Proc. Indian Acad. Sci. ( Sci.), Vol. 90, Numbr 5, October 1981, pp. 477--483. (~ Printed in India.

Reproduction in two speeies of Arundinella Raddi,

G P BASAPPA and M MUNIYAMMA Departmcnt of Post-Graduatc Studies and Reseazch in Botany, University of My~orc, Manasagangotri, Mysorc 570 006, India

MS receivect 7 February 1981 ; revised 27 August 1981

Abstraer, Arundinella mesophylla n = 8 and. A. purpurea n = 10 of the Poaceae, end.emic species of South India are studied, for their mode of reproduction. Meiosis in miGrosporocytes of these two diploid, taxa is regular anct produces notmal spore tetracts. Development and organization of the female gametophytc conforto to the monospori0 Polygonum typc. However, A. mesophylla plx)duces aposporous embryo saos in about 10% of the ovules. Oceasionally two archesporial cel]s func- tion and develop into embryo sacs in A. purpurea.

Keywords. Arundinella mesophylla ; A. purpurea ; Poaeeae ; apomixis ; apospory.

1. Introduction

The tribe Stapf, of Poaceae consisting of 16l species aTranged in 22 genera and 6 main supra generic ~oups (PhJpps 1966) ~S distributed in tropical parts of the world. The Arundinella Raddi, with 47 species (Phipps 1966) is represented in India by 23 species (Bar 1960). A perusal of literature gives cb.romosome counts for about 30 specic•. Tke basic chr~mosome r.umbers range fcom 7-10 and 12. We have been making a survey of cytocmbryological studies in S~,ath Iadian grass~. In thi.~ paper the microsporogen~is eald fcmale gameto- phyte development of Arundinella mesophylla Nees ex Steud., and A. purpurea Itochst. ex Steud., the endemic spccies of South India, ate d~cribed.

2. Materials and methods

Materials were colleeted flora Kodaik;artal, Ta.mil Nada. Spikelets were tixed in f/:3:1 Cornoy's solution. The poUen mother cells were stained with aceto- carmine. Ovules were dissected out and dehydrated irt Xylene-alcohol series, embedded in wax, sectioaed at 10-14 # and stained in H,.~idenhain's haematoxylin. A. solution of IzKI was used to determine pcfilen viability.

477 P.(B)--io 478 G P Basappa and M Muniyamma

3. Observations

3.1. Mierosporogenesis

Arundinella mesophyUa 2n = 16. Regalar pollen mother cell meioois is cbserved. Eight bivalents are being formed at diakinesis (figure t). All these bivalents aligu themnelves on the equatorial plate, and anaphasic I sep~ation is normal (figures 2 and 3). A. dyad is formed at the end of telophase I (figure 4). Second meiotic division which is aBo normal (figure 5) yields a. tetrz.d of mierospores (ti.gafe 6). T• pollen fertility asrevealed by stainability test~ in about 1000 pollen grains is 80%. A. purpurea 2n = 20. Meioe,is is normal and ten bivalen.ts ate observed during diakinesis (figure 7). Alignment of cttromosomes on the equatorial plate of meta- p:~a;e 1[ ii regular. Ozcasionally precoeious movement and [agging chromosomes ate observed (figures 8 and 9). I-Iowever, these lagging chromosomes a.re inclttded

7 " " ...,L:':.',91 ~N~~~~ .... !ii~~..... 84 g2

Figures 1-12. 1-6. Meiosis in poUen mother cells of Arundinella raesophylla. 7-12. Meiosis in PMC's of A. purpurea • 2000. Reproduction in A. raddi, poaceae 479 in the dyad nuclei (figure [0). The second division is also normal (figure 11) and forros mostly isobilateral spoxe tetrads (figure 12). Pollen fertility is 91~ as per stainability tests in about 900 pollen ~ains scozed.

3.2. Development of embryo sacs

In A. mesophytla ah arehesporial cell begin• to differentiate in the young ovule justat the time when the inner integument is being f•rmed (figure 13). TMs ce[I direetly faneti•ns as megaspore mother cell and by undergoing meiotic division yields a lirtear tetrad ofmegaspores (¡ 14-I6). The megaspore of the cttalazal end is the one whieh continues to enlarge and develop while the •ther three mega~,pff,'es deg.'.nerate (¡ 17). The functional ruegan,pote enlarges and divides three times develaping into 8-nucleate embryo sac (figures 18-20). The organized embŸ sac diffz'entiates into an egg apparatus of two synergids anda large egg, two polars and tlaree antipodals (figure 21). The number of antipodats observed remains to be three, which in nota commoa feature of g-asses. These antipodals bcg¡ to degenerate in the inature embryo sac prior to fertilization (figure 22).

13 14 15

Figures 13-23. Megasporogcncsis and fr gamctophyte development in A. meso- phylla. 13. Arohespc,rialcell. 14, 15, 16. Linear tctrad formation. 17. Ptmc- tional mr 18. 2-nucleate embryo sac. 19, 20. Yormation of 4-nuc]eate r sac. 21. Organiscd embryo sac. 22.t Mature r sac. 23. A globular embryo with a large numbcr of cndosl~rm nur 13-22. • 2,000. 23. • 1,400. 480 G P Basappa and M Muniyamma The primary endasperm nucleus divid~ and a largo number of ffee nuclci aro formed by a series of divisions. T/zese nucle~ occupy a pariete.1 positiort cmbedded in t/~e cytopIa~m surro.unding a central vacuole (figuTe 23). In this figure, 9. club- shaped proembryo is seen along with the endosperm. O2casioaally a few aposporous iaitials develop irt tke nucelltts and one or two ea[arge to develop uninucleate sac/s. La mo,st of tI~e ovttle~ the dyad degenerates, later ane to three aposporous cells develop with dcn~e cytoplasm and large nucleus (figure 24). The nucleus of the aposporous sac tklZ~, formed, divides mitotica[ly into two nuclei. Contrary to thc~~,e of the sexue.l embryo sacs, the two nttclei remzin tc~gether either at the micropylar of zt the chalaz2.l end with a large vacuole at the other pole (¡ 25 and 26). Part~er divisior, s and pol~ization of the nuclei are not uniform. Instances of embiyo sacs with 1 +2 (fi~m~xe 27) and 5+2 (tigttre 28) arrangement of the nuclei ate observe& Sometimes all the eiglzt nuclei ag~egate in the centre of the embryo sac without there being ~.ny organization at all (figxtre 29). The gametogenesis in .4. purpurea begins with the differentiation of a hypodermal arcttesporial cell (¡ 30). Oecasionally two arcttesporial cells ate obselved in the nucellus (figure 3 0. Meiosis in megaspore mot/~er cell (figures 32 and 33) y[eld~ a linear la:trad of mcgaspores (¡ 34). The mega~pore ne~est to tb.e ci~.alaza bcgins to grow and dcvelop vacuoles and becomes ffmctional (figure 35), w~aile the other megaspores dcge-erate. The nucleus of the ft~nctional meg~pore uadorgoes three sucee~sive divisions to produce 8 nuclei (figur~ 36 and 37)

24

:~~~~~ i 2~

Figures 24-29. Aposporous embryo sac dcvelopmcnt in A. mesophylla. 24. Uni- nucleate aposporous cmbryo sacs. Noto the dyad dcgeneration. 25, 26. 2-nucleate crnbryo sacs. 27. I + 2 arrangcrncnt of tho nuclei in the aposporous embryo sac. 28. 5+2 arr-91 of the nuclei. 29. Aggregation of 8 nuclei in the centre. x 1,400. Reproduetion in A. raddi, poaceae 48t The m~.ture embryo nae comprises an egg apparatus of two synergids and ah egg, two po.Iars--the largest nuclei of the embryo sae, lying side by side in the vieinity of the egg and three antipodals. Furtker divisions in the antipodaLs result in a eoenocyfic antipodal eomplex (figure 38). A sing[e instanee of two arehesporial cells fanctioning and developing into mature embryo sacs has been abserved (figure 39).

4. Discussion D~~p~te the reports of ekromosome eounts for about 30 spec~es of Arundinella, cytological studie~ are virtua[ly uaknowa. The present eytoembryological investi, g~tion'; in A. mesophylta and A. purpurea are the first record for the genus. Chromosome numbers n = 8 and n = 10 respectively lar these speeies eonfirm

34

2

i

-Ÿ 32

.1"

"~:

L Figures 30-39. Female gametophyte of A. purpurea. 30. Megaspore mother cell. 31. Two archesporial cells in the yotmg ovular priiordium. 32, 33, 34. The formation of a linear tetracL 35. Ftmctioual chalazal megaspore. 36. 2-nucleate embryo sac. 37. 4-nucleate embryo sac. 38. Mature embryo sac with coeno~ytir antipodals. 39. Two mature embryo sacs. 30-37. • 2,000. 38~ 39, • L400. 482 G P Basappa and M Muniyamma

earlier +eport (Muniyamma 1973). The chramosomes assocjate into regular bivalents duriag meiosis I of microsporogenesis and Inter is~bilateraI spore tetradr, produce furtctional poUen. The eytoIogical data obtained in this study indicate that these taxa ate characterized prineipally by sexual reproduction. Nevertheless, A. mesophylla produces I0~ nonfunctional aposporour, embryo sacs. Sexual embryo se.c devc- lopment in both the species is normal. Megasporogenesis results in a linear tetrad of megaspores. Female gametophyte development leads to the monosporic Poly- gonum type (Mahesttwari I950). OccasionaIiy in A. purpurea two archesporiai ceUs t'uncttan and develop into mature embryo sac~,a rare feature repGrted also in Pon pratensis and P. compressa (Anderson 1927) and Themeda cymbaria (Muniyamma 1973). The increasing trend in the numb~ of antipodal cells and their nuelei show a great range of variation in the members of Poaceae. A~atipadals in A. purpurea us in mo~t other grasses--Poa compressa and P. pratensis (Ander'.on 1927) interrupta (Maze and /~~hm 1974) and A. pilvs~da (Muniyamma 197Ca), begin ro pro[ffr before fertilization, ~howing certain abnarmalities. The coeno- cytic nature muy result ti'oro abnormal cell divisions. Sometim~, the antipodal cells fase in later stages of development. These changes in antipodal cells may rettect a hormonal imbalance, ccarelating the studies of Brink and Cooper (1944) and Maze and Bohm (t974). Contrary to this, the presence of only tbaee uni- nucleate antipodals in A. mesophylla us in Eragrostis superba (Streetm-~.n 1963) is rather ah uncommon feature amtmg grasses. Furlher, these antipod.qs obli- terate prior to fertiliza~2on renderiag 5-nu,-/eate condition to the embryo £ A[thoug• there is a correlat~on between diploidy aad sexuality, and polyploi6y and apomixis in scme groups of , diploid apom~cts have been ~epoIttd sporadically in angiosperms. Partitura antidotale 2n = 18 (Shamakurnari 1960) Nardus strtcta 2n = 20 (Rychlewski 1962) and Pennisetum ramosum 2n = 10 (Narayan 1962) ate some of the kaown diploid apomictic grass~s. The diploid A. mesophylla of tLte present study shows a tendency towards the develc~prmnt of apasparous emtryo sac~. That the organJzed aposperous (mb~yo s~cs in g:a;ses ate eit• 4-nucleate of 8-rtucleate is well established (Stebb/n~ 1950; B:own and Emery 1958; Battag[ia 1963 and Nygen I967). In addition to these fanctional embryo saes, however, deviations have been described as abno~rnalities in Poa alpina (H• I943, t944), Poa pratensis (Nielson 1946), ,4gropyron sr (Huir t956), Pennisetum dubium (Gildeahuys and B-ix 1959) and Hiero- ehloe alpina (Wcimiirck t~70). On the otlaer hand, the organization of apospo- rous embryo sacs in A. mesophylla does not conforto to any of the known types. ]~a~,tead, the nuctN .;n the embryo sae show either 1 + 2 of 5+2 arrangement of even they muy aggregate and remain in tke centre, tZarth.ermore, tb.ese embryo saes ate n(mfanctional, a situation parallel to that in Echinochloa stagnina (Muniyarmaa 1978). The izregular distribution and aggregation of nuclei in the centre of the embryo sac, seen in tb.e present study, account for the incomplete penetranee of the genetic factozs in the operation of apomixis, confirming earIier observation in Edzinochloa staguina (Muniyamma 1978). The aposporous embryo sae formation in A. mesophy[[a indicates the initiation of apom/x/s. Yet, [urtker devetopment &ad fanctionmg of embryo sacs are prevented. Ir is, therefore, obvious that the Reproduction in A. raddi, poaceae 483 delieately balanced genetic system of apomixL~ (Clau~en 1954) has f2ilcd to operate successfully.

Acknowledgements Tixe authors wish to thank Dr D A Govindappa fox facilities.

References

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