[Heavy metal]-Chlorophylls Formed in Vivo During Heavy Metal Stress and Degradation Products Formed During Digestion, Extraction and Storage of Plant Material

Deficiency and toxicity of nanomolar copper in low irradiance—A physiological and metalloproteomic study in the aquatic plant Ceratophyllum demersum

“…This usually leads to a decrease in the total fluorescence amplitudes, but not necessarily to a decrease of F v /F m (Fig. 2, Küpper et al, 2006). In the current study, only a small amount of Chls in the LHCIIs were subjected to heavy metal substitution, leaving enough Mg-Chls to transfer the excitons to the RCs that the plants were still viable up to 200 nM Cu.…”

“…Although during the procedure of protein isolation, a certain amount of Cu will bind to proteins that were Cu-free in vivo, our data show that Cu potentially binds to the photosynthetic complexes by replacing Mg in the Chl molecules. The formation of [Cu]-Chl and [Zn]-Chl was shown to take place mainly in the LHCIIs under low light conditions, while in high irradiance it was suggested to take place in the PS II reaction centres (Küpper et al, 2002(Küpper et al, , 2006. Furthermore, recently the insertion of Cd 2+ in the LHCIIs was shown to occur with high efficiency (apparent K D = 10.5 nM) in Cd-stressed C. demersum plants, which previously had only been postulated as [Cd]-Chl is highly unstable and has a very similar UV/VIS absorption spectrum as Mg-Chl .…”

“…[Cu]-Chl does not bind axial ligands, changing the confirmation of the pigment-protein complex (reviewed by Küpper et al, 2006;Janik et al, 2010). Even worse, upon excitation [Cu]-Chl does not transfer the excitons to other chlorophylls, but releases the energy as heat (it is non-fluorescent).…”

“…The substitution of Mg 2+ in the chlorophyll (Chl) molecule by heavy metal ions leads to the formation of a heavy metal substituted chlorophylls, [hms]-Chls (Küpper et al, 1996(Küpper et al, , 2002. Those [hms]Chls are unsuitable for photosynthesis for several reasons (Küpper et al, 2006): Compared to [Mg]-Chl, the singlet excited state is very short-lived, S1 relaxes to the S0 state before the exciton can be transferred. This is especially detrimental when [Cu]-Chl is located in the reaction centre of photosystem II (PSIIRC).…”

“…The light environment is an important factor for the mode of Cu (and other toxic metals) toxicity, as it changes the position of [Cu]-Chl formation. Another reason for the unsuitability of [hms]-Chls is a lower tendency to bind axial ligands (Küpper et al, 2006), which changes the conformation of the antenna molecules and leads to diminished or inhibited exciton transport. Generally, any disturbance in the photosynthetic or respiratory electron transport chain is known to enhance the formation of reactive oxygen species, when electrons are transferred to oxygen instead of their proper acceptor (Asada 2006;Pospíšil 2012).…”