Early detection of drought stress in Arabidopsis thaliana utilsing a portable hyperspectral imaging setup

Close-range hyperspectral imaging (HSI) of plants is now a potential tool for non-destructive extraction of plant functional traits. A major motivation is the plant phenotyping related applications where different plant genotypes are explored for different environmental conditions. HSI of Arabidopsis thaliana is of particular importance as it is a model organism in plant biology. In the present work, a portable HSI setup has been used for the monitoring of a set of 6 Arabidopsis thaliana plants. The plants were monitored under controlled watering conditions where 3 plants were watered as normal and the other 3 plants were given 50% of the normal volume of water. The images were pre-processed utilising the standard normal variate (SNV) and changes over time were evaluated using unsupervised clustering over the time series. The results showed an early detection of stress from day 4 onwards compared to the commonly used normalised difference vegetation index (NDVI), which provided detection from day 9

Identifying autofluorescent stress biomarkers in canola (Brassica napus) under drought conditions

The increasing incidence of drought is concerning as it is a major global threat to public health. In particular, incidences of drought can cause significant financial loss and distress for farmers and farming communities, yield loss and disruption to food security. Current remote methods for drought identification such as NDVI, though valuable in terms of their coverage, are limited by their ability to detect drought stress prior to the onset of physical drought symptoms. Developing a new stress detection method that could detect plant stress prior to visible damage could reduce the risk of yield-loss for this key oilseed plant. Drought stress identification via physiological characteristics of droughted B. napus and a current fluorimeter were explored prior to examining the core aim of this thesis, which was to determine if there were new fluorescent candidates that could be used to indicate drought stress in canola. A hyperspectral method for live leaf analysis was developed to analyse the fluorescent microenvironment of chloroplasts and guard cells in B. napus and identify an ideal fluorescent drought biomarker. Drought affected B. napus was found to be significantly smaller than well-watered plants. Furthermore, chlorophyll, flavonoid, and nitrogen concentrations increased significantly in droughted plants, with drought stress identified in 4-7 days after drought onset. Hyperspectral scans revealed significant increases in both blue-green and red fluorescence intensity in drought-stressed Brassica napus. This finding was supported by spectral phasor analysis, which revealed significant decreases in width (inverse to intensity) within both the red and blue-green regions of the electromagnetic spectrum. Spectral shifts within the blue-green region towards 487 nm were also noted in damaged leaves and guard cells. SIMS scans revealed high levels of sulphur within these guard cells, indicating the presence of sulphur-based compounds such as glucosinolates. Since glucosinolates are known to be present in guard cells and are closely tied with drought responses via abscisic acid signalling, it seems likely that the increase in blue-green fluorescence intensity noted around 487 nm can be attributed to the presence of these compounds. Indole glucosinolates have also previously been reported to fluoresce around 490 nm in combination with p-dimethylaminobenzaldehyde. This fluorescence study indicates that indole glucosinolates may autofluoresce within canola leaves, however further research is required to confirm this. Chemical extraction of indole glucosinolates for fluorescence analysis would assist in determining the origin of the blue-green fluorescence seen during hyperspectral analysis