Abstract
Potassium (K(+)) is the most important cationic nutrient for all living organisms and has roles in most aspects of plant physiology. To assess the impact of one of the main K(+) uptake components, the K(+) inward rectifying channel AKT1, we characterized both loss of function and overexpression of OsAKT1 in rice. In many conditions, AKT1 expression correlated with K(+) uptake and tissue K(+) levels. No salinity-related growth phenotype was observed for either loss or gain of function mutants. However, a correlation between AKT1 expression and root Na(+) when the external Na/K ratio was high suggests that there may be a role for AKT1 in Na(+) uptake in such conditions. In contrast to findings with Arabidopsis thaliana, we did not detect any change in growth of AKT1 loss of function mutants in the presence of NH4 (+) Nevertheless, NH4 (+)-dependent inhibition was detected during K(+) uptake assays in loss of function and wild type plants, depending on pre-growth conditions. The most prominent result of OsAKT1 overexpression was a reduction in sensitivity to osmotic/drought stress in transgenic plants: the data suggest that AKT1 overexpression improved rice osmotic and drought stress tolerance by increasing tissue levels of K(+), especially in the root.
Highlights
Potassium (K+) is the primary cation in most plants
In standard conditions (1 mM K+) no significant differences were observed in relative growth rate (RGR) between loss of function (KO), wild type (WT) and overexpressor (OX) genotypes (Fig 1a)
When plants were grown on a 100 μM K+ medium, AKT1 null mutants grew slightly worse than WT plants but this trend was only significant for akt1-1 and not akt1-2
Summary
Potassium (K+) is the primary cation in most plants. It affects all aspects of crop production including yield, resistance to pathogens and tolerance to abiotic stress such as salinity, lodging, and drought. Its uptake from the soil predominantly takes place via two separate mechanisms, one passive and one active (Maathuis and Sanders, 1996; Maathuis et al, 1997; Véry and Sentenac, 2003; Rodríguez-Navarro and Rubio, 2006). AKT1 channels are expressed predominantly, but not exclusively, in the roots and their activity is increased by membrane hyperpolarization with a threshold voltage of around −120 mV. Other factors such as pH, K+ and Ca2+ concentration impact on open
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