Plant Physiology

Photosynthesis, plants and environment

We are interested in the biogenesis of chloroplasts and their photosynthetic machinery. We aim to elucidate the regulatory networks underlying the build-up and wish to understand how plants integrate environmental fluctuations in order to maintain stable photosynthetic efficiency also under adverse conditions, an important aspect highly relevant to expected issues connected to the climate change.

The structural and functional basics of plant photosynthesis have been extensively studied at cellular and molecular level. At present the construction of the photosynthetic complexes within the thylakoid membrane system of plant chloroplasts is well understood and the position and coordination of proteins, pigments, lipids and co-factors is described even at atomic level. However, the photosynthetic machinery is not static, but rather represents a highly dynamic arrangement of complexes that change position and association depending on environmental conditions. The photosynthetic machinery, therefore, performs two functions:

• The primary function of photosynthesis is the harnessing of sun light and the subsequent conversion into chemical energy.
• The second, less obvious function is the sensing of the environment. The photosynthetic process is highly susceptible to changes in light, temperature or water availibility and further is highly affected by pathogen or herbivore attack.

We are especially interested in the sensor function of photosynthesis as it regulates many plant-internal processes such as metabolism and gene expression. The sensor function, however, controls also photosynthetic function by regulatory feedback loops and acclimates photosynthesis to environmental conditions by structural rearrangements of the photosynthetic apparatus. 

One key regulatory point in photosynthesis is the redox state of the intermittent plastoquinone (PQ) pool that electrochemically connects photosystem II (PSII) and the cytochrome b6f complex. In the lab we manipulate the PQ redox state by preferential excitation of PSII or PSI using artificial light sources that create excitation imbalances between the two photosystems. This way of experimental variation in illumination mimics light quality gradients typically found in dense plant stands (such as crop fields or natural canopies) or under industrial farming conditions such as green houses or vertical farming arrangements.

We aim to understand how photosynthesis acclimates to light quality gradients in natural and artificial surroundings and how this can be exploited to improve agri- and horticultural productivity. Most of our research has been performed with model organisms such as Arabidopsis, Sinapis or Nicotiana. We, however, are also interested in the study of novel plant systems that are of interest for biotechnology and biomass production. To this end we study photosynthesis in duckweeds (Lemnaceae), a family of aquatic plants capable of exponential growth if grown under appropriate conditions. Duckweeds are freshwater plants that can be found ubiquitiously on planet Earth apart from polar habitates. They multiply by vegetative fission and can exhibit tremendous growth rates. In recent years they are heavily investigated for their potential bioeconomic impact in food, feed, biomass and biotechnological  production and application. We study the molecular properties of duckweed photosynthesis with respect to structure and physiological acclimation.