Experiments using in vitro embryo germination and culture have been designed to investigate the effects of cobalt levels of 0, 100, 200, 400 and 800 μM on some growth parameters and chemical changes in Jatropha curcas seedlings. The results showed that excess cobalt levels in MS media produced visual symptoms of toxicity in J. curcas seedlings after 7 d with increasing levels of cobalt ion. The fresh weights of cotyledons and radicles were significantly affected except for hypocotyls at the cobalt concentration of 100 μM. The activity of superoxide dismutase (SOD) significantly increased in the radicles when compared to the control, but decreases in the activity of the hypocotyls were found at the tested cobalt levels. Increase of guaiacol peroxidase (GPX) activity in the cotyledons and hypocotyls was observed at the tested cobalt levels, but a decrease of the activity in the radicles except for at cobalt concentration of 100 μM. Increase in the activity of catalase (CAT) of radicles with increasing cobalt concentrations, and a significant decrease in activity in the hypocotyls was also observed. Increase in phenylalanine ammonia-lyase (PAL) activity of cotyledons and radicles with increasing cobalt concentrations in the range 100–800 μM, but a decline in the activity of hypocotyls was also observed when hypocotyls at the cobalt concentrations of 400 and 800 μM. The present results indicated that SOD, GPX, CAT, and PAL may play an important role in the defensive mechanisms of Jatropha curcas seedlings exposed to excessive cobalt. These findings will help to provide useful bioassays to help in assessment of cobalt contamination in agricultural environments.

28.4.2023