Chlorophyll Fluorescence Imaging

The advantage of chlorophyll fluorescence measurements over other methods for stress monitoring is that changes in chlorophyll fluorescence parameters often occur before other effects of stress are apparent. The method is non-invasive, and the spread of inhibition can be observed and quantified with time. Heterogeneity in the location of inhibition is easily seen and quantified when using imaging systems to measure chlorophyll fluorescence. To this end, high throughput measurements of chlorophyll fluorescence may be used to select mutants or GMOs that maintain high rates of photosynthesis under stress conditions. Qubit Systems offers a wide range of instruments for chlorophyll fluorescence measurements and imaging, ranging from hand-held devices to high throughput screening systems.

Unlike the single flash OJIP method, the PAM technique used in the PlantScreen^TM Imaging Station is the only method that allows in depth analyses of the entire range of chlorophyll fluorescence parameters in relation to PSII activity and its response to environment. Also, the PAM technique allows for a far more accurate measurement of F_o than is possible using other techniques, and thus increases the accuracy of all other fluorescence parameters.  However, should the user wish to measure OJIP, the high frame rate and high resolution of the FluorCam camera also allows for single flash OJIP image capture and analysis at 1000 fps with 1280 x 1024 pixel resolution. A windowing mode allows frame rates of up to 16,000 fps at lower resolution.

Don’t be confused by chlorophyll fluorescence imaging systems that may be offered by other companies.  Often, these only measure continuous fluorescence that is useful only for identifying chlorophyllous tissue against background.  Qubit’s imaging system monitors fluorescence kinetics, which provides a wealth of information about a plant’s photosynthetic capacity, physiological and metabolic condition, as well as its susceptibility to various stress conditions.   For example, most healthy plants have a very conservative value of Fv/Fm of about 0.8.  With many abiotic stresses, this value declines markedly, and well before any visible indicators of stress are apparent visually.  Thus, measurements of Fv/Fm can identify the onset of stress much more effectively than measuring the change in slope of a growth curve.  Changes in Fv/ Fm can also be used as alarms to trigger rescue protocols for stressed plants, such as irrigation of plants undergoing drought conditions.