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Poplar potassium transporters capable of controlling K + homeostasis and K + ‐dependent xylogenesis
Author(s) -
Langer Katharina,
Ache Peter,
Geiger Dietmar,
Stinzing Andrea,
Arend Matthias,
Wind Christa,
Regan Sharon,
Fromm Jörg,
Hedrich Rainer
Publication year - 2002
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2002.01487.x
Subject(s) - xylem , transporter , phloem , potassium channel , chemistry , potassium , guard cell , ion transporter , biophysics , biology , botany , biochemistry , gene , membrane , organic chemistry
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.