Ingenious fine-tuning of plant photosynthesis

February 4, 2015, Umea University
Credit: Bernard Wessels

Malgorzata Pietrzykowska has investigated the specific roles of the two most abundant membrane proteins on Earth, Lhcb1 and 2. Both of them are responsible for light harvesting which is the basis of photosynthesis, the process which sustains life on Earth by providing the oxygen we breathe and the food we eat. She defends her thesis at Umeå University on Friday 6 February.

Light is collected by pigments called chlorophylls, which absorb mainly blue and , whilst is reflected, giving plants their characteristic colour. The majority of chlorophylls are associated with the Lhc (light harvesting chlorophyll) protein superfamily, which in consists of 13 members.

"You have surely noticed that the amount of light during the day is continuously changing. Unlike animals, plants cannot move towards or away from sunlight, therefore they have evolved mechanisms which allow them to cope with the rapid changes in light quality and intensity", says Malgorzata Pietrzykowska.

One such process, called state transition, allows plants to redistribute the from photosystem II (PSII) to photosystem I (PSI), or vice versa. State transitions are regulated by phosphorylation/dephosphorylation of Lhcb1 and Lhcb2.

In the model plant species Arabidopsis thaliana Lhcb1 is encoded by as many as five genes, while Lhcb2 is encoded by three, and the proteins are 98% similar at amino acid sequence level.

"When I started my PhD, I was amazed by the seemingly huge redundancy of these two proteins. Why do need so many copies of almost identical proteins?" asks Malgorzata Pietrzykowska.

Malgorzata Pietrzykowska shows that Lhcb1 is important for regulating the amount of and for providing quenching sites when too much light is absorbed. More importantly, the abundance of Lhcb1 modulates the size and provides flexibility to the photosynthetic membranes.

The role of Lhcb2 on the other hand is mainly in, and limited to, state transitions. When photosystem II is receiving too much energy, Lhcb2 phosphorylation allows detachment of LHCII trimers (consisting of both Lhcb1 and Lhcb2) from PSII, therefore less energy is transferred to PSII. At the same time these trimers attach to photosystem I forming LHCII-PSI complexes, whose formation balances allows energy flow to PSI.

In summary, Malgorzata Pietrzykowska shows that despite their similarity, the functions of Lhcb1 and Lhcb2 are different but complimentary in fine-tuning photosynthetic light absorption.

Explore further: New model of the quality control of photosystem II

More information: The thisis is available online here.

Related Stories

New model of the quality control of photosystem II

June 25, 2014

Thylakoid membranes are piled up to form the grana well known as the site where the Photosystem II (PSII) complexes which play a role in the primary photochemical reaction exist. However, the structures and dynamics of thylakoid ...

New insight into photosynthesis

May 27, 2014

The way that algae and plants respond to light has been reinterpreted based on results from experiments studying real-time structural changes in green algae. Under particular lighting conditions during photosynthesis, the ...

Switching on a dime: How plants function in shade and light

November 13, 2014

Photosynthesis is the process by which plants convert energy from the sunlight into chemical energy in the form of sugars. These sugars are used by plants to grow and function, as well as food for animals and humans that ...

Harvesting light, the single-molecule way

February 16, 2014

New insights into one of the molecular mechanisms behind light harvesting, the process that enables photosynthetic organisms to thrive, even as weather conditions change from full sunlight to deep cloud cover, will be presented ...

Recommended for you

Semimetals are high conductors

March 18, 2019

Researchers in China and at UC Davis have measured high conductivity in very thin layers of niobium arsenide, a type of material called a Weyl semimetal. The material has about three times the conductivity of copper at room ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.