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JXB Advance Access originally published online on December 26, 2008
Journal of Experimental Botany 2009 60(1):279-289; doi:10.1093/jxb/ern285
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Effects of top excision on the potassium accumulation and expression of potassium channel genes in tobacco

Xiao Yan Dai1,2, Yi Rong Su2,*, Wen Xue Wei2, Jin Shui Wu2 and Ye Kuan Fan1

1College of Resource and Enviroment, Huazhong Agriculture University, Wuhan 430070, PR China
2The Key Laboratory of Subtropical Agro-ecology, Institute of Subtropical Agriculture, CAS, Changsha 410125, PR China

* To whom correspondence should be addressed: E-mail: yrsu{at}isa.ac.cn

The effects of the removal of the shoot apex of tobacco on the relative transcript levels of potassium channel genes, determined by real-time PCR, and on the relationship between the expression of genes encoding potassium channels and potassium concentration, were studied. The results from the study indicated that comparatively more assimilates of photosynthesis were allocated to the apex in control plants than in both decapitated and IAA-treated decapitated plants. By contrast, dry matter in the upper leaves, roots, and stems in both decapitated and IAA-treated plants was significantly increased relative to control plants. The potassium level in whole plants decreased post-decapitation compared with control plants, and so did the potassium concentration in middle and upper leaves, stem, and roots. Expression of NKT1, NtKC1, NTORK1, and NKT2 was inhibited by decapitation in tobacco leaves with a gradual reduction after decapitation, but was induced in roots. The relative expression of NKT1, NTORK1, and NKT2 in tobacco leaves was higher than that in roots, whereas the expression of NtKC1 was higher in roots. The levels of inhibition and induction of NKT1, NtKC1, NTORK1, and NKT2 in leaves and roots, respectively, associated with decapitation were reduced by the application of IAA on the cut surface of the decapitated stem. Further results showed that the level of endogenous auxin IAA in decapitated plants, which dropped in leaves and increased in roots by 140.7% at 14 d compared with the control plant, might be attributed to the change in the expression of potassium channel genes. The results suggest that there is a reciprocal relationship among endogenous auxin IAA, expression of potassium channel genes and potassium accumulation. They further imply that the endogenous IAA probably plays a role in regulating the expression of potassium channel genes, and that variations in expression of these genes affected the accumulation and distribution of potassium in tobacco.

Key words: Decapitation, gene expression, potassium channel, potassium accumulation, tobacco (Nicotiana tabacum L.)

Received 10 September 2008; Revised 18 October 2008 Accepted 21 October 2008


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