Medicine and biology / Gyógyászat és biológia
Infrared detection of early biotic stress in plants
Laury Chaerle, Frank De Boever, Dominique Van Der Straeten
Department of Molecular Genetics, Ghent University

When plants are able to recognise an attacking pathogen, they mount a hypersensitive response, characterised by cell death at the site of infection. In certain mutant and transgenic plants, such a process occurs spontaneously. In the model system resistant tobacco - tobacco mosaic virus, an increase in surface temperature was thermographically observed, colocalised with the infection sites, before any visual cell death symptoms became apparent. In the studied cell death mutants, thermography permitted to visualise the evolution of cell death both earlier and with higher contrast, compared to visual-spectrum imaging.

Tobacco infection by tobacco mosaic virus (TMV)

The thermal response to the TMV-infection was characterised by a presymptomatic appearance of 'hot-spots' at the sites of infection (on average 8h before pinpoint cell-death lesions were visible by eye). The expansion of the thermal effect was very rapid, when compared with the visual symptoms. A temperature increase of 0.4 °C was measured at the centre of the thermal spots. The maximum size of the thermal effect was reached after 2 days, whereas the visual symptoms needed on average 7days to expand to the same final size.

When growing resistant tobacco plants infected with TMV at temperatures above 28°C, virus multiplication is not inhibited. When 'shifting' such plants back to 21 °C, a massive resistance response is mounted by the plant, resulting in both more rapid and more extended cell death, when compared with plants that were kept at 21 °C. When thermographically visualised, 'temperature-shifted' plants displayed a more rapid expansion of the thermal effect and a shorter time span between thermal effect and visual cell death

The figure below shows thermal (left) and visual spectrum (right) images of a tobacco leaf, infected with TMV using a localised infection method. After infection, the plant was grown at 32 °C, and then submitted to a temperature shift to 21 °C. 8h later (upper images), the thermal effect has reached its maximum extension, while no visual effects are apparent. 122h after the temperature shift (lower images), the visible pattern of cell death has formed

Conclusions

Thermography enables presymptomatic detection of resistance responses in plants, which could find applications in early disease monitoring and screening for resistance
Thermography clearly permits early and high-contrast visualisation of localised plant cell death. Given the importance of the cell-death response in the resistance to pathogens, robotised thermography could become a screening tool to search for mutants in the cell death response pathway.