Heteromorphic seeds of coastal halophytes Arthrocnemum macrostachyum and A. indicum display differential patterns of hydrogen peroxide accumulation, lipid peroxidation and antioxidant activities under increasing salinity

Reactive oxygen species homeostasis during germination of heteromorphic seeds is not fully understood. This study elucidates changes in levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and enzymatic antioxidants in heteromorphic seeds of contrasting congeneric halophytes Arthrocnemum macrostachyum (C₃ perennial) and A. indicum (C₄ perennial) during germination under increasing salinity. There was no dormancy in A. macrostachyum (black and brown) and A. indicum (large and small) seeds. Seeds of A. macrostachyum displayed greater salinity tolerance compared to A. indicum seeds. Under non-saline conditions, large A. indicum seeds and brown A. macrostachyum seeds showed slightly higher germination than their respective counterparts. H₂O₂ content of black compared to brown A. macrostachyum seeds increased with salinity and that of small compared to large A. indicum seeds increased only in 400 mM NaCl. High catalase and ascorbate peroxidase with constitutive superoxide dismutase levels coincided with unaltered MDA in black A. macrostachyum seeds under salinity. Whereas, there was a decline in most antioxidant enzyme activities alongside low/unchanged H₂O₂ in the brown A. macrostachyum seeds under salinity. Unaltered H₂O₂ and MDA with low/unchanged antioxidant enzyme activities in large A. indicum seeds under salinity occurred. Unchanged enzyme activities alongside a rise in H₂O₂ and MDA levels were observed in the small A. indicum seeds under salinity. These data hence highlight differential H₂O₂ homeostasis strategies in the heteromorphic seeds of the test species.