JXB Advance Access originally published online on July 25, 2006
Journal of Experimental Botany 2006 57(11):2899-2907; doi:10.1093/jxb/erl051
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© 2006 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Nicotine synthesis in Nicotiana tabacum L. induced by mechanical wounding is regulated by auxin
The Key Laboratory of Plant Nutrition and Nutrient Cycling, MOA, Key Laboratory of Plant–Soil Interactions, MOE, Department of Plant Nutrition, China Agricultural University, Beijing 100094, China
*To whom correspondence should be addressed at: Department of Plant Nutrition, China Agricultural University, Yuanmingyuan West Road 2, Beijing 100094, PR China. E-mail: lichj{at}cau.edu.cn
The effects of different kinds of mechanical wounding on nicotine production in tobacco plants were compared, with sand or hydroponics culture under controlled conditions. Both removal of the shoot apex and damage of the youngest unfolded leaves nos 1 and 2 by a comb-like brusher with 720 punctures caused an increase in nicotine concentration in whole plants at day 3, and reached its highest level at day 6. The nicotine concentration induced by excision of the shoot apex was much higher than that induced by leaf wounding. Both treatments also caused an increase in jasmonic acid (JA) concentration within 90 min in the shoot, followed by an increase in the roots (210 min), in which the JA concentration induced by leaf wounding was significantly higher than that induced by excision of the shoot apex. The increase in nicotine concentration occurred throughout the whole plant, especially in the shoot, while the increase in JA concentration in the shoot was restricted to the damaged tissues, and was not observed in the adjacent tissues. Removal of the lateral buds that emerged after excision of the shoot apex caused a further increase in nicotine concentrations in the plant tissues. Removal of mature leaves, however, did not cause any changes in nicotine concentration in the plant, even though the degree of wounding in this case was comparable with that occurring with apex removal. The results suggest that the nicotine production in tobacco plants was not correlated with the degree of wounding (cut-surface or punctures), but was highly dependent on the removal of apical meristems and hence on the major sources of auxin in the plant. Furthermore, immediate application of 1-naphthylacetic acid (NAA) on the cut surface after removing the shoot apex completely inhibited the increase both in nicotine in whole plants and in JA in the damaged stem segment and roots. Application of an auxin transport inhibitor around the stem directly under the shoot apex of intact plants also caused an increase in nicotine concentration in the whole plant. The results strongly suggest that auxin serves as a negative signal to regulate nicotine synthesis in roots of tobacco plants.
Key words: Auxin, jasmonic acid, mechanical damage, nicotine, tobacco (Nicotiana tabacum L.)
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