Biomedical subjects

Emma Pilling

Publications and source records attributed to Emma Pilling.

5 recordsLinked to original sources

PubMed2005

Three-dimensional modelling of wheat endosperm development.

We have developed methods, based on confocal microscopy and three-dimensional (3D) modelling, for the analysis of complex tissues and individual nuclei. These methods were used to study the development of early wheat (Triticum aestivum) endosperm as a whole and of endosperm nuclei undergoing polyploidization. Fixed sections of immature caryopses were either stained with SYTOX Green or used for fluorescence in situ hybridization (FISH) to visualize centromeres, telomeres and a rye chromosome arm substitution. Each section was imaged as a confocal image stack. By using Amira 3.0 for computer image processing, rendered models were produced of the whole endosperm and of individual nuclei. We followed endosperm development up to the formation of a complete syncytium, which develops via a dorsal and a ventral plate of nuclei in the central cell. Modelling of nuclei showed that wheat chromosomes are not anchored to the nuclear membrane and become more randomly positioned in endoreduplicated nuclei. This analysis produced a precise description of the positioning of nuclei throughout the developing endosperm and of chromosomal domains in single nuclei.

Chromosomes, Plant↗

PubMed2003

Feedback from the wall.

The ability of cells to perceive changes in the composition and mechanical properties of their cell wall is crucial for plants to achieve coordinated growth and development. Evidence is accumulating to show that the plant cell wall, like its yeast counterpart, is capable of triggering multiple signalling pathways. The components of the cell wall that are responsible for initiating these signal responses remain unknown; however, recent technological advances in cell wall analysis may now facilitate the identification of these components and accelerate the characterisation of changes that occur in cell wall mutants.

Arabidopsis Proteins↗

PubMed2003

Growth ring formation in the starch granules of potato tubers.

Starch granules from higher plants contain alternating zones of semicrystalline and amorphous material known as growth rings. The regulation of growth ring formation is not understood. We provide several independent lines of evidence that growth ring formation in the starch granules of potato (Solanum tuberosum) tubers is not under diurnal control. Ring formation is not abolished by growth in constant conditions, and ring periodicity and appearance are relatively unaffected by a change from a 24-h to a 40-h photoperiod, and by alterations in substrate supply to the tuber that are known to affect the diurnal pattern of tuber starch synthesis. Some, but not all, of the features of ring formation are consistent with the involvement of a circadian rhythm. Such a rhythm might operate by changing the relative activities of starch-synthesizing enzymes: Growth ring formation is disrupted in tubers with reduced activity of a major isoform of starch synthase. We suggest that physical as well as biological mechanisms may contribute to the control of ring formation, and that a complex interplay of several factors may by involved.

Cytoplasmic Granules↗

PubMed2002

Role of granule-bound starch synthase in determination of amylopectin structure and starch granule morphology in potato.

Reductions in activity of SSIII, the major isoform of starch synthase responsible for amylopectin synthesis in the potato tuber, result in fissuring of the starch granules. To discover the causes of the fissuring, and thus to shed light on factors that influence starch granule morphology in general, SSIII antisense lines were compared with lines with reductions in the major granule-bound isoform of starch synthase (GBSS) and lines with reductions in activity of both SSIII and GBSS (SSIII/GBSS antisense lines). This revealed that fissuring resulted from the activity of GBSS in the SSIII antisense background. Control (untransformed) lines and GBSS and SSIII/GBSS antisense lines had unfissured granules. Starch analyses showed that granules from SSIII antisense tubers had a greater number of long glucan chains than did granules from the other lines, in the form of larger amylose molecules and a unique fraction of very long amylopectin chains. These are likely to result from increased flux through GBSS in SSIII antisense tubers, in response to the elevated content of ADP-glucose in these tubers. It is proposed that the long glucan chains disrupt organization of the semi-crystalline parts of the matrix, setting up stresses in the matrix that lead to fissuring.

Amylopectin↗

PubMed2002

Starch synthesis in Arabidopsis. Granule synthesis, composition, and structure.

The aim of this work was to characterize starch synthesis, composition, and granule structure in Arabidopsis leaves. First, the potential role of starch-degrading enzymes during starch accumulation was investigated. To discover whether simultaneous synthesis and degradation of starch occurred during net accumulation, starch was labeled by supplying (14)CO(2) to intact, photosynthesizing plants. Release of this label from starch was monitored during a chase period in air, using different light intensities to vary the net rate of starch synthesis. No release of label was detected unless there was net degradation of starch during the chase. Similar experiments were performed on a mutant line (dbe1) that accumulates the soluble polysaccharide, phytoglycogen. Label was not released from phytoglycogen during the chase indicating that, even when in a soluble form, glucan is not appreciably degraded during accumulation. Second, the effect on starch composition of growth conditions and mutations causing starch accumulation was studied. An increase in starch content correlated with an increased amylose content of the starch and with an increase in the ratio of granule-bound starch synthase to soluble starch synthase activity. Third, the structural organization and morphology of Arabidopsis starch granules was studied. The starch granules were birefringent, indicating a radial organization of the polymers, and x-ray scatter analyses revealed that granules contained alternating crystalline and amorphous lamellae with a periodicity of 9 nm. Granules from the wild type and the high-starch mutant sex1 were flattened and discoid, whereas those of the high-starch mutant sex4 were larger and more rounded. These larger granules contained "growth rings" with a periodicity of 200 to 300 nm. We conclude that leaf starch is synthesized without appreciable turnover and comprises similar polymers and contains similar levels of molecular organization to storage starches, making Arabidopsis an excellent model system for studying granule biosynthesis.

Amylopectin↗