Introduction

The delayed fluorescence emission, natural to all green plants, has been known to scientists for over fifty decades. Delayed fluorescence (DF) has much in common with the chlorophyll a fluorescence (or prompt fluorescence, PF) because it originates from the same chlorophyll molecules of the Photosystem 2 antenna complexes. Like prompt fluorescence, the properties of the DF emission are highly sensitive to the functional state of Photosystem 2 and the photosynthetic reaction chain as a whole. Theoretically DF bears even more information about the photosynthetic processes than PF. Still, a fluorescence-measuring instrument can be found in almost every plant science research laboratory, while DF has not gained much popularity as a practical method to study the photosynthetic organisms. One reason for such injustice is that DF is harder to register than PF. But the greatest difficulty in using DF is its interpretation, or extracting the valuable information from this extremely complex signal.

Fortunately, in recent years we've witnessed major advances both in the technical aspects of DF registration and in the theory of DF. We are more and more able to utilize DF for practical scientific research. One possible application of the prompt and delayed fluorescence is to measure the effects of photosynthetic herbicides in plants. There are other approaches for doing this, but luminescence (PF or DF) is advantageous over most other methods. First of all, luminescence methods are non-invasive, which means that the measurements can be done in vivo and in situ with minimal disturbance of the plant samples. Secondly, they are highly sensitive and could potentially detect herbicides in extremely low concentrations. Last but not least, luminescence methods are fast, easy, and inexpensive.

We employed the current knowledge on delayed fluorescence and a DF-measuring instrument to develop an experimental method for measuring the effects of herbicides acting on Photosystem 2 in intact plants.

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