GDSYZX-United/PROJECT/project description

Project description

The light can be harmful to plants

Photosynthesis is a necessary process for many plants to produce organics to support their livings.However,the photosynthesis carries great risks to plants beacause the excess energy of light may have a negative effect on the photosynthetic efficiency and photosynthetic apparatus.

Photodamage to plants

If plants are exposed to light intensities that exceed their photosynthetic capacity,photodamage may happen.The light damages the plants mainly by damaging their DNA,the antenna pigments,various protein complexes in the thylakoid membrane, other photosynthetic apparatus and by inducing the production of reative oxygen species(ROS) in chloroplasts.Medium or high concentration of ROS causes apoptosis,or even necrosis of plant cells.Therefore,under extreme light intensities conditions,the cell,tissue or even organism of plants may die.Photodamages in plants are irreversible in many cases.

PhotosystemⅡ can suffer from the process of photosynthesis

The excess light energy may slow down the rate of photosynthesis,which is known as photoinhibition. Photoinhibition mainly takes place in PhotosystemⅡ(PSⅡ),because PSⅡ is more senstitive to light than the rest of the photosynthetic machinery.PSⅡ，which lies in the thylakoid membrane, together with cytochrome b6/f,PhotosystemⅠand ATP synthase funtions in harvesting light and transduce solar energy into chemical energy,while PSⅡitself catalyzes the light-driven water oxidation.

The reaction center of PSII contains the D1/D2/cytochrome b559 complex, which houses the cofactors necessary for electron transport, which together with the nearest light-harvesting chlorophyll binding proteins CP43and CP47, form the core complex.Despite all the regulatory mechanisms against high light,the reaction center within PSⅡis tend to be damaged in all light intensities.

Mechanisms of PSⅡ protection in plants agianst high light

PSⅡ is a very fragile photosynthetic apparatus,and plants have evolved diverse photoprotection mechanism,such as the movement of leaves and chloroplasts,screening of photoradiation,ROS scavenging systems ,dissipation of light energy as thermal energy.

Under high light conditions,the plants cannot protect their PSⅡ via simple protective measures above.Therefore,plant cells deploy a complex PSⅡrepair system which involves disassembly and reassembly of thylakoid membrane protein complexes. Proteins in the PSII reaction center are damaged and undergo rapid repair and reassembly to enable photosynthetic electron transport to continue.When photodamage induce a reversible phophorylation and disassembly of Light-harvesting-complexⅡsupercomplex in plants,damaged PSII core monomers migrate from grana stacks to stroma-exposed membranes. Damaged PSII core monomers then partially disassemble and release CP43,and PSⅡ subunits are degraded by protease.After that,new PSⅡsubunits are synthesized and they are reassembled into new PSⅡ core monomers,which later migrate to grana stalks and reform functional PSⅡ-light-harvesting complex.

Protein HHL1 helps reduce the damage of plants under high light

The excess light energy may slow down the rate of photosynthesis,which is known as photoinhibition. Photoinhibition mainly takes place in PhotosystemⅡ(PSⅡ),because PSⅡ is more senstitive to light than the rest of the photosynthetic machinery.PSⅡ，which lies in the thylakoid membrane, together with cytochrome b6/f,PhotosystemⅠand ATP synthase funtions in harvesting light and transduce solar energy into chemical energy,while PSⅡitself catalyzes the light-driven water oxidation.

The reaction center of PSII contains the D1/D2/cytochrome b559 complex, which houses the cofactors necessary for electron transport, which together with the nearest light-harvesting chlorophyll binding proteins CP43and CP47, form the core complex.Despite all the regulatory mechanisms against high light,the reaction center within PSⅡis tend to be damaged in all light intensities.

Mechanisms of PSⅡ protection in plants agianst high light

PSⅡ is a very fragile photosynthetic apparatus,and plants have evolved diverse photoprotection mechanism,such as the movement of leaves and chloroplasts,screening of photoradiation,ROS scavenging systems ,dissipation of light energy as thermal energy.

Under high light conditions,the plants cannot protect their PSⅡ via simple protective measures above.Therefore,plant cells deploy a complex PSⅡrepair system which involves disassembly and reassembly of thylakoid membrane protein complexes. Proteins in the PSII reaction center are damaged and undergo rapid repair and reassembly to enable photosynthetic electron transport to continue.When photodamage induce a reversible phophorylation and disassembly of Light-harvesting-complexⅡsupercomplex in plants,damaged PSII core monomers migrate from grana stacks to stroma-exposed membranes. Damaged PSII core monomers then partially disassemble and release CP43,and PSⅡ subunits are degraded by protease.After that,new PSⅡsubunits are synthesized and they are reassembled into new PSⅡ core monomers,which later migrate to grana stalks and reform functional PSⅡ-light-harvesting complex.

Protein HHL1 helps reduce the damage of plants under high light

HHL1(Hypersensitive to High Light) is a chloroplast transmembrane protein found in Arabidopsis Thaliana. HHL1 is expressed in response to high light and functions in protecting PSⅡagainst photodamage and photoinbition.Research shows that HHL1 helps maintain the accumulation of PSⅡcomplexes.

How does HHL1 protect plants?

HHL1 helps maintain the formation and stability of the PSⅡ-Light-harvesting-complexⅡ supercomplex,and it also affects the reassembly of PSⅡmonomers under high light .According to some research,HHL1 may function in guiding the release of CP43 from PSⅡcore monomers.To do this,HHL1 associate with PSⅡmonomers after disassembly of photodamaged PSⅡ-Light-harvesting complexⅡsupercomplexes and PSⅡcore dimers into PSⅡcore monomers.It may specially interact with CP47 and CP43 to help form the binding sites for extrinsic proteins to PSII in PSⅡrepair.

References

  1. Honglei Jin, Bing Liu, Lujun Luo, Dongru Feng, Peng Wang, Jun Liu, Qingen Da, Yanming He, Kangbiao Qi, Jinfa Wang, and Hong-Bin Wang(2014)HYPERSENSITIVE TO HIGH LIGHT1 Interacts with LOW QUANTUM YIELD OF PHOTOSYSTEM II1 and Functions inProtection of Photosystem II from Photodamage in Arabidopsis.Plant Cell 26: 1213–1229

  2. Imre Vass(2011)Molecular mechanisms of photodamage in the PhotosystemII complex.Elsevier:1 May 2011