As plant science moves out of the laboratory and the glasshouse into the field, the need for portable measuring systems and suitable field-based measuring protocols is becoming increasingly important. Chlorophyll a fluorescence induction, and in particular the use of the FV/FM ratio (a measure of photosynthetic capacity), is one method that has been successfully transferred to the field. However, the FV/FM ratio is quite insensitive to change and a new collective of fluorescence parameters called the JlP-test may prove more useful in determining plant photosynthetic capacity and performance. Chlorophyll a fluorescence monitors the activity of photosystem II, and the JIP-test permits the quantification of this activity at the levels of photosystem II photon absorption, excitation trapping and electron transport.
While to date the JIP-test has been mainly applied to intact leaves, in this study the test was used to analyse chlorophyll a fluorescence transients at the structural levels of leaves, broken and intact chloroplasts, and isolated thylakoids. The use of the isolated thylakoid and chloroplast systems facilitated the addition of photosystem II electron acceptors, uncouplers and inhibitors. Specific effects of these chemicals on JlP-test parameters could then be measured and analysed. From these results, relationships between the biochemical reactions occurring in photosystem II and specific JIP-test parameters could be established.
The interpretation of results from these in vitro chlorophyll a fluorescence measurements will aid in the interpretation of in vivo (leaf) and in situ (field) measurements. For ecologically based projects, application of the JIEP-test to the analysis of chlorophyll a fluorescence transients recorded in the field would provide more depth of information concerning photosynthetic performance than the widely used photosystem II efficiency indicator - the FV/FM ratio.