Thesis (Th. M.)--Westminster Theological Seminary, Philadelphia, 2001. / Includes bibliographical references (leaves 69-72).

When plant cells grow and when they are mechanically stimulated or wounded or attacked by pathogens, they release ATP into their extracellular matrix. This extracellular ATP (eATP) can induce cell signaling changes that alter cell growth and promote adaptive changes to biotic and abiotic stresses. Cells control the eATP concentration with ecto-phosphatases. Among the most important of these are the nucleoside triphosphate-diphosphohydrolases (NTPDases) called apyrases. There are seven apyrases in Arabidopsis, and at least two of these, APY1 and APY2, help control the eATP concentration. The expression of APY1/APY2 can be inhibited by RNAi, and this suppression leads to growth inhibition. Because prior work showed that increased levels of exogenous ATP can block auxin transport and inhibit the gravitropic response in primary roots of Arabidopsis, in this report I tested whether the expression of APY1/APY2 could influence auxin transport and gravitropism. When the expression of these apyrases was suppressed either genetically or chemically, indirect assays of auxin distribution in primary roots showed that that polar auxin transport was interrupted and that, subsequently, the growth and gravitropic curvature of the roots were inhibited. By microarray and qRT-PCR analyses, we assayed how the suppression of APY1/ APY2 by RNAi in R2-4A mutants changed the expression of genes linked to growth inhibition in seedlings. The most significant gene expression changes induced by apyrase suppression were in genes involved in stress responses, which included those regulating wall composition. These expression changes predicted specific chemical changes in the walls of mutant seedlings, and significant changes in reactive oxygen species (ROS) and wall lignification in roots were verified by direct analysis. A group of class III wall peroxidases that are known to be stress response genes and involved in wall modification is up-regulated in the primary roots of R2-4A seedlings when the expression of APY1 and APY2 is suppressed. Those peroxidases use ROS substrates to produce cross-linking and lignification in cell walls. To verify their roles in root growth, a study of peroxidase knockout mutants was performed in the background of R2-4A mutants. When the expression of APY1/APY2 was suppressed in two of these mutants, per54 and per54/49, their root growth was significantly greater than in R2-4A mutants expressing wild type peroxidases. Taken together the results are consistent with the hypothesis that APY1/APY2 and eATP play important roles in the signaling steps that link polar auxin transport to growth, and stress-induced wall changes to growth inhibition. / text

published_or_final_version / Endodontics / Master / Master of Dental Surgery

published_or_final_version / Dental Materials Science / Master / Master of Science in Dental Materials Science

No description available.

No description available.

No description available.

No description available.

Abscisic acid (ABA) was synthesised in dehydrating leaves and roots of willow (<I>Salix dasyclados</I>) and exogenous ABA in the xylem stream was shown to cause decreases in stomatal conductance. A transient decrease in leaf water potential occurred if water was entirely withheld from roots on one side of a willow plant. This was avoided if roots from all sides of the plant were watered and only root tips were allowed to dehydrate. Partial stomatal closure and decreased leaf extension rate then occurred without any initial perturbation in leaf water potential or leaf ABA. The drying event was associated with an increased content of ABA in root tips and xylem sap. The effects were reversible on either rewatering or excision of the affected root tips. It was concluded that partial dehydration of root tips caused partial stomatal closure and decreased leaf extension, and that changes in the ABA content of root tips and the xylem sap were consistent with a possible causal role for root-sourced ABA in the regulation of leaf physiology in response to root water deficit. Stem-girdling experiments indicated that a major pathway of ABA transport, between leaves on different stems in the shoot system, was in the phloem, without an apparent involvement of transport in the xylem. Damage to the shoot apex caused an increase in stomatal conductance. This was associated with a decreased content of ABA in the xylem sap and in fully extended leaves. It is suggested that these changes may have been associated with a possible import of ABA from mature leaves into the growth sites of axillary shoots. Results are discussed within the context of water deficit and the growth and survival of individual stems in a willow plantation.

No description available.