Chromosome doubling influences the morphological, physiological, biochemical and genetic traits related to essential oil biosynthesis of peppermint (Mentha piperita) under salinity stress

Peppermint (Mentha piperita L.) is an important medicinal aromatic plant. In this study, the morphology, physiology, biochemistry and gene expression of chromosomes doubling peppermint (D1 lines) were analyzed. The analysis showed that D1 lines had larger, thicker and darker leaves, and stronger roots when planted in the pots, but delayed growth in the field condition. Under NaCl stress, the D1 lines increased cell oxidative defense through more active antioxidant enzymes and decreased the oxidative damages of cell membrane, leading to a significantly greater survival rate and photosynthesis intensity than WT lines. The size and density of glandular trichomes of D1 lines was larger, which contributed to its higher essential oil yield. In addition, chromosome doubling reduced the inhibition of NaCl stress on essential oil yield and quality, through changing the expression of genes in the oil biosynthesis pathway. The traits of chromosome doubling peppermint provide new technical and theoretical evidence for peppermint germplasm improvement.