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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Sustainable Perennial Crops Laboratory » Research » Publications at this Location » Publication #337971
Title: Photosynthetic, antioxidative, molecular and ultrastructural responses of young cacao plants to Cd toxicity in the soil

Author
item ROMARIA, A - Universidade Estadual De Santa Cruz
item PEREIRA, L - Universidade Estadual De Santa Cruz
item PEREIRA, L - Universidade Estadual De Santa Cruz
item MANGABEIRA, P - Universidade Estadual De Santa Cruz
item SOUZA, J - Universidade Estadual De Santa Cruz
item AHNERT, D - Universidade Estadual De Santa Cruz
item Baligar, Virupax

Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2017
Publication Date: 10/1/2017
Citation: Romaria, A., Pereira, L.S., Pereira, L.S., Mangabeira, P.A., Souza, J.O., Ahnert, D., Baligar, V.C. 2017. Photosynthetic, antioxidative, molecular and ultrastructural responses of young cacao plants to Cd toxicity in the soil. Ecotoxicology and Environmental Safety. https://doi.org/10.1016/j.ecoenv.2017.06.006.
DOI: https://doi.org/10.1016/j.ecoenv.2017.06.006

Interpretive Summary: Cacao in South America is grown on soils that have high levels of cadmium (Cd). Cacao plants are efficient in transporting soil Cd to aerial parts and into cacao beans. Cd toxicity causes inhibition and abnormalities in the overall growth of many plant species, by interfering in the physiological and biochemical processes. High levels of Cd in cacao beans have an impact on international trade of cacao beans due to stricter regulations imposed by importing countries. In this paper we report that toxic levels of Cd in the soil caused damage to photosynthesis, antioxidative metabolism, gene expression and irreversible damage to the cell and root ultrastructure and consequently affecting the growth and development of cacao plants. This information will be useful to scientists and farmers to avoid land areas that are high in Cd levels to grow sustainable cacao and to produce cacao beans with low Cd content to protect its market value.

Technical Abstract: Cadmium (Cd) is a highly toxic metal for plants, even at low concentrations in the soil. Humans and animals by ingesting plants, fruits, seeds or their derivatives contaminated with Cd can develop a number of chronic diseases, including cancer. The annual production of world cacao beans is approximately 4 million tons. Most of these fermented and dried beans are used in the manufacture of chocolate. Recent work has shown that the concentration of Cd in these beans has exceeded the critical level (0.6 mg kg-1 DM). On the other hand, most of the information on toxicity and tolerance to Cd comes from plants grown in nutrient solutions, where the element is 100% available. The objective of this study was to evaluate the toxicity of Cd in young plants of the CCN 51 cacao genotype grown in soil with different concentrations of Cd [control (without additional Cd), 0.05 and 0.1 g kg-1 soil] for photosynthetic, antioxidative, molecular and ultrastructural changes. It was observed, with the increase of the Cd concentration in the soil, that there was (i) increase in translocation and accumulation of Cd in the aerial parts of the plants, (ii) alterations in mineral nutrient absorption by competition or synergism, (iii) changes in photosynthetic activity caused by reduction in chloroplastidic pigment content and damage to the photosynthetic machinery evidenced by the Fv/Fm ratio and expression of the psbA gene and (iv) increased GPX activity in the root and leaf SOD. In addition, there was repressed gene expression for the majority of the evaluated genes in the plants grown at the 0.1 g Cd kg-1 soil concentration, whereas plants grown in the 0.05 g Cd kg-1 soil had a higher gene expression for the psbA, phyt and met2b genes. Ultrastructural alterations in the roots and leaves were also evidenced with the increased Cd concentrations in the soil, whose toxicity caused rupture of biomembranes in root and leaf cells, reduction of the number of starch grains in foliar cells, increase of plastoglobules in foliar chloroplasts and the presence of multivesiculated body in root cells. It was concluded, that soil Cd toxicity caused damage to the photosynthetic machinery, antioxidative metabolism, gene expression and irreversible damage to the cell and root ultrastructure of plant cells of the CCN 51 genotype. The intensity of the damage depended on the exposure time to the metal.