Comparative effects of neutral salt and alkaline salt stress on seed germination, early seedling growth and physiological response of a halophyte species <i>Chenopodium glaucum</i>

Abstract

Effects of neutral salt (NaCl) and alkaline salt (NaHCO₃) stress on seed germination, early seedling growth and physiological response of 15-day-old seedling of Chenopodium glaucum, a halophyte widely distributed in temperate saline areas of China, were determined. Results show that NaCl stress of higher concentration (≥ 300 mM) more seriously retarded and postponed seed germination of C. glaucum, however, the inhibitory effect of NaHCO₃ stress on radicle and hypocotyl elongation was greater than NaCl stress even at lower concentration. Relative water content (RWC) of C. glaucum remained high even under the highest salt or alkali stress. No obvious increase of osmolytes (proline, soluble sugar, betaine) was detected under lower concentration of NaCl and NaHCO₃ stress. The Na+ content and Na⁺/K⁺ ratio increased while the K⁺ content decreased under both stresses, the changing extents under NaHCO₃ were greater than those under NaCl stress. Moreover, seedlings exposed to lower concentration of NaHCO₃ generated higher levels of reactive oxygen species (ROS, O2ˉ, H₂O₂), meanwhile significant increase of antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POX)] activity and non-enzymatic antioxidants [Carotenoids (Car), ascorbic acid (AsA)] content were detected in seedlings treated with lower concentration of NaHCO₃. Results suggest that the destructive effects of alkaline salt stress on the growth, ion balance and anti-oxidant system of seedling of C. glaucum were more severe than those under neutral salt stress. Different pH circumstance might be the key reason for the distinctive difference between them.

Key words: Chenopodium glaucum, enzymatic antioxidant, non-enzymatic antioxidant, osmolytes, oxidative stress, salt stress and alkali stress, seed germination.