Contributor: Givemore Munashe Makonya
Plant photosynthetic health is an important part of producing high yielding and quality crops. A reliable approach to quantify photosynthetic health is by measuring chlorophyll fluorescence, which is the re-emission of red wavebands by chlorophyll molecules in plants. This occurs during photosynthesis and serves as a key indicator of plant vitality.
More specifically, chlorophyll fluorescence measurements act as a diagnostic tool to detect stress factors within the plant. Stress factors could include heat stress or other environmental stressors. This information could be useful to breeders by revealing how different plant genotypes respond to external factors. Moreover, it provides an objective tool for selecting more resilient genotypes.
Often chlorophyll fluorescence and photosynthesis measurements are used together when conducting physiological research on plants. This is so that a more complete understanding of crop productivity and physiological intricacies can be assessed.
Collecting chlorophyll fluorescence data requires a chlorophyll fluorimeter, for example a Pocket PEA or several other options available on the market. Light exclusion clips are briefly attached to facilitate the dark adaptation of the youngest, fully expanded leaf of the plant being measured. This process is done to allow the photosystem II (PSII) to relax. After about 30 minutes of dark adaptation, the chlorophyll fluorometer rapidly records a chlorophyll fluorescence (Fv/Fm) value.
To interpret the data some calculations need to be completed first. The maximum quantum yield of PSII, a protein located within plants, is calculated by using the equation (Fm-Fo)/Fm = Fv/Fm. In this equation, Fo equals the minimal fluorescence, and Fm is the maximal fluorescence.
Once the maximum quantum yield of PSII (Fv/Fm) has been calculated, it can be compared to reference data found in publications. Reference data on specific stress conditions or from healthy plants can also be used. When the necessary control data has been obtained, interpretations between it and the chlorophyll fluorescence calculations can be conducted.
Depending on the research question, measuring chlorophyll fluorescence can be very advantageous relative to other physiological measurements. For one, measuring chlorophyll fluorescence is nondestructive, preserving the integrity of the plants. Additionally, it is a rapid method so results can be quickly assessed. When rapid methods are employed, changes to the crops’ physical and environmental conditions can be quickly altered.
Measuring chlorophyll fluorescence measurements is a valuable and effective method that sheds insight on plant stress and how plants are responding to their surroundings.