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Although the cryo-fixation methods we employed preserved novel features of tapetum cellular content and membranes, the fragility of middle layer cells still presented challenges. The second division occurs in the generative cell and forms the male germ unit or sperm cells McCormick, In a study characterizing DEFECTIVE EXINE1 DEX1 protein function in pollen wall formation, the formation of structured components within the primexine matrix, known as probaculae and protecta, and the importance of microspore undulations in the formation of these structures were demonstrated by comparing high-pressure frozen and freeze 34 substituted Arabidopsis wild-type and dex1 mutant anthers in the tetrad stage Paxson-Sowders et al. These tapetal cells were cytoplasmically dense, with ER, ribosomes, mitochondria and vacuoles Figure 2. Generative Art, Summer The biochemical data on the components of tapetosomes and elaioplasts have been correlated with their ultrastructure in chemically fixed specimens, however these structures are rich in membranes and lipids, so structural features are sometimes ambiguous. Generative Art, Summer

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The ultrastructure of the mature pollen wall was striking: No gaps or locule fluid were observed between layers of the pollen wall and the callose wall or microspore plasma membrane, in contrast to many previous reports.

This preliminary work led to the hypothesis that ABCG26 functions to export sporopollenin constituents from tapetal cells. To examine pollen wall and tapetum morphology at higher resolution in the abcg mutant relative to wild-type plants, scanning electron microscopy SEM and TEM were used.

In vitro assays revealed the surprising preference 12 of recombinant ACOS5 enzyme for non-phenolic substrates, delineating a distinct function for this enzyme from true 4CLs involved in phenylpropanoid metabolism Kienow et al. Within the outer exine wall, nexine is a thin layer of wall neighbouring the intine, and the sexine forms the outer sculptured component. To address these hypotheses, my thesis had four specific objectives: These data suggest that MS2 functions as a plastid-localized fatty acyl-ACP reductase and its fatty alcohol products form sporopollenin constituents or precursors in Arabidopsis.

The block was submerged in liquid nitrogen, transferred under vacuum to a fracturing chamber and fractured by removing the upper hat from the sample.

Therefore, this thesis addresses the major question of how constituents of the exine wall sporopollenin exit tapetal cells. Among these adaptations, external barriers encasing yishi dominant plant body and its reproductive offshoots were forefront in preventing desiccation and ensuring the transmission of genetic information Wallace et al. The identification of multiple genes encoding putative LTPs through co-expression analyses with ACOS5, suggested additional export components in the traffic of sporopollenin.

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The four asterisks denote four microspores of one tetrad. Alternatively, when the transcript with the retained intron was expressed, functional protein could have been produced by splicing out of the retained intron with its premature stop codon. Although little is known about the composition of probaculae and protecta, these structures appear to contain an early form of sporopollenin Heslop-Harrison, c. However, occasional abcg anthers with bulbous yellow surfaces consistent with pollen that was not shed were identified, and occasional fully fertile siliques were observed, suggesting a low rate of fertile pollen formation.

Created a software installation for the Whitney Gala. ACTIN2 expression was monitored as a control.

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To Lacey, the master mentor, your energy, creativity and enthusiasm for science are inspirational. The biochemical data on the components of tapetosomes and elaioplasts have been correlated with their ultrastructure in chemically fixed specimens, however these structures are rich in membranes and lipids, so structural features are sometimes ambiguous.

The wall encasing pollen is highly specialized, consisting of an inner intine cellulosic wall, and an outer exine wall containing a highly stable and recalcitrant biopolymer called sporopollenin Southworth ; Scott Simultaneously, tapetal cells gradually appeared thinner and became almost entirely occupied by densely staining organelles Figure 2.

E In the early uninucleate microspore stage anther stage 9developing microspore in close proximity to plasma membrane PM of tapetum during exine deposition. Investigation of anther and microspore development by light microscopy and transmission electron microscopy TEM have improved our knowledge of pollen wall formation and provided a context for understanding the mechanism of sporopollenin formation.

Like many other specialized plastids, the neutral lipids of elaioplasts are held within the globuli, maintained in part by plastid lipid-associated proteins PAPs Kim et al. Cryo-SEM of cryo-fractured anther with all cell layers of the sporophytic anther wall present: According to Heslop-Harrisonearly primexine is acetolysis-sensitive, while late primexine bearing developed probaculae in Lilium longiflorum becomes acetolysis-resistant, suggesting the presence of sporopollenin in the latter Heslop-Harrison, c.

In collaboration with Ben Fry. B Coloured overlay of the micrograph from panel A, highlighting and differentiating the sporopollenin green 2.7cc pollen coat orange constituents of the pollen exine, from the intine pinkplasma membrane black and pollen cytoplasm txg. With cryo-SEM, it was clear that middle layer cells persist after the release of free microspores and into the late stages of uninucleate microspore development, where they appear alive based on their subcellular contents.

The electron-translucent component, presumably containing steryl esters, formed small and often circular inclusions within an electron-dense meshwork. Lipid analyses ysohi Brassicaceae pollen coats have identified a mixture of primarily neutral-ester lipids, free fatty acids, very-long-chain wax esters, volatile lipid derivatives, flavonoids, alkanes and hydroxycinnamoyl spermidines Piffanelli et al.

Morphology and surface structure of mature pollen from Arabidopsis anthers B Magnification from panel A, showing pollen grains on the epidermal cells of the carpel. Inhibitor treatments, radiolabeling, and chemical breakdown studies have yielded complementary information on the constituents present in sporopollenin, which is typically accepted to contain phenolics and polyhydroxylated aliphatics, covalently coupled by ether and ester bonds Guilford et al.

D Tapetosome ultrastructure, showing bundles of tightly associated linear tubes magnified in G and an intricate matrix of coiled fibrils H that make up the majority of each tapetosome. However, as the material fortifying the late-primexine walls of tetrads of ta did not stain in a manner similar to mature sporopollenin, it was considered to differ from sporopollenin, and was termed protosporopollenin.