PSII Imaging

Measurement of Kautsky effect for physiological photosystem screening

The PSII Fluorescence sensor is utilized to spatially measure the Kautsky of dark- or light-adapted plants from small plants like Arabidopsis up to medium size corn plants.  The sensor system can image the activity of photosynthesis using a short intense LED pulse of light and induce the induction curve of the chlorophyll fluorescence. By capturing several fluorescence images the activity of photosynthesis is calculated as an image expressed for every pixel as Fv/Fm (variable fluorescence divided by the maximum fluorescence). Other than PAM-like measurements the Kautsky based measurements are independent on leaf angle or leaf distance from the sensor. 

Chlorophyll fluorescence imaging

High power LEDs with red color are used to excite the chlorophyll to induce the induction curve of photosynthesis (max 0.8 seconds). A protocol that images the start and saturation of this induction curve is used; chlorophyll fluorescence of plants is imaged using a fast, highly sensitive megapixel camera. From these images the activity of photosynthesis is calculated for each pixel as VF/F_m values (variable fluorescence divided by the maximum fluorescence) and represented as an image of 1.4 Mp in 14 bit grey value (or color classified to emphasize the difference for the human eye). Different sizes are available for a screening area up to 80 x 80 cm (screening from top only).

Pre imaging plant adaption

Measurement parameter of dark adapted plants
After dark adaptation the maximum efficiency of photosynthesis can be measured. If any damage had occurred, this can be observed in the image. The system is measuring (Fm-F0)/Fm,which correlates with the maximal quantum yield of photochemistry. The definition for Fv is: Fv = Fm-F0.

Measurement parameter of light adapted plants
Under light adaptation the effective efficiency of photosynthesis can be measured. This gives a value how the plant performs at a certain light intensity. This is an important value that correlates with the productivity of crops. Furthermore, in light conditions some stress influences are easier to measure, because the combination of stress and light yields a higher contrast in the image. This happens for instance with drought stress. The system measures (Fm’-F’)/Fm’, this correlates with the effective quantum yield of photochemistry. Here the ‘prime’ means that the measurements were performed in the light.

Adaptation tunnel
Under light and dark adaptation the photosynthesis process needs time to get in a steady state. Normally this takes about 15 minutes. The adaption tunnel can create homogenous light adaption settings with up 1000 mumol/m²s as well as complete darkness by using a double door lock.

Tolerance to leaf angle

The PSII sensor technologies provided by LemnaTec are tolerant to changes of leaf to camera angle. For inclined leaves, the light intensity will be different. One has to take care that for these situations the light intensity is still high enough to saturate the photosynthesis. As the light pulse is very high this is the case. Therefore the result will hardly depend on the inclination, because in the calculation of the efficiency of photosynthesis one divides by Fmax and thus one obtains a relative value.

The images show the largely non-angle dependence of a tomato leaf. A tomato plant was imaged and one leaf was fixed to a plate and the angle of this plate could be changed. Here 0 degrees means that the leaf is perpendicular to the camera lens, which means the projected area is maximal. At 80 degrees the leaf is almost parallel to the lens. The other line is the control that is a leaf that remains at an angle of zero degrees.