Oligoalginates from Padina pavonica obtained by chemical and mechanical fractionation differentially induce resistance of date palm vitroplants to biotic and abiotic stresses

Alginate and/or oligoalginates are known as plant defense stimulators that become a novel alternative to agrochemicals. The elicitor effects of alginate and oligoalginates derived from the brown algae Padina pavoniva on the date palm vitroplants was tested. Firstly, alginate (SAPP) was extracted and the structure was characterized by ATR-FTIR, GC/MS and H-1/C-13 NMR. The M/G ratio was 0.8 indicating that G units were abundant in the alginate polymer. Secondly, alginates depolymerization was performed using ball milling as mechanical depolymerization (OABM) and acid hydrolysis as chemical fractionation (G + M, G and M). The expression level of four plant defense marker genes PAL, SOD, PR1 and DHN in date palm vitroplants after 48 h treatments with alginate (SAPP), dried algae powder treated by ball milling (PPBM), and oligoalginates were investigated. The four genes were up-regulated differentially, according to the elicitor treatment. The highest transcription levels of PAL (phenylalanine ammonia-lyase), PR1 (pathogenesis-related protein 1), SOD (superoxide dismutase) and DHN (dehydrin) (similar to 11, 7, 5 and 4-fold respectively more than obtained in control vitroplants) were observed in the vitroplants treated with OABM followed by oligoalginates obtained by chemical hydrolysis. The lowest transcription levels were observed in both SAPP and PPPM treated plants. OABM treated vitroplants showed increased resistance to salt, drought and fungal contamination. These findings open up promising prospects for a new depolymerization method of alginate as a more efficient tool to induce a defense response in plants against abiotic and biotic stresses.