As so-called primary producers, plants use solar energy to synthesize the foodstuffs that sustain other forms of life. This process of photosynthesis works in much the same way as the solar panels that supply energy for domestic heating. Like these, plant leaves must cope with variations in the level and quality of ambient light. LMU researcher Professor Dario Leister and his colleagues at LMU Munich have been studying how this is accomplished in the thale cress, Arabidopsis thaliana. "It turns out that, depending on lighting conditions, photosynthesis can rapidly switch between two modes of action, called states 1 and 2", says Leister, "and some years ago we reported that the 1-to-2 transition depends on the enzyme STN7, which attaches phosphate to a key protein." In their latest publication the researchers together with collaborators in Italy, have identified the enzyme that reverses this modification, thus flipping the system back to state 1. The discovery adds a critical element to the understanding of photosynthesis but has also practical implications for improving the growth of plants under low-light conditions, which favour state 2. (PLoS Biology, 26 January 2010)
The photosynthetic machinery is embedded in specialized membranes called thylakoids located in the chloroplasts of leaf cells. Thylakoids contain two types of so-called photosystems, PSI and PSII. Each consists of an antenna complex and a reaction center. The antenna complex channels light energy to the reaction center, where it serves to detach electrons from chlorophyll molecules. The energy imparted to the electrons is captured in a controlled manner as they pass along a sequence of carrier molecules, and is used to power all other cellular activities.
The two photosystems contain different antenna proteins, called light-harvesting complexes (LHCs), and differ in their sensitivity to light of different colours. PSII is most sensitive to red light, while PSI responds
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