Effects of spermidine and salinity stress on growth and biochemical response of paraquat-susceptibe and -resistant goosegrass (Eleusine indica L.)

This study aimed to investigate the interaction effect of spermidine (Spd) and salinity stress on growth, photosynthetic rate, antioxidant system and free polyamines (PAs) contents of goosegrass (Eleusine indica L.) seedlings. E. indica was raised in a growth chamber under normal and toxic salt stress (100 mM of NaCl) and sprayed with 0 and 1.00 mM of Spd. The degree of growth inhibition caused by salt stress was lower in a paraquat-resistant (R) biotype compared to a paraquat-susceptible (S) biotype. Salt stress significantly elevated the accumulation of malondialdehyde, electrolyte leakage and proline and resulted in the degradation of chlorophyll; reduction in chlorophyll fluorescence; and a decrease in photosynthetic rate, relative water content and biomass. Spd-treated plants maintained higher activities of antioxidant enzymes (catalase, superoxide dismutase and peroxidase), a greater rate of photosynthesis and lower osmotic pressure than untreated plants in the S biotype. Endogenous Spd content was reduced significantly in response to salt stress in both biotypes, but free PAs content in the S biotype was remarkably enhanced with exogenous Spd application under normal or salinity stress conditions. The result indicated that the S biotype was more sensitive to salinity than the R biotype; meanwhile, exogenous Spd maybe play an important role in protecting S biotype plants from salt stress.