Plant and Cell Physiology Advance Access originally published online on August 30, 2006
Plant and Cell Physiology 2006 47(9):1323-1336; doi:10.1093/pcp/pcj102
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Robotized Thermal and Chlorophyll Fluorescence Imaging of Pepper Mild Mottle Virus Infection in Nicotiana benthamiana
1 Unit of Plant Hormone Signaling and Bioimaging, Ghent University, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium
2 Department of Biochemistry, Cell and Molecular Biology of Plants, Estación Experimental del Zaidín, C/Profesor Albareda, no. 1, CP 18008, Granada, Spain
3 Department of Plant Breeding, Estación Experimental La Mayora, 29750 Algarrobo-Costa, Málaga, Spain
* Corresponding author: Matilde Barón, E-mail, mbaron{at}eez.csic.es; Fax, +34-95-81-29-600; Dominique Van Der Straeten, E-mail, dominique.vanderstraeten@ugent.be; Fax, +32-9-264-5333.
After infecting a susceptible host, pathogens spread throughout the plant. Depending on pathogen type and strain, the severity of symptoms varies greatly. In the case of pepper mild mottle virus (PMMoV) infection in Nicotiana benthamiana, newly developing leaves display visual symptoms (symptomatic leaves). In this study, two PMMoV strains were used, the Spanish strain (PMMoV-S) being more virulent than the Italian strain (PMMoV-I). Plants infected with PMMoV-I could recover from the virus-induced symptoms. Leaves that were fully developed at the start of PMMoV infection remained symptomless. In these asymptomatic leaves, an increase in temperature, initiating from the tissue adjacent to the main veins, was observed 7 d before the Chl fluorescence pattern changed. Virus immunolocalization on tissue prints matched well with the concomitant pattern of Chl fluorescence increase. The temperature increase, associated with the veins, was shown to be related to stomatal closure. Upon PMMoV-I infection, the appearance of thermal and Chl fluorescence symptoms as well as virus accumulation were delayed by 3 d compared with PMMoV-S-induced symptoms. The temperature increase of whole symptomatic leaves was also correlated with a decrease in stomatal aperture. In contrast to the persistent increase in symptomatic leaf temperature observed during PMMoV-S infection, the temperature of symptomatic leaves of PMMoV-I-infected plants decreased gradually during recovery. We propose that the earliest temperature increase is caused by a systemic plant response to the virus infection, involving the control of water loss. In conclusion, thermography has potential as an early reporter of an ongoing compatible infection process.
4 These authors contributed equally to this work.
(Received June 27, 2006; Accepted August 3, 2006)
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