Increasing salinity leads to differential growth and H2O2 homeostasis in plants produced from heteromorphic seeds of the succulent halophyte Arthrocnemum indicum.

Information about responses of plants grown from heteromorphic seeds is limited and inconclusive. This is especially true of subtropical halophytes where such studies have yet to be published. Therefore, growth, water-relations, and oxidative stress mitigation of plants germinated from the heteromorphic seeds of the succulent halophyte Arthrocnemum indicum under increasing (0, 300, and 900 mM NaCl) salinity were studied. Growth of plants from only small seeds was stimulated in moderate (300 mM NaCl) salinity. High (900 mM NaCl) salinity inhibited the growth of plants emerged from both small and large sized seeds. Plants germinating from both seed sizes demonstrated similar patterns of osmotic adjustment and did not develop signs of oxidative damage under increasing salinity. However, the magnitude of hydrogen peroxide and antioxidant responses differed between plant types. Under moderate salinity, plants from small seeds showed constitutive activities of most antioxidant enzymes (except superoxide dismutase) and levels of non-enzymatic antioxidants (except ascorbate). Conversely, a decline in activities of most antioxidant enzymes and levels of most non-enzymatic antioxidants occurred in plants from large seeds. While under high salinity, increased ascorbate peroxidase, glutathione, and polyphenol levels, along with unaffected ascorbate and superoxide dismutase levels, occurred in plants from small seeds. In plants from large seeds, there were increased ascorbate and polyphenol levels, but changes to the ascorbate peroxidase levels were not observed. These results thus indicate differential growth and hydrogen peroxide homeostasis in A. indicum plants emerged from heteromorphic seeds.

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.