Impact of Ferrous Sulfate on Thylakoidal Multiprotein Complexes, Metabolism and Defence of Brassica juncea L. under Arsenic Stress

Abstract

Forty-day-old Brassica juncea (var. Pusa Jai Kisan) plants were exposed to arsenic (As, 250 µM Na2HAsO4·7H2O) stress. The ameliorative role of ferrous sulfate (2 mM, FeSO4·7H2O, herein FeSO4) was evaluated at 7 days after treatment (7 DAT) and 14 DAT. Whereas, As induced high magnitude oxidative stress, FeSO4 limited it. In general, As decreased the growth and photosynthetic parameters less when in the presence of FeSO4. Furthermore, components of the antioxidant system operated in better coordination with FeSO4. Contents of non-protein thiols and phytochelatins were higher with the supply of FeSO4. Blue-Native polyacrylamide gel electrophoresis revealed an As-induced decrease in almost every multi-protein-pigment complex (MPC), and an increase in PSII subcomplex, LHCII monomers and free proteins. FeSO4 supplication helped in the retention of a better stoichiometry of light-harvesting complexes and stabilized every MPC, including supra-molecular complexes, PSI/PSII core dimer/ATP Synthase, Cytochrome b6/f dimer and LHCII dimer. FeSO4 strengthened the plant defence, perhaps by channelizing iron (Fe) and sulfur (S) to biosynthetic and anabolic pathways. Such metabolism could improve levels of antioxidant enzymes, and the contents of glutathione, and phytochelatins. Important key support might be extended to the chloroplast through better supply of Fe-S clusters. Therefore, our results suggest the importance of both iron and sulfur to combat As-induced stress in the Indian mustard plant at biochemical and molecular levels through enhanced antioxidant potential and proteomic adjustments in the photosynthetic apparatus.