PEREIRA-NETTO, ADAUCTO B.*, JULIANA M. MENESTRINA, ANA MARIA A. CARNEIRO LEAO, AND MARCELO IACOMINI. 1Dept. of Botany-SCB-University of Parana; 2 Dept. of Biochemistry-SCB-University of Parana; 3 Dept. of Animal Morphology and Physiology-University of Pernambuco. - A novel lysine-rich arabinogalactan with regulatory effects on carrot (Daucus carota) cells growth and differentiation.
Arabinogalactan-proteins (AGPs) are a class of proteoglycans found in
cell secretions and plasma membranes. Attention is currently focused
on their structure and their potential role in plant cell growth and
development. An acid arabinogalactan has previously been shown to be
the major component of the cashew nut tree (Anacardium
occidentale) gum exudate [Menestrina, J.M. et al., 1998
(Phytochemistry, 47: 715-721)]. Steric exclusion chromatography
revealed that this arabinogalactan has a molecular weight of 11.2 x
103 of which 0.5 % (w/w) consists of protein. Analysis of
the amino acid composition of the polysaccharide protein moiety showed
that it has a high lysine content (82.1%), a low serine (9.5%) and
alanine (2.2%) content, and also undetectable amounts of proline or
hydroxyproline. Significant (p=0.05) reduction on the number of
somatic embryos, regardless differentiation stage, was found for
carrot (Daucus carota) cells grown in a culture medium enriched
with this arabinogalactan. However, no significant change on the
number of somatic embryos, at the cotiledonary stage, was found for
carrot cells grown in this arabinogalactan-enriched culture medium. No
significant (p=0.05) difference was found for fresh weight of carrot
cells grown in the arabinogalactan-enriched culture medium. However,
significant reduction on the cells’s fresh weight was noticed when the
cells were grown in a culture medium containing a sulfated (D.S. =
1.13) form of the arabinogalactan. Based on these results, we
hypothesize that the hydroxyprolin, serine, and alanine-rich protein
moiety, which characterizes AGPs, is not a requirement for the
arabinogalactans to be able to change the plant cell growth (fresh
weight) or differentiation (embryogenetic potential) pattern.
Key words: Arabinogalactan, cell differentiation, Daucus carota, proteoglycans, somatic embryogenesis