Light harvesting and photo-protection in photosynthesis

Speaker: Lijin Tian
 Biophysics of photosynthesis
Light harvesting and photo-protection in photosynthesis
Location: TU Delft
Date: 24-05-2017

Author: Kristian Blom

At the 24th of June I visited a talk given by dr. Lijin Tian, a postdoc candidate for the Nynke Dekker lab who is currently working in the lab of Prof. dr. Roberta Croce in the department of biophysics of photosynthesis at the VU. The main research goal of Prof. dr. Croce is to get an understanding of the light reactions of photosynthesis at the molecular level, with particular emphasis on light absorption, excitation energy transfer and photo-protection.

Dr. Lijin Tian started the talk by introducing photosynthesis and the main actors involved in this process. Photosynthesis can be divided in two separate processes: light-dependent and light-independent. In the light-dependent process the solar energy is harvested by chlorophylls and thereafter converted into chemical energy. In the light-independent reactions, called the Calvin cycle, carbohydrate molecules are assembled from carbon dioxide using the chemical energy harvested during the light-dependent process. For the light-dependent process there are two multiprotein complexes, called Photosystem I and II, who catalyze the process of light harvesting and conversion of light energy into chemical energy. Both these complexes can on their turn be divided into two parts: an antenna system that harvest the light energy and is responsible for the energy transfer to the reaction center, and a core complex in which charge separation and electron transfer takes place.

For the harvesting of light energy there is an critical value regarding the amount of energy influx into the reaction centers. Above this value irreversible damage to the photosynthetic system can be caused. To circumvent this problem, photo-protective mechanisms in the antenna system can reduce the energy influx by quenching excess excitation energy as heat in a process known as nonphotochemical quenching (NPQ). In their latest research paper, Prof. dr. Roberta Croce and her lab show that LHCII, the main light harvesting complex of algae, can only switch to a quenched conformation as a response to a pH change when LHCSR1 (light-harvesting complex stress related 1) is present in low concentration.

Figure 1: Fluorescence traces of LCHII-only and LCHII+LHCSR1 cells. (A) LHCII-only, (B) LHCII+LHCSR1 cells with (red)/without (black) nigericin. The signal was collected at 680 nm. Nigericin (100 μM) addition and pH changes are indicated by arrows.
Image from: E Dinc, L Tian, LM Roy, R Roth, U Goodenough, R Croce (2016) “LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells”

Regarding the talk itself, I didn’t found it that interesting. For me it was hard to follow the story, since the speaker his English wasn’t that good. Also, and this is not the first time that I notice this, the slides were overcrowded with images and data. It was quite surprising for me that there isn’t any research lab in BN that focusses on photosynthetic systems, since it is such a fundamental field in cell biology. At the end of the talk one of the PI’s of BN asked a lot of questions regarding the status of the research field in photosynthetic systems. From my point of view it almost looked like he/she was planning to start a new lab with a specialization in the biophysics of photosynthesis. Perhaps that within a few years from now we have a new lab in the BN department.



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