Maize
Genetics Cooperation Newsletter vol 87 2013
Buenos Aires, Argentina.
IEGEBA-CONICET
and LACyE, Departamento de Ecolog�a, Gen�tica y Evoluci�n, Facultad
de Ciencias Exactas y Naturales, Universidad de Buenos Aires.
MEIOTIC ANALYSIS OF F1 HYBRIDS AMONG TEOSINTES
Gonz�lez GE*, MF Fourasti�,
MF Realini and L Poggio
The association
of homologous or homeologous chromosomes in the
meiotic behaviour of F1
hybrids reveals the relative affinity between genomes of parental species.
Chromosomal rearrangements and genetic incompatibilities producing abnormal
meiosis (abnormal spindle, laggard chromosomes, among others) acting as
reproductive isolation mechanisms, could also be
detected. In the present work the genome affinities based on the chromosome
association of seven artificial hybrids among teosintes
are discussed. Moreover, pollen stainability is
reported.
Artificial crossings
between teosintes were carried out in the greenhouse to obtain
the F1 hybrid plants. The taxa using as
parental differs in chromosome sizes and total DNA amounts: Zea mays ssp. mexicana (2n=20; 2C=6.79pg), Zea mays ssp. parviglumis (2n=20; 2C=5.86pg), Zea luxurians
(2n=20; 2C=8.83pg), Zea diploperennis
(2n=20; 2C=6.36pg) and Zea perennis
(2n=40; 2C=11.36pg) (Tito et al.,
1991, TAG 83:58-64). Young panicles from each F1 hybrid were fixed
in a 3:1 solution of absolute ethanol: acetic acid and squashed in 2% acetic haematoxylin.
Normal (stained) and aborted (unstained) pollen grains were
distinguished using Alexander's stain
(Alexander 1969, Biotech Histochem 44:117-122).
Table 1 shows
the meiotic configurations and pollen stainability of
the studied F1 hybrids.
The hybrids with 2n=20
involving Z. luxurians
as one of the parental presented:
heterozygosis for heterochromatic blocks at pachytene;
5 to 10 heteromorphic bivalents, univalents with different sizes and two asinchronous groups of 5 bivalents each at diplotene-metaphase I. At anaphase
I, a maximum of 10 laggard chromosomes were observed, some of them with early
separation of their chromatids. Particularly, the meiotic behaviour of the F1
hybrids Z. luxurians
x Z. m. ssp. parviglumis revealed
differences in paracentric inversions among parentals,
since up to 3 bridges with fragments were recorded at anaphase I. The
lack of pairing and the presence of heteromorphic bivalents are probably due to
partial homology among chromosomes, and/or differences in DNA content and
chromosome sizes between the parental species.
Z. m. ssp. parviglumis x Z.
diploperennis hybrids show, at diakinesis-metaphase I, 10 bivalents as the most frequent
configuration and two asynchronous groups of 5 bivalents each. Moreover,
evidences of abnormal spindles at anaphase I and citomixis (cell fusion) were frequently detected.
The low viability of pollen, jointly with evidence of citomixis
detected suggests the existence of genetic incompatibility between the two
parent species.
The hybrids with 2n=30, Z. perennis x Z. luxurians and Z. perennis x Z. diploperennis, showed 5III+5II+5I
as the more frequent meiotic configuration, with trivalents
type "fry-pan" and homomorphic bivalents.
Summarizing, the variation in total genomic DNA content among the
progenitor species of the analyzed hybrids, which reflects differences in
chromosome sizes, explains the high frequency of heteromorphic bivalents and univalents of different sizes detected, particularly when Z. luxurians
is involved as one of the parental species. The presence of bridges and
fragments in the hybrids indicate differences in structural rearrangements (paracentric inversions) between parents. The low pollen
viability is probably due to structural/genic differences between parents,
responsible for the postcigotic reproductive
isolation detected among them.
These
results show that the genomic relationships between teosintes,
revealed through of meiotic behavior of their F1 hybrids, are relevant in the
study of genome organization and diversification of the genus Zea.
|
Hybrids |
(2n) |
III (X�SD) (range) |
II (X�SD) (range) |
I (X�SD) (range) |
Most frequent configurations (%) |
N� of cells |
Pollen stainability (%) |
|
Z. m. ssp.
parviglumis
x Z .m. ssp.
mexicana |
20 |
- |
9.83 � 0.38 (9-10) |
0.33 � 0.0 (0-1) |
10 II (83%) |
77 |
84% |
|
Z. luxurians
x
Z. diploperennis
(1) |
20 |
- |
8.65 � 0.12 (7-10) |
2.7 � 0.23 (0-6) |
9 II + 2 I (38%) 8 II + 4 I (45%) |
84 |
5% |
|
Z. luxurians
x
Z. m. ssp.
parviglumis |
20 |
- |
9.16 � 0.96 (5-10) |
1.68 � 1.59 (0-10) |
10 II (45%) 9 II + 2 I (33%) |
145 |
7% |
|
Z. luxurians
x
Z. m. ssp.
mexicana |
20 |
- |
7.5� 1.34 (5-10) |
5 � 2.44 (0-10) |
8II + 4 I (36%) |
67 |
7.25 % |
|
Z. m. ssp.
parviglumis x Z.
diploperennis |
20 |
- |
9.49� 0.56 (8-10) |
1.01 � 0.51 (0-4) |
10 II (52%) 9 II + 2 I (44%) |
63 |
6% |
|
Z. diploperennis
x Z. perennis (2) |
30 |
4.91 (1-8) |
5.25 (2-10) |
4.73 (2-8) |
5 III + 5 II + 5 I
(40%) |
168 |
2% |
|
Z. luxurians
x
Z. perennis (1) |
30 |
5.26 � 0.19 (3-8) |
4.76 � 0.23 (2-8) |
4.70 � 0.20 (2-7) |
5 III + 5 II + 5 I
(37%) |
46 |
2% |
Table 1: Meiotic
configurations of the F1 artificial hybrids. I: Univalents.
II: Bivalents. SD: Standard deviation. III: Trivalents.
(1):
From Poggio et
al., Genome 42:993-1000, 1999.
(2): From Naranjo et
al., Acad. Nac.
Cs. Ex. F�s. Nat., Buenos
Aires, Monogr. 5:43-53, 1990.
Please Note: Notes submitted to the Maize Genetics
Cooperation Newsletter may be cited only with consent of authors.