The role of OsAKT1 in ammonium uptake and osmotic stress tolerance in relation to nitrogen supply

Ginsawaeng, Orarat (2016) The role of OsAKT1 in ammonium uptake and osmotic stress tolerance in relation to nitrogen supply. MSc by research thesis, University of York.

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Abstract

Nitrogen is an essential plant macronutrient: it not only affects the growth, development and yield of plants, but also contributes to stress tolerance. OsAKT1, a rice homolog of a K+ channel AKT1 at the plasma membrane of root hair cells, is permeable to ammonium and therefore potentially plays a role in the uptake of this nutrient. Beside taking part mainly in K+ uptake in the roots, OsAKT1 is also involved in drought and osmotic stress tolerance in rice. Therefore, I investigated the role of NH4+ uptake via OsAKT1 and the function of the channel in osmotic stress tolerance related to NH4+. Growth experiments which compared the growth of wild-type (WT) and akt1 knockout rice (KO) in media with different predominant form of nitrogen (either NO3- or NH4+) under control and osmotic stress of -0.21 MPa (8% PEG 4,000) showed that the OsAKT1 role in osmotic stress tolerance is not associated with NH4+. Nevertheless, NH4+ depletion experiments illustrated that OsAKT1 functions in NH4+ uptake at low external NH4+ concentrations of 0.2 mM. Depletion assays at 2 mM NH4+ and the complementation growth studies in yeast mutants lacking NH4+-specific uptake systems (Δmep1-3) also suggested the possibility of NH4+ uptake at high NH4+ concentrations via OsAKT1. In all, the data imply that OsAKT1 takes up small amounts of NH4+ irrespective of external NH4+ concentrations.