Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 191 (2011)
Are non-methylated uronic acids involved in limiting extension
growth of maize shoot in the first phase of salt stress?
Nesar Uddin, Ruben Leubner, Philipp Eitenmüller, Stefan Hanstein and
Sven Schubert
Institute of Plant Nutrition, Universität Gießen. E-Mail: mnesar_bau@yahoo.com
Introduction
The carboxyl groups in pectins are highly esterified with methyl groups during
biosynthesis in the golgi and are deesterified later, as the cells ceasing growth, due
to the action of pectin methylesterases. De-esterified pectins form stiff gels through
Ca 2+ -mediated cross-linking of carboxyl groups through ionic and coordinate bonds
(Cosgrove, 2005). Changes in pectins and methylesterification of pectins in cell walls
of different maize genotypes in the first phase of salt stress may explain their
differential inhibition of growth.
Results and Discussion
In order to investigate the changes of non-methylated pectin concentrations in cellwall
as affected by salt stress, three maize genotypes namely Pioneer 3906, SR 12
and SR 03 were cultivated in 1 mM (control) and 100 mM NaCl. Pectin and
methylesterification of pectin were determined colorimetrically. The concentrations of
non-methylated uronic acids were increased in young growing shoot cell-wall of
Pioneer 3906 and SR 12 but decreased in SR 03. However, studies with the
youngest and younger shoot cell-wall of SR 12 and Pioneer 3906 revealed that the
relative increase of non-methylated uronic acid concentration is delayed in SR 12
compared to Pioneer 3906, which perhaps favored SR 12 to grow relatively better
than Pioneer 3906 under salt stress. Previous studies revealed that only SR 03 can
maintain proton pump-mediated acidification of apoplast while SR 12 and Pioneer
3906 cannot maintain wall acidification under salt stress (Pitann et al., 2009; Hatzig
et al., 2010). This suggests that increasing concentrations of non-methylated uronic
acids may be involved in decreasing shoot elongation by forming Ca-pectate and
other types of wall cross-links in cv. Pioneer 3906 and SR 12. However, the growth
inhibition in SR 03 might come from other types of cross-links rather than nonmethylated
uronic acid in the first phase of salt stress.
References
Cosgrove, D.J. 2005. Growth of the plant cell wall. Nat. Rev. Mol. Cell. Biol. 6(11):850-861.
Hatzig, S., Hanstein, S., Schubert, S. 2010. Apoplast acidification is not a necessary determinant for
the resistance of maize in the first phase of salt stress. J. Plant Nutr. Soil Sci. 173:559-562.
Pitann, B., Schubert, S., Mühling, K. H. 2009. Decline in leaf growth under salt stress is due to an
inhibition of H + -pumping activity and increase in apoplastic pH of maize leaves. J. Plant Nutr. Soil
Sci. 172:535-543.