Metals and selenium induce medicarpin accumulation and excretion from the roots of fenugreek seedlings: a potential detoxification mechanism

Medicarpin (M), an isoflavonoid phytoalexin, accumulates in plants of the Fabaceae family as a response to biotic and abiotic stresses. In an attempt to investigate the potential participation of M in metal detoxification, we studied the effect of three metals (copper, cadmium, and aluminum) and selenium on M synthesis and excretion from the roots of fenugreek (Trigonella foenum-graecum L.) seedlings. Medicarpin content and gene expressions were determined by RP-HPLC and RT-PCR, respectively. All treatments significantly induced increase in the expression of M biosynthetic genes and concomitant increase of M content in the roots and the culture medium. The metal and Se-induced M excretion inhibited by either orthovanadate or KCN, an ATPase and an ATP synthesis inhibitor respectively, and the elicitor-induced increase of GST transcript levels may imply the involvement of an ABC-type transport system in which GST is involved. Interestingly, a parallel increase of citrate exudation, a common metal detoxification agent, was measured in response to the elicitors used. The above results, along with the moderate effects of these elicitors on root growth and the plasma membrane integrity, imply that M as well as citrate exudation may participate in metal and Se detoxification, as part of a non element-specific resistance mechanism.