The current study was conducted to evaluate the physiological and molecular response of self-regenerating annual Medicago species (M. polymorpha and M. lupulina) to juglone exposure. A randomized complete block design was performed in which two treatment groups consisted of a control and juglone (10-4 M) allotted to main plots and genotypes assigned to subplots. A significant increase in the concentration of GSH and the GSH/ GSSG ratio was observed in both annual Medicago species in response to juglone exposure. However, such response was greater in M. lupulina than M. polymorpha. The activity of all antioxidant enzymes (CAT, APX, GST, and GPOX) was significantly increased by juglone. In response to juglone, the expression of WRKY was significantly decreased. The transcription of CBF4, Zpt2-2, CAT, and GST genes was highly induced by juglone in annual Medicago species. Higher expression of CBF4, Zpt2-2, CAT and GST genes in M. lupulina which showed more juglone-tolerance can be associated with higher tolerance against allelochemical stress. It can be concluded that M. polymorpha is juglone-sensitive because it started to show chlorosis of leaves after a week subjecting to juglone. Though M. lupulina seems to be more juglone-tolerant at least in short term, long-term exposure of juglone should also be examined to find out its suitability to grow in walnut orchards. Considering the presence of cross-talk between different stresses, we can propose that M. lupulina is more tolerant to other abiotic stresses compared to M. polymorpha.
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