Plant Science 157 2000 165 – 172
Changes in lipid composition during somatic embryogenesis in leaves of Cichorium
Axelle Blanckaert
a
, Lionel Belingheri
b,
, Jacques Vasseur
a
, Jean-Louis Hilbert
a
a
Laboratoire de Physiologie Cellulaire et Morphogene`se Ve´ge´tales, USTLINRA, Uni6ersite´ des Sciences et Technologies de Lille, F-
59655
Villeneu6e d
’
Ascq Cedex, France
b
Laboratoire de Physiologie des Parois Ve´ge´tales, Uni6ersite´ des Sciences et Technologies de Lille, F-
59655
Villeneu6e d
’
Ascq Cedex, France Received 26 October 1999; received in revised form 13 April 2000; accepted 13 April 2000
Abstract
The present studies were conducted to investigate the changes in lipid and fatty acid composition during the earliest stages of somatic embryogenesis in leaf tissues of the Cichorium hybrid ‘474’. The presence of glycerol in the culture medium during the
induction step allowed to separate two phases in the embryogenic process. Firstly, cells are induced for morphogenetic competence induction phase and secondly, they express an embryogenic competence expression phase. The analysis of fatty acid
composition of total lipids showed that the percentage of linolenic acid 18:3 decreased while that of linoleic acid 18:2 increased throughout the culture period. A comparison with a non-embryogenic genotype of Cichorium indicated a higher increase of
linoleate content in embryogenic genotype. The incorporation of [
14
C] glycerol into lipid classes was studied in leaf tissues. During the induction step, label was confined almost exclusively in polar lipids, particularly in phosphatidylcholine PC. An important
increase of labeled triacylglycerols TAG amounts was noted during the expression step. The accumulation of 18:2 was observed in PC and also in TAG. These results show that the early stages of somatic embryogenesis are associated with the increase of PC
and TAG which are mainly enriched in 18:2. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Cichorium; [
14
C] glycerol; Fatty acid composition; Lipid classes; Somatic embryogenesis www.elsevier.comlocateplantsci
1. Introduction
Lipids are essential constituents of all plant cells and play major roles in higher plants metabolism
[1]. While triglycerides are an efficient storage form of reduced carbon, particularly in seeds,
phospholipids serve as the primary nonprotein components of plant and are also sources of sec-
ond messengers. Somatic embryogenesis is a good model to investigate the morphological and molec-
ular events during early development of higher plants. Lipids have been studied in relation to
indirect somatic embryogenesis in species such as Arachis hypogaea [2], Daucus carota [3,4], Papa6er
orientalis [5] and Vitis 6inifera [6]. These studies were carried mainly on accumulation and utiliza-
tion of triglycerides during the development of somatic embryos but only little information is
available on lipid composition and changes during the early stages of the somatic embryogenesis
process.
Direct somatic embryogenesis can be obtained in the leaf mesophyll cells of the Cichorium hybrid
‘474’ by a two steps process [7]. The addition of glycerol to the culture medium of foliar fragments
during 5 days allowed the synchronization of the first division of embryogenic cells [8]. After 5 days
of culture D5, cells have acquired the embryo- genic competence induction phase. At this stage,
leaves were transferred in the same medium with-
Abbre6iations
:
DGDG, digalactosyldiacylglygerol; MGDG, mono- galactosyldiacylglycerol;
PC, phosphatidylcholine;
PE, phos-
phatidylethanolamine; PI, phosphatidylinositol; PL, phospholipids; TAG, triacylglycerols.
Corresponding author:
Tel.: + 33-3-20434071; fax:
+ 33-3-
20336302. E-mail address
:
lionel.belingheriuniv-lille1.fr L. Belingheri. 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 2 7 9 - X
out glycerol and cells expressed their embryo- genic competence expression phase. Multicellu-
lar dense embryos appeared 3 days after transfer in the expression medium. The presence of glyc-
erol delays the first division of the embryogenic cell, making of this system a valuable tool to
investigate the early events taking place during somatic embryogenesis. In previous studies, we
have shown the presence of proteins related to somatic embryogenesis during the induction step
in leaf tissues [9,10] and in extracellular condi- tioned medium of leaf explants [11,12].
In this paper, we report the changes in total fatty acid composition in leaf tissues of a nonem-
bryogenic responsive genotype and a embryo- genic
responsive genotype
of Cichorium
submitted to embryogenic conditions. The acyl and lipid class composition was investigated in
Cichorium hybrid ‘474’ during the embryogenic process. Moreover, we labelled plant lipids with
[
14
C] glycerol and we carried out a chase experi- ment during which the labeling of polar and
nonpolar lipids was studied.
2. Materials and methods
