Ammonium induces aquaporin gene expression in Guzmania monostachia (Bromeliaceae) under drought

The leaves of Guzmania monostachia, a tank epiphytic bromeliad, present a functional division: the base performs water and nutrient uptake through absorbing trichomes, while the apex presents higher photosynthetic activity and nitrogen (N) assimilation. Drought conditions induce Crassulacean acid metabolism (CAM) in the apex portion, with N nutrition influencing this process. Ammonium (NH₄⁺) induces higher CAM activity, reducing greater water loss compared to nitrate (NO₃⁻). Aquaporins play a crucial role in regulating membrane permeability in leaf tissues under drought. This study aimed to evaluate how different N sources (NO₃⁻ and NH₄⁺) in combination with drought affect the diurnal gene expression of aquaporins along the leaf blade of G. monostachia. Detached leaves were immersed in 30% (w/v) polyethylene glycol 6000 solution containing NO₃⁻ or NH₄⁺ for 7 days. Leaf apexes and bases were harvested at dawn and dusk. At dawn, NH₄⁺ improved water conservation and upregulated the expression of five aquaporin genes in the apex compared to NO₃⁻, including GmNIP5;1. In the leaf base at dawn, GmNIP5;1 was the most upregulated gene by NH₄⁺, suggesting its involvement in NH₄⁺ transport to the apex, intensifying CAM and other aquaporin genes' expression under drought. At dusk, NH₄⁺ led to pronounced downregulation of TIPs and NIPs than NO₃⁻ in both leaf portions, possibly ensuring lower membrane permeability and higher water retention during drought. These results offer valuable insights for future studies on the functions of aquaporins in drought tolerance and nitrogen-use efficiency in plants.