Altered physiology, cell structure and gene expression of Theobroma cacao seedlings submitted to Cu toxicity

Authors: SOUZAA, VANIA - University Of Santa Cruz - Brazil; DE ALMEIDAA, PEDRO - University Of Santa Cruz - Brazil; DE SOUZAA, JADIEL - University Of Santa Cruz - Brazil; MANGABEIRA, PEDRO - University Of Santa Cruz - Brazil; DE JESUS, RAILDO - University Of Santa Cruz - Brazil; PIROVANI, CARLOS - University Of Santa Cruz - Brazil; AHNESRT, DARIO - University Of Santa Cruz - Brazil; Baligar, Virupax; LOGUERCIO, LEANDRO - University Of Santa Cruz - Brazil

Submitted to: Environmental Science and Pollution Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2013
Publication Date: 6/1/2013
Publication URL: http://handle.nal.usda.gov/10113/59062
Citation: Souzaa, V.L., De Almeidaa, P.S., De Souzaa, J.S., Mangabeira, P.A., De Jesus, R.M., Pirovani, C.P., Ahnesrt, D., Baligar, V.C., Loguercio, L.L. 2013. Altered physiology, cell structure and gene expression of Theobroma cacao seedlings submitted to Cu toxicity. Environmental Science and Pollution Research. DOI:10.1007/s11356-013-1983-4.

Interpretive Summary: Copper (Cu) is an essential micronutrient required for metabolism, healthy growth and development of plants. However at toxic levels Cu is very detrimental to growth and development. Soils under cacao invariably contain very low levels of Cu that leads to Cu deficiency in cacao. But in well managed cacao plantations, repeated applications of copper-fungicides for long periods of time have led to Cu toxicity in cacao. Research was undertaken to evaluate adequate to toxic levels of Cu in nutrient medium on the physiology, leaf structure, and mineral nutrition of young cacao plants. In cacao, excess Cu in the growth medium significantly affected the photosynthesis, cell structure and transport of nutrients to the shoot. This information will be of use by fungicide manufacturers, fungicide applicators and farmers to control the levels of Cu entry into cacao plantations to avoid buildup of excess soil levels of Cu. Findings also helps cacao farmers reduce excess Cu-fungicide applications which are detrimental to the health and productivity of cacao and leads to environmental contamination.

Technical Abstract: Theobroma cacao seedlings from the genotype CCN 51 were grown under greenhouse conditions and exposed to increasing concentrations of Cu (0.005, 1, 2, 4, 8, 16 and 32 mg Cu L-1) in nutrient solution. When doses were equal or higher than 8 mg Cu L-1, after 24 h of treatment application, leaf gas exchange was highly affected and changes in chloroplasts thylakoids of leaf mesophyll cells and plasmolysis of cells from cortical region of the root were observed. In addition, cell membranes of roots and leaves were damaged. In leaves, 96 h after treatments started, increases in the percentage of electrolyte leakage through membranes were observed with increases of Cu. Moreover, there was an increase in the concentration of TBARS in roots due to lipid peroxidation of membranes. Chemical analysis showed that increases in Cu concentrations in vegetative organs increased with the increase of the metal, but there was a greater accumulation of Cu in roots than in shoots. The excess of Cu interfered in the levels of Mn, Zn, Fe, Mg, K and Ca in different vegetative organs. Analysis of gene expression via real time quantitative PCR showed increased levels of expression of MT2b, SODCyt and PER-1 genes in the roots and of MT2b, PSBA, PSBO, SODCyt and SODChI genes in leaves. Hence, it was concluded that Cu in nutrient solution at doses equal and above 8 mg L-1 significantly affected leaf gas exchange, cell ultrastructure and transport of mineral nutrients in seedlings of this T. cacao genotype.