The effect of exogenous N-acetylcysteine on the phenolic profile and antioxidant enzyme activities in two betalainic red beet (Beta vulgaris L.) leaves under salt stress

Salinity stress adversely affects plant growth and development and causes other stresses, such as osmotic and oxidative stress. Salt-tolerant crops capable of inhabiting salty agricultural land will be useful for farming. Red beet (Beta vulgaris L.) is an economically important plant for high salt tolerance, and also contain rich in valuable ingredients including betacyanins, vitamin, antioxidant, and minerals. Exogenous treatment of chemical components facilitates the improvement of crop productivity under salt stress. N-acetyl-L-cysteine (NAC) derived from cysteine amino acid is a precursor of thiol compounds, an antioxidant, and a chelating agent. The 45-day red beets (Beta vulgaris ‘Scarlet Supreme’, B. vulgaris var. crassa ‘Ruby Queen’) were subjected to three NAC levels (100, 250, and 500 µM) and one salinity level (150 mM NaCl) for 1 week to determine the effect of applications on enzymatic and non-enzymatic antioxidant defense systems by comparing two red beets leaf extracts. NAC treatment in combination with NaCl induced an increase in total phenolic content (TPC), total flavonoid (TF), total betalain, and phenolic acid contents in ‘Ruby Queen’, while these contents decreased under the same conditions in ‘Scarlet Supreme’. The antioxidant capacity values were significantly correlated (P < 0.01) with the TPC content in both red beets. In addition, combination treatment stimulated the activity of some of the antioxidant enzymes in comparison to salt stress alone. The GSH content in the red beets was also enhanced by the combination treatments. Furthermore, TBARS values were negatively correlated with GSH or some AsA–GSH cycle enzyme activities and to some extent with POX activity in the leaves of red beets. These results suggest that NAC treatment alleviated many of the deleterious effects of salt stress in beet leaves, which was achieved by enhancing antioxidant defense system-modulating enzymatic and non-enzymatic antioxidant components.