INTRODUCTION

Meiosis, a special mode of division in repro-ductive cells, is conditioned by a series of genes,which are site, stage and/or sex specific (KAUL

and MURTHY 1985). A change in any of thesegene(s) can cause a shift in the usual course ofmeiosis with significant implications. One gene-controlled event of great genetical and evolu-tionary significance is the formation of chias-mata, the cytologically visible manifestation ofcrossing over. Considerable variation in cyto-genetical characters have been found among

CARYOLOGIA Vol. 55, no. 3: 251-261, 2002

Sex incidences of chiasmata variation in respect ofposition, distribution and frequency in someimportant legumes and grassesK.K. KOUL1, * and RANJNA NAGPAL2

1 Hindu College, University of Delhi, Delhi-110007, India.2 Deshbandhu College, Kalka Ji, New Delhi-110019, India.

Abstract - To find out whether the chromosomes behave in the similar fashion intwo sex mother cells i.e. the pollen mother cells (PMCs) and the embryo sac moth-er cells (EMCs) in the bisexual plants, 13 species (19 accessions) of the familiesFabaceae (7 spp; 12 acc.) and Poaceae (6 spp; 7acc.), were studied for male andfemale meiosis, ten (14acc.) being studied for the first time. The present studybrought to light several facts not recorded earlier. Asynchrony was observed in thebehaviour of chromosomes in the two sex cells with respect to the frequency, dis-tribution and position of chiasmata. While a higher chiasmata frequency wasrecorded in the pollen mother cells (PMCs) of Lathyrus odoratus, L. sativus, L. apha-ca, Lupinus albus and Pisum sativum, in species like Lolium perenne, L. multiflorumand Hordeum vulgare a reciprocal situation existed. Further, in L. perenne and L.multiflorum while bivalents showed distally localized chiasmata in the PMCs, inEMCs their distribution was random. However, in Vicia faba, Phaseolus vulgaris,Secale cereale, Lolium temulentum and Phalaris minor absence of a sex differencein meiosis was noted. Significant differences also existed in the bivalent size of thetwo sex cells in Lathyrus odoratus, L. sativus, V. faba and H. vulgare. In all thesespecies, barring H. vulgare, the bivalent size was bigger in the PMCs studied. In H.vulgare a reverse situation existed. Sex difference in meiosis was distinctly evidentin Lupinus albus. Of the two populations studied while one population showed syn-chronous behaviour of chromosomes in the two sex cells, the other populationalthough showed normal microsporogenesis, its megasporogenesis was abnormal(desynaptic) being characterized by the failure of synapsed chromosomes to retainchiasmata in 61.11 per cent cells at diakinesis. It is concluded that the contributionof the two sex cells towards generating variability through recombination is not thesame. In desynaptic L. albus while the effective recombination is brought about bythe male meiosis, the female sex cells provide for the retention of certain linkagegroups. The possible cause(s) and the significance of differential behaviour ofchromosomes in the two sex mother cells of different species studied is discussed.

Key words: chiasma frequency variation, desynapsis, female meiosis, geneticcontrol, male meiosis.

* Corresponding author: e-mail: k_koul@hotmail.com

different individuals of the same species most ofwhich presumably being the result of variationin chiasma frequency. Presence of chiasmatacauses extensive restructuring of chromosomesthrough the reshuffling of genetic materialwhich creates an array of gametes, all differentfrom each other and from the parental gametes(ZARCHI et al. 1972). This genetic variationdetermines the rate of increase in fitness of anorganism when exposed to the effect of natur-al selection. It allows for the flexibility of thepopulation and/or family, which can success-fully invade new habitats. On the contrary,absence of chiasmata or its presence in low fre-quency provide genetic fixity to an organismwhich becomes stable or less flexible ecologi-cally. According to DARLINGTON (1956) a com-promise is often, or even always, achievedthrough the control of crossing over within thechromosome and recombination between them(DARLINGTON 1956; VED BRAT 1965). ZARCHI etal. (1972) suggests that the excess of stabilitycaused by selfing should be compensated by ahigher rate of recombination whereas in outcrossing species the flexibility is achievedthrough the repeated reshuffling of geneticmaterial following the mating of unrelated indi-viduals.

Realizing that regulation of variability in aspecies is determined by its chromosome behav-iour and that immediate fitness of a speciesdepends on a certain uniformity of genotypewith long term survival depending on therelease of adequate variability, it becomesimportant to study the behaviour of chromo-somes with respect to chiasma frequency anddistribution in both the sex mother cells of aplant i.e. pollen mother cell (PMC) and embryosac mother cell (EMC). However, a review ofavailable literature reveals that compared toseveral thousands of plants studied for malemeiosis, the female meiosis has been studied inonly a handful (about 54) of plants (FOGWILL

1958; VED BRAT 1965; BENNETT et al. 1973;DAVIES and JONES 1974; GOHIL and KAUL 1980,1981; KOUL 1983; KOUL and GOHIL 1989;KOUL and RAINA 1996; KOUL et al. 1995, 1999,2000). The technical difficulties encounteredin locating and handling the female sex cellshas made its study much more tedious than thecorresponding study in male sex cells. Owing tothe lack of information on female meiosis sev-eral unsupported, even false and dogmatic

statements have not been uncommon. Oneuntenable assumption has been that chromo-somes in both the sex cells behave similarly andwhat is true of male meiosis is true of femalemeiosis as well. In effect, there existed a trendof extending generalization from one sex cell tothe other which is erroneous. Further, in somecases the intensity of irregularity in chromo-some pairing on female side was deduced bycomparing pollen fertility, ovule abortionand/or seed setting on controlled and open pol-lination (KATAYAMA 1964; KODURU and RAO

1981) which is not justified. Poor seed settingon account of ovule abortion may not always bethe result of genetic defect. Such breakdowncould be the manifestation of altered physio-logical conditions as well. Since we haveentered a phase of molecular cytogenetics, lot ofattention is now being given to techniques likechromosome banding/painting , in situhybridization, micromanipulation, flow cytom-etry and several others (FRELLO and HESLOP-HARRISON 2000; HESLOP-HARRISON 1996; GILL

and FRIEBE 1998), and it is apprehended thatour knowledge of chromosome behaviour infemale sex cells, which represents the secondcomponent of two track heredity (DARLINGTON

1971), will remain inadequate. Realizing thatfor a complete understanding of genetic and/orbreeding system of an individual, informationon the behaviour of chromosomes in the twosex cells is important, the present work was ini-tiated. This paper explores whether or not thetwo sex cells show similar behaviour of chro-mosomes and contribute similarly towards gen-erating the variability. The present studyinvolves 13 species (19acc.) representing twofamilies i.e. Fabaceae (7 spp; 12acc.) andPoaceae (6 spp; 7acc). These include Pisumsativum L., Lathyrus sativus L., L. odoratus L.,L. aphaca L., Vicia faba L., Lupinus albus L. andPhaseolus vulgaris L. representing the familyFabaceae and Lolium perenne L., L. temulen-tum L., L. multiflorum Lam., Phalaris minorRetz, Hordeum vulgare L. and Secale cereale L.of the family Poaceae. These species wereselected for their economic importance, orna-mental and/or forage value. Female meiosis inall these species, barring H. vulgare, S. cerealeand V. faba has been studied for the first time.The latter three species were restudied with aview to compare our observations with the ear-lier reported ones.

252 KOUL and NAGPAL

MATERIALS AND METHODS

Seven species (12 acc.) of family Fabaceae i.e.Pisum sativum, Lathyrus aphaca, L. odoratus, L. sativus,Lupinus albus, Vicia faba and Phaseolus vulgaris andsix (7acc.) of family Poaceae i.e. Hordeum vulgare,Secale cereale, Lolium perenne, L. temulentum, L. mul-tiflorum and Phalaris minor were studied for male andfemale meiosis. The buds and/or panicles/spikes of P.sativum, L. odoratus, H. vulgare, L. albus, V. faba andP. vulgaris were obtained from the plants growing inthe Botanical Gardens of Delhi University (DU)and/or Hindu College (HC), whereas for L. sativus, S.cereale, L. temulentum and L. multiflorum seed sam-ples were obtained from Western Regional PlantIntroduction Station, Pullman, Washington and plantswere raised in the experimental field for obtainingthe buds/panicles. For L. perenne, P. minor and L.aphaca buds were obtained from wild growing plants.

Young buds of appropriate size were fixed in 1:3acetic alcohol for 24 hrs and anthers and ovaries were

isolated stained together with leucobasic Fuchsin afterhydrolysis in 5N HCl at room temperature for 45min. For male meiotic studies anthers were directlysquashed in 45 per cent acetic acid whereas for femalemeiotic studies ovules were first dissected out ofovaries in a drop of fixative under a dissection micro-scope on a glass slide using long pointed needles.Care was taken not to allow the fixative to dry out. Adrop each of 1 per cent acetocarmine and 45 per centacetic acid was placed over the ovule and cover slipwas then gently lowered on to the ovule and the slidewas viewed under the low power to study the orien-tation of ovule and the possible position of female sexcell (EMC). Later the slide was gently tapped betweendouble folds of blotting paper with frequent checksunder the microscope to make sure the sex cell hasnot broken and/or got displaced, which usually hap-pens. Later, the cover slip was sealed with rubbersolution to prevent drying out. All the observationswere made from the temporary slides and photomi-crographs of selected cells were taken by Olympus

SEX INCIDENCES OF CHIASMATA IN IMPORTANT LEGUMES AND GRASSES 253

Table 1 – Mean number of chiasma observed in PMCs and EMCs of some legumes.

Collection No. of cells Stage Chiasmata Term. % reductionSpecies Acc. No. 2n site analyzed analyzed frequency / cell Coeff. in chiasmata

(per bivalent) ± S.D. PMC / EMC

Lathyrus - 14 DU, BG * PMC 30 Metaphase-I 18.06 ± 1.31 / 2.58 .16 - 10.24aphaca EMC 19 Metaphase-I 16.21 ± 1.19 / 2.31 .13

L. odoratus - 14 DU, BG PMC 30 Metaphase-I 20.2 ± 1.85 /2.88 .19 - 20.54EMC 19 Metaphase-I 16.05 ± 0.94 / 2.29 .05

14 HC, BG ** PMC 30 Metaphase-I 21.33 ± 1.46 / 3.04 .07 - 29.44EMC 19 Metaphase-I 15.05 ±1.19 / 2.15 .04

L. sativus+ PI 567853 14 Turkey PMC 30 Metaphase-I 13.31 ± 1.44 / 1.90 .31 - 5.25EMC 21 Metaphase-I 12.61 ±2.93 / 1.80 .24

PI 422541 14 Former USSR PMC 30 Metaphase-I 12.26 ± 1.28 / 1.75 .19 - 6.44EMC 21 Metaphase-I 11.47 ± 1.29 /1.63 .24

Lupinus - 48 DU, BG PMC 30 Diakinesis 29.4 ± 2.02 / 1.22 .61 - 67.68 albus EMC 18 Diakinesis 9.5 ± 5.98 / 0.39 .58

48 HC, BG PMC 30 Metaphase-I 25.3 ±2.28 / 1.05 .46 1.78 -EMC 17 Metaphase-I 25.76 ±_2.43 / 1.07 .49

Phaseolus - 22 HC, BG PMC 30 Metaphase-I 16.36 ± 1.86 / 1.48 .29 3.48 -vulgaris EMC 20 Metaphase-I 16.95 ± 2.22 /1.54 .46

Pisum - 14 DU, BG PMC 30 Metaphase-I 19.42 ± 1.35 / 2.77 .17 - 23.01sativum EMC 21 Metaphase-I 14.95 ± 1.13 /2.13 .24

14 HC, BG PMC 30 Metaphase-I 18.13 ± 1.64 /2.59 .07 - 19.91 EMC 23 Metaphase-I 14.52 ±1.05 / 2.07 .04

Vicia faba - 12 DU, BG PMC 30 Metaphase-I 23.06 ± 0. 95 / 3.84 .10 - 0.21EMC 19 Metaphase-I 23.01 ± 1.23 / 3.83 .10

12 HC, BG PMC 30 Diakinesis 23.23 ± 0.73 / 3.87 .07 - .07EMC 23 Diakinesis 23.06 ± 0.91 / 3.84 .05

*DU, BG Delhi University Botanical Garden.**HC, BG Hindu College Botanical Garden.+ Seed samples were obtained from Western Regional Plant Introduction Station, Pullmann, Washington.

CH 30 microscope fitted with photomicrographicattachment.

The most serious methodological problem in thepresent study was that of the stage in which chiasma-ta were to be studied. Since pollen mother cells(PMCs) are produced in large number per anther allmeiotic stages were available for analysis. However, theproblem existed with the embryosac mother cells(EMCs) which are not only difficult to handle butalso exist in very small number per flower whichmakes their detailed study even more difficult. There-fore, it became mandatory to compare and analyzeonly those stages which were obtained in large numberin EMCs with the corresponding stage in PMCs. Thetwo stages selected for present study were diakinesisand metaphase-I. Although the diplotene stage wasalso observed in both the sex cells in most of thespecies, it was not considered because of the longerbivalents which often create confusion in distinguish-ing a true chiasmata from a mere twist in a bivalent.While examining the chiasmata position, distributionand frequency adequate care was taken to select cellsshowing no or least overlapping of bivalents. Further,when a chiasmata did not show any chromosome armsbeyond it, it was considered as a terminal chiasmataand when the chromosomal arm beyond it could beseen, it was scored as an interstitial chiasmata. Statis-tical tests like students t-test, Fischer’s variance ratiotest (F- test), normal (Z) test and standard error ofmean (S.E.), were carried out to determine whetherthe variation in chiasma frequency of the two sex cells,wherever observed, was significant or not.

RESULTS

Male and female meiosis has been studied in13 species (19 acc.) of families Fabaceae andPoaceae. Tables 1 and 2 sums up the salientfeatures of meiosis in these taxa. Members ofFabaceae (Papilionaceae) are characterized bythe presence of zygomorphic flowers withdescending imbricate aestivation and diadelp-hous condition of stamens. The ovary is supe-rior, unilocular with many ovules aligned onthe ventral suture with marginal placentation.The diadelphous condition of stamens and thepresence of a large number of ovules in 1-2rows facilitate the study of PMC and EMCmeiosis. On the other hand, in the members offamily Poaceae the EMC study is very difficult.This is so on account of the small size of the flo-rets and the presence of a single ovule per flo-ret. Besides, a very high frequency of poly-ploidy and small size of chromosomes in mostof the species make such study even more com-plicated.

Meiosis in FabaceaeEMC and PMC meiosis in the presently stud-

ied legumes, barring the DU collection of L. albus,revealed normal chromosome behaviour duringdiakinesis and/or metaphase-I stages (Figs.1-12).However, the two sex cells varied with respect to

254 KOUL and NAGPAL

Table 2 – Mean number of chiasmata observed in the PMCs and EMCs of some grasses.

Collection No. of cells Stage Chiasmata Term. % reductionSpecies Acc. No. 2n site analyzed analyzed frequency / cell Coeff. in chiasmata

(per bivalent) ± S.D. PMC / EMCHordeum - 14 DU, BG PMC 30 Diakinesis 14.23 ± 1.35 (2.03) 0.49 10.79 -vulgare

EMC 21 Diakinesis 15.95 ± 1.04 (2.27) 0.3914 HC, BG PMC 30 Diakinesis 14 ± 0.89 (2.0) 0.54

EMC 20 Diakinesis 15.5 ± 1.07 (2.21) 0.48 9.67 -

Lolium PI 14 Poland PMC 30 Diakinesis 13.26 ± 0.92 (1.89) 0.92 37.89 -multiflorum 272118

EMC 17 Diakinesis 21.35 ± 0.90 (3.05) 0.26

L. perenne - 14 Simla PMC 30 Diakinesis 14.40 ± 0.84 (2.05) 0.29 26.53 -EMC 15 Diakinesis 19.6 ± 0.71 (2.8) 0.10

L. temu- PI 14 Turkey PMC 30 Metaphase-I 15.63 ± 1.30 (2.23) 0.66 1.26 -lentum 545600

EMC 18 Metaphase-I 15.83 ± 1.30 (2.26) 0.63

Phalaris - 14 HC, BG PMC 30 Diakinesis 14.73 ± 0.77 (2.10) 0.58 0.47 -minor EMC 15 Diakinesis 14.80 ± 0.65 (2.11) 0.57

Secale AR 14 Italy PMC 30 Metaphase-I 16.53 ± 1.40 (2.36) 0.27 - 2.4cereale 594/97

EMC17 Metaphase–I 16.12 ± 1.30(2.0) 0.31

SEX INCIDENCES OF CHIASMATA IN IMPORTANT LEGUMES AND GRASSES 255

Figs. 1-12 – Male and female meiosis in some legumes. Figs. 1-2 PMC and EMC of Pisum sativum (n = 7) at metaphase-I,respectively. Note the nucellar tissue at arrows. Figs. 3-4 PMC and EMC of Lathyrus aphaca (n = 7) at metaphase-I, respec-tively. Figs. 5-6 PMC and EMC of Lathyrus sativus (n = 7) at metaphase-I, respectively. Note the small sized bivalents in EMC.Figs. 7-8 PMC and EMC of Lathyrus odoratus (n = 7) at metaphase-I, respectively. Note the small sized bivalents in EMC.Figs. 9-10 PMC and EMC of Vicia faba (n = 6) at metaphase-I, respectively with EMC showing small bivalents. Figs. 11-12PMC and EMC of Lupinus albus (n = 24; HC collection) at metaphase-I respectively. Bar 10 µm.

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the frequency of chiasmata and/ or the size of thebivalents. While similar chiasmata frequency wasrecorded in P. vulgaris, V. faba and the HC col-lection of L. albus (Table 1), in L. aphaca, L. odor-atus, L. sativus and P. sativum it was higher in thePMCs. This apart, the size differences in the biva-lents was also observed in the two sex cells ofL. sativus, L. odoratus and V. faba with PMCsshowing large sized bivalents (Figs. 5, 7, 9). Inrest of the species no difference in the size of thebivalents of the two sex cells was noticed. Forchiasmata frequency estimation individual biva-lents could not be treated separately on account oftheir almost similar size. However, in V. faba asingle large bivalent could be recognized easilyand it invariably showed 6-7 chiasmata in both thesex cells. The remaining five similar sized bivalentsin both PMCs and EMCs, whether studied in DUcollection and/or the HC collection, had on anaverage 3.4 and 3.6 chiasmata per bivalent, respec-tively. Although the bivalents in EMCs were small-

er in size than PMCs and appeared tightly coiled,it did not affect the chiasmata frequency whichwas almost similar in both the sex cells studied atdiakinesis and metaphase-I (Figs. 9, 10). Itappeared as if the chiasmata had experienced lit-tle movement during these stages in V. faba. Nev-ertheless, in the two species i.e. L. odoratus andL. sativus the PMCs with larger bivalents had anincreased number of chiasmata.

Meiosis in Lupinus albus (n = 24) was inter-esting. Of the two populations studied while theHC population showed perfect bivalent forma-tion at metaphase-I in both the sex cells (Figs. 11,12), in the DU population the two sex cells varieddrastically with respect to the pairing behaviourof chromosomes. As against the regular pairing ofbivalents discerned in the PMCs at diakinesis(Fig. 13), the EMCs showed a high frequency ofunivalents which ranged from 0-48 per EMC(Figs.14, 15). The 48 chromosomes appeared as24II, 22II + 4I, 21II +6I, 20II +8I, 8II +32I, 1II

256 KOUL and NAGPAL

Table 3 – Statistical values obtained to test the significance for the difference of mean and variance in various legumes.

Species Collection Site F-ratio (df) Z- value t- value S.E. valueLathyrus aphaca DU,BG 1.19 (47) 4.97 4.89 5.01

L.odoratus DU,BG 1.76 (47) 10.64 8.86 10.17HC,BG 1.51 (47) 16.74 15.99 16.14

L.sativus Former Soviet Union .92 (49) 1.88 2.12 2.07Turkey .94 (49) 1.91 1.85 1

Lupinus albus DU, BG 2.87 (46) 12.43 14.10 12.43

HC, BG 0.86 (45) 2.16 2.11 2.19

Phaseolus vulgaris HC, BG 0.66 (48) 0.98 0.98 0.98

Pisum sativum DU, BG 1.41 (49) 13.54 12.47 12.88HC, BG 1.55 (51) 9.75 11.98 9.80

Vicia faba DU, BG 1.71 (47) 1.04 2.04 1.91HC, BG 0.94 (51) 2.25 2.25 2.30

Table 4 – Statistical values obtained to test the significance for the difference of mean and variance in various grasses.

Species Collection site F – ratio (df) Z – value t - value S.E.valueHordeum vulgare DU, BG 1.47 (49) 7.81 5.10 8.03

HC, BG 1.89 (48) 5.35 5.41 5.25

Lolium multiflorum Poland 0.99 (45) 30.64 28.43 32.36

L. perenne Simla, India 1.82 (43) 11.81 20.08 21.91

L. temulentum Turkey 0.96 (46) 0.38 0.50 0.51

Phalaris minor HC,BG 0.54 (43) 0.40 0.39 1.48

Secale cereale Italy 0.10 (45) 1.76 1.74 1.87

+46I and 48I in 38.88, 11.11, 16.66, 11.11, 11.11,5.55 and 5.55 per cent EMCs, respectively. Wher-ever the 48 chromosomes formed 24 bivalentsthey were open rings or cross type bivalents withonly one (rarely two) chiasmata present at thedistal end. Owing to high frequency of univa-lents the chiasmata frequency in the EMCs washighly reduced (Table 1). This plant showed 27per cent seed abortion.

Meiosis in PoaceaeMale and female meiosis in all the six species

(7acc.) studied was normal with regular bivalentformation observed at all meiotic stages (Figs.16-23). However, these species, like the legumes,also varied in respect of chiasma frequency, posi-

tion and distribution. While in H. vulgare, L.perenne and L. multiflorum, chiasmata frequencywas higher in EMCs (Table 2) with H. vulgareshowing larger bivalent size in EMCs (Fig. 19),which is in contrast to the observation made inlegumes, in S. cereale, L. temulentum and P. minorthe chiasma frequency was more or less similar inthe two sex cells (Table 2). Besides the variationin chiasma frequency, the chiasmata also varied intheir position. While in L. multiflorum and L.perenne the chiasmata were distally localized in allthe PMCs studied giving a ring shape to the biva-lents at diakinesis stage (Figs. 21, 23), in theEMCs they were randomly distributed (Figs. 20,22). Perhaps this localization of chiasmata lead tothe variation in its frequency in the two sex cells.

SEX INCIDENCES OF CHIASMATA IN IMPORTANT LEGUMES AND GRASSES 257

Figs. 13-23 – Male and female meiosis in some legumes and grasses. Figs. 13-15 PMC (Fig. 13) and EMCs (Figs. 14,15) of Lupi-nus albus (n = 24; DU collection) at diakinesis showing 24 II, 21 II + 6 I and 1 II + 46 I, respectively. Note the nucellar tis-sue at arrow. Figs. 16-17 PMC and EMC of Lolium temulentum (n = 7) at metaphase-I, respectively. Figs. 18-19 PMC andEMC of Hordeum vulgare (n = 7) at diakinesis. Note the large size of scattered bivalents (at arrows) in EMC. Figs. 20-21 EMCand PMC of Lolium perenne (n = 7) at diakinesis, respectively. Note the chiasma distribution in the two cells. Figs. 22-23 EMCand PMC of Lolium multiflorum (n = 7) at diakinesis, respectively. Note the random versus localized distribution of chias-mata in the PMC and EMC, respectively. Bar 10 µm.

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To test whether the differences in mean chi-asmata frequency in the two sex mother cells ofboth legumes and grasses studied were signifi-cant various statistical tests were applied whichincluded F-test, t- test, normal (Z) test and stan-dard error of the mean (S.E.). These tests wereperformed taking the null hypothesis (i.e. H0: µ1= µ2) which asserts that there is no true differencein the two variables (i.e. chiasmata frequency inthe EMC and PMC) and that the differencefound is accidental and unimportant arising outof fluctuations of samples. The values obtained(Tables 3, 4) show that the F–ratios calculated inall the species, barring DU collection of Lupinusalbus, did not exceed the tabulated F- ratio value(i.e. 1.96) at 5 per cent level of significance sug-gesting that the variance within the two popula-tions of male and female sex mother cells is notsignificant and/or the two populations did notshow any significant variation from the mean. InDU collection of L. albus the calculated valueexceeds the tabulated value at 1 per cent level ofsignificance (i.e. 2.58) suggesting that the vari-ances within the two populations of male andfemale sex cells is highly significant. The presenceof varying frequency of univalents in differentfemale sex cells of desynaptic mutant probablyaccounts for the high value obtained.

The calculated values obtained from t- test, Z-test and standard error of mean (S.E.) were foundto be much higher than the 1.96 S.E. and 2.58 S.E.value and/or the tabulated value at 5 per cent and1 per cent level of significance in Lathyrus aphaca,L. odoratus, Lolium perenne, L. multiflorum,Pisum sativum, Hordeum vulgare and the DU col-lection of Lupinus albus thus rejecting the nullhypothesis. This means that the variations in thechiasma frequency of two sex cells is highly sig-nificant and that the two variables did not followsimilar distribution pattern and/or did not repre-sent the same population. However, in Lathyrussativus, Phaseolus vulgaris, Vicia faba, Loliumtemulentum, Phalaris minor, Secale cereale and theHC collection of Lupinus albus the null hypothe-sis hold true which means that the chiasma fre-quencies in the two sex cells are almost identical.In L. sativus although 5.25 and 6.44 per centreduction in chiasmata frequency was recorded inthe EMC’s of two populations (Table 1), the sta-tistical tests applied revealed the difference in chi-asmata frequency of two sex cells to be insignifi-cant. It seems likely that such variations couldhave arisen due to fluctuations of sample.

DISCUSSION

The present male and female meiotic studieshave revealed asynchrony not only in the behav-iour of chromosomes in the two sex cells withrespect to the position, distribution and fre-quency of chiasmata, but also in the size of thebivalents. While higher frequency of chiasmatawas observed in the PMCs of Lathyrus sativus, L.aphaca, L. odoratus, Pisum sativum and the DUcollection of Lupinus albus, in species like Loliumperenne, L. multiflorum and Hordeum vulgare thesituation was other way round i.e. the EMCsshowed a higher chiasma frequency. Absence ofsex difference was noted in Phalaris minor, Loli-um temulentum, Secale cereale, Phaseolus vulgaris,Vicia faba and the HC collection of Lupinus albus.Besides the variation in chiasmata frequency, intaxa like L. perenne and L. multiflorum localizedversus random distribution of chiasmata wasnoticed in the PMCs and EMCs, respectively.Interestingly, variations also existed in the size ofthe bivalents which was larger in the EMCs of H.vulgare and PMCs of L. odoratus, L.sativus and V.faba as compared to their size in PMCs andEMCs, respectively. However, the extreme case ofsex difference was observed in the DU collec-tion of ornamental Lupinus albus in which themicrosporogenesis proceeded with precisionwhereas the megasporogenesis, interestingly,exhibited desynapsis. Since these species, bar-ring V. faba, S. cereale and H. vulgare, have beenstudied for the first time for female meiosis thepresent variations in meiotic behaviour in thetwo sex cells is being reported for the first time.In V. faba, H. vulgare and S. cereale although thesimilarity in the chiasmata frequency of two sexcells (as in V. faba and S. cereale) support the ear-lier findings of KOUL et al. (1999) and DAVIES

and JONES (1974), the large sized bivalents inPMCs of V. faba and higher chiasmata frequencyin EMCs of H. vulgare accompanied with thelarge size of bivalents is being reported for thefirst time.

Scrutiny of earlier literature available on maleand female meiosis in both animals and plants,though studied in a small number of species, haspredominantly shown a higher chiasma frequen-cy in female sex cells accompanied by the largebivalent size (WATSON and CALLAN 1952; FOG-WILL 1958; HANDERSON 1963; VED BRAT 1966;VOSA 1972; FOX 1973). Therefore, the presentobservations of higher chiasma frequency in the

258 KOUL and NAGPAL

PMCs accompanied by large bivalent size areunusual. While the higher chiasma frequency inEMCs has been attributed to 1) large size offemale nucleus, 2) longer time allowed for pairingand crossing over, and 3) greater torsion in thebivalent that could increase the frequency ofcrossing over (FOGWILL 1958), the large size ofthe bivalents in EMCs is explained on the basis of1) good nutrient supply available for femalenucleus as compared to male sex cells whichcompete with each other for nutrient suppliesfrom the tapetal layers, and 2) the large periodavailable for chromosomal reproduction (FOG-WILL 1958). In the present study although theexistence of higher chiasma frequency in theEMCs (as in H. vulgare, L. perenne, L. multiflo-rum) accompanied by large size of the bivalent (asin H. vulgare) could be attributed to the abovementioned factors, such factors, however, are notapplicable to the PMCs showing similar or morechiasma number and/or large bivalent size (as inL. odoratus, L. sativus, L. aphaca, P. sativum, V.faba). Therefore, it appears more likely that someother factor(s) unknown, whether physiologicalor genetical, may be involved in the manifestationof differential behaviour of chromosomes in thetwo sex cells. Here it will not be out of place tomention that the role of gene controlling thehomologous synapsis, chiasma frequency, itslocalization and formation is well established(DARLINGTON 1929, 1932; REES 1961; RILEY andLAW 1965; BAKER et al. 1976; SINGH 1993). Andthat DAVIES and JONES (1974) while working onvarious inbred lines of rye and SANDLER et al.(1968) on meiotic mutant of Drosophila mela-nogaster reported similar behaviour of chromo-somes in rye and achiasmate versus chiasmatemeiosis in male and female sex cells in Drosophi-la and attributed such behaviour to single jointcontrol of genes and two independent geneticcontrols operational in the two sex cells, respec-tively. Therefore, following the earlier observa-tions and views one may attribute the presence ofsynchrony or asynchrony in the behaviour ofchromosomes in the two sex cells, whereverobserved, to the presence of single or two sepa-rate genetic controls respectively. However,reaching to any conclusion regarding genetic con-trol will be too premature. This is so because asingle joint control, if present, can manifest twodifferent effects under differing conditions of twosex cells. Similarly, if two separate controls areoperational they could act convergently to pro-

duce similar effect in the two sex cells (DAVIES

and JONES 1974). To know the exact nature ofgenetic control operational it is important tostudy a range of genetically different types likemeiotic mutants and inbred lines. Nevertheless,whatever be the controlling mechanism opera-tional in the two sex cells, the unavoidable con-clusion arrived from the present study is that thetwo sex cells contribute differentially towardsgenerating variability. This view is strongly sup-ported by the presence of localized versus ran-domly distributed chiasmata in the PMCs andEMCs of L. perenne and L. multiflorum, respec-tively, and more so by the presence of desynapticmeiosis in the EMCs of L. albus. In these taxawhile the PMCs (in L. perenne and L. multiflo-rum) and EMCs (in L. albus) provide for theretention of certain linkage groups, the other sexcell i.e. PMC or EMC with randomly distributedchiasmata causes the reshuffling of genes throughcrossing over. In L. albus desynaptic versus synap-tic behaviour of chromosomes could be instru-mental in releasing diverse types of cytotypes pro-vided the female gametes containing deviantchromosome numbers, formed as a result of dis-cordant anaphase-I segregation that generally fol-lows metaphase-I in desynaptic mutants, are ableto survive. In L. albus since 27 percent seed abor-tion was recorded it seems more likely that thefemale gametes have failed to participate in seedproduction.

In conclusion, the present study of differen-tial chromosome behaviour in two sex cells hasmade the long held assumption, that meiosis inPMCs and EMCs is synchronous, untenable.Variations in chiasma frequency, distribution andposition can provide a clue for the overall level ofrecombination in the species, useful for roughlyestimating the size of population required for areasonable chance to find recombinationbetween a desired gene or gene complex.Besides, detailed male and female meiotic stud-ies can give an impression of the distribution ofrecombination i.e. are there important segmentspractically without recombination or else showhigh level of recombination. The studies onfemale meiosis can benefit both the breeders andthe genetic engineers attempting to engineerapomixis into the important cultivated crops tofix a novel character permanently. Female mei-otic studies can provide clues about the pres-ence or absence and also the nature of apomix-is, if present, in various plants. Therefore, there

SEX INCIDENCES OF CHIASMATA IN IMPORTANT LEGUMES AND GRASSES 259

is a need to study a large number of plant speciesand particularly those representing familyPoaceae since most of them carry genes forapomixis that can be fruitfully exploited inimprovement programmes.

Acknowledgments – The senior author (KKK)gratefully acknowledges the financial support pro-vided by the Department of Science and Technolo-gy (DST). Thanks are also due to Dr. Kavita Shar-ma, the Principal, Hindu College, Delhi for pro-viding various facilities during the course of inves-tigations.

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Received February 14, 2002; accepted May 16, 2002

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