Effects of High Toxic Boron Concentration on Protein Profiles in Roots of Two Citrus Species Differing in Boron-Tolerance Revealed by a 2-DE Based MS Approach

Abstract

Citrus are sensitive to boron (B)-toxicity. In China, B-toxicity occurs in some citrus orchards. So far, limited data are available on B-toxicity-responsive proteins in higher plants. Thirteen-week-old seedlings of “Sour pummelo” (Citrus grandis) and “Xuegan” (Citrus sinensis) was fertilized every other day until dripping with nutrient solution containing 10 μM (control) or 400 μM (B-toxicity) H3BO3 for 15 weeks. The typical B-toxic symptom only occurred in 400 μM B-treated C. grandis leaves, and that B-toxicity decreased root dry weight more in C. grandis seedlings than in C. sinensis ones, demonstrating that C. sinensis was more tolerant to B-toxicity than C. grandis. Using a 2-dimensional electrophoresis (2-DE) based MS approach, we identified 27 up- and four down-accumulated, and 28 up- and 13 down-accumulated proteins in B-toxic C. sinensis and C. grandis roots, respectively. Most of these proteins were isolated only from B-toxic C. sinensis or C. grandis roots, only nine B-toxicity-responsive proteins were shared by the two citrus species. Great differences existed in B-toxicity-induced alterations of protein profiles between C. sinensis and C. grandis roots. More proteins related to detoxification were up-accumulated in B-toxic C. grandis roots than in B-toxic C. sinensis roots to meet the increased requirement for the detoxification of the more reactive oxygen species and other toxic compounds such as aldehydes in the former. For the first time, we demonstrated that the active methyl cycle was induced and repressed in B-toxic C. sinensis and C. grandis roots, respectively, and that C. sinensis roots had a better capacity to keep cell wall and cytoskeleton integrity than C. grandis roots in response to B-toxicity, which might be responsible for the higher B-tolerance of C. sinensis. In addition, proteins involved in nucleic acid metabolism, biological regulation and signal transduction might play a role in the higher B-tolerance of C. sinensis.

Boron toxicity in higher plants: an update

“…The authors demonstrated that 'Clementine' mandarin and 'Navelina' orange plants grafted on 'sour orange' rootstock are more sensitive to high B compared to those grafted on 'Swingle citrumelo' due to lower B uptake, which resulted in decreased B accumulation in leaves (Papadakis et al 2004a, b). Recently, a proteomic approach carried out in roots of C. sinensis and C. grandis revealed that under high B concentration proteins involved in many cellular processes, including B transport and accumulation, are differentially expressed in the two species and play a key role in conferring B-tolerance to C. sinensis (Sang et al 2017). Therefore, understanding the intimal mechanism of B transport within plant and the mechanisms which allow tolerant genotype to cope better with higher B concentration is of crucial importance to drive, for example, future breeding programs aimed to select tolerant genotypes.…”

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

“…Proteins were extracted using a phenol extraction procedure [80] and their concentration was measured as described by Bradford [81]. 2-DE was performed according to Sang et al [82]. Stained gels were scanned with an Epson Scanner (Seiko Epson Corporation, Japan) at a resolution of 300 dpi.…”

Low pH-responsive proteins revealed by a 2-DE based MS approach and related physiological responses in Citrus leaves

“…Proteins were independently extracted thrice from pH 2.5-, 3- and 6-treated samples using a phenol extraction procedure as described previously [ 32 ] and their concentrations were determined according to Bradford [ 33 ]. Both 2-DE and image analysis were performed as described by Sang et al [ 34 , 35 ] and Yang et al [ 36 ]. Background subtraction, Gaussian fitting, gel alignment, spot detection, matching and normalization were made with PDQuest version 8.0.1 (Bio-Rad, Hercules, CA, USA).…”