Fatty acid variation associated with somatic embryogenesis and calli growth of flax (Linum usitatissimum L.)

Abstract

Hypocotyl segments of in vitro grown flax (Linum usitatissimum L.) seedlings were placed on a somatic embryogenesis induction medium and culture samples were taken at time 0 (t0), after 2 (t1), 5 (t2) and 7 (t3) weeks. The developmental stages of the cultures varied from the original hypocotyl segments (HS) and segments with incipient calli formation (HSC) at t1, to embryogenic calli (EC), non-embryogenic calli and somatic embryos (SE) at t2 and t3. Freeze-dried powdered material were extracted and fractioned giving total, neutral and acid lipid fractions. The free fatty acids (FFA) present in the acid fraction and the esterified fatty acids (EFA) present in the neutral fraction were derivatized by methylation and the fatty acid methyl esters (FAMEs) were analyzed by GC and GC-MS. The main objective of this work was to study the lipid ontogenesis associated with in vitro somatic embryogenesis and with calli growth. A statistical approach (principal component analysis) was performed to rescue, from the bulk data, a latent structure related to those processes. During dedifferentiation of hypocotyl tissues and calli formation a decrease in all lipid fractions was observed. The development of SE was associated with a decrease in neutral lipids. Both FFA and EFA increased significantly with the dedifferentiation and the early calli formation, leveling off for posterior growth phases (t2 and t3). The main FFA in all samples were 16:0, 18:0, 18:1, 18:2 and 18:3. EFA fractions revealed to be more diverse in composition, specially in some uncommon FA. Predominant or sample-specific FA were also found. Important FA variations related to: 1) the dedifferention of hypocotyl tissues and growth of non-embryogenic calli, 2) the somatic embryogenesis process and 3) the development of somatic embryos, were observed. The value of some FA as biochemical markers of SE autotrophic capacity and calli embryogenic capacity is discussed.