to study aquaporins.