Cytologia 50: 473-482, 1985
Karyomorphological Studies in South Indian AcanthaceaeT
. Govindarajan and D. Subramanian
CytogeneticsLaboratory, Botany Department, Annamalai University, Annamalainagar608 002, Tamil nadu, India
Accepted July 24, 1984
The South Indian Acanthaceae consist of 38 genera and 209 species (Gamble 1957). In South India, the species occur much wide spread in the plains as well as in the hills. Even where the chromosome numbers have been determined (Fedorov 1974), the knowledge concerning the details of karyotype pertaining to chromo some measurements which are vital to the understanding of karyological affinities, is still meagre. It was therefore, felt that detailed and critical karyological work in this family was desirable. Already there are a few published reports of karyo types of the members of this family (Rangaswamy 1941, Kaur and Nizam 1970, Krishnaswami and Madhava Menon 1974 and Vasudevan 1976). The present paper, in addition to the author's previous communication (Govindarajan and Subramanian 1983), deals with the details of chromosome measurements of 23 taxa of Acanthaceae from South India.
Materials and methods
The materials used in this present investigation were collected from different localities of South Indian plains and hills, the voucher specimens of which have been deposited in the hortus siccus of the Botany Department, Annamalai Uni versity. The identification of plants was verified with the help of the Botanical
Survey of India, Coimbatore. Healthy root tips were pretreated in 0.002M hy droxyquinoline kept at 4•Ž for 3 hours. After thorough washing, the root tips were fixed in 1:3 acetic alcohol for a period of 24 hours. Then, they were squashed following Marimuthu and Subramaniam's (1960) iron alum haematoxylin squash method. Important plates were drawn with Abbe's camera lucida and photo graphed. The measurements of chromosome were made from the drawn figures with the help of ocular micrometer, under oil immersion lens with a magnification of •~1125. Long arm, short arm, satellites were measured separately and the re sults tabulated.
Observations
The chromosomes of Acanthaceae are generally rather small. It is of par ticular interest to note that the very short chromosomes measured less than a mi cron, while the long chromosome measured more than 5.0 microns. Based on the length, the chromosomes have been grouped into very short, short, medium and long chromosomes. Under each of these groups, the following categories of chro 474 T. Govindarajan and D. Subramanian Cytologia 50 mosomes have been recognized:
Long (more than 5.0ƒÊm)
Type A Chromosomes with submedian centromere and satellites on the
short arm or long arm
Type B Chromosomes with median centromere and satellites
Type C Chromosomes with submedian centromere
Type D Chromosomes with median centromere
Type E Chromosomes with subterminal centromere
Medium (3.0-5.0ƒÊm)
Type F Chromosomes with submedian centromere and satellites on the short
arm or long arm.
Type G Chromosomes with median centromere and satellites
Type H Chromosomes with submedian centromere
Type I Chromosomes with median centromere
Type J Chromosomes with subterminal centromere
Short (1.0-3.0ƒÊm)
Type K Chromosomes with submedian centromere and satellites on the short
arm or long arm
Type L Chromosomes with median centromere and satellites
Type M Chromosomes with submedian centromere
Type N Chromosomes with median centromere
Type O Chromosomes with subterminal centromere
Very short (less than 1.0ƒÊm)
Type P Chromosomes with submedian centromere
Type Q Chromosomes with median centromere
Type R Chromosomes with subterminal centromere In the following tables (Tables 1 and 2) the details of chromosome measure ments are given.
Table 1. 1985 Karyomorphological Studies in South Indian Acanthaceae 475
Table 1. (cont.) 476 T, Govindarajan and D. Subramanian Cytologia 50
Table 1. (cont.) 1985 Karyomorphological Studies in South Indian Acanthaceae 477
Table 1. (cont.) 478 T. Govindarajan and D. Subramanian Cytologia 50
Table 1. (cont.)
Discussion The chromosome number of 23 species belonging to 16 genera determined in the present study are listed in Table 3. They range from 2n=18 to 2n=80. Among the 23 species studied, first record of chromosome numbers has been made in 17 species, namely Acanthus mollis, Adhatoda zeylanica, Andrographis lobelioides, Andrographis neesiana, Asystasia crispata, Barleria involucrata, Barleria longiflora, Beloperone plumbaginifolia, Dyschoriste depressa, Eranthemum nervo sum, Hemigraphis colorata, Hygrophila quadrivalvis, Pseuderanthemum malabaricum, Strobilanthes barbatus, Strobilanthes lawsoni, Sotrobilanthes zenkerianus and Ste nosiphoniumparviflorum. In Fittonia argyoneura, Justicia quinqueangularis, Ruellia rosea and Stro bilanthes isophyllus the present report of chromsome number confirms the earlier reports (Fedorov 1974). 1985 Karyomorphological Studies in South Indian Acanthaceae 479
In Justicia glauca Ellis (1962) has reported 2n=26 chromosomes, Kaur (1965) 2n=24 chromosomes and Krishnappa and Ranganath (1982) 2n=36 chromo somes. The present study shows 2n=26 chromosomes in this species. As reveal ed by the present study, there are 2n=18 chromosomes in Justicia procumbens, but according to Grant (1955), the diploid chromosome number is 2n=18 and Kri shnappa and Ranganath (1982) 2n=36. In Andrographis lobelioides, the somatic chromosome number is 2n=48 and in A. neesiana 2n=24 chromosomes. The basic number may be 12 represented by Andrographis neesiana whereas A. lobelioides represents an euploid series.
Table 2.
According to earlier observations in Barleria noctifiora and B. cuspidata, there are 2n=24 and 2n=40 chromosomes respectively (Govindarajan and Subramanian 1983) and in B. prionotis 2n=30 chromosomes (Narayanan 1951) and 2n=40 chro mosomes (Raman and Kesavan 1964). There are 2n=40 chromosomes in Barleria involucrata and B. longiflora as evidenced by the present investigation. It may be considered that these species should have evolved from two different ancestral stocks, one having 12 haploid mumber and the other 20 haploid numbers, as evi denced by the present investigation. In Justicia betonica, the earlier report of somatic chromosome number is 2n= 28 (Narayanan 1951) and 2n=34 (Ellis 1962, Govindarajan and Subramanian 480 T. Govindarajan and D. Subramanian Cytologia 50
1983). In Justicia gendarussa the earlier report of somatic chromosme number is 2n=28 (Basak 1959), 2n=30 (Joseph 1964) and 2n=32 (Narayanan 1951). In the present study 2n=18 chromosomes in Justicia procumbens and J. quinqueang ularis and 2n=26 in J. glauca were observed. It may be considered that these species should have evolved from different ancestral stocks with 9, 13, 14, 15, 16 and 17 as haploid chromosomes.
Table 3. Summarized karyomorphological features of the taxa investigated here
1. Chromosome number (2n) 2. Size range in millimicrons 3. Number of chromosomes with satellite 4. Number of chromosomes with submedian centromere 5. Number of chromosomes with median centromere 6. Number of chromosomes with subterminal centromere 7. Absolute chromosome length 8. Average chromosome length
9. TF %: [Total length of short chromosomes/(Total length of long chr. + total . length of short chr.)] •~100
According to earlier observations in Strobilanthes isophyllus and S. dyerianus, there are 2n=20 (Grant 1955, Takizawa 1957) and 2n=30 chromosomes (Grant 1955) respectively and in S. luridus and S. papillosus 2n=32 chromosomes (Ellis 1962, Raman and Kesavan 1963). There are 2n=20 chromosomes in Strobilanthes isophyllus, 2n=30 chromosomes in S. lawsoni and 2n=32 chromosomes in S. bar batus and S. zenkerianus as evidenced by the present investigation. It may be possible to consider that the haploid chromosome number in this genus may be 10 1985 Karyomorphological Studies in South Indian Acanthaceae 481
and Strobilanthes isophyllus (2n=20) may be a diploid species , S. dyerianus (2n=30) and S. lawsoni (2n=30) may be considered as euploids and S . luridus, S. papillosus,
S. barbatus and S. zenkerianus (2n=32) are aneuploids . Therefore both euploidy and aneuploidy plays an important role in the origin and evolution of the species
of Strobilanthes.
The Acanthanceae show a wide range of basic numbers from 8 to 34 (Govin
darajan and Subramanian 1983), but in the present study it is 9 to 40 . The basic
number 9 has been observed in Justicia procumbens and J . quinqueangularis. The commonest basic number in the family is x=16, x=8 is assumed to be the original
basic number of the family and that x=16 is derived by polyploidy . Evolution of an aneuploid series (x=10, 12, 13, 14, 15, 17 , 18, 20, 21, 24 and 40) from the original number x=8, followed by polyploidy might well have given rise to the wide range
of basic numbers now observed in the family. The formation of an aneuploid
series prior to polyploidy is indicated by Andrographis neesiana (2n=24), Asystasia
crispata (2n=26), Beloperone plumbaginifolia (2n=28), Hemigraphis colorata (2n=
28), Adhatoda zeylanica (2n=30), Dyschoriste depressa (2n=30) , Strobilanthes lawsoni (2n=30), Stenosiphonium parviflorum (2n=30) , Hygrophila quadrivalvis (2n= 32), Strobilanthes barbatus (2n=32), S. zenkerianus (2n=32), Ruellia rosea (2n=34)
and Fittonia argyoneura (2n=36). There are two distinct lines of evolution among
the species studied, one represented by 2n=30 and 32 chromosomes and the other
by 40 and 42 chromosomes, as these numbers are occurring in maximum number
of species. This is evidenced by the study of frequency of diploid chromosome
numbers in various species of Acanthaceae studied and this confirms the previous
conclusions (Govindarajan and Subramanian 1983).
In Acanthus mollis and Barleria longiflora the chromosomes are more in num
ber and longer in size representing a mixture of both derived and underived fea
tures. But on the otherhand, the chromosomes are fewer in number and shorter
in size in Justicia procumbens and J. quinqueangularis, again showing both derived
and underived features.
Therefore, there is no definite trend of either phylogenetic increase or decrease
of chromosome size and thereby DNA content among the species of Acanthaceae
studied. Similar observations showing neither phylogeneticin crease or decrease
of chromosome size and thereby DNA content have been made among the species
of South Indian Araceae (Ramachandran 1978).
Besides the numerical changes discussed above, the karyotypes in the species
of Acanthaceae also indicated variations in chromosome size and nuclear DNA content in evolution. Very short chromosomes (below 1ƒÊm) are observed in
Andrographis lobelioides. Longer chromosomes (above 5ƒÊm) have been noticed in
Acanthus mollis and Barleria longiflora. The other species investigated in the present study, most of the chromosomes are short sized and some of them medium sized
(Table 2).
The maximum absolute chromosome length has been found in Acanthus mollis, while the minimum length in Justicia procumbens. The maximum average chro mosome length has been observed in Acanthus mollis while the minimum length in
Andrographis lobelioides. The maximum TF % has been found in Strobilanthus law 482 T. Govindarajan and D. Subramanian Cytologia 50 soni while the minimum in Acanthus mollis (Table 3). In all the species studied the chromosomes with symmetrical karyotypes have exceeded in number, when compared to the chromosomes with asymmetrical karyo types. The chromosomes are more or less equal in size. The metacentric and submetacentric chromosomes are more in number in each species. The telocentric chromosomes are lesser in uumber. Therefore, symmetrical karyotypes have been observed in all the 23 species, showing the primitive character.
Summary
Karyomorphological details pertaining to chromosome measurements in 23 taxa of South Indian Acanthaceae have been described. Chromosome numbers determined in the present study ranges from 2n=18 to 2n=80. Karyotypes in the family also show differences in absolute chromosome length indicating changes in nuclear DNA in evolution. No definite trend of either phylogentic increase or dercrease of chromosome size is indicated by the available data.
References
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