Do mitochondria play a role in remodelling lace plant leaves during programmed cell death?

<p>Abstract</p> <p>Background</p> <p>Programmed cell death (PCD) is the regulated death of cells within an organism. The lace plant (<it>Aponogeton madagascariensis</it>) produces perforations in its leaves through PCD. The leaves of the plant consist of a latticework of longitudinal and transverse veins enclosing areoles. PCD occurs in the cells at the center of these areoles and progresses outwards, stopping approximately five cells from the vasculature. The role of mitochondria during PCD has been recognized in animals; however, it has been less studied during PCD in plants.</p> <p>Results</p> <p>The following paper elucidates the role of mitochondrial dynamics during developmentally regulated PCD <it>in vivo </it>in <it>A. madagascariensis</it>. A single areole within a window stage leaf (PCD is occurring) was divided into three areas based on the progression of PCD; cells that will not undergo PCD (NPCD), cells in early stages of PCD (EPCD), and cells in late stages of PCD (LPCD). Window stage leaves were stained with the mitochondrial dye MitoTracker Red CMXRos and examined. Mitochondrial dynamics were delineated into four categories (M1-M4) based on characteristics including distribution, motility, and membrane potential (ΔΨ_m). A TUNEL assay showed fragmented nDNA in a gradient over these mitochondrial stages. Chloroplasts and transvacuolar strands were also examined using live cell imaging. The possible importance of mitochondrial permeability transition pore (PTP) formation during PCD was indirectly examined via <it>in vivo </it>cyclosporine A (CsA) treatment. This treatment resulted in lace plant leaves with a significantly lower number of perforations compared to controls, and that displayed mitochondrial dynamics similar to that of non-PCD cells.</p> <p>Conclusions</p> <p>Results depicted mitochondrial dynamics <it>in vivo </it>as PCD progresses within the lace plant, and highlight the correlation of this organelle with other organelles during developmental PCD. To the best of our knowledge, this is the first report of mitochondria and chloroplasts moving on transvacuolar strands to form a ring structure surrounding the nucleus during developmental PCD. Also, for the first time, we have shown the feasibility for the use of CsA in a whole plant system. Overall, our findings implicate the mitochondria as playing a critical and early role in developmentally regulated PCD in the lace plant.</p

Identification of differentially expressed genes during lace plant leaf development

Premise of research.The lace plant is an excellent and unique model for studying developmentally regulated programmed cell death (PCD) in plants. Perforations form in highly predictable and easily accessible and distinguishable areas in lace plant leaves. However, little is known about the genes involved in regulation of this PCD or leaf development. In this study, for the first time, a general gene expression profile for lace plant leaf development was investigated.Methodology.A cDNA-amplified fragment length polymorphism involving 64 primer combinations was used for a half-genome analysis of 4666 transcripts. Two hundred and thirty differentially expressed transcript-derived fragments (TDFs) were sequenced. A partial expressed sequence tag (EST) database for window-stage (in which PCD is occurring) leaves was also established. Through a reverse transcription polymerase chain reaction, the possible role of ubiquitin in lace plant PCD was investigated.Pivotal results.Seventy-nine TDFs were successfully annotated. The isolated TDFs and ESTs encoded genes involved in processes such as photosynthesis, biosynthesis pathways, gene regulation, stress responses, defense against pathogens, and PCD, among others. Indirect evidence through ubiquitin transcript levels suggests involvement of proteasome machinery in lace plant development and PCD. This study provides a foundation for selective studies on regulation of lace plant leaf development and PCD

The pathway of cell dismantling during programmed cell death in lace plant (Aponogeton madagascariensis) leaves

Abstract Background Developmentally regulated programmed cell death (PCD) is the controlled death of cells that occurs throughout the life cycle of both plants and animals. The lace plant (Aponogeton madagascariensis) forms perforations between longitudinal and transverse veins in spaces known as areoles, via developmental PCD; cell death begins in the center of these areoles and develops towards the margin, creating a gradient of PCD. This gradient was examined using both long- and short-term live cell imaging, in addition to histochemical staining, in order to establish the order of cellular events that occur during PCD. Results The first visible change observed was the reduction in anthocyanin pigmentation, followed by initial chloroplast changes and the bundling of actin microfilaments. At this stage, an increased number of transvacuolar strands (TVS) was evident. Perhaps concurrently with this, increased numbers of vesicles, small mitochondrial aggregates, and perinuclear accumulation of both chloroplasts and mitochondria were observed. The invagination of the tonoplast membrane and the presence of vesicles, both containing organelle materials, suggested evidence for both micro- and macro-autophagy, respectively. Mitochondrial aggregates, as well as individual chloroplasts were subsequently seen undergoing Brownian motion in the vacuole. Following these changes, fragmentation of nuclear DNA, breakdown of actin microfilaments and early cell wall changes were detected. The vacuole then swelled, causing nuclear displacement towards the plasma membrane (PM) and tonoplast rupture followed closely, indicating mega-autophagy. Subsequent to tonoplast rupture, cessation of Brownian motion occurred, as well as the loss of mitochondrial membrane potential (ΔΨm), nuclear shrinkage and PM collapse. Timing from tonoplast rupture to PM collapse was approximately 20 minutes. The entire process from initial chlorophyll reduction to PM collapse took approximately 48 hours. Approximately six hours following PM collapse, cell wall disappearance began and was nearly complete within 24 hours. Conclusion Results showed that a consistent sequence of events occurred during the remodelling of lace plant leaves, which provides an excellent system to study developmental PCD in vivo. These findings can be used to compare and contrast with other developmental PCD examples in plants.</p