Chlorophyll Fluorescence And Photosynthesis The Basics
Figure gives a set of measurements from leaves of a healthy and an Uromyces infected Euphorbia plant, measured from the base of the plant to its top. Fo as well as Fm in both plants are increasing from base to top suggesting that the chlorophyll concentration in the leaves is increasing upwards. Both parameters may be used as approximation to the chlorophyll concentration in field experiments (11). While in healthy plants the typical three step transient kinetics OJIP with an increase in total fluorescence from the base to the top of the plant is seen, the maximum fluorescence in the infected plant is strongly diminished and only leaves near the top (leaf 13 and 14) demonstrate the normal three step transients.
Chlorophyll fluorescence and photosynthesis ..
Photosynthesis is the key process for plant growth and development. The determination of chlorophyll fluorescence kinetics allows the quantification of effects on photosynthetic processes triggered by environmental stress factors such as, e.g., the infection by fungal phytopathogens. The technique is non-invasive, rapid and well suited for experimental field work.
The leaves of infected plants were not uniformly pigmented, the chlorophyll concentration shows visibly a gradient, suggesting that the pigment concentration is decreasing from the leaf base to the tip. The absolute fluorescence emission signal was up to five times larger for the leaf base compared to its tip (not shown). A difference between base and tip is also seen in the normalized transient curves, especially when both are compared with the signal from healthy leaves (Fig. ). In the leaf tip the J-level is reached more rapidly compared to the base, indicating together with the reduced absolute signal size a stronger stress effect at the tip. Both transients show a faster rise of the fluorescence in relation to the uninfected control. The corresponding mean values of the Fv/Fm drop from 0.69 for the leaf base to 0.35 for the leaf tip. In the evenly green leaves of healthy plants the differences in the induction transients between the base and the tip is small and the corresponding Fv/Fm values stay close around 0.8 (Table ).