Thick Endexine Research Articles

Ultrastructure and cytochemistry of Eucalyptus globulus (Myrtaceae) pollen grain

The morphology, ultrastructure and cytochemistry of Eucalyptus globulus mature pollen were investigated using light (LM), scanning electron (SEM) and transmission electron microscopy (TEM). The pollen morphology is typically myrtaceous with a suite of characters that allows its distinction from the pollen of other Eucalyptus species. The exine consists of a thick endexine and a massive ectexine with hardly distinguishable columellae. The endexine is 2‐layered towards the apertural regions where the inner and spongy‐granulate layer forms a continuous colpus membrane and a thinner pore membrane. Under the pores the intine is 3‐layered forming complex onci. The spindle‐shaped generative cell (GC) is deeply undulated and located in a cup‐shaped depression of the vegetative cell (VC) nucleus. In the dense VC cytoplasm the main storage reserves are lipid bodies and insoluble carbohydrates in the cytosol, although proteins are also present. The most characteristic feature of the VC cytoplasm is the extremely well‐developed rough endoplasmic reticulum (RER), which forms extensive stacks filling large areas of the central cytoplasm. Single RER cisternae are also scattered throughout the cytoplasm, most of them establishing an intimate association with lipid bodies, storage vacuoles, the VC plasmalemma and a few proplastids. The physiological significance of the RER stacks and of the RER cisternae association with other cell components, as well as the structure and function of an endomembrane compartment, found only in the freeze‐fixed pollen, are discussed.

Pollen Characters ofAmborella trichopoda(Amborellaceae): A Reinvestigation

Pollen of Amborella trichopoda was reinvestigated. Pollen is oblate to spheroidal and monoaperturate (ulcerate) at the distal pole, with a poorly defined aperture margin. The exine consists in the nonapertural region of ektexinous tectal elements (“cupules”), a smooth foot layer, and a thin, nonlamellate endexine. In the apertural area, the foot layer is lacking, as are most of the tectal elements. However, a thick endexine (including some ektexinous globular elements) and a conspicuous, channeled intine are present. The thick apertural endexine generally ruptures along the circular apertural area and forms an operculum. Orbicules show the same electron density as the tectal elements and recall their shape. Pollen characters of Amborella are compared with those of other basalmost angiosperms. The unique tectal elements (cupules) and the thick homogeneous endexine, which form an odd operculum in the apertural area, are unusual angiosperm pollen characters. Only Austrobaileya (Austrobaileyaceae) shares some...

Pollen development of Rondeletia odorata (Rubiaceae)

Pollen wall ontogeny of RONDELETIA: odorata was studied with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) from tetrad stage until maturity. The ontogenetic sequence of wall development in RONDELETIA: follows, to some extent, the basic scheme in the angiosperms, i.e., development starts centripetally with the pro-columellae in a plasmalemma surface coating (primexine) at the early tetrad stage when the microspores are still enveloped by callose, until intine formation in young pollen grains. The main ontogenetical features of Rondeletia odorata pollen are (1) the very thin irregular foot layer, (2) development of a continuous layer of radially oriented membranous granular material under the thick endexine, (3) initiation of intine before first mitosis with characteristic radial plasmalemma invaginations, and (4) a strong stretching force upon engorgement just prior to dehiscence, which leads to reduction in thickness of all wall layers. The possible function of Golgi vesicles in the considerable increase in surface area of the plasmalemma at intine initiation is discussed. The endocingulum observed on acetolyzed and sectioned mature grains is explained ultrastructurally.

Pollen morphology, exine structure and systematics of Acalyphoideae (Euphorbiaceae): Part 2. Tribes Agrostistachydeae ( Agrostistachys, Pseudagrostistachys, Cyttaranthus, Chondrostylis), Chrozophoreae ( Speranskia, Caperonia, Philyra, Ditaxis, Argythamnia, Chiropetalum, Doryxylon, Sumbaviopsis, Thyrsanthera, Melanolepis, Chrozophora), Caryodendreae ( Caryodendron, Discoglypremna, Alchorneopsis), Bernardieae ( Bernardia, Necepsia, Paranecepsia, Discocleidion, Adenophaedra) and Pycnocomeae ( Pycnocoma, Droceloncia, Argomuellera, Blumeodendron, Podadenia, Ptychopyxis, Botryophora)

This is the second paper of an extensive study of pollen morphology and exine structure of Acalyphoideae (Euphorbiaceae) following the most recent system of Webster. Part 2 describes the pollen of 30 genera assigned to tribes Agrostistachydeae, Chrozophoreae, Caryodendreae, Bernardieae and Pycnocomeae. In Agrostistachydeae, members of Agrostistachys and Pseudagrostistachys have similar but unspecialized pollen; grains of Cyttaranthus have weakly suprareticulate tecta of widely varying thickness and small densely spaced columellae; pollen of Chondrostylis has a croton sculpture and precisely defined bridges of ectexine over the endoaperture. Of the 11 genera assigned to tribe Chrozophoreae, pollen of Caperonia has prominent opercula, thick exines and punctate tecta, pollen of Ditaxis and Argythamnia is colpate, has large columellae, and the unevenly thick and complete tecta associated with suprareticulate sculpture or derivations thereof, and pollen of Chiropetalum has operculate apertures, diminutive columellae, and an incomplete finely reticulate tectum, characteristics which argue against a supposedly close relationship to Ditaxis and Argythamnia. Three of the four genera assigned to subtribe Doryxylinae, Doryxylon, Sumbaviopsis, and Melanolepis have similar pollen — thin exines with irregular foot layers, and irregular short columellae, whereas pollen of the fourth genus, Thyrsanthera, has thicker exines with a well-defined foot layer and more elongate columellae. The eight examined species of Chrozophora have 6–9 aperturate pollen and robust exines; two species have punctate tecta and zonorate endoapertures; the remaining species have heterobrochate tecta and lolongate endoapertures. The three genera comprising Caryodendreae, Caryodendron, Discoglypremna and Alchorneopsis, have small 3-colporate pollen with punctate tecta. Pollen of the five genera assigned to tribe Bernardieae, Bernardia, Necepsia, Paranecepsia, Discocleidion and Adenophaedra is of a similar, but unspecialized type — a punctate, deeply punctate, or microreticulate tectum, small endoaperture, and usually a prominent margo. The present concept of tribe Pycnocomeae as comprising Pycnocoma, Droceloncia, Argomuellera, Blumeodendron, Podadenia, Ptychopyxis and Botryophora is not supported by the pollen data. Members of Pycnocoma have pollen with a derived exine structure — a conspicuously thick endexine throughout the grain, threadlike foot layers, and columellae reduced to a point on the proximal side of the tectal elements. The pollen data are somewhat ambiguous about a close relationship between Droceloncia and Argomuellera, the two remaining genera in the subtribe Pycnocominae. The genera allied as subtribe Blumeodendrinae, Blumeodendron, Podadenia, Ptychopyxis, and Botryophora, share pollen with short narrow colpi, a croton sculpture, and mostly irregular columellae.

Pollen morphology of the tribe Swartzieae (subfamily Papilionoideae: Leguminosae). 2. The genera Aldina Endlicher and Swartzia Schreber and systematic conclusions

The pollen morphology of 39 taxa of Swartzia Schreber and 4 species of Aldina Endlicher is described. Pollen of the Neotropical species of Swartzia is small, generally spheroidal to subprolate, tricolporate, frequently syncolporate with a characteristic coarsely granular colpus membrane. There is much variation in exine ornamentation and stratification. The tectum may be finely reticulate-regulate, perforate, microperforate ranging to striate-reticulate or striate-regulate. The stratification may be simple with endexine, foot layer, regularly spaced collumelae and clearly defined tectum ranging to highly complex with a thick endexine, poorly defined foot layer, granular interstitium and very divided microchannelled tectum. There is a continuum of increasing complexity of exine ornamentation and stratification through the genus. However, the pollen is for convenience divided into 5 types and 8 subtypes. These types contain groups of taxonomically related species as well as unrelated species. Where unrelated species are grouped together often the pollen morphology is simple and unspecialized. Another situation occurs where taxonomically related species are placed in different but adjacent pollen types which suggest a trend of increasing complexity in related taxa. The two African species of Swartzia with prolate, thin walled pollen differ from the Neotropical species, but also differ from one another in a number of characters. The Aldina has uniform spheroidal, tricolporate pollen with a perforate tectum and simple exine stratification with rather long columellae in the mesocolpium and the endexine is distinctly lamellated adjacent to the endoapertures. The pollen morphology of the genera within the tribe and also the position of the tribe in the classification of the family is discussed, but to fully understand the complex pollen morphology of the Neotropical species of Swartzia a further review of macromorphology and systematics is required. The African species of Swartzia might be treated as a separate genus. The pollen morphology of Baphiopsis would support the exclusion of the genus from the tribe. Pollen suggests that Swartzieae shows closer affinities with the subfamily Caesalpinioideae than with the subfamily Papilionoideae.

POLLEN MORPHOLOGY OF THE TRIBE SWARTZIEAE (SUBFAMILY PAPILIONOIDEAE: LEGUMINOSAE). 1. INTRODUCTION AND ALL GENERA EXCLUDING ALDINA AND SWARTZIA

The pollen morphology of 9 of the 11 genera of the tribe Swartzieae is described together with that of Holocalyx and Cyathostegia, two genera recently removed from the tribe based on macromorphology. The pollen is small, spheroidal to subprolate, primarily tricolporate with a perforate tectum and generally typical of the Leguminosae. Nonetheless, many of the genera have distinctive pollen morphology. Baphiopsis is 6‐colporate. The genera Harleyodendron, Lecointea and one species of Exostyles have supratectal spinules. Bocoa viridiflora has striate/rugulate ornamentation very distinct from the other species of the genus Bocoa. The exine stratification is varied but Candolleodendron has a very thick endexine and narrow foot layer. The pollen of African taxa does not differ significantly from that of South American taxa. Pollen morphology does not clarify the taxonomic relationships of the tribe and provides little evidence to assist in positioning Holocalyx and Cyathostegia.

Pollen Morphology of the Tribe Swartzieae (Subfamily Papilionoideae: Leguminosae). I. Introduction and All Genera Excluding Aldina and Swartzia

The pollen morphology of 9 of the 11 genera of the tribe Swartzieae is described together with that of Holocalyx and Cyathostegia, two genera recently removed from the tribe based on macromorphology. The pollen is small, spheroidal to subprolate, primarily tricolporate with a perforate tectum and generally typical of the Leguminosae. Nonetheless, many of the genera have distinctive pollen morphology. Baphiopsis is 6-colporate. The genera Harleyodendron, Lecointea and one species of Exostyles have supratectal spinules. Bocoa viridiflora has striate/rugulate ornamentation very distinct from the other species of the genus Bocoa. The exine stratification is varied but Candolleodendron has a very thick endexine and narrow foot layer. The pollen of African taxa does not differ significantly from that of South American taxa. Pollen morphology does not clarify the taxonomic relationships of the tribe and provides little evidence to assist in positioning Holocalyx and Cyathostegia.

Wall development and its autofluorescence of sterile and fertileVicia faba L. Pollen

The ultrastructural changes of the pollen wall of three types of fertile and one of sterileVicia pollen were related to the autofluorescence of the pollen wall, measured by a microspectroscopic method. Till the liberation of the microspores from the tetrad, the spectrum of the ectexine shows sometimes two maxima and has a very low intensity. After this period the endexine is formed and its spectrum has one maximum with a high intensity. The differences of the pollen wall between the sterile and fertile pollen exist of the presence of one spectral maximum during the tetrad stage, a thick endexine and the absence of the intine in the sterile pollen. The different types show much differences during the tetrad stage in the callose wall as well as the ectexine. The autofluorescence illustrates the complexity and specificity of the pollen wall development.

The Pollen Morphology of Macrotyloma (Leguminosae: Phaseoleae)

The pollen morphology of all 24 species of the genus Macrotyloma is very distinctive and is unique in the subfamily Papilionoideae. The tectum is finely rugulate with supratectal tubercles, spines, bacula or clavae. There is a very thick endexine, no foot layer, very short dense columellae and very thin tectum. There are two aperture types, tricolporate and triporate. The taxonomically least specialised species M. ciliatum, M. decipiens and M. maranguense have tricolporate pollen while the remaining more derived species have triporate pollen.