Nepal Journal of Science and Technology 4 (2002) 123-128
Inconstancy in Chromosome Number in Some Species
of Cassia L. Found in Nepal
B.P. chaulagainl and S.R. sakya2
1
Himalayan College ofAgricultura1 Sciences and Technology (HICAST), Bhaktapur
2
Central Department of Botany, Tribhuvarz University, Kirtipur
e-mail: bidurchaulagain @ hotmail.com
Received August 2001; accepted January 2002
Abstract
Chromosome count of five species of the genus Cassia L. (sensu lato, s.1.) viz. C. nairobensis Hort. and taxa of
sensu stricto (s.s.) like C. mirnosoides L. (Chamaecrista mimosoides (L.) E. Greene, s.s.), C.floribunda Cav. (Senna
septemtrionalis H. Irwin & Barneby, s.s.), C. occidentalis L. (Senna occidentalis (L.) Link., s.s.) and C. tora L.
(Senna tora (L.) Roxb., s.s.) was carried out. Inconstancy in somatic chromosome number of the species was
recorded. The dominant frequency of diploid chromosome number of C. floribunda was 2n =14, the variation in
chromosome number ranging from 2n =14 to 26. Similarly, 2n = 18 for C. mimosoides (varying from 14 to 30),
2n = 20 for C. nairobensis (varying from 16 to 28), 2n = 26 and 28 for C. occidentalis (varying from 16 to 38) and
2n = 22 for C. tora (variations, 2n = 16 to 38) were observed.The chromosome number of C. nairobensis Hort. is
reported here for the first time. The inconstancy of chromosome number with the instability of heteromorphic
nature of chromosome depicts the chromosomal numerical polymorphism in the taxa. The numerical polymorphism
of the chromosomes seems to be the factor responsible for the evolution of Linnaean genus Cassia L. s.1. and its
complex (Cassia, s.s. Chamaecrista & Senna) formation.
Keywords: Chamaecrista, Heteromorphic nature, Numerical polymorphism,Senna
Introduction
The Linnaean genus Cassia belongs to the pea family
Leguminosae Juss. (Fabaceae Rendl.). In Nepal, the
species of genus Cassia are mostly tropical and
subtropical in distribution and comprises about nine
species. At present, the floristic and taxonomic study
of Nepal Himalayas is in considerable progress. Since
the legumes are one of the major floras of the country
their biosystematics investigations are equally
important to know their interrelationship and general
evolutionary tendencies. The present investigating
genus Cassia L. is generally in the life form of herb,
erect shrub to under tree. Their propagation means is
mainly due to its seeds.The taxon of the genus Cassia
L. has been splited into three segregated genera such
as Cassia sensu stricto (s.s.), Chamaecrista and Senna.
The newly formed genera share a characteristic
appearance, however, they are distinguishable by
morphological characters, floral ontogeny, and other
genetic marker (Irwin & Barneby 1981, 1982,
Wiersemaet. a1 1990,Tucker 1996,Whitty et. a1 1994).
Of the world flora, out of 650 genera of legumes, the
cytological information's of 370 genera (57%) is
known (Polhill & Raven 198l).The cytogenetical data
of more than the half of the genera of the sub-family
Caesalpinioideae including more than three-fourth of
the species of Cassia too are 1acking.Thepresent study
has been carried out to analyze chromosome numbers
during mitosis in five species of Cassia.
Materials and Methodology
The materials for the study were collected from
different parts of Nepal. The phenological period of
the taxon is noted. The identification of the specimens
was based on the taxonomic treatments of Malla
(1986).They were latter tallied with the herbarium
specimens deposited in the Central Department of
Botany, Tribhuvan University (TU), National
Herbarium and Plant Laboratory, Royal Botanical
Garden, Godawari, Nepal. Voucher specimen of the
herbaria was deposited in the Central Department of
Botany (TU).
Germination of seeds: The fresh ripened seeds were
B.P. Chaulagain & S.R. SakydNepal Journal of Science andTechnology 4 (2002) 123-128
directly collected from the plant except the two-yearold seed of Cassia mimosoides collected from
herbarium specimens. The seeds were subjected to
germination in petri dish provided with wet wool cotton
in room temperature. The species of C.-floribunda,C.
occidentalis and C. tor-awere germinated well (above
50%) in control condition. But the rest of the species
C. nairobensis and C. inimosoides germinated in very
low percentage and subjected to concentrated sulfuric
acid treatment for 5 minutes to obtain higher frequency
of germinating seeds as suggested by Porter (1949)
and Koler and Cohen (1959).
Root tip Excision: The seeds subjected for germination
were allowed to grow the root tip up to 2-3 cm long.
As the time of root tip collection has an effect on the
frequency of mitotic cells (Sakai, 1941), all collections
were made between 10: 00 a.m. and 11: 00 a.m.
Then the root tips were washed thoroughly in running
water after exposing them to sunlight for about 10
minutes to fasten the successive cell divisions as well
as to ensure turgidity of the cells before fixation
(Wagley 1984).
Pretreatment andfixation: After exposing to sunlight
the root tip was treated in 0.5% colchicine for 20 to 30
minutes at room temperature. Then the tips were
washed thoroughly and subjected to fixation. In present
work, glacial acetic-alcohol (Carnoy's fluid) was
applied and some modifications were made for the
effectiveness. The species of Cassia have been found
very poor in taking fixative and took longer times.
Malakar (1978) also noticed such experience in the
speciesfloribunda. The blackening or browning of the
tissue was observed during the fixation.The blackening
of tissue is due to the reaction of tannin present in the
meristem with the metal dissolved in the acetic acid
(Li 1954, 1957).
To get well fixed tissue some modification was
made in the fixative. The preparation of the fixative
was modified by replacing the acetic acid by
chloroform and formaldehyde in ratio of 90 ml ethyl
alcohol (70%): 5 ml, chloroform: 5 ml formaldehyde.
The root tips were then fixed in above prepared fixative
and then stored in room temperature. Root tips under
microscopic observations were immersed in acetic acid
(45%) for 15 minutes to soften, then hydrolyzed in
1N-HC1 at 6 0 ' ~for 10-15 minutes and washed in
running water for 2 0 minutes as suggested by
Naruhashi and Iwatsubo (1993).
Staining and slide przparation: After hydrolysis
the select root tips were transferred to mixture of 2%
acetic-orcein and 1N HCl solution in a proportion of
9: 1 in a test tube and gently heated over a sprit flame
near to boil for 5-10 minutes interval. Then the root
tips were allowed for at least one day to take the stain.
The much densely stained apex portion of the root
meristems were cut out and washed in 45% acetic acid
to remove the debris and impurities. The tip was
macerated in 45% acetic acid solution in a clear glass
slide. The permanent slide was made using Celariar's
acetic acid -T-butyl alcohol schedule and mounted in
euparal.
Results and Discussion
Different workers have reported chromosome number
of Cassia species from different regions of the globe.
For the species C.floriburzda, Irwin and Turner (1960),
Mehra (1976) andTandon & Bhat (1970) have reported
2n=28. At present observation, the counting of
chromosomes shows that there has been an inconstancy
in somatic chromosome number from one cell to other
cell even in the same individual plant. The dominant
chromosome number of C. floribunda (Coll. No. 1 &
2) was 2n=14 (Table 1A &1B, Fig.1). The other
chromosome numbers were recorded from 2n=16 to
24. The observed number 2n=14 is shown its frequency
in two collections as 20.94 and 23.30 percent
respectively. The present result agrees with that of
Irwin (1960), Irwin and Turner (1960) and Malakar
(1978) for 2n = 14 for the taxa.
Similarly, the dominant frequency of chromosome
counts was 2n=18 in C. mimosoides with its other
variable numbers as 2n = 14, 16,20,22,24,26,28 and
30 (Table 1C). Such variations were observed within
an individual root cells as well as from root meristem
of different seeds. The heteromorphic nature of some
somatic chromosomes was observed in some cells
(Fig. 1.2-3). Earlier reports show that the chromosome
number of species C. mimosoides is 2n =16 (D'AmatoAvanzi 1956, Miege 1960, Irwin 1964, Bogman
1964, Kodama 1967, 1970, & Bir & Kumari 1970),
and 2n = 32 (Irwin & Turner 1960). The haploid
number n=8 is reported by George & Bhavanandan
(1994). The variable numbers of somatic chromosome
of the above taxon has been reported as 2n=16,28,32,
42, 48, and 56 by Kowakami (1930) and Randel
(1970).
Present work also shows the inconstancy in
chromosome numbers in C. occidentalis where
collection of species from three different populations
have shown their chromosome variations as 2n=16,
18, 19, 20, 20,22, 23, 24, 25, 26, 28, 30, 32, 34, 36,
and 38 within individual or in different collections
(Table l E , l F &lG).The highly established frequency
was 2n = 26, which accounts 12.3 percent of total cells
observed. The heteromorphic nature of chromosomes
was also observed in this species (Fig. 1.7- lO).The
B.P. Chaulagain & S.R. SakyaNepal Journal of Science andTechnology 4 (2002) 123-128
Table 1. Chromosome counts in five species ofCassia L. s.1. collected from different parts of Nepal
A. C. floribunda Coll. No.1- Kirtipur. Total no. of cells observed -191
14
16
18
20
22
24
Number of cells observed
40
36
31
29
34
21
Frequency (%)
20.94
18.85
16.23
15.18
17.80
10.99
B. C.floribunda; Coll. No. - 2 Bhaktapur; Total no. of cells observed - 260 20
Chromosome number (2n)
14
16
18
19
20
22
24
26
Number of cells observed
58
47
39
23
24
I8
26
15
Frequency (%)
20.94
18.1
15
8.9
9.2
6.9
13.9
5.8
C. C. mimosoides; Coll.No.3 -Taplejung; Total no. of cells observed -258
Chromosome number (2n)
14
16
18
20
22
24
26
28
30
Number of cells observed
12
34
55
49
42
36
14
6
10
Frequency (%)
4.65
13.18
21.31
19.0
16.28
13.95
5.43
2.32
3.87
D. C. nairobensis: CoU.No. 4 - Kirtiour. Total no. of cells observed -162
20
22
24
25
26
28
Chromosome number (2n)
16
18
38
18
Number of cells observed
9
36
29
7
11
14
23.46
11.11
5.55
22.22
Frequency (%)
17.90
4.32
6.79
8.64
E. C. occidentalis ; Coll. No. 5 - Swoyambhu; Total no. of cells observed-207
Chromosome number (2n)
18
19
20
22
24
25
26
28
32
34
38
Number of cells observed
14
14
17
15
22
24
25
29
15
18
14
Frequency (%)
6.8
6.8
8.1
7.3
10.6
11.6
12.1
14.0
7.3
8.7
6.8
F. C, occidenta1is;Coll. No. 6-Swoyambhu; Total no. of cells observed -338
Chromosome number (2n)
16
18
20
22
23
24
26
28
30
32
34
36
Number ofcells observed
17
26
34
20
27
36
40
38
24
28
16
18
Frequency
5.0
7.7
10.1
5.9
8.0
10.7
11.8
11.2
7.1
8.3
4.7
5.3
. (%)
G. C. occidentalis; Cou. No. 7- Santapu~Total no. of cells observed -328
Chromosome number (2n) 16
18
20
21
22
26
24
28
29
30
32
34
36
38
Numberofcellsobserved 13
17
19
38
12
29
31
27
24
19
21
30
17
12
Frequency (%)
4.2
5.5
6.1
4.2
9.4
10
12.3
8.7
9.4
6.1
6.8
9.7
5.5
3.9
H. C. tora; Coll.No. 9-Swoyambhu; Total no. of cells observed-328
Chromosome number (2n) 16
18
20
21
22
24
26
28
30
34
35
38
Number of cells observed 21
26
29
7
59
43
34
36
24
20
15
14
Frequency (%)
6.4
7.9
8.8
2.1
18
13.1
10.4
11
7.3
6.1
4.6
4.3
I. C. tom ; Coll. No. 8- Santapur; Total no. of cells observed - 446
Chromosome number (2n) 16
18
19
20
22
24
25
26
28
30
32
34
35
36 38
Number of cells observed 29
32
18
37
68
45
16
28
32
37
32
20
16
14 22
Frequency (%)
6.5 7.2
4
8.3
15.3 10.1 3.6
6.3
7.2
8.3
7.2
4.5
3.6
3.1 4.9
Chromosome number (2n)
previous chromosome reports have shown the somatic
number as 2n=28 (Senn 1938, Pantulu 1940,Turner
1956, HSU 1968,Tandon & Bhat 1970, Larsen 1971,
Gupta & Gupta 1971, Bir & Kumari 1977, Gill 1978a)
and 2n=26 (Bir & Sidhu 1966) and 2n=26 to 28 (Mehra
1972).
Present investigation in the species Cassia tora
indicates 2n=22 for its dominant diploid numbe~The
variation was 2n= 16, 18, 19, 20, 21, 23, 24, 25, 26,
28, 30, 32, 34, 35, 36, and 38 (Table ID). The
heteromorphic nature of chromosomes was noticed
which were variable. Some chromosomes were found
sticky in nature causing disparity in chromosomes
during polar movement (Fig. 1.11-15). Previous
investigation in this species were reported as 2n=26
(Datta 1933, Senn 1938, Bir & Sidhu 1966, Larsen
1971), 2n=28 (Jacob 1940, Tandon & Bhat 1970,
Sharma 1970), and 2n =26 and 52 (Katayama 1953,
Miege 1960).
Similarly, 2n=20 has been recorded in the species
B.P. Chaulagain & S.R. SakyaNepal Journal of Science andTechnology 4 (2002) 123-128
Fig. 1.1. C.floribunda (Coll. No. 2), metaphase.Fig. 1.2-6. C. mimosoides (Coll. No.3) metaphase chromosomes with variable
number and heteromorphic nature.Fig. 1.4 - 6. C. nuidensis, metaphase with sticky chromosornes.Fig. 7-8. C. occidentdis
(coll. No. 3,metaphase (2n=26 and 24 respectively) with heterochromatin.Fig.1.9 - 10. C. occidentalis(Col1.No. 7), metaphase.
Fig. 1.11 - 12. C. tora (Coll. No. 9), metaphase chromosomes with heteromorphic natureFig. 1.13 -14. C. tora (Coll. No. lo),
metaphase. Fig. 1.15. C. tora (Coll. No. lo), sticky metaphase
C. nairobensis with variable chromosome number as
2n= 16,18,22,24,26 and 28 (Table IC). The frequency
of predominant number was 23.45 percent. The
chromosome morphology found differing from cell to
cell and some were sticky in nature (Fig. 1.4-6).
At present, the instability in somatic chromosome
number within individual taxa should not be subjected
to artificial treatments. The results, however, should
be interpreted upon the basis of naturally occurring
phenomena. Sharma and Sharma (1956), Hegwood and
Hough (1958), Sarvella (1958), Nielson and Nath
(1961), Thompson (1962), Lewis (1962), Wagley
(1984), Sakya and Joshi (1990) had also observed such
cases in different plant species. Wagley (1984) argued
such phenomenon in Codium variegatum as cytomoxis
while Love (1938) believed such somatic variation of
chromosome numbers in hybrid wheat is due to
hybridity. Darlington andThomas (1937) has reported
anomalous numerical polymorphism of chromosomes
in Festuca-Lolium hybrid and argued for the cause due
to spindle deformities.
T h e occurrence of variations of somatic
B.P. Chaulagain & S.R. SakyaNepal Journal of Science andTechnology 4 (2002) 123-128
chromosome numbers has been confined greatly in
the plant species of those families that have highest
species diversity viz. Asteraceae(1250-1300 genera,
20,000-25,000 species), Orchidaceae (750 genera,
20,000-25,000 species) and Poaceae (900 genera,
11000 species). The Cassias belongs to such family
with one of the largest species diversity with 650 genera
and 18,000 species (Takhtajan 1981, Cronquist 1988).
The occurrence of somatic chromosome number
variation in Cassia could be depicted to the causes that
have been found in the species of families like
Asteraceae, Poaceae, and Orchidaceae.
Gildenhuys and Brix (1958a, 1958b) observed
somatic instability, abnormal meiosis, and apomixis in
Pennisetum dubium and marked it as gene control
mechanism. Snoad (1955a, 1955b)proposed that aberrant
chromosomenumbers are heritable through incompatible
gene combinations rather than to the germinal line and
that even chromosomally unbalanced gametes can be
functional. Pantulu and Rao (1977) observed intra-plant
variation in chromosome in a cross between Pennisetum
p u r p u r e u m and P. typhoides and their backcross
progenies and interpreted it as attribution to spindle
abnormalities as the result of 'duality' of the nucleus
(hybrids) in foreign cytoplasm with resultant unbalanced
enzyme and amino acid. The nature of the abnormal
achromatic figures of chromatin and chromosome
number variations can be attributed, perhaps, to
unbalanced nucleo-protein systems that resulted from
the combination of distantly related gametes in the
formation of the inter- or intra-generic hybrids as
suspected by Neilsen and Nath (1961). Howeveg such
breeding experiments in the present taxa are not known
except fertile natural hybrids of Xfloribunda (S.
septemtrionalis X S. multiglandulosa) (W~ersemaet a1
1990).Besides the above-mentioned facts, cytomixis as
well as accessory chromosomes may responsible to
display such somatic instability in the presently studied
taxa.
Acknowledgments
We are thankful to Central Department of Botany,
Tribhuvan University for providing laboratory facilities
during work. We are also thankful to National
Herbarium and Plant Laboratory, Department of Plant
Resource, Godawari, for herbaria facilities and to Dr
K.K. Shrestha for providing seeds of C a s s i a
mimosoides. A part of the work was presented at the
I11 National Conference on Science and Technology1999 organized by RONAST in Kathmandu.
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