Ultrafast fluorescence of photosynthetic crystals and light-harvesting complexes

Sunlight is the main source of energy for life on earth1. A crucial step in the use of light-energy is the conversion of this “raw” energy into chemical energy, via a processcalled photosynthesis. Organisms capable of oxygenic photosynthesis are plants, algae andcyanobacteria. The major sunlight-driven chemical pathway in oxygenic photosynthesis isthe production of sugars from carbon-dioxide and water, releasing oxygen as a by-product.

The sugars and oxygen can be consumed by other organisms, thereby producing carbon-dioxide and water, which in turn can be used for photosynthesis, and so on, and soon.

Photosynthesis is therefore of paramount importance for the existence of life on earth. Apart from the fundamental significance, a better understanding of structure,organization, function and flexibility of the photosynthetic apparatus may help increasecrop yields, plant fitness, and allow mimicking photosynthesis in vitro, aiming at energyproduction. The focus of this thesis is on an adaptative molecular mechanism, which worksin photosystem II to protect it against photo-induced damage.

This thesis describes experiments on photosynthetic complexes that are involved in the early steps of photosynthesis. The first chapters describe light-harvesting andphotoprotection. These two functions are fulfilled by the same group of pigment-proteincomplexes (proteins that bind chlorophyll and carotenoid pigments). Under low-lightconditions these pigments “harvest light”: They absorb the sunlight that drivesphotosynthesis. In high light intensities they protect the photosynthetic apparatus againstphotodamage. The switching between these two functions is studied in the first chapters ofthis thesis. In the chapter 6, intact photosystem I is studied, and the results help to betterunderstand the processes that lead to the initial photochemical reactions of photosynthesis.

The outline of this introduction is as follows: First, in section 1.1 the process of conversion of light-energy into chemical energy is described. The next sections describe the pigments involved in light-harvesting (section 1.2), and the pigment-protein complexesstudied in this thesis (section 1.3). Section 1.4 describes protection against photodamage,and in sections 1.5 and 1.6 the experimental techniques and data analysis used in this thesis are discussed. Finally, section 1.7 contains a short outline of the thesis.