Alterations in Lignin Peroxidase and Ascorbate Peroxidase Activities in Crocus sativus L. Corms Exposed to Copper

Excessive copper uptake induces toxicity that has been linked to the production of reactive oxygen species (ROS), thereby inducing DNA mutations, lipid peroxidation, damage to proteins structure and function. Peroxidases scavenge ROS while also performing other functions, such as lignification in plants. In this research, the activity of ascorbate peroxidase, as well as that of lignin peroxidase, was investigated in extracts prepared from Crocus sativus L. corms cultivated for 6 days in distilled water and in water supplemented with copper sulfate concentrations ranging from 0.0006 mM to 12 mM. Ascorbate peroxidase activity was assayed by monitoring the H2O2-mediated oxidation of ascorbate at 290 nm, while lignin peroxidase activity was assayed by monitoring the H2O2-mediated oxidation of ferulic acid at 310 nm as well as the H2O2-mediated oxidation of 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) at 414 nm. Results showed that ascorbate peroxidase activity decreased as the copper ion concentration increased in the cultivation medium: from a 10 % drop in 0.0006 mM Cu2+ to a 50 % drop in 12 mM Cu2+. Lignin peroxidase activity measured with ferulic acid as the reducing substrate increased in extracts from corms cultivated in the presence of low copper ion concentrations, reaching three times the control value in 0.0012 mM Cu2+ and being still twice the control value in 0.006 mM Cu2+. The activity progressively dropped to one third of the control value in 0.3 mM Cu2+ and then increased again to one and a half times the control value in 12 mM Cu2+. When ABTS was used as the reducing substrate, more moderate increases and more progressive decreases in enzymatic activity were observed with no new increase at higher Cu2+ concentrations. Results revealed a fine tuning in the relative activities of various peroxidases in response to metal stress and in relation with rooting.

Keywords:

ABTS , ferulic acid , metal toxicity , oxidative stress , rooting