Chalazal Chamber Research Articles

Significance of seed morphology and anatomy in the systematics of Musaceae

AbstractThe paper deals with the seed morphology and anatomy of 32 wild Indian Musaceae by using light microscopy (LM) and scanning electron microscopy (SEM). This is the first comprehensive investigation into the seed micro-morphological and anatomical aspects of two genera of the family. Seed characters including shape, size, surface sculpturing (LM and SEM), seed coat thickness, layer characters and chalazal chamber column were considered. Seed characters play a significant role in the delimitation of taxa as they are more stable than vegetative (anatomical) and pollen features. Four types of seeds (oblate, ovoid, sub-globose and ellipsoid) were observed in the family, oblate seeds being the most common. LM revealed that most of the seeds have verrucate surface sculpturing, but some are smooth-verrucate or smooth. Seed size also plays an important role in the identification of the taxa to some extent. Number of layers and seed coat thickness are directly proportional to seed size. However, the thickness of endotesta, tegmen and inner endosperm layers (aleurone layers) differ in small and large seeds. The present study revealed eight types of outer sculpturing and three inner sculpturing patterns with diverse nature of anticlinal and periclinal cell walls. Based on the seed characters, a phenetic analysis was also carried out.

Revision of putative Alpinia (Zingiberaceae) fossils from the Paleogene and Neogene of western Europe

The fossil floras described by Dieter Mai and Harald Walther are invaluable for understanding the past plant diversity in Europe, and provide important information on the occurrence of taxa in the fossil record that is critical for evolutionary studies. Among the taxa they recognized were seeds assigned to the extant genus Alpinia Roxb. (Zingiberaceae, Zingiberales). We reinvestigated 28 specimens that were assigned to Alpinia arnensis (Chandler) Mai, Alpinia cf. arnensis, and Alpinia bivascularis Mai from the Ypresian (lower Eocene) of the UK, upper Eocene of Germany, and lower Miocene of Germany using non-destructive synchrotron-based X-ray tomography to reveal internal anatomy. None of the samples studied show an anatomy consistent with extant Alpinia or even Zingiberales. The fossils lack the globose shape, often striate external surface, seed coat structure, operculum, and micropylar collar seen in all Alpinia, and lack the chalazal chamber seen in many Alpinia species. Two specimens from the lower Miocene of Germany showed the structure of fruits of Caricoidea Chandler (Cyperaceae) with a single-layered exocarp, thick mesocarp, and sclerified endocarp. The other specimens are recognized as Carpolithes albolutum nom. nov. (incertae sedis) from the Ypresian of the UK, C. phoenixnordensis sp. nov. (incertae sedis) from the upper Eocene of Germany, C. bivascularis comb. nov. (incertae sedis) from the lower Miocene of Germany as well as indeterminate tegmens from the lower Miocene of Germany. This reinvestigation demonstrates that there is, as yet, no confirmed fossil record for the extant genus Alpinia. Furthermore, at least four different taxa are recognized from what had been two extinct species, enhancing our understanding of these important European Cenozoic carpofloras.

Evolutionary significance of seed structure in Alpinioideae (Zingiberaceae)

Alpinioideae is the largest of the four subfamilies of Zingiberaceae and is widely distributed throughout the New and Old World tropics. Recent molecular studies have shown that, although Alpinioideae is a strongly supported monophyletic subfamily with two distinct tribes (Alpinieae and Riedelieae), large genera, such as Alpinia and Amomum, are polyphyletic and are in need of revision. Alpinia and Amomum have been shown to form seven and three distinct clades, respectively, but, for many of these clades, traditional vegetative and floral synapomorphies have not been found. A broad survey of seeds in Alpinioideae using light microscopy and synchrotron-based X-ray tomographic microscopy has shown that many clades have distinctive seed structures that serve as distinctive apomorphies. Tribes Riedelieae and Alpinieae can be distinguished on the basis of operculum structure, with the exception of three taxa analysed. The most significant seed characters were found to be various modifications of the micropylar and chalazal ends, the cell shape of the endotesta and exotesta, and the location of an endotestal gap. A chalazal chamber and hilar rim are reported for the first time in Zingiberaceae. In addition to characterizing clades of extant lineages, these data offer insights into the taxonomic placement of many fossil zingiberalean seeds that are critical to understanding the origin and evolution of Alpinioideae and Zingiberales as a whole.

Female gametophyte and seed development inMusella lasiocarpa(Musaceae), a monotypic genus endemic to Southwestern China

Musella is a monotypic genus composed of a single species, Musella lasiocarpa (Franch.) C.Y. Wu ex H.W. Li, endemic to Southwestern China. The genus status of Musella remains controversial. Musella had been placed first in Musa , then in Ensete , and back to Musa before its monotypic status was recognized. Musella was reported to be extinct in the wild and maintained through cultivation only via vegetative propagation through sprouting of rhizomes. In this study, female gametophyte and seed development of Musella are described to assess its systematic position and possible reasons why the wild population is now extinct. The ovules are anatropous, bitegmic, and crassinucellar. The micropyle is formed by both integuments. The megaspore mother cell undergoes meiotic division and forms a linear megaspore triad or more rarely, a T-shaped megaspore tetrad. The chalazal megaspore develops into a Polygonum type embryo sac. A nucellar pad forms, and a hypostase differentiates. Fertilization is porogamous. Endosperm formation is of the nuclear type. The zygote degenerates and so the process by which the embryo develops, if it does, remains unclear. An operculum, micropylar collar, and chalazal chamber form in mature seeds. The storage tissue is mainly endosperm containing large, compound starch grains and some perisperm. The seed coat has lignified exotestal cells, 25–30 cell layers of sclerotic mesotestal cells, and unspecialized endotesta cells; the tegment consists of two layers of longitudinally elongated cells. The seed is inviable. After comparison with the other Musaceae s. str. taxa using embryological and botanical features, we conclude that Musella should be a distinct genus. Female sterility in Musella may be the main reason why the wild population is extinct. Based on these findings, we propose conservation strategies for this endemic species, including habitat protection as well as ex-situ conservation.

Comparative anatomy of the chalazal endosperm cyst in seeds of the Brassicaceae

Data from this study show that the chalazal cyst is a consistent feature of the Brassicaceae that exhibits variation of potential taxonomic value. The U-shaped seeds of mustards comprise three development chambers: micropylar (MC), central (CC), and chalazal (ChC). Early in seed development the syncytial endosperm in the ChC becomes differentiated into a cyst that remains distinct from storage endosperm. In early syncytial stages, the cyst is stratified into three zones: (1) an apical zone containing nuclei, plastids and mitochondria, (2) a mid-zone rich in endomembranes but depleted of large organelles, and (3) a basal portion that is bordered by a labyrinthine wall. The basal zone has projections that range from foot-like extensions to thread-like haustoria that penetrate the underlying maternal chalazal proliferative tissues (CPT). No cell-to-cell connections occur between endosperm and maternal tissue, but the extensive labyrinthine walls closely invest cell lysate resulting from degradation of the CPT. Structural data from light, confocal and transmission electron microscopy suggest that the cyst is active in uptake and transport of metabolites into the developing seed. Four types of cyst reflecting position and size of the ChC are recognized. In general, they correlate with major tribes of Brassicaceae. Data support recent molecular studies indicating that classification of the Lepidieae is artificial and suggest that Thlaspi is a candidate for realignment. The most divergent morphology in a tribe is seen in the two species of the Hesperidae. Erysimum has a more typical chalazal chamber and cyst morphology while the tubular chalazal chamber and filiform cyst of Chorispora is of the most extreme type encountered in the survey. This suggests that the tribe is paraphyletic and should be reinvestigated to clarify relationships. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 144, 375−394.

Cytoskeletal organization of the micropylar endosperm in Coronopus didymus L. (Brassicaceae).

The micropylar chamber of the mustard Coronopus didymus is a developmental domain distinct from the contiguous central chamber and the more extreme chalazal chamber. Early in syncytial development the micropylar endosperm surrounding the embryo becomes populated with unusual fusiform to multilobed nuclei. These nuclei are sheathed by unique parallel arrays of microtubules that focus at tips of the nuclei and flare to connect with a reticulate network in the common cytoplasm. F-actin does not closely invest the nuclei but instead forms an extensive but separate cytoplasmic reticulum. When the embryo is in the early heart stage, the cytoskeleton of the endosperm undergoes a remarkable transition in preparation for cellularization. Microtubules become reorganized into radial arrays emanating from the nuclei, which themselves become spherical. Radial microtubule systems (RMSs), which replace both the parallel microtubules and the cytoplasmic reticulum, organize the common cytoplasm into evenly spaced nuclear cytoplasmic domains (NCDs). F-actin gradually becomes coaligned with the RMSs. Phragmoplasts are initiated adventitiously at the interfaces of opposing RMSs in the absence of mitosis. Cell plate deposition, which is initiated at multiple sites, results in a network of walls formed more or less simultaneously around the densely packed NCDs. The walls, which are rich in 1-3-beta-glucans, join with one another and with the existing walls of both the central cell and embryo to complete cellularization in the micropylar chamber. In the adjacent central chamber where the syncytium is restricted to a thin peripheral layer by the large central vacuole, basic organization of the syncytium into NCDs is followed by alternating cycles of alveolation and periclinal cell division resulting in cellularization.

Patterns of Cytoskeletal Organization Reflect Distinct Developmental Domains in Endosperm ofCoronopus didymus(Brassicaceae)

New data on the interrelationships of F‐actin and microtubules during endosperm development reveal distinct domains in the micropylar chamber (MC) containing the embryo, the large curved central chamber (CC), and the small chalazal chamber (ChC). Reported for the first time in any endosperm are the following: (1) data on the interrelationships between microtubules and F‐actin during development in all three chambers, and (2) an early stage of syncytial endosperm characterized by unusual fusiform to multangular nuclei sheathed by parallel arrays of microtubules. As is characteristic of nuclear endosperm development, the common cytoplasm is organized into nuclear cytoplasmic domains (NCDs) defined by radial microtubule systems, which determine placement of walls at the cellularization stage. Both microtubules and F‐actin are reorganized in preparation of the syncytium for simultaneous cytokinesis. Cellularization directly follows formation of adventitious phragmoplasts in the MC but is delayed in the CC as ...

The development of embryo and endosperm inRanalisma rostratum

The embryo and endosperm development inRanalisma rostratum was studied in this paper. The zygote divides by a transverse wall to form basal and apical cells. The larger basal cell undergoes no further division and becomes the basal suspensor cell. The embryo development conforms to the Caryophyllad type. In the mature seed, the embryo is U-shaped and forms the embryonic shoot apex accompanied by one intraseminal leaf. The endosperm development belongs to the Hebolial type. The primary endosperm nucleus (invariably lying in the chalazal part of the embryo sac) divides and forms a large micropylar chamber and a small chalazal chamber. The chalazal endosperm chamber remains uninucleate, and free nuclear divisions occur in the micropylar chamber. Cellularization of the endosperm begins simultaneously from the micropylar and the chalazal ends. The cellularization is related to phragmoplast and cell plate, and does not arise from the free growth wall. Accompanying the embryo development, the endosperm degrades and does not exist in the mature seed. In the proembryo developing stages, the basal suspensor cell and chalazal endosperm cell grow to a considerable size. The nucleus and cytoplasm stain densely. Sometimes, binucleate or trinucleate was observed in both of the two cells. In the laterally concave embryo stage, they begin to degenerate which coincides with the cellularization of the endosperm. They are presumed to participate in the nourishment of the embryo proper in the early stages of embryo development.

Upper Cretaceous Zingiberalean Fruits with in Situ Seeds from Southeastern Coahuila, Mexico

In the southeastern region of Coahuila, Mexico, 1,844 fruits with characteristics that relate them to the order Zingiberales have been recovered from Upper Cretaceous (Campanian) sediments. They are tricarpellate and trilocular and have axial placentation and numerous anatropous, operculate, small seeds per locule. Two types of fruits are distinguishable. Striatornata sanantoniensis gen. et sp. nov. is closely related to Spirematospermum, and both are interpreted as members of the Musaceae based on the presence of a chalazal chamber and hilar cavity. Tricostatocarpon silvapinedae gen. et sp. nov. is difficult to accommodate within an extant family of the Zingiberales; however, the opercular structure, integumentary anatomy, and general fruit morphology strongly support its recognition as a member of the order, perhaps related to Musa cardiosperma. Comparison of integumentary anatomy reveals that while the integuments of the fossil seeds have a similar construction pattern, this is not comparable to any of...

Systematic embryology of the Araceae

Embryological data of systematic significance to the family Araceae are reviewed and analyzed, with special attention given to the determination of character-state polarities. Character-states considered primitive within the family include: presence of endothecial thickenings; binucleate, starchless pollen; anatropous, crassinucellate ovules with a thick nucellar cap and a single, unbranched funicular bundle; solanad or caryophyllad embryogeny; helobial endosperm development, with 2–8 cells in the chalazal chamber andab initio cellular division in the micropylar chamber; and endosperm present in ripe seeds. The phylogenetic implications of these conclusions are discussed, and promising avenues for future research are indicated.

EMBRYOLOGICAL DEVELOPMENT OF LACHNANTHES CAROLINIANA (HAEMODORACEAE)

Embryological development of Lachnanthes caroliniana was studied utilizing standard anatomical techniques and SEM. Lachnanthes has a monocotyledonous anther wall development (endothecial cells with spiral secondary wall thickenings), successive microsporogenesis, and amoeboid (periplasmodial) tapetal development. Mature pollen grains are 2‐nucleate with a proximal, fusiform generative cell. Ovules are initiated as 5–7 cylindrical primordia from a common placental base. Basal ovular swellings collectively contribute to the enlarged, peltate placenta. Mature ovules are pleurotropous, anatropous, bitegmic, and crassinucellate; the nucellus consists of a chalazal hypostase, radially elongate lateral cells, and a prominent micropylar nucellar cap. Megasporogenesis is successive, forming a linear tetrad of megaspores. Megagametogenesis is monosporic; the female gametophyte is of the Polygonum‐type with relatively large, pyriform antipodals. Endosperm formation is helobial, resulting in the establishment of a ring of four thick‐walled basal endosperm cells (the chalazal chamber) and numerous free nuclei (in the micropylar chamber). The mature cellular endosperm is filled with starch grains and has a chalazal cavity and a thick‐walled peripheral layer. The discoid, peltately attached seeds have marginal wings derived by anticlinal divisions and buckling of the outer integument alone. Inner and middle cuticular layers are present in the seed coat. Lachnanthes is similar to all other investigated members of the Haemodoraceae in major embryological features. The significance of embryological evidence with regard to interfamilial classification is discussed. Future studies of ovule and seed development may prove valuable in phylogenetic studies in assessing the homology of placental, ovule, and seed morphology and anatomy.

Development of endosperm inScrophularia himalensis with a discussion on the variation in the endosperm of the tribeScrophularieae (Scrophulariaceae)

Scrophularia himalensis has anab initio cellular endosperm. A transverse division separates a micropylar chamber from a chalazal chamber. The second division is vertical in both, the third is also vertical but at right angles to the second and restricted to the micropylar chamber just as the fourth transverse division. The four-celled micropylar haustorium is branched, highly aggressive, and persists for a long time during seed development. The bicelled chalazal haustorium is non-aggressive and is relatively short-lived. The endosperm proper is ruminate. Variation in the early ontogeny of the endosperm and the structure of endosperm haustoria in the tribeScrophularieae are evaluated.

The development of cells in the coenocytic endosperm of the African blood lily Haemanthus Katherinae

The endosperm of the African blood lily Haemanthus Katherinae Bak. follows the helobial pattern of development in which two chambers of endosperm are formed. In the earliest observed stage of development a large micropylar chamber and a smaller dome-shaped chalazal chamber of endosperm are present. Both are coenocytic and contain wall ingrowths of the transfer cell type along the embryo sac wall. Freely growing walls grow centripetally from the embryo sac wall, branch, and eventually meet, forming a layer of cells along the embryo sac wall. This process occurs first in the micropylar chamber. After four or more layers of endosperm cells are present, phragmoplasts form in association with karyokinesis and give rise to cross walls situated between the freely growing walls. When 10 or more layers of endosperm cells are present, free wall-less cells are present in the central vacuole near the edge of the cellular endosperm of the micropylar chamber. The free cells originate from mitosis of nuclei at the inner wall-less edge of the endosperm and the subsequent pinching off and release of the free cells into the large central vacuole. The free cells may undergo karyokinesis and become binucleate. The chalazal chamber of endosperm also becomes cellular by means of freely growing walls.

Paleozoic Seed Studies: A New Pennsylvanian Pachytesta from Southern Illinois

Pachytesta stewartii, a new species found in Middle Pennsylvanian coal ball deposits in southern Illinois, is 2.5 cm long and approximately 1.5 cm in width at its greatest diameter. Commissured ribs are pronounced near the apex and progressively less distinct toward the base. The integumentary system is delimited into 3 regions: outer sarcotesta, middle sclerotesta, and thin endotesta. Conspicuous in the new species is a pronounced basal extension with an enclosed chamber that may be the result of decomposition of thin-walled parenchyma cells. Relationships with other species and possible significance of the chalazal chamber are discussed.

PALEOZOIC SEED STUDIES: A NEW PENNSYLVANIAN PACHYTESTA FROM SOUTHERN ILLINOIS

Pachytesta stewartii, a new species found in Middle Pennsylvanian coal ball deposits in southern Illinois, is 2.5 cm long and approximately 1.5 cm in width at its greatest diameter. Commissured ribs are pronounced near the apex and progressively less distinct toward the base. The integumentary system is delimited into 3 regions: outer sarcotesta, middle sclerotesta, and thin endotesta. Conspicuous in the new species is a pronounced basal extension with an enclosed chamber that may be the result of decomposition of thin‐walled parenchyma cells. Relationships with other species and possible significance of the chalazal chamber are discussed.

Some Embryological Aspects of Amomum dealbatum and Hedychium acuminatum

1. Certain aspects of the embryology of Amomum dealbatum Roxb. and Hedychium acuminatum Rosc. are described. In Amomum the anther wall consists of seven to eight layers. Cells of the one- to two-layered tapetum break down, giving rise to a periplasmodium. Pollen grains are shed at the two-celled stage. 2. The ovules are anatropous, bitegmic, crassinucellate, and possess a well-marked hypostase and epistase. Tetrads are both linear and T-shaped in Amomum but only linear in Hedychium. Development of the embryo sac conforms to the Polygonum type. Migration of nucellar nuclei into the embryo sac cavity is common. 3. Development of the endosperm in Hedychium is of the Helobial type. The chalazal chamber may remain uninucleate, become binucleate, or become two-celled. The basal apparatus aborts at the globular stage of the proembryo. 4. Development of the embryo conforms to the Asterad type, and a definite suspensor is lacking. Polyembryony was observed in Hedychium. One of the embryos develops from the egg and...

SEED DEVELOPMENT IN ADHATODA VASICA NEES

The events following fertilization up to the maturation of the seed in Adhatoda vasica have been described. The first two transverse divisions accompanying the division of the primary endosperm nucleus partition the embryo sac into (1) a micropylar chamber, (2) a chalazal chamber, and (3) a central endosperm chamber. The first two develop into binucleate haustorial structures, while the bulk of the endosperm is derived from the products of the central endosperm chamber. An unusual case of a micropylar haustorium containing four hypertrophied nuclei and four small nuclei has been observed. The central endosperm chamber is partly cellular and bears a tubular free nuclear basal apparatus. The latter, however, ultimately becomes cellular. The embryo development is of the Solanad type. The mature seed has only two layers of thin-walled endosperm cells and a wavy testa representing the persistent epidermis of the integument. The rest of the integument is consumed by the endosperm. The uneven surface of the testa results from unequal development of the integumentary parenchyma and not due to either unequal radial stretching of the epidermis or irregular growth of the endosperm as in Andrographis serpyllifolia.