UV-B AND UV-A RADIATION EFFECTS ON PHOTOSYNTHESIS AT THE MOLECULAR LEVEL - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 118

related to the damage of pigments, lipids, amino acids as well as complex enzyme systems
of the photosynthetic apparatus.
The reaction series of photosynthesis, which connects the light driven oxidation of
water with the incorporation of carbon from atmospheric CO 2 into energy rich organic
compounds takes place in the chloroplasts (Figure 1). The so-called light reactions are

Chloroplast

O 2

Grana

St r o m a

CH O 6 2 6

ATP+
NADPH

Calvin
cycle

CO 2

Th y l a k o i d

UV- B

PSI I

NADPH

b/f

PQ

PC

PSI

Th y l a k o i d
lumen

ATPa s e

ADP

ATP

Figure 1. The structure of the photosynthetic apparatus . In plants photosynthesis takes place in the cell
organ called chloroplast. The light reactions are mediated by electron/proton transport proteins embedded
in the thylakoid membrane and result in the oxidation of water and the production of ATP and NADPH.
These energy rich compounds are utilized in the process of CO 2 fixation mediated by the water soluble
enzymes of the Calvin cycle. The main targets of UV-B radiation in plant cells are the nucleic acids, the
Calvin cycle enzymes and the light-energy converting Photosystem II complex.

mediated by large pigment-protein complexes in the thylakoid membrane, which perform
the oxidation of water as well as the production of ATP and NADPH. These compounds
are utilized in the process of CO 2 fixation, performed by the soluble enzymes of the Calvin