Study of excited-state kinetics of photosystem I and II in intact spinach leaves by picosecond fluorescence lifetime measurements

Shazia Farooq, Herbert van Amerongen
Wageningen University, Wageningen, the Netherlands

When plants are exposed to excess light, more excitations are created in the pigments than the reaction centres of the plant cell can handle. Because this can be harmful to the cell, it has to get rid of this excess energy. One of the easiest ways to dissipate energy is by heat through non-photochemical energy (NPQ) [1]. Heat dissipation in plants cannot be measured directly, but can be studied by following the decrease of chlorophyll fluorescence (NPQ).

We studied the excited-state kinetics of photosystem I (PSI) and photosystem II (PSII) in both open and close state in spinach leaves in vivo as function of actinic light intensity of about 1300μE/m2/sec. To understand the kinetics of the early steps in photosynthesis and its photo-protective mechanism, we use non-invasive picoseconds fluorescence measurements on intact spinach leaves.                                              

Picosecond fluorescence measurements have been performed with a streak-camera setup and the data have been analyzed by global analysis [2]. Intact spinach leaves were placed between two glass plates in a rotating cuvette which also moves horizontally. Fluorescence kinetics has been measured for the upper surface of the leave at 1300μE/m2/sec. 2 components in case of open reaction centre (RC), whereas 3 components in case of close RC were sufficient to describe the fluorescence at all wavelengths. 85 ps decay lifetime observed under all conditions corresponds largely to PSI and partly to PSII and the 2nd and 3rd component correspond to PSII. Later we also compared the kinetic rate for both open and closed NPQ states, these results will be discussed on the poster and oral presentation.

Acknowledgement

We acknowledge funding from the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO).

References

[1] Müller P, Li X-P, Niyogi KK (2001Plant Physiology 125: 1558-1566
[2] K. M. Mullen and I. H. M. van Stokkum (2007J. Stat. Software 18: 1-46.