Effects of Pb2+ on the Structure and Function of Photosystem II of Spirodela polyrrhiza

Abstract

Lead (Pb(2+)) is a well-known highly toxic element, and Spirodela polyrrhiza is one of the hydrophytes most sensitive to Pb(2+), which might be highly toxic to photosynthesis. However, the mechanism by which Pb(2+) inhibits energy transfer and conversion efficiency remains unclear. Here, we report the effects of Pb(2+) on the secondary structure and function of photosystem II (PS II) of S. polyrrhiza using spectral methods. We found that Pb(2+) accumulated in PS II and damaged its secondary structure, decreased the absorbance of visible light, inhibited energy transfer among amino acids within the PS II protein-pigment complex, and reduced energy transport from tyrosine residue to chlorophyll a. Taken together, Pb(2+) exposure damaged the structure and function of S. polyrrhiza PS II.

Lead Uptake, Toxicity, and Detoxification in Plants

“…Lead also significantly inhibited Hill reaction activity in spinach chloroplasts, in addition to photophosphorylation; moreover, lead had a more conspicuous effect on cyclic photophosphorylation than on noncyclic photophosphorylation (Romanowska et al 2008). Recently, Qufei and Fashui (2009) reported that the accumulation of Pb 2+ in photosystem II resulted in damage to its secondary structure and induced decreased absorbance of visible light and inhibited energy transfer among amino acids. Moreover, Jiang and Liu (2010) reported mitochondrial swelling, loss of cristae, and vacuolization of endoplasmic reticulum and dictyosomes during a 48-72 h lead exposure in A. sativum.…”

“…• inhibition of plastoquinone and carotenoid synthesis (Kosobrukhov et al 2004;Chen et al 2007;Liu et al 2008;Cenkci et al 2010), • obstruction of the electron transport system (Qufei et al 2009),…”

Lead toxicity in rice: effects, mechanisms, and mitigation strategies—a mini review

“…Pb diminished chlorophyll production by reduced uptake of Mg and Fe (essential components of chlorophyll) (Burzynski 1987). The main reasons of reduced photosynthetic activity due to Pb may be the affinity of lead for protein N and S ligands; cause damage to chloroplastic ultrastructure (Islam et al 2007); hindrance in the electron transport chain (ETC) reactions (Qufei and Fashui 2009); breakdown of chlorophyll contents by enhanced activity of chlorophyllase (Liu et al 2008); inhibition and substitution of Mg and Fe by Pb (divalent cations) in chlorophyll (Chatterjee et al 2004;Cenkci et al 2010); reduced activities of ferredoxin NADP + reductase as well as delta-aminolevulinic acid dehydratase at the source of chlorophyll production (Gupta et al 2009); reduced CO 2 levels due to stomatal closure (Romanowska et al 2006); plastoquinone and carotenoid inhibition Cenkci et al 2010); and inhibited enzymatic catalysis of Calvin cycle (Liu et al 2008).…”

“…It triggers NAD + -malate dehydrogenase activity in leaves' protoplasts, hampered hill reaction, and severely affects cyclic photophosphorylation than noncyclic photophosphorylation (Romanowska et al 2002). Along with damaging secondary structures of PSII, Pb + also blocked energy transfer pathways among amino acids and renders absorption of visible light (Qufei and Fashui 2009). Pb also caused swelling of mitochondria, vacuolization of dictyosomes and endoplasmic reticulum, and damage to cristae (Jiang and Liu 2010).…”

Effect of Pb2+ ions on photosynthetic apparatus

“…Moreover, inhibition of electron flow also on the acceptor side of the PS2 reaction centre was confirmed at high Pb concentrations what was reflected in an increase in Chla fluorescence (Prasad et al 1991). Qufei and Fashui (2009) studied the effects of Pb 2+ ions on the secondary structure and function of PS2 of Spirodela polyrrhiza and found that Pb 2+ ions accumulated in PS2 and damaged its secondary structure, decreased the absorbance of visible light, inhibited energy transfer among amino acids within the PS2 protein-pigment complex, and reduced energy transport from tyrosine residue to Chla. Rashid and Popovic (1990) (Rashid et al 1994).…”