Poplar potassium transporters capable of controlling K+ homeostasis and K+-dependent xylogenesis.
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.
Langer
Katharina
K
Julius-von-Sachs-Institut, Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany.
Ache
Peter
P
Geiger
Dietmar
D
Stinzing
Andrea
A
Arend
Matthias
M
Wind
Christa
C
Regan
Sharon
S
Fromm
Jörg
J
Hedrich
Rainer
R
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D046508:Culture Techniques; D004926:Escherichia coli / Q000235:genetics; D020224:Expressed Sequence Tags; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000502:physiology; D010802:Phylogeny; D018514:Plant Structures / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D032107:Populus / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012621:Seasons; D019789:Tetraethylammonium / Q000494:pharmacology; D014981:Xenopus
D027682:Cation Transport Proteins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D019789:Tetraethylammonium; D011188:Potassium; D002118:Calcium