Physiological responses and tolerance of flax (Linum usitatissimum L.) to lead stress

Flax (Linum usitatissimum L.) is a common commercial crop that is widely cultivated for fibre, oil and medicinal products globally. To select flax varieties with lead (Pb) tolerance and explore the associated tolerance mechanism under Pb stress, 19 flax varieties were grown using a hydroponic method with added Pb(NO3)2. Our results showed that L. usitatissimum ‘Milas’ displayed the highest tolerance to Pb stress, whereas L. usitatissimum ‘Yuan 2000’ was the most sensitive variety under 1 mM of Pb(NO3)2. ‘Milas’ accumulated lesser Pb than ‘Yuan 2000’. In addition, under Pb stress, the activities of peroxidase (POD) and superoxide dismutase (SOD) were higher in ‘Milas’ than in ‘Yuan 2000’, whereas the malondialdehyde (MDA) content of the aerial part and the root were lower in ‘Milas’ than in ‘Yuan 2000’. The expression levels of heavy metal stress-related genes were higher in ‘Milas’ than in ‘Yuan 2000’. Our results provide information about breeding flax varieties with Pb tolerance and the mechanisms underlying the response to Pb stress.