Extracellular Glycoproteins in Embryogenic Culture of Pumpkin (Cucurbita pepo L.)
Dunja Leljak-Levanić1*, Hana Čipčić Paljetak1, Lidija Uzelac2, Snježana Mihaljević2, Nataša Bauer1, Marijana Krsnik-Rasol1 and Sibila Jelaska1
1Department of Molecular Biology, Faculty of Science, University of Zagreb, Horvatovac 102A, HR-10000 Zagreb, Croatia
2Department of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia
Article history:
Received May 18, 2010
Accepted January 20, 2011
Key words:
Cucurbita pepo L., extracellular glycoproteins, hormone-free medium, nitrogen sources, pumpkin, somatic embryogenesis
Summary:
The extracellular proteins in three distinctly induced embryogenic lines of pumpkin (Cucurbita pepo L.) cultivated in four MS media modified regarding the nitrogen composition or auxin presence/absence have been analyzed. Extracellular glycoproteins containing α-D-mannose were specifically detected by the lectine concavalin A. During the cultivation of embryogenic tissue in the medium supplemented with reduced nitrogen, the embryos were mostly arrested at preglobular and globular developmental stages, which coincide with the absence of protein secretion. Secreted glycoproteins of 76, 68, 37 and 34 kDa were detected only if any of the three lines were cultivated in the medium that stimulates embryo development, irrespectively of the addition of 2,4-dichlorophenoxyacetic acid or tunicamycin. The glycoprotein of 64 kDa was detected in all lines cultivated in hormone- free MS medium with conventional nitrogen sources and it appears to be associated with embryo maturation. Tunicamycin treatment did not influence embryogenesis, although it specifically affected glycosylation of proteins in the investigated lines. Our results show that besides auxin, the source of nitrate is of great importance for proper protein glycosylation, excretion and developmental transition of pumpkin somatic embryos.
*Corresponding author: 
++385 1 460 6263
++385 1 460 6286