Browsing by Subject "programmed cell death"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item A study of programmed cell death in cotton (gosypium hirsutum) fiber(2009-05-15) Roche, Meghan C.Cotton fiber has been postulated to undergo a process of programmed cell death (PCD) during the maturation phase of development. A parallel may exist between cotton fibers and xylem tracheary elements, which have periods of elongation, secondary cell wall deposition and death. Secondary wall formation and PCD are purported to be coupled events in tracheary elements. In this study, an attempt was made to observe the occurrence and timing of PCD in cotton fibers by TUNEL staining to detect DNA strand breaks, and also to monitor DNA content by PI staining. The staining patterns produced by PI and TUNEL left room for interpretation. TUNEL-positive and PI-stained areas were observed, but failure to observe nuclei of conventional appearance in my cytological preparations at any time-point, along with possible nonspecific staining or autofluorescence of cell wall and intracellular components, made it difficult to draw firm conclusions of significance. Thus, additional analyses will be needed to prove or disprove current PCD theories. Nevertheless, the differences in TUNEL and PI signals across fiber development stages indicate that the observed fluorescence patterns are marking discrete developmental phases. The PI signal is dispersed throughout the cell during the elongation phase (5-15 DPA) and appears to condense during secondary cell wall synthesis (25- 40 DPA). TUNEL-positive signal may be observed as early as 25 DPA, but the signal is not widespread until 45 DPA. At 50 DPA and beyond, PI staining is reduced. Visually detectable DNA can be extracted from cotton fiber nuclei between 5 and 40 DPA, although a laddering pattern was not visible at any time-point. The results, although inconclusive, point to the possibility that PCD may be a process leading to maturation in the cotton fiber, succeeding completion of secondary cell wall synthesis.Item Role of Programmed Cell Death in Disease Development of Sclerotinia sclerotiorum(2012-02-14) Kim, Hyo JinPlant programmed cell death (PCD) is an essential process in plant-pathogen interactions. Importantly, PCD can have contrasting effects on the outcome depending on context. For example, plant PCD in plant-biotroph interactions is clearly beneficial to plants, whereas it could be detrimental to plants in plant-necrotroph interactions. Sclerotinia sclerotiorum is an agriculturally and economically important necrotrophic pathogen. Previous studies have shown that S. sclerotiorum secretes oxalic acid (OA) to enhance Sclerotinia virulence by various mechanisms including induction of PCD in plants. A recent study has also shown that reactive oxygen species (ROS) generation correlates with induction of PCD during disease development. These studies focus on links between ROS, oxalate, and PCD, and how they impact S. sclerotiorum disease development. I examined the involvement of ROS in pathogenic development of S. sclerotiorum. I identified and functionally characterized two predicted S. sclerotiorum NADPH oxidases (Nox1 and Nox2) by RNAi. Both nox genes appear to have roles in sclerotial development, while only Nox1-silenced mutants showed reduced virulence. Interestingly, the reduced virulence of the Nox1-silenced mutant correlated with decreased production of OA in the mutant. This observation suggests that regulation of ROS by S. sclerotiorum Nox1 may be linked to OA. The next study details the phenotype of plants inoculated with an S. sclerotiorum oxalate deficient mutant (A2), which showed restricted growth at the infected site. This response resembles the hypersensitive response (HR), and is associated with plant resistance responses including cell wall strengthening, plant oxidative burst, and induction of defensin genes. Conversely, leaves infected with wild type showed unrestricted spreading of cell death and were not associated with these resistant responses. Furthermore, previous work had shown that a Caenorhabditis elegans anti-apoptotic gene (ced-9) conferred resistance to wild type S. sclerotiorum, while this gene had negligible effects on the phenotype of plant leaves inoculated with A2 mutants. These findings suggest that HR-like cell death by A2 and PCD by wild type S. sclerotiorum may be regulated by different pathways. As a whole, these results reveal the importance of ROS, oxalate, and PCD in Sclerotinia disease development as well as the significance of interplay between them. These studies contribute to the understanding of the underlying mechanisms of Sclerotinia disease.