Barley plasma membrane intrinsic proteins (PIP Aquaporins) as water and CO₂ transporters

We identified barley aquaporins and demonstrated that one, HvPIP2;1, transports water and CO₂. Regarding water homeostasis in plants, regulations of aquaporin expression were observed in many plants under several environmental stresses. Under salt stress, a number of plasma membrane-type aquaporins were down-regulated, which can prevent continuous dehydration resulting in cell death. The leaves of transgenic rice plants that expressed the largest amount of HvPIP2;1 showed a 40% increase in internal CO₂ conductance compared with leaves of wild-type rice plants. The rate of CO ₂ assimilation also increased in the transgenic plants. The goal of our plant aquaporin research is to determine the key aquaporin species responsible for water and CO₂ transport, and to improve plant water relations, stress tolerance, CO₂ uptake or assimilation, and plant productivity via molecular breeding of aquaporins.