365 research outputs found
Subcellular Responses of Plant Cells to Phosphate Starvation and Exogenous Sucrose Supply
No full textMichael Wozny, University of Guelph, 2015. Advisor: Dr. Jaideep Mathur. Stromules are thin tubules of the plastid envelope, filled with stroma. The function of these enigmatic structures is unclear, as is the mechanism of their formation. Stromules are known to closely align with and be shaped by the rearrangement of the endoplasmic reticulum. As such, the pulling force caused by the movement of plastids and other organelles connected by membrane contact sites has been proposed as a means of initiating stromule formation. This study reports that stromule frequency is affected by phosphate starvation in a sucrose dependent manner. Replacement of extraplastidic phospholipids with plastid synthesized galactolipids is a well characterized phosphate starvation response which is also responsive to sucrose availability. Transcripts of phosphate starvation induced galactolipid synthase genes were found in greater abundance following sucrose treatment of plants which also increase stromule frequency. Phosphate starvation induced lipid remodeling and trafficking is thought to be concentrated at membrane contact sites between the plastid and other organelles. Conclusions drawn from this investigation as well as other reports of increased stromule frequency suggest that increased galactolipid synthesis and trafficking between plastids and other organelles is a causative factor influencing stromule frequency.Ontario Graduate ScholarshipCanada Foundation for InnovationNatural Sciences and Engineering Research Council of Canad
Early intracellular response profiling of plants: Dissecting sub-cellular dynamics in response to reactive oxygen species
No full textThis thesis investigates early sub-cellular responsiveness of plants to reactive oxygen species (ROS) using peroxisomes as rapidly responding, model organelles, that display varying degrees of motility and pleomorphy. The work has resulted in the creation of new transgenic lines in ' Arabidopsis' that carry multiple fluorescent probes and allow visualization of up to three organelles simultaneously. Further, a 4-D live-imaging aided analysis of peroxisomal response to ROS has revealed hitherto unknown links between peroxisome behaviour and the dynamics of the endoplasmic reticulum (ER). The peroxisome-ER link was analyzed in-depth using an 'Arabidopsis' dynamin related protein (DRP3A) mutant 'apm1-1,' and a chlorophyll biosynthesis mutant ' flu' and is supported by both confocal laser scanning microscopy and ultra-structural electron microscopic studies. The observations presented in this thesis constitute the necessary groundwork, and provide the 'proof of concept' for the long-term goal of creating an Early Intracellular Response Profile of Plants (EIRPP)
Investigating the Effects of Oligogalactolipid-Synthesizing Sensitive To Freezing 2 (SFR2) on Plastid Shape and Behaviour in Arabidopsis thaliana
No full textThe plastid is the site of numerous metabolic activities in the plant cell, including photosynthesis and de novo fatty acid synthesis. While generally ellipsoid, plastids spontaneously extend and retract stroma-filled tubules (stromules) through mechanisms and for functions not yet understood. Our laboratory’s investigations on stromule formation have led us to consider to the synthesis of galactolipids, the predominant and exclusive constituents of plastid membranes. While galactolipids mainly consist of bilayer-distorting monogalactosyldiacylglycerol and bilayer-promoting digalactosyldiacylglycerol, bilayer-promoting oligogalactolipids accumulate under certain membrane-damaging conditions (s.a. freezing stress). This study explores the relationship between galactolipid synthesis and stromule formation with focus on the outer envelope membrane-localized oligogalactolipid synthesizer SENSITIVE TO FREEZING 2 (SFR2; At3g06510). Using model plant species Arabidopsis thaliana, the transgenic overexpression of fluorescently-tagged SFR2 along with a stromule-inducing 40 mM sucrose treatment have been characterized through lipidomic and stromule formation frequency analyses.University of Guelph2026-02-0
Understanding the Role of the Arp2/3 Complex and its Upstream Regulator in Actin Cytoskeleton Mediated Organization of the Endoplasmic Reticulum in Plant Cells
No full textThe Actin Related Protein (ARP) 2/3 complex is a major regulator of the actin cytoskeleton that is implicated in cell morphogenesis in plants. However, a similar role is attributed to the endoplasmic reticulum (ER). My research explored the relationship between the two systems by using transgenic plants simultaneously expressing fluorescent proteins highlighting F-actin and ER organization in living cells. A comparison of F-actin organization in cells of wild type Arabidopsis thaliana and mutants with aberrant actin cytoskeleton suggests bundling in the distorted2 mutant but a relatively fine F-actin arrangement in klunker. These differences correlate with ER organization into cisternae, fenestrated sheets and tubules. A model relating ER-organization to the degree of actin bundling in a cell emerges and is supported by drug-induced interference in actin polymerization, altered ionic conditions and temperature. The study adds to the mechanistic understanding of cell morphogenesis in plants
Investigations on Mitochondrial Pleomorphy and Interactions with the Endoplasmic Reticulum and Peroxisomes
No full textMitochondria are pleomorphic organelles capable of constant fusion and fission. Live fluorescent microscopy was employed to investigate mitochondrial pleomorphy during fluctuations in light, sugar and O2. Light and sugar are shown to induce fission whereas a green-to-red photo-convertible mEos fluorescent protein targeted to mitochondria (mitoEos) reveals that hypoxia induces fusion, leading to giant mitochondria. The endoplasmic reticulum (ER) is shown to be a mediator of mitochondrial fission and acts as a mould for morphological transitions displayed by mitochondria. Simultaneous live-imaging also reveals sustained mitochondria-peroxisome interactions, which are apparent in anisotropy1, a cell wall mutant shown here to be light sensitive. Triple transgenic lines were created to differentially label mitochondria, peroxisomes and the ER and show that the ER cages the other organelles including chloroplasts during these sustained interactions. Together, simultaneous live-imaging of mitochondria, peroxisomes and the ER using double and triple Arabidopsis thaliana transgenics further illuminate organelle pleomorphy and interactivity
Investigating the Role of Endoplasmic Reticulum (ER) in Plastid Division
No full textPlastids generally multiply by binary division across the mid-plane of a pre-existing plastid, yielding two equal-sized daughter plastids. A crucial player in this process is the cytosolic protein Accumulation and Replication of Chloroplast 5 (ARC5), which constricts and severs the plastid membrane. During plastid division, ARC5 localizes to the division site by interacting with plastid envelope membrane proteins. However, the precise mechanism of its recruitment to this site remains unknown. Moreover, daughter plastid separation following membrane fission is poorly understood. Based on findings described for the division of other organelles, this study investigated if the endoplasmic reticulum (ER) participates in plastid division. Time-lapse imaging-based observations of stable transgenics of Arabidopsis thaliana expressing ER and ARC5-targeted fluorescent proteins strongly support ER involvement in facilitating ARC5 recruitment to the plastid division site and daughter plastid separation.2025-04-1
Investigating a role for phospholipids in plastid pleomorphy
No full textPlastids, a defining feature of plants, produce stroma-filled extensions or tubules known as stromules. Although stromules are reliably induced upon exogenous sucrose treatment and inhibited upon silver nitrate treatment, a clear mechanism and function behind this phenomenon remains to be elucidated. The lack of inorganic phosphate appears to affect stromule levels as well as simultaneously cause a conversion of extraplastidic membrane lipids from phospholipids to galactolipids, suggesting a lipid-based mechanism for their formation. Non-specific phospholipase C 4 and non-specific phospholipase C 5, while responsible for this conversion, do not affect stromule formation. The origin of plastidial phosphatidylcholine upstream of phospholipid to galactolipid conversion is likely due to the presence of plastid associated membranes and does not play a role in stromule formation. The observations from my microscopy based studies demonstrate the organelle pleomorphy influencing ability of lysophosphatidylcholine, implicating acyl-editing, better known as the Lands cycle, in stromule formation.Natural Sciences and Engineering Research Council of Canad
An Investigation into Plastid Localized Lipases at Membrane Contact Sites with the Endoplasmic Reticulum using Live-Imaging
No full textFluorescent protein-based imaging revealed that transient tubules extend and retract from plastids. One hypothesis is that tubulation is a result of pulling force from the endoplasmic reticulum (ER) exerted at membrane contact sites (MCSs). A Brassica napus chloroplast lipase protein 1 (BnCLIP) appeared to mark ER-plastid MCSs; therefore plastids, ER and BnCLIP were observed in live transgenic plants using confocal microscopy. This study found that BnCLIP marked sites where the ER and plastids maintained prolonged contact and where plastid tubules extended by apparent pulling force from the ER. BnCLIP frequency increased significantly following phosphate starvation but not 40mM sucrose treatment. The potential for native Arabidopsis thaliana lipase proteins to localize in a similar manner was explored. This study provides the first demonstration of the role that plastid-ER MCSs play in living cells to modulate the shape and dynamic behaviour of plastids.Ontario Graduate FellowshipUniversity of GuelphNatural Sciences and Engineering Research Council of CanadaCanada Foundation for Innovatio
An Investigation into Membrane Contact Sites between the Endoplasmic Reticulum and Plastids
No full textDirect communication and inter-organelle exchanges are facilitated by membrane contact sites (MCSs), where organelle membranes encounter close apposition. In plants, MCSs involving major organelles like the plasma membrane, mitochondria, and Golgi bodies often have the endoplasmic reticulum (ER) as a common interacting organelle. Similarly, for chloroplasts, plastid-associated membranes (PLAMs) with a unique lipidome at the plastid-ER interface are hypothesized to accommodate proteins that foster contact sites. Due to the significant lipid flux in this region, lipases—essential for lipid modifications—are likely to facilitate lipid exchange at the plastid-ER contact sites. This study uses time-lapse imaging to analyze plastid movement and pleomorphy in transgenics expressing fluorescent fusion proteins targeted to the plastid stroma and ER, along with Brassica napus chloroplast lipase protein1 (BnCLIP1), a lipase, and other proteins localized to the plastid envelope to demonstrate their role in plastid and stromule behavior, while also elucidating their functional implications.2025-08-1
Book Ends & Odd Books : Publications Refuting Conventional Form from the Banff Centre Library Collection
No full textMathur explains how he "unselected" nearly 200 works for this exhibition of unconventional publications by international artists and authors, recognizing the influence of Ulises Carrion's article "The New Art of Making Books." The author reflects upon the roles of language and poetics, the distinction between book and text, and how politics and power affect the making and reception of these works. 2 bibl. ref
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