Localization of aquaporins during the formation of casparian bands in the roots of barley plants

There are two main pathways for water transport in plants. One of them is water transport along the cell walls and xylem vessels, called apoplastic pathway, and the other is from cell to cell through the membrane water channels aquaporins. Formation of Casparian bands by suberin and lignin deposition reduces conductivity of the apoplastic pathway. So the role of membrane water transport should increase, as mentioned in many reviews. The aim of this research was to localize barley aquaporins of the HvPIP2 family in different root zones depending on the differentiation of cell walls and deposition of Casparian bands. It was shown that the intensity of berberine fluorescence was insignificant in the zone closer to the root tip (at a distance of 3–4 cm), however fluorescence increased in the endodermis and the central cylinder of the root basal zone, indicating high lignification of cell walls and deposition of lignin and suberin in developing Casparian bands. Localization of HvPIP2;1 and HvPIP2;5 aquaporins showed no differences in their level between different root zones. The use of antibodies against aquaporins HvPIP2;2 and HvPIP2;3/4 revealed a local increase in fluorescence in the endodermal region of the basal zone of the roots characterized by high level of lignification and suberinization which apparently should compensate for the expected decrease in hydraulic conductivity as a result of the formation of apoplastic barriers. It is possible that the role of different aquaporins in water transport varies depending on the growing conditions of plants.