Factors involved in desiccation tolerance in oil palm embryos

Oligosaccharides and "dehydrin-like" proteins are supposed to play a role in the protection of membranes and proteins during water loss. Raffinose and stachyose may prevent sucrose crystallization during dehydration, allowing the occurrence of a glassy state and. preventing degradative processes. Desiccation of developing seeds is characterised by the accumulation of LEA (Late Embryogenesis Aboundant) mRNA and proteins. Their sequence analysis and structure prediction indicate that LEA proteins are rich in hydrophilic amino acids. This suggests that LEA proteins could play a structural role as desiccation protectants. These factors were investigated during oil palm (Elaeis Guineensis Jacq.) embryo development. Between the 4th and the 6th month after fertilisation, water content of embryo was stable (around 1.5 g H2O/g DW) and decreased down to 0.09 g H2O/g DW in the dry seed. Sugar analysis indicated that sucrose, raffinose and stachyose were present at high levels in embryos. On the contrary, reducing sugars were not detected. The sucrose content was stable during embryo development (ca 13.7 mg/g DW) and increased at mature stage up to 21.5 mg/g DW. The raffinose content increased progressively between the 4th and the 6th month after fertilisation and doubled up to 4.9 mg/g DW m dry mature embryos. Stachyose appeared during the 5th month after fertilisation and was accumulated in dry mature embryos (2.1 mg/g DW). Western blot analyses using antiserum raised against a lysine-rich sequence common to the group 2 LEA proteins indicated several variations in the patterns of "dehydrin-like" proteins during embryo development. The dehydrin antibody recognised 34, 31 and 26 kD proteins which appeared to be present only during immature stage. Polypeptid bands at 17 and 18.5 kD in mature embryos were absent both in immature embryos and young seedlings. In embryos excised from the seed 5 days after imbibition, 19.5, 21.5, 34 and 43 kD proteins were detected via western blots. Dry mature oil palm embryos are characterised by high oligosaccharide levels and specific "dehydrin-like" protein signals. The presence of these compounds has to be now correlated with anhydrobiosis. Theses results give valuable informations on desiccation tolerance in oil palm embryos in the aim of storing desiccated somatic embryos. (Texte intégral)