Differential antioxidative and biochemical responses to aluminium stress in Brassica juncea cultivars

Aluminium (Al) toxicity in acidic soils limits crop production worldwide. We evaluated eleven genotypes of Brassica juncea (Mustard) under Al stress on basis of their growth and shortlisted two best among them for further comparative analysis. Our objective was to elucidate individual and differential oxidative damage and defence response elicited by Al treatment in selected mustard genotypes, Pusa Tarak' and Pusa Vijay'. Thirty-day-old plants of both genotypes were subjected to Al stress for a period of 24h and 72h. Concentration of superoxides was visible much higher in leaves of Pusa Vijay' both at 24h and 72h, also confirmed by oxidative stress marker thiobarbituric acid reactive substances (TBARS). The activities of the enzymatic antioxidants superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione S-transferase (GST), and catalase (CAT) were significantly higher in Pusa Tarak' compared to control and Pusa Vijay' at both time stages. Levels of non-enzymatic antioxidants glutathiones and ascorbates were already higher in Pusa Vijay'; however, Al treatment increased their levels in both genotypes with non-significant changes on inter-genotypes basis. More and significant decline by Al in chlorophylls was observed in Pusa Vijay'. Interestingly, increase in proline content by Al was much prominent in Pusa Tarak' compared to Pusa Vijay'. The in vitro antioxidant capacity estimation of mustard genotypes, evaluated by measuring 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and hydroxyl radical scavenging (HRSA) activities proved that extract of Pusa Tarak' can detoxify more radicals than Pusa Vijay'. We conclude that Pusa Tarak' can upregulate cellular antioxidants and osmoregulation, and quench more radicals compared to Pusa Vijay'. The results will contribute for selection of better Brassica genus to be grown in Al rich acidic soils, and help in designing strategies for crop breeding and cultivation.