Effects of high NH(+)(4) on K(+) uptake, culm mechanical strength and grain filling in wheat

It is well established that a high external NH(+)(4) concentration depresses many processes in plant development, but the underlying mechanisms are still not well understood. To determine whether the negative effects of high levels of NH(+)(4) are related to competitive cation uptake, wheat was grown in a field with moderate (18 g N m(−2)) and high (30 g N m(−2)) supplies of NH(+)(4) in the presence or absence of additional K(+) (6 g K(2)O m(−2)) to examine culm mechanical strength, the main components of the vascular bundle, nitrogen (N) remobilization and the grain-filling rate. The results indicated that an excessive supply of NH(+)(4) significantly decreased culm mechanical strength, the cellulose and lignin contents of vascular bundles, the N remobilization efficiency (NRE) and the grain-filling rate compared with a moderate level of NH(+)(4). The additional provision of K(+) considerably alleviated these negative effects of high NH(+)(4), resulting in a 19.41–26.95% increase in culm mechanical strength during grain filling and a 34.59% increase in the NRE. An assay using the scanning ion-selective electrode technique (SIET) showed that the net rate of transmembrane K(+) influx decreased by 84.62%, and measurements using flame photometry demonstrated that the K(+) content decreased by 36.13% in wheat plants subjected to high NH(+)(4). This study indicates that the effects of high NH(+)(4) on culm mechanical strength, cellulose and lignin contents, the NRE and the grain-filling rate are probably associated with inhibition of K(+) uptake in wheat.