Excess Copper-Induced Alterations of Protein Profiles and Related Physiological Parameters in Citrus Leaves

Abstract

This present study examined excess copper (Cu) effects on seedling growth, leaf Cu concentration, gas exchange, and protein profiles identified by a two-dimensional electrophoresis (2-DE) based mass spectrometry (MS) approach after Citrus sinensis and Citrus grandis seedlings were treated for six months with 0.5 (control), 200, 300, or 400 μM CuCl2. Forty-one and 37 differentially abundant protein (DAP) spots were identified in Cu-treated C. grandis and C. sinensis leaves, respectively, including some novel DAPs that were not reported in leaves and/or roots. Most of these DAPs were identified only in C. grandis or C. sinensis leaves. More DAPs increased in abundances than DAPs decreased in abundances were observed in Cu-treated C. grandis leaves, but the opposite was true in Cu-treated C. sinensis leaves. Over 50% of DAPs were associated with photosynthesis, carbohydrate, and energy metabolism. Cu-toxicity-induced reduction in leaf CO2 assimilation might be caused by decreased abundances of proteins related to photosynthetic electron transport chain (PETC) and CO2 assimilation. Cu-effects on PETC were more pronounced in C. sinensis leaves than in C. grandis leaves. DAPs related to antioxidation and detoxification, protein folding and assembly (viz., chaperones and folding catalysts), and signal transduction might be involved in Citrus Cu-toxicity and Cu-tolerance.

Adaptive Responses of Citrus grandis Leaves to Copper Toxicity Revealed by RNA-Seq and Physiology

“…Superoxide dismutase (SOD) can rapidly dismutase superoxide anion into H 2 O 2 and O 2 . Our findings that Fe/Mn-SOD and Cu/Zn-SOD ( CSD ) were downregulated and upregulated in LCGSEC, respectively is in agreement with the reports that Fe-SOD abundance was reduced and CSD abundance was elevated in Cu-sufficient Arabidopsis leaves [ 58 ] and that Cu-toxicity increased CSD abundance, but had no influence on Fe-SOD abundance in C. grandis leaves [ 20 ]. Plants that suppress Fe-SOD and induce CSD under Cu-toxicity can keep superoxide anion scavenging and prevent the Cu-toxic effect on photosynthesis by buffering Cu concentration [ 11 , 58 , 59 ].…”

“…‘Shatian’ pummelo [ Citrus grandis ) (L.) Osbeck] is one of the main rootstocks of pummelo. Recent work from our laboratory indicated that ‘Shatian’ pummelo had a higher tolerance to Cu-toxicity and was an ideal material to investigate the adaptive mechanism of Cu-toxicity [ 2 , 20 ]. Herein, 400 μM Cu was chosen as the Cu-toxicity treatment because it led to significant but not too severe alterations of biomass, nutrient uptake, photosynthesis and related parameters in C. grandis seedlings [ 2 ].…”

“…Herein, 400 μM Cu was chosen as the Cu-toxicity treatment because it led to significant but not too severe alterations of biomass, nutrient uptake, photosynthesis and related parameters in C. grandis seedlings [ 2 ]. Additionally, we identified more differentially abundant proteins from leaves of 400 μM Cu-treated seedlings than from leaves of 200 or 300 Cu-treated seedlings [ 20 ]. As shown in Figure 1 , root and shoot growth was inhibited greatly in 400 μM Cu-treated seedlings.…”

“…Therefore, Cu deposition in the root cell wall is considered as a primary strategy of plant physiology displaying tolerance and detoxification under Cu-toxicity [ 18 , 19 ]. In addition to reducing Cu transport from roots to leaves, different internal detoxification mechanisms of Cu have been developed in leaves, including compartmentation of Cu by import to the vacuole, chelation of Cu by lignin in the cell wall, and intracellular chelation of Cu by Cu chelators [viz., amino acids, reduced glutathione (GSH), phytochelatins (PCs), metallothioneins (MTs), organic acids and phenolics], and induction of Cu-tolerant enzymes [ 7 , 9 , 18 , 20 , 21 ]. It is worth mentioning that Cu binding by the cell wall could impair cell wall metabolism, thus limiting leaf cell growth [ 22 , 23 ].…”

Mitigation of Copper Stress in Maize by Inoculation with Paenibacillus polymyxa and Bacillus circulans

“…However, owing to various anthropogenic activities, this HM has gained particular attention among plant stress physiologists due to its dual nature in the plant system: essential as well as toxic at an optimum and high level respectively [9,10]. An excess of Cu concentration in plant tissues induces oxidative stress via enhanced biosynthesis of various reactive oxygen species (ROS), resulting in damage to photosystem pigment proteins, DNA, RNA, lipids, enzymes, altered thylakoid membranes composition, decreased chlorophyll and mineral nutrient contents and hampered meristems development [11][12][13][14][15]. Hence, given its dual nature (essential as well as toxic), this HM could involve complex mechanisms of uptake, transport, sequestration and detoxification inside the plant tissues at the cellular level.…”