Apomixis and abnormal anther development in Calotis lappulacea Benth. (Compositae)

1968 ◽  
Vol 16 (1) ◽  
pp. 1 ◽  
Author(s):  
GL Davis
Keyword(s):  
New South ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Anther Wall ◽  
Male Gametes ◽  
Globular Stage ◽  
South Wales ◽  
Vertical Division ◽  
Endosperm Formation ◽  
Embryo Sac Formation

A comparative study was made of material collected from four localities in New South Wales and Queensland and a number of embryological aberrations were found to be common to all districts. During microsporogenesis, certain tapetal cells not only failed to contribute to the tapetal periplasmodium but, after increasing in size, they separated from the anther wall and resembled one-, two-, or four-nucleate embryo sacs developing among the microspores. In one anther a structure was present which was very similar to a fully differentiated embryo sac. Although the pollen grains of some anthers contained male gametes, most anthers dehisced when the pollen was two-celled and some shrivelled soon after meiosis. Megasporogenesis was followed by the formation of linear tetrads of megaspores, but embryo sac formation was the result of somatic apospory and C. lappulacea appears to be an obligate apomict. The enlarging somatic cell usually invades the nucellar lobe and replaces the megaspores but one or more such celis commonly develop also in the chalaza, and up to eight embryo sacs were found in one ovule. Enlargement of a chalazal embryo sac sometimes resulted in penetration of the ovular epidermis and its invasion of the loculus as a haustorium-like structure. Extrusion of a developing embryo sac through the micropyle was common. Embryogeny is of the Asterad type, but vertical division of the terminal cell ca was delayed until after the basal cell cb had given rise to superposed cells m and ci. Polyembryony was common but only one embryo in each ovule reached maturity. Endosperm formation was independent of embryogeny but unless it was initiated before the globular stage of the embryo, the embryo sac collapsed and the embryo degenerated.

Embryological studies in the compositae. IV. Sporogenesis, gametogenesis, and embryogeny in Brachycome ciliaris (Labill.) Less

1964 ◽  
Vol 12 (2) ◽  
pp. 142 ◽  
Author(s):  
GL Davis
Keyword(s):  
New South ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Egg Cell ◽  
Male Sterile ◽  
Morphological Variations ◽  
Secondary Nucleus ◽  
South Wales ◽  
Mother Cells ◽  
Antipodal Cells

Material of two varieties of Brachycome ciliaris was obtained from several localities in southern Queensland and western New South Wales, and no embryological differences were found between populations in spite of considerable morphological variations. The plant was highly male-sterile, and although development of the anthers was normal up to the formation of microspore mother cells, presumed meiotic abnormalities resulted in failure to form microspore tetrads except in one instance. The formation of plasmodial microspore mother cells and unreduced pollen grains is described and the occurrence of normal pollen grains in two capitula is recorded. In the ovule, meiosis is suppressed and the megaspore mother cell becomes vacuolate and functions directly as the uninucleate embryo sac. Three nuclear divisions precede the formation of an eight-nucleate embryo sac in which the antipodal cells undergo secondary multiplication. There is circumstantial evidence that the polar nuclei divide simultaneously to form the fist four endosperm nuclei and do not first fuse to form a secondary nucleus. The egg cell develops parthenogenetically and cleavages follow the asterad type of development. The eariy stages of embryogeny are completed before the opening of the florets.

The floral morphology and embryology of Themeda australis (R. Br.) Stapf

1964 ◽  
Vol 12 (2) ◽  
pp. 157 ◽  
Author(s):  
PS Woodland
Keyword(s):  
Embryo Sac ◽  
Pollen Grains ◽  
Low Fertility ◽  
Linear Tetrad ◽  
Polygonum Type ◽  
Morphological Variations ◽  
Endosperm Formation ◽  
Secretory Type ◽  
Successive Cytokinesis ◽  
Mother Cells

A comparative study was carried out between diploid and tetraploid races of Themeda australis from Armidale and Cobar, respectively. Some morphological variations occur in both populations, but sporogenesis and gametogenesis are identical. The anther is tetrasporangiate and the development of its four-layered wall is described. The tapetum is of the secretory type and its cells become binucleate at the initiation of meiosis in the adjacent microspore mother cells which undergo successive cytokinesis. Microspore tetrads are usually isobilateral and the pollen grains are three-celled at dehiscence, which takes place by lateral longitudinal slits. The ovule is of a modified anatropous form and bitegmic, the broad micropyle being formed of both integuments. The single hypodermal archesporial cell develops directly into the megaspore mother cell and the nucellar epidermis undergoes periclinal and anticlinal divisions to form a conspicuous epistase. The chalaza1 megaspore of the linear tetrad gives rise to a Polygonum-type embryo sac. Material from the Armidale population showed one embryo sac per ovule, but two to five embryo sacs were present in that from Cobar. Embryogeny is typically graminaceous and endosperm formation is at first free-nuclear, later becoming cellular. Polyembryony follows fertilization of several embryo sacs within the same ovule. The reasons for low fertility of T. australis and poor germination of seeds are discussed.

scholarly journals Embriología de Erythroxylum havanense Jacq. (Erythroxylaceae)

2017 ◽  
pp. 25
Author(s):  
Sonia Vázquez-Santana ◽  
César A. Domínguez ◽  
Judith Márquez-Guzmán
Keyword(s):  
Seed Coat ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Endosperm Development ◽  
Anther Wall ◽  
Starch Grains ◽  
Reproductive Structures ◽  
Exine Sculpturing ◽  
Erythroxylum Havanense ◽  
Mature Anther

We studied the development of reproductive structures in pin and thrum morphs of Erythroxylum havanense. The young anther wall consists of an epidermis, endothecium , 1-3 middle layers anda binucleate secretory tapetum. The mature anther wall has only two layers: epidermis and endothecium. Microspore tetrads are tetrahedral or isobilateral. Mature pollen grains are tricolporate, bicellular and contain starch grains. Exine sculpturing is verrugate in thrum pollen and reticulate in pin pollen. The ovule is sessile, pendulous, anatropous, bitegmic and crassinucellate. The embryo sac is heptacellular. An endothelium is differentiated. The endosperm development is nuclear, and the basal part of the nucellus persists during early endosperm development. Both integuments form the seed coat.

Sporogenesis, Gametogenesis, and embryogeny of Wahlenbergia bicolor N. Lothian

1963 ◽  
Vol 11 (2) ◽  
pp. 152 ◽  
Author(s):  
G Want
Keyword(s):  
Mother Cell ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Type A ◽  
Middle Layer ◽  
Anther Wall ◽  
Suspected Case ◽  
Polygonum Type ◽  
Chalazal Megaspore ◽  
Coastal Species

In Wahlenbergia bicolor, the anther wall is composed of four layers: epidermis, endothecium, middle layer, and tapetum. Wall formation and microsporogenesis are described, and the pollen grains are shed at the two-celled condition. The ovules are tenuinucellate, with a hypodermal archesporial cell which develops directly as the megaspore mother cell. Megasporogenesis is normal, and a monosporic eight-nucleate embryo sac of the most common Polygonum type develops from the chalazal megaspore. The antipodals degenerate before fertilization. The development of the embryo is of the solanad type. A suspected case of polyembryony was observed. The endosperm is cellular from its inception, and so conforms to the Codonopsis type. A micropylar and a chalazal haustoriurn, both consisting of two uninucleate cells, are formed from the endosperm. Comparative studies were made with a known but as yet undescribed coastal species of Wahlenbergia, and no differences were found.

Floral morphology and the development of gamethophytes in Eucalyptus melliodora A. Cunn

1968 ◽  
Vol 16 (1) ◽  
pp. 19 ◽  
Author(s):  
GL Davis
Keyword(s):  
Soviet Union ◽  
Floral Morphology ◽  
Embryo Sac ◽  
Pollen Grains ◽  
The Black Sea ◽  
Anther Wall ◽  
Polygonum Type ◽  
Threefold Increase ◽  
The Soviet Union ◽  
Sea Area

Flower buds are first recognizable in late December at the commencement of new growth, and the deciduous bracts enclosing each cyme are shed about 3 weeks later. The buds increase rapidly in size, but anthesis does not occur until the end of September and the seeds are not shed from the capsules until the following August. The development of the double operculum and the floral parts is traced. Archesporal tissue is differentiated in the anthers in late February but ovule primordia are not formed until the end of March, by which time the stamens have reached their full size and anther wall formation is well advanced. In each bud events in the anthers and ovules are broadly comparable, but variation in the stages of development occurs between buds on the same branch. Meiosis takes place during the winter months, and embryo sac development follows the Polygonum type. The components of the egg apparatus undergo a threefold increase in size after their formation and, whereas the egg contains little cytoplasm, the synergids become densely cytoplasmic and laterally hooked. The pollen grains are two-celled when they are shed through the slits at the apices of the anthers. A comparison is made of the embryology of E. melliodora and that of species cultivated in Italy and the Black Sea area of the Soviet Union.

Dacrycarpus (Podocarpaceae) macrofossils from Miocene sediments at Elands, eastern Australia

2000 ◽  
Vol 13 (3) ◽  
pp. 395 ◽  
Author(s):  
Robert S. Hill ◽  
Sung Soo Whang
Keyword(s):  
New South ◽  
New South Wales ◽  
Pollen Grains ◽  
Phylogenetic Significance ◽  
South Wales ◽  
Eastern Australia ◽  
Male Cones

Vegetative remains and male cones containing pollen grains from Miocene sediments at Elands in northern New South Wales are assigned to the new Podocarpaceae species Dacrycarpus elandensis. This species represents the most complete and best preserved Dacrycarpus macrofossil remains known. These fossils are morphologically most similar to extant D. imbricatus and fossil D. latrobensis and D. linifolius, but the phylogenetic significance of many of the characters used to make this comparison is unknown. Dacrycarpus is now extinct in Australia, but D. elandensis confirms a presence for it in eastern Australia at a time when rainforest was drying and retracting and Eucalyptus was expanding its range in the region.

Embryological studies in Taraxacum udum Jordan (sect. Palustria)

Botany ◽  
2013 ◽  
Vol 91 (9) ◽  
pp. 614-620 ◽  
Author(s):  
Krystyna Musiał ◽  
Patrycja Górka ◽  
Maria Kościńska-Pająk ◽  
Paweł Marciniuk
Keyword(s):  
Rare Species ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Type Ii ◽  
Additional Source ◽  
Storage Tissue ◽  
Mode Of Reproduction ◽  
Autonomous Endosperm ◽  
Endosperm Formation ◽  
Single Locality

The present paper reports our observations on the mode of reproduction in Taraxacum udum (sect. Palustria), a very rare species in Poland, known only from a single locality. Based on the analysis of the developmental processes in the ovules, it can be concluded that this bog dandelion is an obligate and autonomous apomict. Its reproduction involves (i) restitutional diplospory, also known as Taraxacum type; (ii) parthenogenesis; and (iii) autonomous endosperm formation. Moreover, observations on the anatomy of ovules confirmed the occurrence of a special storage tissue around the embryo sac, which is considered to be an additional source of nutrition for the embryo. An examination of the anthers showed that, in spite of highly disturbed meiosis, apomictic T. udum produces pollen but pollen grains are heterogeneous in size and stainable using an acetocarmine test.

Development of the female gametophyte of Minuria cunninghamii (DC). Benth, Ccompositae)

1964 ◽  
Vol 12 (2) ◽  
pp. 152 ◽  
Author(s):  
GL Davis
Keyword(s):  
Comparative Study ◽  
Female Gametophyte ◽  
New South ◽  
Embryo Sac ◽  
Mature Embryo ◽  
Polygonum Type ◽  
South Wales ◽  
Significant Difference ◽  
Female Gametophyte Development ◽  
Two Populations

Minuria cunninghamii is widely distributed throughout the drier parts of Australia, and a comparative study was made of the female gametophyte development in two populations 300 miles apart in western New South Wales. In specimens collected 120 miles south of Menindee, the embryo sac was monosporic in origin and of the Polygonum type, whereas in those from Wanaaring it was usually bisporic and of the Allium type. No significant difference was found in mature embryo sacs from the two localities, although an unusual feature of both was the occurrence of vacuoles in the apices of the synergids.

Floral morphology and the development of the gametophytes in Eucalyptus stellulata Sieb

1969 ◽  
Vol 17 (2) ◽  
pp. 177 ◽  
Author(s):  
GL Davis
Keyword(s):  
Continuous Process ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Late Summer ◽  
Early Spring ◽  
Normal Embryo ◽  
Egg Apparatus ◽  
Wide Range ◽  
Sterile Pollen ◽  
Embryo Sac Formation

Bud formation on new growth is a continuous process which extends from early spring until midsummer, and at any time except during the winter months a wide range of floral development is exhibited on each tree. The main flowering period in the Armidale district is late summer to early autumn but sporadic flowering may occur at any time. The development of the single operculum and the floral parts is traced but, owing to the prolonged period over which bud primordia are formed, stages of organogenesis cannot be related to definite seasons. At the onset of meiosis the buds enlarge and rupture the two fused bracts which enclose the inflorescence, and these are shed. Embryo sac formation is of the Polygonum type and the components of the egg apparatus undergo a threefold increase in size before anthesis. In more than half the embryo sacs the endosperm mother cell becomes multinucleate and its subsequent degeneration is followed by that of the egg apparatus. Such abnormal ovules continue their growth and cannot be distinguished externally from those containing normal embryo sacs. The fertile pollen grains are two-celled when shed but a high proportion of flowers produces only sterile pollen whose development has been arrested at the one-nucleate stage.

Sign in / Sign up

Export Citation Format

Share Document