Botanical Studies (2007) 48: 311-317.
*
Corresponding author: E-mail: msanso@vet.unicen.edu.ar;
Tel. +54-2293-439850.
INTRODUCTION
Alstroemeria andina Phil. var. venustula (Phil.) M.
Munoz (sub nom. A. andina Phil. subsp. venustula
(Phil.) Ehr. Bayer) is a perennial, small herb, 5-16 cm
tall, that occurs at 2,800-3,700 meters above sea level,
exceptionally at 2,300-2,400 meters above sea level, in
populations of limited distribution from Argentina and
Chile (Sanso, 1996). This taxon inhabits the IV Region of
Coquimbo in Chile and the departments of Iglesias and
Calingasta, San Juan province, in Argentina (Bayer, 1987;
Sanso, 1996). Its habitat comprises stony or sandy slopes
and screes of the Anden mountains (Sanso, 1996).
The basic karyotype structure in the entire genus
Alstroemeria is apparently uniform, and most species of
this one have normal male meiotic behaviour with eight
bivalents and the larger pair showing up to three visible
chiasmata (Sanso, 2002). The karyotype formula of A.
andina var. venustula was: 3 m pairs, 1 sm pair, 3 t and 1 t
(st) pair, with microsatellites observed on pairs n¢X 3 and n¢X
6. Chromosome lengths ranged from 5.55 £gm to 22.78 £gm
(Sanso, 2002).
This paper reports the first meiotic characterization of
a population of A. andina var. venustula, with results that
are totally different from all previous karyological studies
of the genus.
MATERIALS AND METHODS
Plant materials for this study were collected from
San Juan province, Calingasta department, Puesto de
Gendarmeria, Las Juntas, at 31¢X41¡¦49" S-70¢X14¡¦13" O,
Argentina. Voucher specimens, Fortunato & Kiesling
5631, were deposited at Herbarium of Instituto Darwinion
(SI).
Flower buds of individuals collected from the wild
population were fixed in ethanol-chloroform-glacial acetic
acid (6:3:1) and later transferred into 70% ethanol and
stored at 4-5¢XC. The cytogenetic analysis of this reduced
population of A. andina var. venustula revealed that
only five buds presented appropriate cells to analyze the
course of meiosis, even when flower and anther sizes were
suitable for it. Immature anthers were dissected out and
CYTOGENETICS
Meiotic irregularities in Alstroemeria andina var. venustula
(Alstroemeriaceae)
Andrea Mariel SANSO
1,2,
* and Arturo Federico WULFF
1
1
CONICET, Dpto. de Ecologia, Genetica y Evolucion, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos
Aires, 1428 Buenos Aires, Argentina
2
Laboratorio de ADN, Dpto. de Biologia, Facultad de Ciencias Veterinarias, Universidad Nacional del Centro de la
Provincia de Buenos Aires, Campus Universitario, Paraje Arroyo Seco, 7000 Tandil, Argentina
(Received August 30, 2006; Accepted April 16, 2007)
ABSTRACT.
Alstroemeria andina Phil. var. venustula (Phil.) M. Munoz (sub nom. A. andina Phil. subsp.
venustula (Phil.) Ehr. Bayer) is a perennial, small herb, 5-16 cm tall, that occurs mainly at 2,800-3,700
meters above sea level, in populations of limited distribution from Argentina and Chile. The course of the
meiosis was analyzed in a population of this taxon (2n = 2x = 16), and it proved to be highly irregular. It was
characterized by presenting bridge and fragment configurations both at anaphases I and II. The highest number
of bridges at anaphase I found in one cell was two, suggesting heterozygosity for as many as two paracentric
inversions. Typical chiasmata were almost not detectable, even though they actually existed. The chiasma-
like structures observed may be regarded as concealed chiasmata as it has been described in cryptochiasmate
meiosis. A high frequency of tetrads with micronuclei was observed, implying significant levels of unbalanced
gametes. Pollen stainability ranged between 28 and 30%. In Alstroemeria species the meiotic behaviour is
highly regular, and the presence of rearrangements is very uncommon. The whole situation led us to suggest
that some environmental factors have drastically affected the chromosome structure and the control of the
meiotic process. The present study constitutes the first report of remarkable meiotic irregularities found in a
wild population of this genus.
Keywords: Alstroemeriaceae; Chromosomes; Cryptochiasmate meiosis; Meiotic behaviour; Pollen staining;
Structural heterozygosity.
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Botanical Studies, Vol. 48, 2007
slides were performed by the squash method in propionic
acid haematoxylin (2%) using ferric citrate as a mordant
(Nunez, 1968).
For estimation of pollen viability, pollen grains
of flowers at anthesis were stained with Alexander's
differential stain (Alexander, 1969).
RESULTS
A strong disturbance of synchronization was detected
in the development of pollen mother cells leading to a
broad range of variation in meiotic stages. Cells from the
diplotene stage (Figure 1A), microspores, and even pollen
grains (Figures 3E and 3F) were present within the same
anther, which is uncommon in Alstroemeria species.
The individuals showed eight bivalents, two of them
were easily identifiable because of their notably larger size
(pairs no 1 and 2). Striking differences in the morphology
of the bivalents compared with the previously studied
Alstroemeria species were observed. Chromosome pairing
seemed to be normal since univalents were seldom
observed at diakinesis or metaphase I. From diplotene
until diakinesis, or even metaphase I, the eight bivalents
could be observed with the homologue chromosomes
so intimately associated, that they gave the appearance
of being composed of a single element (Figures 1A-D).
The opening-out of the bivalents in the reductional plate,
which usually occurs at the very beginning of diplotene,
was postponed until first metaphase and in some cells it
even did not occur at all until the homologues were pulled
apart at anaphase. Separation of non-sister chromatids
was suppressed, and there was thus no typical diplotene-
diakinesis, and synapsis of homologue chromosomes was
prolonged up to metaphase I (Figures 1A-D). Chiasmata
were almost undetectable at these stages, even though
they actually existed. The reductional split opened up at
metaphase (exceptionally late diakinesis), revealing some
chiasmata (Figures 1E and 1F). The centromeres co-
orientated, and gradually became separated, and the paired
segments were consequently pulled apart towards the
distal ends by the centromere movement (Figures 1G, 2A
and 2B).
Different abnormalities were observed at anapahase I
(Table 1). In summary, only 46 out of 213 cells (21.60%)
at first anaphase showed neither bridges nor fragments.
The highest number of bridges at anaphase I found
in one cell was two (34 cells = 20.36%), suggesting
heterozygosity for as many as two paracentric inversions.
Most of these cells with two bridges (Figures 2C,
D) presented also two fragments (28 out of 34). The
fragments usually lagged at the equator and in some cells,
non congressed, lagged univalents or bivalents were found
at anaphases I near them (Table 1, Figure 2D). Bivalents
forming double bridges and fragments were also observed.
(They could be explained as a four-strand double
crossover within the inversion.) (Figure 2A). In that same
cell (Figure 2A), a chromatid loop (arrowhead) indicated
the presence of another inversion in heterozygosis in a
different chromosome pair. A possible explanation for
this meiotic figure is if, in addition to a chiasma in a
paracentric inversion loop, one occurs in the interstitial
segment between the centromere and the inversion. In
this case, the anaphase I bridge is converted into a loop
plus a fragment in one of the chromosomes of the original
bivalent (Sybenga, 1992, page 115). At anaphase II the
loop becomes a bridge that is not formed when a bridge is
present at first anaphase. The remaining chromosome of
the pair is present in the other pole of this cell, but it was
difficult to individualize it.
At anaphases II one (Figure 2E) or two bridges (Figure
2F), bivalents, chromosome fragments, and/or chromatid
fragments (Figure 2E) could also be observed. With
regard to the relationship between the bridges and the
fragments, it was noted that in most cases, every bridge
was accompanied by one fragment (two dicentric bridges,
two fragments). However, some cells were found to have
only bridges (with no fragments) and other ones, with
more bridges than fragments (Table 1).
In the tetrad analysis, we found that only about 18%
of the tetrads lacked micronuclei, and most of them
presented from 1 to 4 micronuclei (Table 2): 1 (56%), 2
(27%, Figure 3A), 3 (19%, Figures 3B and 3C), 4 (3%,
Figure 3D). A very low pollen grain number was present
within the anthers, and in some cases they were almost
Table 1. Number and percentage of cells presenting or not presenting bridges, fragments and/or univalents/bivalents at anaphase I.
Normal cells
Cells presenting dicentric bridges
Total number
of cells
One bridge
a
Two bridges
a
Only +1f +1f+2I or 1II +1f+1I Only +2f +2f+1-2I or 1II +1f
39 79
12
3
2 22
6
4
46
133
34
213
79.64%
20.36%
21.60%
78.40%
100%
a
f = acentric fragment; I = univalent; II = bivalent.
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SANSO and WULFF ¡X Meiotic irregularities in
Alstroemeria andina
313
completely absent. Although pollen stainability ranged
between 28 and 30%, the pollen fertility value is suspected
to be significantly lower, bearing in mind the percentage
of observed tetrads presenting micronuclei. Furthermore,
two kinds of pollen grains were found: small sized with
supposedly normal chromosome complements (Figure 3E)
and very large ones with abnormal chromosome numbers
and fragments (Figure 3F).
DISCUSSION
In Alstroemeria species meiotic behaviour is highly
regular and the presence of rearrangements very
Figure 1. Meiosis in Alstroemeria andina var. venustula (n = 8). A: diplotene; B, C, and E: diakinesis; D and F: metaphase I; E and F:
bivalents showing clearly some of the chiasmata; G: early anaphase I: seven opening-out bivalents, plus one bivalent (empty arrow)
and one fragment out of equatorial plane (full triangle). In B and D, arrowheads point out the positions of secondary constrictions of
chromosome pair n¢X 1, in C, the region between two homologous chromosomes of a bivalent which had been almost pulled apart. All
photomicrographs are with the same enlargement. Bar = 10 £gm.
Table 2. Number and percentage of tetrads with or without mi-
cronuclei.
Micronuclei number 0 1 2 3 4 Total
Tetrads number
24 62 30 16 3 135
Tetrads percentage
56% 27% 19% 3%
17.78%
82.22%
100%
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Figure 2. Anaphases in Alstroemeria andina var. venustula. A-D: anaphase I; A, B: almost all homologue chromosomes are segregated
except the largest pair; A: chromosome pair n¢X 1 with double bridges. In the same cell, a chromatid loop (arrowhead) indicated the
presence of another paracentric inversion in heterozygosis in a different chromosome pair (a possible explanation for this meiotic
figure: if in addition to a chiasma in a paracentric inversion loop, one occurs in the interstitial segment between the centromere and
the inversion; the remaining chromosome of the pair is present in the other pole of this cell, but it was difficult can individualize it);
B: chromosome pair n¢X 1 with a dicentric bridge; C: cell with two dicentric bridges, one acentric fragment (arrowhead) possibly
accompaning a bridge and at least three chromosome fragments, probably derived from breakages (empty triangles); D: cell with
two dicentric bridges, one acentric fragment (arrowhead), one possible univalent (empty triangle) and one small chromatid fragment
(full triangle) (incomplete complement); E-F: anaphase II, E: cell with a dicentric bridge, an acentric fragment (arrowhead), a small
chromatid fragment (full triangle), and two bivalents (stars), F: cell with two dicentric bridges (incomplete chromosome complement).
Figures A, B, D and figures E, F, with the same enlargement. Bar = 10 £gm.
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SANSO and WULFF ¡X Meiotic irregularities in
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315
uncommon (Sanso and Hunziker, 1998; Sanso, 2002).
The present study constitutes the first report of meiotic
irregularities from a wild population of this genus.
Although a few meiotic irregularities had been observed in
A. hookeri Lodd. subsp. cummingiana (Herb.) Ehr. Bayer
(Sanso, 2002), the studied material of this taxon endemic
to Chile was obtained from plants cultivated in a botanical
garden.
One of the striking observed features in this population
of A. andina var. venustula was the particular morphology
of bivalents during meiotic prophase. Although almost
no typical chiasmata were detected, the chiasma-like
structures observed may be regarded as concealed
chiasmata as it has been described in cryptochiasmate
meiosis. In this kind of atypical chiasmate meiosis,
numerous chiasmata are concealed between closely
Figure 3. Tetrads and pollen grains in Alstroemeria andina var. venustula. A-D: tetrads with two (A), three (B, C), or four micronuclei
(D); E, F: pollen grains, E: normal, n = 8; F: abnormal, with larger size, anomalous number of chromosomes, and chromosomal
fragments. Micronuclei are indicated by arrows. All photomicrographs are with the same enlargement. Bar = 10 £gm.
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Botanical Studies, Vol. 48, 2007
synapsed homologues, and they are apparently not
responsible for, or play a subsidiary role in, maintaining
the bivalent up until the later meiotic stages (White,
1965). Cryptochiasmate meiosis has been described in
Thericles males (loc. cit.) and has been seen previously
only in animals. This kind of meiosis is assumed to be a
transitional step from chiasmate to achiasmate meiosis
(Noda, 1975). The achiasmate condition, in which the
recombination may be virtually abolished, is usually
confined to one sex (Debus, 1978; Oakley, 1982; Morag
et al., 1982; Shanahan and Hayman, 1990). In plants,
achiasmate meiosis has been reported in pollen mother
cells of species belonging to the Fritillaria japonica
group (Noda, 1975) and in a diploid mutant, completely
male steril, described in Allium fistulosum L. (Jenkins and
Okumus, 1992).
In this population of A. andina var. venustula, in spite of
the apparent normal synapsis seen at diplotene, diakinesis,
and metaphase I, several irregularities were observed at
later stages. Bridge and fragment configurations observed
both at anaphase I and II suggested heterozygosity for
paracentric inversions. The one or two m larger pairs
were probably involved in bridge/s and fragment/s in the
anaphase cells, and the size of the observed fragment/s
in different cells was reasonably similar. It is known that
in the absence of chiasma localization the frequency of
bridge formation in an inversion reflects the length of
the segment (Dyer, 1979). In the case of the pair no 1, the
inverted segment must be extraordinarily long as bridges
were observed in 78.40% of the cells. Moreover, the large
size of this inverted segment could be inferred by the
double-dicentric bridges, which evince that more than one
crossing over may occur within the inversion.
All the described meiotic irregularities lead either to
meiotic arrest or gametic loss and cell restitution, with
the eventual formation of unbalanced gametes. As a
consequence of these disturbances during meiosis, the
plants have greatly reduced their fertility. Indeed, the
number of recombinants at least in the male meiosis is
very low since only about 20% of the tetrads did not
present micronuclei, and we cannot be assured that all of
them are genetically normal.
Alstroemeria species are long-lived herbs, with
rhizomes that stay several years underground, and sexual
reproduction is not their only way of multiplication
(Sanso and Xifreda, 2001). Alstroemeria aurea Graham
reproduces sexually by seeds and vegetatively by clonal
rhizomatous growth (Puntieri, 1991; Souto and Premoli,
2003). Alstroemeria andina would be also a clonal plant,
but in this case, it would reproduce mainly by rhizomes.
This mode of reproduction would explain the existence of
individuals such as the ones here described, which could
have accumulated several structural rearrangements and
mutations.
The possibility that these plants may be hybrids
combining genomes from different populations or species
must be put aside since the population is geographically
isolated from other Alstroemeria populations. The whole
situation led us to suggest that some environmental factors
have drastically affected the chromosome structure and
the control of the meiotic process. A plausible explanation
is that the cell division is being disturbed by natural
soil pollution, probably the proximity of a mineral bed.
The studied population was collected from a mountain
region, where mining exploration projects are being
evaluated. Alstroemeria andina var. venustula inhabits the
IV Region of Coquimbo in Chile and the departments of
Iglesias and Calingasta, San Juan province, in Argentina
(Bayer, 1987, sub A. andina subsp. venustula; Sanso,
1996). Alstroemeria andina var. andina is found in three
regions of Chile, III, IV and the Metropolitan Region of
Santiago (Bayer, loc. cit.). Further cytogenetic studies of
other populations of A. andina var. venustula in different
geographical areas and of A. andina var. andina would
be advisable in order to confirm or reject these factors as
responsible for this irregular meiotic behaviour.
Acknowledgements. AMS would like to thank to Dr.
Roberto Kiesling for supplying the plant material. Both
authors are also deeply grateful to Dr. Alba Papeschi and
two anonymous reviewers for their valuable comments
and important improvements on the manuscript. This
work was supported by the National Research Council
(CONICET) and the National University of Buenos Aires
(UBA), Argentina.
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