Proceedings of the XLVII Italian
Society of Agricultural Genetics - SIGA Annual Congress
Verona,
Italy - 24/27 September, 2003
ISBN 88-900622-4-X
Poster
Abstract - 4.10
CHARACTERIZATION OF A MAIZE MUTANT AFFECTING EMBRYO
AND SEEDLING DEVELOPMENT
M. Colombo*, A. Adamo*, C. Dall’Aglio*, F. Dalla Vecchia**, S.
Dolfini***, G. Gavazzi*, A. Giulini*, R. Pilu*, N. Rascio**, G. Consonni*
*) Dipartimento di Produzione Vegetale,
Università degli Studi di Milano, Via Celoria 2, 20133 Milan
**) Dipartimento di Biologia, Università degli
Studi di Padova, Via Colombo 3, 35121 Padova
***)
Dipartimento di Genetica e di Biologia dei Microrganismi,
Università degli Studi di Milano, Via Celoria 23, 20133 Milano
maize, developmental mutants, seedling development,
cell wall
In
maize embryogenesis the coleoptile and first leaves make their appearance
during the period from 14 to 20 days after pollination. The coleoptile is
formed initially as a ridge of tissue surrounding the central cell stem
meristem. The ridge develops more rapidly above then below the central meristem
and forms a sheating structure that envelops the stem tip and embryonic leaves.
During germination, the plumule and the coleoptile begin to elongate: at first
the coleoptile grows faster than the plumule but when it reaches the surface of
the soil and is thus exposed to light, it soon ceases to grow and the plumule
breaks out from the tip.
Characterization
of the fused leaves (fdl) mutant phenotype suggested that the fdl gene
is required during the initial phases of seedling growth. Homozygous fdl
seedlings are retarded in their germination when compared to wild-type
siblings. Moreover they show regions of fusion between the coleoptile and the
first leaf, and between the first and the second leaf. Studies performed at
ultrasctructural level have revealed that these fusions involve the cell wall
of epidermal cells. The cuticle layer is not present between the two epidermis
that appear joined by a single cell wall.
We have analysed
the expression of Beta-expansins in the mutant seedlings. Expansins are plant
cell wall proteins first discovered in studies of plant cell enlargement as the
mediators of acid growth. Expansins are classified in two families, which are
called alfa and beta-expansins and many cDNA and genes have been identified in
plants. They have unique “loosening” effects on plant cell walls
and are thought to have a role in different processes, including cell
separation (1). A higher level of ExpB2 mRNA was detected in fdl
mutant seedlings during initial phases of seedling growth when leaves are still
enrolled inside the coleoptile.
Longitudinal
sections of fdl mutant embryos have shown that in the shoot apex
coleoptilar cells occupy an ectopic position in the central region, which is
normally occupied by leaf primordia.
Embryo rescue
experiments have confirmed that fdl mutation affects
the pre-germinative phase of development and have allowed us to assay the
effect of exogenous auxins application to cultivated immature embryos. We will
present data on the different sensitivity of the mutant embryos to the hormone
treatments.
Taken together
these observations suggest that the mutation has a pleiotropic effect on both
embryo and seedling growth in maize.
fdl has been located on the long arm of chromosome 7
between UMC 1342 and UMC 1125. Molecular genetic analysis indicate that the
mutation is presumably caused by insertion of an Spm
element in the fdl locus. Efforts aiming at cloning the gene are
underway.
1. Daniel J. Cosgrove. Enzymes and other agents that enhance cell wall extensibility. Annu. Rev. Plant Physiol. Plant Mol. Biol. 50:391-417 (1999)