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ARTICLE IN PRESS
Journal of Plant Physiology 166 (2009) 90—100

www.elsevier.de/jplph

Exogenous spermidine, arsenic and b-aminobutyric acid modulate tobacco resistance to tobacco mosaic virus, and affect local and systemic glucosylsalicylic acid levels and arginine decarboxylase gene expression in tobacco leaves
Lisa Lazzaratoa, Grazia Trebbia, Cristina Pagnuccob, Cinzia Franchinb,Patrizia Torrigianib,1, Lucietta Bettia,Ã
a

b

Dipartimento di Scienze e Tecnologie Agroambientali, Universita di Bologna, Viale Fanin 42, 40127 Bologna, Italy ` Dipartimento di Biologia Evoluzionistica Sperimentale, Universita di Bologna, Via Irnerio 42, 40126 Bologna, Italy `

Received 4 July 2007; received in revised form 18 January 2008; accepted 18 January 2008

KEYWORDS Argininedecarboxylase; Arsenic; Salicylic acid; Spermidine; Systemic acquired resistance

Summary
The polyamine spermidine and the metalloid arsenic increased resistance responses in the well-known pathosystem NN tobacco/tobacco mosaic virus (TMV). Both the hypersensitive response to TMV in a leaf disk model system (inoculated disks floating in the 0.1 mM treatments) and systemic acquired resistance (SAR) inwhole plants were significantly affected. In the latter case, 1 mM foliar sprays of spermidine and arsenic were as effective as TMV and DL-b-aminobutyric acid (BABA), both taken as positive controls, in improving the plant’s response to subsequent challenge inoculation with TMV. Moreover, this phenotypic response was correlated with changes in the endogenous concentration of the SAR-related moleculesalicylic acid and in transcript levels of some pathogenesis/stress-related genes (pathogenesisrelated proteins PR-1a and PR-2 and arginine decarboxylase (ADC)). Concentrations of free salicylic acid and of 2-O-b-D-glucosylsalicylic acid and mRNA amount of PR-1a, PR-2 and ADC were analyzed in plants treated with either spermidine or arsenic, and compared with those from untreated plants and frompositive (TMV-inoculated or BABA-treated) controls. Conjugated salicylic acid content and ADC transcripts were

Abbreviations: ADC, arginine decarboxylase; As, arsenic; BABA, DL-b-aminobutyric acid; HR, hypersensitive response; PR, pathogenesis related; ROS, reactive oxygen species; SA, free salicylic acid; SAG, 2-O-b-D-glucosylsalicylic acid; SAR, systemic acquired resistance; Sd, spermidine;TMV, tobacco mosaic virus. ÃCorresponding author. Tel.: +39 51 2096734; fax: +39 51 2096770. E-mail address: lucietta.betti@unibo.it (L. Betti). 1 Present address: Dipartimento di Colture Arboree, Universita di Bologna, Viale Fanin 46, Bologna, Italy. ` 0176-1617/$ - see front matter & 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2008.01.011

ARTICLE IN PRESS
Spermidine, arsenicand b-aminobutyric acid modulate tobacco resistance 91

found to significantly increase, at both the local and systemic levels, relative to untreated controls. & 2008 Elsevier GmbH. All rights reserved.

Introduction
Plant treatment with various biotic and abiotic agents can lead to the induction of local and systemic resistance to subsequent pathogen attack (Walters et al., 2005; Roberts andPaul, 2006). This broad-spectrum and long-lasting induced resistance rarely leads to the complete control of pathogens following subsequent inoculation (challenge inoculation), but rather results, for example, in a reduced symptomatology (Kuc, 1982). Thus, to determine whether a certain stress represents a resistance inducer, a frequently used approach consists of challenge inoculating the plantwith a known pathogen and then measuring the resulting lesions. A well-established form of induced resistance is systemic acquired resistance (SAR; Ross, 1961). Depending on the plant and on the elicitor, SAR is characterized by the systemic accumulation of salicylic acid and of pathogenesis-related (PR) proteins throughout the plant (Vallad and Goodman, 2004). Salicylic acid itself is considered...
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