Mitigation of Cd toxicity by Mn in young plants of cacao, evaluated by the proteomic profiles of laves and roots

Authors: OLIVEIRA, B - University Of Santa Cruz - Brazil; ALMEIDA, A - University Of Santa Cruz - Brazil; PIROVANI, C - University Of Santa Cruz - Brazil; BARROSO, J - University Of Santa Cruz - Brazil; NEO, C - University Of Santa Cruz - Brazil; SANTOS, N - University Of Santa Cruz - Brazil; AHNERT, D - University Of Santa Cruz - Brazil; MANGABEIRA, P - University Of Santa Cruz - Brazil; Baligar, Virupax

Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2020
Publication Date: 2/27/2020
Citation: Oliveira, B.R., Almeida, A.A., Pirovani, C.P., Barroso, J.P., Neo, C.H., Santos, N.A., Ahnert, D., Mangabeira, P.A., Baligar, V.C. 2020. Mitigation of Cd toxicity by Mn in young plants of cacao, evaluated by the proteomic profiles of laves and roots. Ecotoxicology and Environmental Safety. 29:340–358. https://doi.org/10.1007/s10646-020-02178-4.
DOI: https://doi.org/10.1007/s10646-020-02178-4

Interpretive Summary: In South America, soils under cacao often have high levels of Cadmium, Cd. Cacao tends to absorb high level of Cd, which is toxic to cacao and inhibits growth and reduces the quality of beans. The presence of high levels of Cd in cacao beans have an impact on international trade of cacao due to stricter regulations imposed by importing countries that have been established to reduce Cd levels in chocolate. Therefore, mitigation of toxic levels of soil Cd is of paramount concern. In this paper, we report the mechanisms of Manganese, Mn and its mitigation of Cd toxicity in young cacao genotype CCN-51 through changes in the protein profiles and protein concentrations in leaves and roots. Our results show that Mn mitigated the Cd toxicity by increasing protein accumulation and by the induction of proteins related to the detoxification of Cd. There was greater induction of proteins that mitigate toxic effects of Cd in roots than in leaves. These findings will be used to identification cacao genotypes that could be used as rootstock to reduce Cd transport to grafted high yielding cacao scions. These findings will be used by researchers, plant breeders and farmers, who could apply Mn-fertilizers to soil that are high in Cd to improve cacao bean quality and reduce Cd toxicity in cacao.

Technical Abstract: Cd is a non-essential metal and highly toxic to plants, animals and humans, even at very low concentrations. Cd has been found in cocoa beans and in their products, as in the case of chocolate. Mn plays an important role in photosynthetic machinery involving O2 and can interact with Cd and attenuate its toxic effects on plants. The objective of this work was to evaluate the mechanisms of Mn response in the mitigation of Cd toxicity in young plants of the CCN 51 cacao genotype submitted to 0.8 mmol Cd kg-1, 1.6 mmol Mn kg-1 or the combination of 0.4 mmol Cd kg-1 + 0.8 mmol Mn kg-1 soil, together with the control treatment (without addition of Cd and Mn in soil), by means of analysis of changes in the profile of exclusive proteins (EP) and differentially accumulated proteins (DAP). Leaf and root proteins were extracted and quantified from the different treatments, followed by proteomic analysis. About eight DAP and 38 EP were identified in leaves, whereas in roots 43 DAP and 21 EP were identified. Some important proteins induced in the presence of Cd and repressed in the presence of Mn+Cd or vice versa, were ATPases, isoflavone reductase, proteasome and chaperonin. Cd toxicity affected proteins of defense response and leaf stress and metabolic processes in the roots. Combination of Mn+Cd promoted greater accumulation of proteins involved in metabolic processes in leaves and response to defense and stress in roots. In addition, the majority of DAP and EP found in leaves are related to photosynthetic processes (35%), while the majority identified in roots are related to other functions (30%). It was verified by immunodetection that the toxicity of Cd was mitigated by Mn as a result of the higher accumulation of catalase in the presence of Cd (2x) and lower accumulation in the presence of Mn+Cd. It was concluded that proteins involved in oxidoreduction and defense and stress response processes, in addition to other processes, were induced in the presence of Cd and repressed in the presence of Mn+Cd. This demonstrated that Mn was able to mitigate the toxic effects of Cd on young plants of the CCN 51 cacao genotype.