© 2003 The Japan Mendel Society Cytologia 68(4): 375–378, 2003 Cytological Studies in Wiesneria triandra (Dalz.) Micheli (Alismataceae) Illairaja Ismail Mujawar 1 , Sayajirao Pandurang Gaikwad 1, * and Srirang Ramchandra Yadav 2 1 Department of Botany, Shivaji University, Kolhapur-416 004 2 Department of Botany, Delhi University, Delhi-7, India Received June 19, 2003; accepted September 9, 2003 Summary Somatic chromosome number (2n) and karyomorphology have been reported for first time in Wiesneria triandra (Dalz.) Micheli, a member of most archaic family Alismataceae. In general, the chromosomes are long with median, submedian and subterminal primary centromeres. The karyotype is reasonably asymmetrical and indicated advances in general. 10 distinct bivalents at diakinesis were observed during meiosis. The subclass Alismatidae (Helobiae) have been considered to be the most archaic group of Liliopsida (monocots) (Cronquist 1981). Among families of subclass Alismatidae, Alismataceae possesses some of the very archaic characters and considered to be one of the most primitive family in angiosperms in general and monocots in particular. Current taxonomic treatment lists about 70 species belonging 13 genera assigned in 7 tribes (Pichon 1946). Genus Wiesneria Micheli with three species belongs to tribe Wiesneriinae is considered to be a highly specialized alismataceous taxon (Eames 1961). Wiesneria triandra (Dalz.) Micheli occurs in India while W. filifolia J. D. Hooker and W. schweinfurthii J. D. Hooker are African species. Wiesneria triandra is a phylogenetically isolated, endemic species of Peninsular India (Camenisch and Cook 1996). It grows in temporary ponds and puddles on lateritic plateaus at low altitude (100–300 m above sea level) particularly in West coast of India during June–October with sessile or subsessile flowers born in whorls at the nodes (Fig. 2a, b). Inspite of its importance as a primitive taxa with specialized characters, there are few publications mainly dealing with morphology, anatomy, palynology and ecology of the species (Stant 1964, Sivadasan 1986, Cook 1988, Camenisch and Cook 1996), probably due to its narrow range of distribution and sporadic occurrence. Therefore, determination somatic chromosome number, karyomorphology and meiosis has been studied in the species. Materials and methods Living individuals were collected during July–August from different localities viz. Achirne, Dapoli, Deogad, Lolium, Malwan, Manipal, Pavas, and Vengurla scattered over West coast of India. The plants were transplanted in plastic tubs and cement tanks in Botanical garden of Botany department, Shivaji University, Kolhapur, Maharashtra, India. For karyotypic studies, healthy root tips were used after pretreatment with p-dichlorobenzene for 3 to 4 h at 1261°C. The slides were prepared by usual smear technique. Propionic orcein, (2%), was used as stain. Measurement of chromosomes made from photoplates of 20 different somatic plates. For classification of karyotype asymmetry, the scheme of Stebbins (1971) and nomenclature proposed by Levan et al. (1964–1965) is followed. For meiosis, young anthers were squashed in 2% propionic orcein. All photomicrographs were taken from temporary preparations using MEAK’s system of Janaval Carl Zeiss micro* Corresponding author, e-mail: sajajig@yahoo.com 376 Illairaja I. Mujawar et al. Cytologia 68(4) scope. Observations Somatic chromosome number 2n520 was observed in W. triandra (Fig. 2c). In general, the chromosomes are long (6.75–13.5 m m). With a view to describe the karyotype following categorization of chromosomes has been made. The idiogram of species is represented in Fig. 1. Type A: One pair of very long chromosomes (13.5 m m) with a primary constriction in the submedian (sm) region. Type B: Two pairs of comparatively long chromosomes (11.4–12.7 m m) with a primary constriction in the median (m) region. Type C: Three pairs of medium sized chromosomes (8.6–9.7 m m) with a primary constriction in the terminal (t) region. Type D: Four pairs of short chromoFig. 1. Showing idiogram for haploid complement of Wiesneria triandra (Dalz.) Micheli. somes (6.75–8.3 m m) with a primary con- Fig. 2. a) Habit of Wiesneria triandra (Dalz.) Micheli. b) Inflorescences. c) Somatic chromosomes (2n520). d) Diakinesis with 10 bivalents. 2003 377 Cytological studies in Wiesneria triandra (Dalz.) Micheli Table 1. Number of chrom. Pair 1 2 3 4 5 6 7 8 9 10 Showing values of chromosome pairs Length of Chrom. in m m Short Arm (S) Long Arm (L) 4.561.0 5.760.9 4.360.8 1.460.2 1.060.1 1.160.1 1.560.1 1.160.1 1.060.1 1.160.1 9.061.3 7.061.6 7.161.4 8.361.8 8.060.5 7.561.2 6.861.1 6.561.0 6.061.1 5.761.0 Total length (S1L) 13.562.3 12.762.5 11.462.1 9.762.0 9.060.6 8.661.3 8.361.2 7.661.1 7.061.2 6.7561.1 Difference between Long arm and Short arm in m m D5L2S 4.5 1.3 2.8 6.9 7.0 6.4 5.3 5.4 5.0 4.7 Ratio between Long arm and Short arm in m m R5L/S 2.00 1.22 1.65 5.92 8.00 6.81 4.53 5.90 6.00 5.42 striction in the terminal (t) region. The karyotype formula is 2Asm14Bm16Ct18Dt. According to Stebbins classification, karyotype is classified in a ‘3b’ category. Formation of 10 bivalents at diakinesis was observed during meiosis (Fig. 2d). Discussions Cytological studies in Wiesneria triandra revealed that karyotype is reasonably asymmetrical and indicated advances in general. Sharma and Chatterjee (1967) in their extensive cytotaxonomic studies of Helobiae showed that in various genera of Alismataceae (excluding Wiesneria), Butamaceae and Hydrocharitaceae the first pair of chromosomes is distinctly larger than the rest of the chromosomes and this pair has a median primary constriction and regarded as a marker chromosome for all those genera. However, in W. triandra this marker is of submedian type and other two long chromosomes are of median type and thus differs from all those genera of Alismataceae. These structural alternations in chromosomes may be attributed to the evolution of species. Absolute symmetrical karyotype has not been found in any of the Alismataceae species. Only in the genus Alisma considerable amount of symmetry in the karyotype has been noted in comparatively long chromosomes (Harada 1956). Similar trend of symmetry is observed in W. triandra in its 3 long chromosomes. It is admitted on cytological grounds that Alismatales has highly advanced taxa evolving in divergent directions (Sharma and Chatterjee 1967). Which is also supported by present study on W. triandra. In Alismataceae basic chromosome number ranges from 5–13 (Darlington and Wylie 1955). Such a great diversity in basic numbers indicates that polyploidy and aneuploidy have played a major role in the evolution of these members. Wiesneria triandra supports this view by having n510 which might have easily arised as a multiple of 5, a primary basic number for the family. However, through investigation into cytology of remaining two species may provide confirmation to this assumption. Acknowledgements Authors are thankful to Head, Department of Botany, Shivaji University Kolhapur, Maharashtra, India for providing research facilities and to Department of Science and Technology, Govt. of India for financial assistance under SERC FAST TRACK SCHEME FOR YOUNG SCIENTIST. 378 Illairaja I. 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