embryological studies in capparidaceae

E M B R Y O L O G I C A L S T U D I E S I N C A P P A R I D A C E A E

I. Sporogeneses and the Development of Gametophytes in Cleome viseosa Linn.

BY TASNEEM FATHIMA AND P. KUSUMA KUMARI (Department of Botany, University of Agricultural Sciences, Hebbal, Bangalore-24)

Received March 6, 1970

(Communicated by Prof. L. Narayana Rao, t~.A.se.)

ABSTRACT

Microsporogenesis, development of male gametophyte, megasporogenesis and the development of the female gametophyte in Cleome viscosa Linn. have been described.

The archesporium in the anther develops as a plate of three to four hypodermal ceils. The anther wall is composed of epidermis, fibrillar endothecirm, two middle layers and glandular tapett, m. The tapetal cells become multinucleate. The endothecial thickenings extend on all the cells of the anther except the epidermis and the vascular strand. The epidermis becomes discontinuous and wavy. The microspore tetrads are of decussate ard tetrahedral type. The pollen grains are shed at the three-celled stage. A stomium is organised during dehiscence.

The ovules are campylotropous, bitegminal and crassinucellar. The archesporit'm is hypodermal and cuts off a parietal cell. The megaspore tetrad is linear. The chalazal megaspore is functional but occasionally the third megaspore in the tetrad functions further and the others degenerate. The development of the female gametophyte corresponds to the monosporic, Polygonum type. The synergids are hooked. The embryo sac is filled with starch grains.

INTRODUCTION

ThE family Capparidaceae is one of the seven families under Rhoedales, in- eluding about 46 genera and 700 species of Paleotropieal distribution (Lawe- renee, 1951). Engler and Prantl (1891) have recognized five subfamilies in Capparidaeeae while Hooker (1872) considers his order XI. Capparideae to be composed of two tribes with 23 genera and 300 species of tropical distribution. Embryological studies in this family are far from adequate. The previous work on Capparidaceae (Davis, 1966) indicates that much more remains to be done. Considering the inadequacy of work and the

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208 TASNEEM FATHIMA AND P. KUSUMA KUMARI

interesting embryological features, the present work was undertaken. It includes the sporogeneses and gametogeneses in Cleome viscosa Linn.

The genus Cleome is included under the subfamily Cleomoideae (Engler and Prantl, 1891). It is one of the largest genera in the family with about 200 species (Lawerence, 195I). Cleome viscosa, the object of the present study is one of the most common species of thisgenus, found growing in fields and waste lands. The only previous work on this species is that of Tiwary (1936) on the megasporogenesis and the development of embryo. However, it does not include any details of develolzment o f anther, endosperm or embryo. Hence it was felt necessary to work out the embryology o~ this species in detail.

METERIAL AND METHODS

The material of Cleome viscosa was collected from the wet lands and waste lands in Hebbal Campus during the flowering season (October to December). Young flower-buds, flowers and frults were fixed in Formalin- acetic-alcohol for 24 hours, infiltrated and embedded in wax. The material was microtomed at2-15 microns and the sections were stained in Heiden- hein's iron-alum haematoxylin. Fast green and Gentian violet were used as counter stains. Smear preparations of microsporocytes were made in Acetocarmine and examined.

OBSERVATIONS

Cleome viscosa is an erect annual herb reaching about 1-2 feet in height. All the aerial parts of the plant are viscous with stalked glands. The leaves are 3-5 foliate with ovate or obovate leaflets. The flowers are in recemes. They are long pedicelled, hermaphrodite, hypogynous, heterochlamydeous and yellow in colour. The calyx consists of four spreading sepals. The corolla is composed of four reflexed petals. Androecium is constituted by 12-20 stamens with basifixed anthers. The gynoecium shows a sessile bicar- pellary, monolocular, superior ovary with an indefinite number of ovules borne on two parietal placentas. The fruit is a glandular pubescent capsule.

Microsporogenesis and the Development of the Male Gametophyte

A young anther in transection consists of a homogeneous mass of meri- stematic ceils. It becomes four-lobed and a plate of three to four densely cytoplasmic cells with conspicuous nuclei develops in each of the four lobes, constituting the archesporium (Fig. 1). The archesporial cells undergo

Embryological Studies in Capparidaceae--I 209

periclinal divisions to form an outer layer of primary parietal cells and an inner layer of primary sporogenous cells (Figs. 1, 2). The primary parietal cells divide further and form four layers of cells (Figs. 2, 3). Thus the anther wall consists of five layers of cells, viz., the epidermis, the endothecium, two middle layers and the tapetum (Fig. 4). The middle

• 1

II

l~es. 1-13

210 TASNEEM FA]HIMA AND P. KUSUMA KUMARI

layers degenerate at the time of tetrad formation. The tapetal cells are uninucleate in the beginning but later they enlarge enormously, their cytoplasm becomes highly vacuolated and the nuclei undergo divisions resulting in an increase in number which ranges from two to four in some cells (Fig. 7). However, the nuclei have a tendency to fuse together so tha tmost of the cells remain binucleate. The tapetum disorganises as the pollen grains are formed. Simultaneous with this, the cells of the endothecium elongate both tangentially and radially and develop fibrous bands of thickenings which extend from their inner tangential walls. These dense bands of thickenings extend all over the inner cells adjacent to the locules; hence all the cells towards the connective side of the anther except the vascular strand are invaded by them (Figs. 11-13). The epidermal cells become compressed along their radial walls making the epidermis appear discontinuous (Figs. 12, 13). The development of the anther wall corresponds to the Dicotyledonous type (Davis, 1966).

Simultaneously, the primary sporogenous cells undergo periclinal as well as anticlinal divisions and form a mass of microsporocytes (Figs. 3, 4). The microsporocytes become rounded off and undergo meiosis forming microspore tetrads. The divisions are simultaneous and the tetrads formed are of tetrahedral and decussate types (Figs. 5, 6), both types being equally frequent. The microspores thus formed are spherical and soon separate out from the mother wall that encloses them. The centrally situated nucleus of the microspore migrates towards the wall and divides to form a large vegetative cell and a small lenticular generative cell (Figs. 8, 9). The nucleus of the generative cell undergoes a division to form two cells which detach from the wall and lie engulfed in the cytoplasm of the vegetative cell close to the nucleus of the same (Fig. 10). The pollen grains are thus shed at the three-celled stage. They are triporate and possess a very thick spinascent exine and a thin intine.

Dehiscence of the anther takes place at the junction of the pollen sacs. A stomium consisting of a transverse row of two to four thin-walled cells is organised between the adjacent pollen sacs. These cells break down and release the pollen grains (Figs. 11-13).

Megasporogenesis and the Development of the Female Gametophyte

The campylotropous ovules ar;se as small cylindrical protuberances on the placenta. They are bitegminal and crassinucellar. The initials for the inner integument differentiate simultaneous with the differentiation of the archesporium. The initials for the outer integument develop at a slightly


lower level subsequent to the division of the archesporial initial. The outer integumentary initials grow faster so that when the megaspore tetrad is formed, the outer integument completely encloses the inner integument which in turn arches over the nucellus. The exostome and the endostome do not lie in the same line ; hence the micropyle is zig-zag, being formed by both the irttegurrents.

14

16

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2

~ i ~ PC ''''--

15 DEG MS / 17

i 18 FMS'

19

J "r

FIGS. 14-22

The hypodermal archesporium is usually single-celled and differentiates as a densely cytoplasmic cell with a conspicuous nucleus in the nucellar dome.

212 TASNEEM FA~HJ~A A~]9 P. KUSU~A KU~ARI

Occasionally the archesporium consists of two to four cells (Fig. 14), but invariably only one of them develops into a gametophyte and the rest degenerate. The functional archesporial initial divides periclinally cutting off a primary parietal cell and a sporogenous cell towards the inner side (Fig. 15). The primary parietal cell undergoes both periclinal and anticlinal divisions to form a parietal tissue (Figs. 15-19). The sporogenous cell enlarges and transforms itself into a megasporocyte (Fig. 16). Meiotic divisions in the megasporocyte result in a linear tetrad of megaspores (Figs. 17, 19). The chalazal megaspore from the tetrad enlarges and functions further, pushing through the three micropylar ones which degenerate (Fig. 18). The degenerating remains of these could be seen at the four-nucleate stage of the embryo sac (Fig. 21). Occasionally the third megaspore in the tetrad may function further, in which case the other three degenerate (Fig. 19). The nucleus of the functional megaspore divides mitotically and the resultant nuclei are pushed to the two opposite poles by the appearance of a central vacuole (Fig. 20). They divide and form a four-nucleate embryo sac (Fig. 21). An eight-nucleate embryo sac is ormed by the division of the four nuclei in the embryo sac. The eight nuclei

thus resulted organise into an egg apparatus; polar nuclei and the antipodals. Of the micropylar quartet, a pair of hooked synergids and a rounded egg constitute the egg apparatus. The fourth nucleus becomes the micropylar polar. In the chalazal region, three antipodal cells are organized and the fourth of the quartet becomes the chalazal polar (Fig. 22). Thus the development of the embryo sac is of Polygonum type (Maheshwari, 1950).

DIscussioN

The anther wall cons sts of the epidermis, fibrillar endothecium, a single middle layer and tapetum in Cleome monophylla (Rao, 1967). The number of middle layers however, differs in other genera. It is reported to be two to five in Capparis decidua and Crataeva nurvala (Narayana, 1962, 1965) and two in Cadaba indica (Narayana, 1965). In the present species, the anther wall shows two middle layers as in Cadaba indica (Narayana, 1965). The number of nuclei show considerable variation in different species. The tapetal cells are binucleate in Cleome monophylla (Rao, 1967) and Cadaba indica (Narayana, 1965) while they are four-nucleate in Crataeva nurvala (Narayana, 1965). In Cleome viscosa, the tapetal cells become multinucleate at later stages with the number of nuclei ranging from two to four in some cells. The nuclei have a tendency to fuse, as in Gynandropsis pentaphylla (Raghavan, 1938). A fibrillar endothecium is a common feature shared


by all the members investigated so far in Capparidaceae, but the extension of the thickenings to the inner adjoining cells has been reported only in Cadaba indica (Narayana, 1965). In this feature, Cleome viscosa shows similarities with Cadaba indica (Narayana, 1965). The fibrillar thickenings are found all over the cells adjacent to the locules except for the epidermis and the vascular strand. Three types of microspore tetrads, viz., tetrahedral, isobila° teral and decussate types have been reported in Cleome monophylla (Rao, 1967), while only tetrahedral and decussate types are reported in Capparis decidua, Cadaba indica and Crataeva nurvala (Narayana, 1962, 1965). In the present investigation also only tetrahedral and decussate types have been observed. According to Rao (1967) the pollen grains are shed at the uninucleate stage in Cleome monophylla, while Narayana (1962, 1965) has reported the pollen grains to be two-celled in Capparis decidua and Cadaba indica and two-celled and three-celled in Crataeva nurvala. In Cleome viscosa, they are three-celled at the time of the dehiscence. However, they do not ger- minate in situ as in Capparis decidua (Narayana, 1962).

The ovules are generally campylotropous, crassinucellar and bitegminal in all the members investigated so far including the present investigation. However, they are anatropous at the time of fertilization in Crataeva nurvala (Narayana, 1965). There have been conflicting reports on the development of integument in various members. The inner integument develops earlier than the outer in Cleome monophylla (Rao, 1967), while the outer grows faster than the inner in Capparis decidua, Cadaba indica and Crataeva nurvala (Narayana, 1962, 1965). Cleome viscosa resembles the latter genera in this respect. The micropyle is organised by both the integuments in all members of Capparidaceae studied so far except Capparis sp. where only the inner integument is involved (Davis, 1966). Cleome viscosa shows similarities with other members in this aspect.

The hypodermal archesporium in the present species is usually single- celled but occasionally many-celled as in other members. In Cleome monophylla (Rao, 1967) the integumentary initials develop subsequent to the differentiation of the archesporium. In all the members including Cleome viscosa, the development of the inner integumentary initials is simultaneous with the differentiation of the archesporium. A parietal tissue is formed by the division of the archesporium in all the members including the present species. However, in Maerua arenaria (Rao, 1936) and Cleome chelidonii (Raghavan, 1937), the cells of the nucellar epidermis undergo periclinal divisions and form a nucellar cap to supplement the parietal tissue. Such a feature was not observed in the present investigation.

214 TASNEEM FATHIMA AND P. I(USUMA KUMARI

The megaspore tetrad is linear or T-shaped in Capparis decidua, Cadaba indica, Crataeva nurvala (Narayana, 1962, 1965) and Cleome moaophylla (Rao, 1967). However, only a linear tetrad of megaspores was observed in the present species. The chalazal megaspore functions further to give rise to a Polygonum type of embryo sac in all species. In Cleome viscosa, occasionally the third megaspore is functional and the other three degenerate. In C. monophylla (Rao, 1967) the synergids are neither hooked nor beaked and a filiform apparatus is also lacking while in other members the synergids are hooked. A filiform apparatus is noticed in Maerua arenaria (Rao, 1936), Capparis decidua, Cadaba indica and Crataeva nurvala (Narayana, 1962, 1965). In Cleome viscosa the synergids are hooked but a filiform apparatus is, however, absent. The embryo sac is filled with starch grains as in C. monophylla (Rao, 1967).

ACKNOWLEDGEMENTS

The authors are indebted to Dr. G. Boraiah, Associate Professor and Head of the Department of Botany, U.A.S., for making available the facilities and encouragement.

REFERENCES

Davis, G. L.

Engler, A. and Prantl, K.

Hooker, J. D.

Lawerence, G. H. M. Maheshwari, P.

Narayana, H. S.

Raghavan, T, S,

Rao, V. S.

. . Systematic Embryology o f Angiosperms, John Wiley and Sons, Inc., 1966.

. . Die naturlichen pflanzenfamilien, III, Tiel. 2., Abteilung, Leipzig, 1891.

. . Flora o f British India, Vo]. I, London, 1872.

. . Taxonomy o f Vascular Plants, New York, 1951. . . An Introduction to the Embryology o f Angiosperms, Delhi, 1950. •. Recent Advances in the Embryology o f Angiosperms, Delhi, 1963. .. "Studies in Capparidaceae. I. Floral morphology and embryo-

logy of Capparis decidua (Forsk.) Pax.," Phytomorphology, 1962, 12, 167-77.

.. "Studies in Capparidaceae. II. Floral morphology and embryology of Cadaba indica Lamk. and Crataeva nurvala Buch.-Ham.," Ibid., 1965, 15, 158-75.

.. "Studies in the Capparidaceae. I. The life-history of Cleome chelidonii Linn.," J. Linn. Sac. (Bat.), 1937, 51, 43--47.

.. "Morphological and cytological studies in the Capparidaceae. II. Floral morphology and cytology of Gynandropsis pentaphylla DC.," Ann. Bat. (Land.), 1938, 2, 75-95.

.. "Studies in Capparidaceae. I. The embryo-sac of Maerua arenaria Forsk.," J. Indian bat. Sac., 1936, 15, 71-75.

Rao, A. V. N.

Sachar, R. C.

Tiwary, N. K.

Embryological Studies in Capparidaceae--I

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215

"Embryological studies in Cleome monophylla Linn.," Proc. Ind. Acad. ScL, 1967, 65 ]! (6) 249-56.

"The embryology of Isomeris A reinvestigation," Phyto- morphology, 1956, 6, 346-63.

"Megasporogenesis and embryo development in Cleome viscosa Linn.," Sci. and Cult., 1936, 1, 476-77.

EXPLANATION TO DRAWINGS

Fins. 1-13. Microsporogenesis and the development of the male gametophyte in Cleome viscosa Linn. Fig. 1. T.S. anther lobe showing arehesporiai initiais, × 1,455. Fig. 2. T.S. anther lobe showing primary parietal layer and primary sporogenous layer, × 1,455. Fig. 3. T.S. anther lobe showing epidermis, parietal layers, tapetum and sporogenous cells, × 1,500. Fig. 4. T.S. anther lobe showing epidermis, endothecium, middle layers, tapetum and sporogenous tissue, × 1,455. Fig. 5. Tetrahedral microspore tetrad, × 1,500. Fig. 6. Decussate, microspore tetrad, x 1,500. Fig. 7. T.S. portion of anther waU showing epidermis, endothecium, middle layers and multinucleate tapetal cells, × 1,500. Fig. 8. Uninucleate pollen grain, × 2,000. Fig. 9. Two-celled pollen grain, × 2,000. Fig. 10. Three-celled pollen grain, x 2,000. Fig. 11. T.S. anther showing the region of dehiscence, x 200. Fig. 12. Portion

marked 'X' in Fig. 11 enlarged to show the fibrillar endothecium and the region of dehiscence, × 675. Fig. 13. T.S. anther lobe showing the fibrillar endothecium and fibrillar thickenings on the inner cells of the anther, × 450.

(D, dehiscence; Tc, Tapetal cells.)

F/os. 14--22. Megasporogenesis and the development of female gametophyte in Cleome viseosa Linn. Fig. 14. L.S. portion of ovule showing two-celled archesporium, × 1,455. Fig. 15. L.S. portion of ovule showing the parietal cells, the sporogenous cell and the initials for the inner integument, × 1455. Fig. 16. L.S. nucellus showing parietal tissue and megasporocyte, × 1,500. Fig. 17. L.S. nucellus showing parietal cells and the megasporocyte under anaphase I, × 1,455. Fig. 18. L.S. nucellus showing parietal tissue, three degenerating megaspores and the functional one, × 1455. Fig. 19. L.S. nucellus showing degenerating megaspores and the third functional one, × 1,455. Fig. 20. L.S. portion of the ovule showing degenerating megaspores and two-nucleate embryo sac, × 1,500. Fig. 21. Four-nucleate embryo sac, × 1,500. Fig. 22. Eight-nucleate embryo sac after cellular organization, × 1,455.

(DEG MS, degenerating megaspores; FMS, functional megaspore; INI, initials for the inner integument; PC, parietal cells; PT, parietal tissue.)

embryological studies in capparidaceae

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