Poplar potassium transporters capable of controlling K⁺ homeostasis and K⁺‐dependent xylogenesis

Abstract

Summary The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA+), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium‐dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem‐ and xylem‐physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT‐PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de‐polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de‐polarization. PtKUP1 was expressed in a K+ uptake‐deficient Escherichia coli strain, where this K+ transporter rescued K+‐dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+‐dependent wood production.

Phosphatidylinositol (4,5)Bisphosphate Inhibits K+-Efflux Channel Activity in NT1 Tobacco Cultured Cells

“…S2), providing additional support for identifying these channels as K + -selective K + -release channels, NtORK channels (Sano et al, 2007). Actually, although two genes, NtORK1 and NtORK2, have been mentioned in the literature, only NtORK1 has been characterized to some extent so far (Langer et al, 2002;Kasukabe et al, 2006;Sano et al, 2007). Because our measurements do not indicate clearly two separate types of channels, we use the inclusive name, NtORK.…”

Roles of ion channels and transporters in guard cell signal transduction

“…1 and 3). Among K þ in channels, expression in heterologous systems demonstrates that KAT1 is activated by acidification of either cytosol or apoplast [45]; KAT2 is activated by external acidic pH [34], and channels of the AKT2 subfamily are inhibited by acidification as a result of H + block of the channel pore [46,47]. In planta, whole cell inward K + currents of V. faba guard cells are enhanced by external acidification but show little response to changes in internal pH [48,49].…”

Effects of potassium application and soil moisture on the growth of Corymbia citriodora plants

“…Variáveis de crescimento das plantas de Corymbia citriodora em função dos limites de umidade do solo associados às doses de potássio. area was probably the driving force for cell expansion (LANGER et al, 2002), which resulted in the growth of the stem diameter. Interaction between soil moisture levels and potassium doses had a significant effect on leaf number (Table 2).…”