Abstract
The tropical and subtropical naturalized physic nut (Jatropha curcas L.), has been explored for biodiesel production in recent times. The oil is extracted from the seeds and, for the production to be feasible, utilization of the residual seed cake is crucial. Although the cake could be employed as a protein source in animal feed, it is rich in phorbol ester, which is toxic for animals. Therefore, breeding programs have been working to reduce or eliminate the phorbol ester content in physic nut. In this context, the present work aimed to evaluate the physic nut oil of toxic and non-toxic varieties (containing known or undetectable amounts of phorbol ester, respectively) with regards to phytotoxicity in a model experiment with Lactuca sativa L. For this, the percentage of germinated seeds was evaluated after 8, 16, 24, 36 and 48 hours of exposure to the treatments with toxic and non-toxic oil at concentrations of 22.5 %, 45 % and 67.5 % of emulsion (physic nut oil energetically mixed with distilled water). Root growth was determined after 48 hours of exposure and the germination speed index was obtained. The different stages of mitotic division as well as possible chromosomal and nuclear alterations were also recorded. The mitotic index was calculated as the number of dividing cells, as a fraction of the total number of cells, and the frequency of chromosome and nuclear alterations, expressed as the percentage of number of alterations divided by the total number of cells. Both varieties exhibited phytotoxicity, inducing significant reductions in percentage of germinated seeds (reduction of 98 %), germination speed index (reduction of 24.44) and root growth (reduction of 8.54 mm). In microscopic analysis, a mitodepressive effect was observed for both oils at the three concentrations used when compared to the negative control; however, it was possible to distinguish between the toxic and the non-toxic varieties based on the more expressive reduction of division promoted by the first, 2.19 %. Significant increments in the frequency of mitotic cells showing chromosome alterations as well, as the presence of condensed nuclei, were observed in the treated cells. However, these parameters were not significantly different from the control in the cells treated with both physic nut oils. In conclusion, the evaluation of root growth and cell division in the plant model L. sativa, can be proposed as an alternative to animal tests to distinguish the varieties with high and low phorbol ester concentration, thus contributing to the detection of toxicity in varieties used in breeding programs. Rev. Biol. Trop. 66(2): 495-502. Epub 2018 June 01.
Highlights
The use of physic nut cake is of interest as feeding supplement for sheep, swine and other livestock, as well as for fertilization in agriculture, where it may generate important income and make these cultures more economically viable (Mendonça & Laviola, 2009)
Compared to the soybean oil, significant difference was observed in the percentage of germinated seeds (GR) and germination speed index (GSI) in relation to water, demonstrating that the reductions in germination after hours (GR) and root growth (RG) in the treatments with physic nut oil are due to its chemical components (Table 1)
Lettuce is an excellent model for macroscopic analyses, as it allows the evaluation of adverse events of a toxic compound on germination and root growth from the early initial phases of seed development in according to Valerio, García and Peinado (2007)
Summary
The use of physic nut cake is of interest as feeding supplement for sheep, swine and other livestock, as well as for fertilization in agriculture, where it may generate important income and make these cultures more economically viable (Mendonça & Laviola, 2009). (lettuce) – a plant model employed to detect macroscopic alterations, via seed germination and root growth, as well as microscopic changes, involving cytogenetic bioassays to evaluate the mitotic index and occurrence of chromosomal and nuclear alterations (Silveira, Lima, Reis, Palmieri, & Andrade-Vieria, 2017). This way, efficiency of the plant model in distinguishing the studied varieties shall be verified, incorporating such tests in the toxicity analyses of different cultivars and in the validation of detoxication experiments, avoiding animal assays
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