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.
Highlights
Microelement copper (Cu) is highly toxic to plants when in excess
Biomass was lower in C. sinensis seedlings than that in C. grandis seedlings at each given Cu supply
Leaf Cu concentration increased with Cu supply and did not differ between the two Citrus species with the exception that its concentration in leaves was higher in C. sinensis than that in C. grandis at μM (Figure 1A)
Summary
Microelement copper (Cu) is highly toxic to plants when in excess. Cu contamination in agriculture soils is on the rise all over the world [1,2]. Cu accumulation in soils can cause Cu-toxicity and related nutritional disorders, resulting in a series of adverse effects on plants ranging from morphological and physiological to molecular levels [1,3]. In old Citrus orchards, the excess accumulation of Cu in soils is a common phenomenon because of the extensive and continued use of Cu-containing agricultural chemicals against fruit and foliar diseases such as anthracnose and canker [3,4]. Cu concentration and availability in soils under continuous Citrus production orchards increase with increasing production
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