Influence of the sulfate content of the exopolysaccharides from Porphyridium sordidum on their elicitor activities on date palm vitroplants

Given the increasing interest that is being paid to polysaccharides derived from algae as plant natural defense stimulators, the degree of sulfation of exopolysaccharides produced by P. sordidum for inducing defense responses in date palm vitroplants was investigated. Firstly, the culture parameters of P. sordidum were optimized to maximize the amount of sulfate in EPS using a Box–Behnken experimental design and the elicitor effects of two EPS which differ in the sulfation degrees were compared. Results demonstrated that the concentrations of NaCl, NaNO3 and MgSO4 set at 28, 0.54 and 16.31 g/L, respectively yielded the best sulfate contents. To elucidate defense-inducing activities in date palm vitroplants, EPS with the highest sulfate content (EPS1) were prepared for comparison with those obtained under standard conditions (EPS0). A fucoidan extracted from Cystoseira compressa was used as positive control and MgSO4 as negative control. Both EPS and the fucoidan displayed H2O2 accumulation and expression of PR1, SOD, PAL and WRKY genes. Interestingly, EPS1 was significantly more bioactive than EPS0 and the fucoidan suggesting that the elicitor activity is positively correlated with the sulfate groups content of this polysaccharide.