© 2004 Oxford University Press
Three Types of Tobacco Calmodulins Characteristically Activate Plant NAD Kinase at Different Ca2+ Concentrations and pHs
1 Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510 Japan
2 Plant Physiology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602 Japan
3 PROBRAIN, Japan Science and Technology Corporation, Chiyoda-ku, Tokyo, 101-0062 Japan
4 Genome and Drug Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510 Japan
We previously reported that three types of tobacco calmodulin (CaM) isoforms originated from 13 genes are differently regulated at the transcript and protein levels in response to wounding and tobacco mosaic virus-induced hypersensitive reaction (HR); wound-inducible type I and HR-inducible type III levels increased after wounding and HR, respectively, while type II, whose expression is constitutive and wound responsible, remained unchanged. Here, we show that these CaMs differentially activate target enzymes; rat NO synthase was activated most effectively by type III, moderately by type I and weakly by type II, and plant NAD kinase (NADK) was activated in the inverse order. Furthermore, we found that a suitable Ca2+ concentration differs by type; type II activated NADK at lower Ca2+ of around 0.1 µM, which is the cytosolic concentration in unstimulated cells, type I did so at 1–5 µM, which is the increased Ca2+ concentration in stimulated cells, while type III did not at any Ca2+ level. NADK activation was highest over a pH range of 7.1–6.8 for which the cytosolic pH reportedly changed from 7.5 after being stimulated. Thus, tobacco CaMs, especially type I, effectively activate NADK in stimuli-induced conditions.
5 These two authors contributed equally to this work.
6 Present address: National Agricultural Research Center, Joetsu, Nigata, 943-0193 Japan
7 Corresponding author: E-mail, yohashi{at}affrc.go.jp; Fax, +81-298-38-7469.
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