Maize Genetics Cooperation Newsletter vol 85 2011

SARATOV, RUSSIA
Saratov State University

Embryological peculiarities of tetraploid parthenogenetic maize forms
Kolesova AY; Tyrnov VS

Apomixis is manifested, as a rule, on polyploid level, and so we started the
work on producing of analogues of the parthenogenetic lines. The tetraploid
maize form, produced by pollination of tetraploid form KrP-1 by pollen of
the diploid parthenogenetic line AT-1 was investigated. Line AT-1 is
characterized by autonomous embryo- and endospermogenesis, and, as result,
the plants of this line form with the high frequency polyembryos and
haploids. Producing of tetraploid parthenogenetic line became possible owing
to formation at line AT-1 of sporadical unreduced male gametes, that lead to
development of tetraploid plants after fertilization of diploid eggs of
tetraploids.

We carried out the analysis of 2800 embryo sacs (ES) at 18 plants. With that
purpose, we fixed preliminary isolated ears in 10 days after occurrence of
stigma. Formation of additional elements (nuclei and cells) in egg apparatus
of ES and/or autonomous development of embryo was noted at 16 plants. The
frequency of ES development with additional elements in egg apparatus varied
from 0.5 to 5.9%. ES with 4-10 cells in egg apparatus and ESs with one,
rarely with two embryos were discovered. Embryos were bicellular or
globular, containing up to 92 cells. The eggs and/or synergids in 6 ES with
three-cellular egg apparatus contained 1-4 additional nuclei.

ES with disturbed differentiation of egg apparatus were found in 13 plants.
In the main, they are ES with sinergid-like egg (to 13.2%), in which the
nucleus occupies a basal position. ES with egg-like synergid (to 2.3%) and
ES with undifferentiated egg apparatus were found. At 6 plants ES with 3.4
and 6 polar nuclei were observed. Autonomous development of endosperm was
found at 4 plants (to 3.0%).

The growing of the cells of antipodal complex was noted in the ovules of all
investigated plants. Big growing cells, reaching up to 2/3 ES size, always
adjoined antipodes. The number of ES with growing cells was from 1.14 to
49.4%. Usually 1-2 cells were growing, rarely more (to 9). The large
cells contain more often 1-2 nuclei, the cells with 3-12 and more high
number of nuclei has been also observed (up to 66).

The analysis has shown, that produced tetraploid form is characterized by
autonomous development of embryo and endosperm. Atypical ES are like in many
respects the ES of initial diploid parthenogenetic line AT-1.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of authors.