Transient salinity stress promotes secondary metabolites and antioxidant enzymes in Brassica plants

This study investigated salinity stress time-dependent responses of pak choi (Brassica campestris L.), arugula (Eruca sativa Mill.), and red frill (Brassica juncea L.), focusing on growth parameters, secondary metabolites, and antioxidant activities. Salinity stress (NaCl) solution with electrical conductivity (EC) of 12.6 dS∙m⁻¹ was introduced to the rhizosphere at the specific time: from 2:00 pm on day 6 to 2:00 pm on day 7 (1st week (W)), 2:00 pm on day 13 to 2:00 pm on day 14 (2nd W), and 2:00 pm on day 20 to 2:00 pm on day 21 (3rd W). Plant growth parameters were assessed at 1, 2, and 3 weeks after transplantation (WAT), showing detailed changes over time. Pak choi exhibited a significant increase in biomass at 2nd W, whereas arugula and red frill showed no marked differential reactions. Glucosinolates (GLS), phenolic compounds, and antioxidant activities were analyzed at 2 and 3 WAT. Maximum GLS concentrations in pak choi and arugula plants occurred in the 3rd W under 3 WAT. Phenolic concentrations in the arugula peaked under the 2nd W treatment. Regarding pak choi, the 1st W treatment at 3 WAT and 2nd W treatment at 2 WAT exhibited maximum DPPH scavenging activity and peroxidase (POD). The 2nd W treatment at 2 WAT indicated the highest total phenol concentration and POD activity in arugula. Red frill exhibited significantly elevated total glucosinolate concentrations under salinity conditions at 3rd W. This analysis reveals how salinity stress affects growth and biochemical responses in these vegetables, offering insights for optimizing cultivation under saline conditions.