Cytological Studies in Some Aquatic Angiosperms

CYTOLOGICAL STUDIES IN SOME AQUATIC ANGIOSPERMS BY D. G. KRISHNAPPA (Department of Botany, Central College, Bangalore) Received June 20, 1970 (Communicated by Prof. L. Narayana Rao, r.A.Se.) ABSTRACT The paper deals with the cytological investigation of eight taxa, viz., Hydrolea zeylanica Vahl (2n = 24), Ipomoea aquatica Foisk. (2n = 30, 2n = 30 -{- 1), Ottelia al~smoides Pers. (2n = 22 and 33), Monochoria vaginalis Presl ex Kunth (2n = 52), £ichhornia crasslpes Sohns (2n=32), Pistia stratiotes L. ~2n =28), Limnophyton obtusifoiium Miq. (2n = 22) and Ammannia salicifolia Monti (2n-----28) which were collected from the suburbs of Mysore. OI these, the chromosome numbers for Hydrolea zeylanica and Ammannia salici_[blia are newly reported. Karyomorphological studies have been made in 11ydrolea zeylcutica, Ammannia saHcifolia, lpomoea aquatica, Ottelia alismoides, Eichhornia crassipes and Lymnophyton obtusifolium. Mitotc studies Of Ottelia alis- rnoides reveal the occurrence of both diploid and triploid races. Of these, triploid number of 2n = 33 is the first report. An extra small chlomosome from somatic nuclei is also the first record in lpomoea aquatica. Further, Ottelia alismoides shows the occurrence of univalents, tetravalents and hexavalents, while Limnophyton obtusifolium reveals the presence of chromatin bridge, fragment chromosome and micronuclei. INTRODUCTION AQUATIC angiosperms are very interesting on account of their characteristic forms and striking adaptations to aquaticenvironment and provide useful information on cytology. Although a number of aquatic plants are found in India, cytological data is still wanting in many of them. The taxa included in the present study are Hydrolea zeylanica Vahl, lpomoea aquatica Forsk., Ottelia alismoides Pers., Monochoria vaginalis Presl ex Kunth, Eichhornia crassipes Solms, Pistia stratiotes L., Limnophyton obtusifolium Miq. and Ammannia salicifalia Monti (semi-aquatic form). The previous cytological reports in.many of them mostly reveal the chromosome count. 179 180 D.G. KRIS~NAVFA The present investigation gives further information on the chromosomo number and their behaviour in these eight taxa collected from the suburbs of Mysore. Somatic chromosomes have been observed in six taxa using Tjio and Levan's (1950) acetoorcein squash technique; meiotic studies have been made in six taxa. Although the present work confirms certain previous reports on chromosome numbers, it reveals a few cytological variations. Further, it newly records the chromosome numbers for two species giving detailed cytological data. CYTOLOGICAL OBSERVATIONS Hydrolea ze)laniea.--Tbe chromosome number of 2n= 24 is recorded from bothmitotic and meiotic studies (Figs. 25, 26). This species has small cbromosomes. There iS difference in size among the chromosomes. One pair is found to have satellites. Seven pairs of chromosomes have submcdian centromeres and the rest have nearly median centromeres. Meiosis is regular. Twelve bivalents are seen at diakinesis. Most of them are closed bivalents having terminal chiasmata. Ipomoea aquatica. The somatic nuclei of this species consist of 2n = 30 chromosomes. There is not much difference in the size of the chromo- seines. The mitotic observations reveal the occurrence of an extra chromosome which was not noted previously(Figs. 2, 19). This extra chromosome is very small and looks like a fragment. Meiotic studies have shown norm~d behaviour with fifteen bivalents at M-I and they distribute them- selves regularly at A-L The extra chromosome is found to be precociously moving to one pole at M-i in some cells (Fig. 18) andlagging in a few others at A.-I (Fig. 17). Ottelia alismoides.mTh~ somatic chromosome nvmber is found to be 2n ---- 22 (Fig. 15). Out of the 11 pairs of chromosomes one pair is exceptionally long having median centromeres; seven pairs are medium in which 2 pairs have submedian centromeres, 4 pairs nearly subterminal ovntromeres and one pair median centromeres. Th0 remaining 3 pairs are short chromosomes. Among these~ short chromosomes two pairs have submedian centromeres and one pair subterminal centromeres. A triploid race in this species is observed for the first time with chromosome number of 2n ~ 33 from root tip squashes. Karyotype analysis, of this race at prometaphase reveals the presence of three genomes (Fig. 16). Three exceptionally long chromosomes are seen with nearly median oentro- :ineres. Out of" the 21-medium chromosomes six have submedian, twelve Cytological Studies in Some Aquatic Angiosperms 181 P'--~ IM . .i, ~ .'~m - k,- $~ • M e 22".' ~ "" qb 15 19 • : e ": '-""-,-.-"." 4' " t~/~ ' #'Gs .A .: " L ~p Ib 4b 23 "¢ ' fs II " % tl* IP 24 z5 z6 FIGs. 17-26. Figs. 17-19. Ipomoea aquatica: Fig. 17. The extra chromosome is lagging at A-I, x 1,250. Fig. 18. The extra chromosome is precociously moving to one pole at M-I, X 1,250. Fig, 19. Somatic,metaphase chromosomes to show 2n = 30 and an extra chromosome (shown by arrow). Figs. 20-21. Pistia stratiotes: Fig. 20. A-I showing 14-14 distribution of chromosomes to the poles. Fig. 21. Diakinesis revealing 14 bivalents. Fig. 22. Ammannia salisi- folia. Shows 28 somatic metaphase chromosomes. Fig. 23. Eichhornia crassipes, Somatic metaphase chromosomes of 2n = 32. Fig. 24. 26 bivalents at late diakinesis in Monochorit vagtnalis, × 1,250. Figs. 25-26. Hydrolea zeylanica.-Fig. 25. Diakinesis showing 12 bivalents; note the association of 2 bivalents with nucleolus. Fig. 26. Somatic motaphase chromosomes sl~wing 2n.,= 24. Figs. 19-23 and 25-26, × 1,800. 182 D.G. KRiSHNAPPA nearly subterminal and three median centromeres. The remaining nine chromosomes are short, three with subterminal and six with submedlan centromeres. Meiotic studies in one of the diploid plants show certain irregularities in pollen mother cells. In a few cells two univalents are observed at M-I (Fig, 12), Tetravalent formation is also noted (Fig. I 1). Diakinesis stages have revealed hexavalent configuration (Fig. 10). However, meiosis is found to be normal in a different plant (Figs. 13, 14). Monochoria vaginalis.--The chromosome number of 2n= 52 is recorded in this species. Meiosis is normal both at first and second divisions. Twenty-six bivalents are observed at late diakinesis (Fig. 24). Among them 25 are closed bivalents and one is an open bivalent. All the bivalent* have terminal chiasmata. M-1 also shows normal behaviour with 26 bivalents (Fig. 3). Eichhornia crassipes.~The chromosome number of 2n = 32 is found in somatic nuclei (Figs. 1, 23). There is variation in their size. Among four pairs of long chromosomes, two pairs have nearly median centromeres and two pairs submedian centromeres. Eight pairs of medium-sized chromosomes possess two pairs with median and the other six with submedian centromeres. The rest of the chromosomes in the complement are comparatively short a.nd possess submedlau centromeres. Pistia stratiotes.--Meiotic chromosome number is found to be n = 14. The beliaviour of the chromosomes is normal. All the bivalents are of closed type and have terminal chiasmata (Fig. 21). A-I is regular with the distribution of 14--14 chromosomes to the poles (Fig. 20). Limnophyton obtusifolium.--The chromosome number of 2n = 22 is observed in somatic nuclei. One pair of chromosomes in the somatic complement is distinctly longer than the other chromosomes and has nearly median centromeres; the rest of the chromosomes have nearly subterminal centromeres (Fig. 4). Meiosis is normal showing 11 bivalents both at diakinesis and M-I (Figs. 5, 6). All the bivalents at diakinesis are observed to have both interstitial and terminal ehiasmata. Meiotic study in a different plant has revealed certain irregularities such as micronuclei at T-I and T-II (Figs. 7, 9). Chromatin bridge and a fragment are also noticed at A-II (Fig. 8). Ammannia salicifolia.--The chromosome number of 2n = 28 is recorded from somatic nuclei for the first time. They are very small with little Cytological Studies in Some Aquatic Angiosperms 183 difference in their size (Fig. 22). Nine pairs of chromosomes ha,re nearly median centromeres and five pairs have submedian centromeres. DISCUSSION AND CONCLUSION Although many aquatic angiosperms have yet to be cytologically studied, good many of them have been known for their chromosome number. A list of chromosome numbers in Indian aquatic plants has been given by Subra- manyam (1962). Additional cytological information such as the occur. rence of a triploid race in Ottelia alismoides with a chromosome number of 2n----33 is a new report. Such variations in chromosome number in this species have also been recorded previously revealing 2n = 22 (Rue,, 1950), 2n ~- 44 (Snbramanyam, 1962), 2n -~ 52 (Sharma and Bhattacharya,. 1956), 2n=66 (Rue, 1950) and 2n--72 (Subramanyam, 1962). Rue (1950) is of the opinion that the polyploid races are indistinguishable mor- phologically; polyploid has played but little role in speciation. The cytological investigation of plants from Mysore also reveals the chromosome number of 2n----- 22 as reported by Rao (1950). Karyom0rphological study of this species mostly confirms the work of Rue (1950). In addition to this the present work newly records the occurrence ofunivalents, tetravalent and hexavalent in diploid plant. There is one previous report on the chromosome number of 2n = 52 in Monochoria vaginalis (Subramanyam, I962). This report is confirmed in the present work and the meiotic behaviour is also studied. The basic chromosome number of n = 15 in Ipomoea aquatica, was reported by Rao (1947), Stmrma and Datta (1958). Latter authors have also made karyotypic study revealing one pair of SAT-chromosomes, 12 pairs of chromosomes with median centromeres and two pairs with, submedian centromeres. SAT-chromosomes as mentioned by Sharma.and Datta (1958) are not observed here in Ipomoea aquatica from Mysore. But in the somatic nuclei an extra very small chromosome is observed at meta-, phase. It looks like a fragment and it is difficult to locate the centromere in it. However, the extra chromosome moves precociously at M-I in pollen mother cells.

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