Robotized Thermal and Chlorophyll Fluorescence Imaging of Pepper Mild Mottle Virus Infection in Nicotiana benthamiana

Abstract

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.

Comparison of a compatible and an incompatible pepper-tobamovirus interaction by biochemical and non-invasive techniques: Chlorophyll a fluorescence, isothermal calorimetry and FT-Raman spectroscopy

“…The temperature increase associated with the veins was shown to be related to stomatal closure. This temperature increase indicated a systemic plant response to infection, involving the control of water loss (Chaerle et al, 2006).…”

“…Lipid peroxidation and heat production have been already shown to accompany the hypersensitive response in TMV-inoculated resistant tobacco leaves. Probably the increased oxygen uptake and the accumulation of ROS significantly contributed to the increased heat production (Chaerle et al, 2006;Fodor et al, 2007). The leaf surface temperature is known to be controlled by transpiration in infected plants (Chaerle et al, 2004(Chaerle et al, , 2006).…”

“…Probably the increased oxygen uptake and the accumulation of ROS significantly contributed to the increased heat production (Chaerle et al, 2006;Fodor et al, 2007). The leaf surface temperature is known to be controlled by transpiration in infected plants (Chaerle et al, 2004(Chaerle et al, , 2006). An increase in leaf temperature, initiating from the tissue adjacent to the main veins, was observed also in Nicotiana benthamiana leaves after inoculation with different PMMoV strains.…”

Picturing pathogen infection in plants

“…Non-invasive techniques to image the patterns of multispectral fluorescence or leaf temperature across infected leaves have greatly increased our understanding of plant responses to biotic stress [1,2]. Visualization of the light signals emitted by plants can track the spreading of a pathogen through its host [3][4][5]. Furthermore, these techniques could be very useful for presymptomatic stress detection, depending on the extent in the changes in plants metabolism in response to pathogens.…”

“…Thermal imaging has been used to monitor plant stress caused by viruses [3,85,86], bacteria [33,34] and fungi [26,35,87].…”