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Udgivelsesdato: JUL 22

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003., Includes bibliographical references (leaf 79)., The I-Lab heat exchanger is a remotely controlled heat exchanger experiment that has been used on the Internet by students in a variety of chemical engineering courses. The hardware consists of a general service unit, custom designed and fabricated (HT-30XC, Armfield, Ltd., England), on which is mounted a heat exchanger (flat plate, shell-and-tube, or double pipe). Both fluid flowrates, their direction (cocurrent or countercurrent), and the inlet hot temperature are monitored and are under the control of the students. Monitoring and control is carried out with a computer/web server using LabVIEW 6.1 software (National Instruments, USA). Data is published to web-accessible LabVIEW graphical user interfaces (GUI) or via a DataSocket server to a Java2 GUI. A database (Microsoft SQL) and ASP.NET web forms are used for registering, authentication, and scheduling. The database is also used for collaboration management software (Java2). Student response has been favorable in general, and students appreciate the ability to take data from real equipment, especially in engineering science courses that otherwise contain no laboratory component., by Marc Q. Knight., M.Eng.

Stomatal pores of higher plants close in response to decreases in atmospheric relative humidity (RH). This is believed to be a mechanism that prevents the plant from losing excess water when exposed to a dry atmosphere and as such is likely to have been of evolutionary significance during the colonization of terrestrial environments by the embryophytes. We have conducted a genetic screen, based on infrared thermal imaging, to identify Arabidopsis genes involved in the stomatal response to reduced RH. Here we report the characterization of two genes, identified during this screen, which are involved in the guard cell reduced RH signaling pathway. Both genes encode proteins known to be involved in guard cell ABA signaling. OST1 encodes a protein kinase involved in ABA-mediated stomatal closure while ABA2 encodes an enzyme involved in ABA biosynthesis. These results suggest, in contrast to previously published work, that ABA plays a role in the signal transduction pathway connecting decreases in RH to reductions in stomatal aperture. The identification of OST1 as a component required in stomatal RH and ABA signal transduction supports the proposition that guard cell signaling is organized as a network in which some intracellular signaling proteins are shared among different stimuli.

The pollutant tropospheric ozone can cause reductions in crop yield and damage to forests. Ozone and other reactive oxygen species (ROS) derived from ozone are implicated in cell death and visible injury in plants. Arabidopsis thaliana transformed with the photoprotein apoaequorin have been used to investigate changes in cytosolic free calcium [Ca2+]cyt following exposure to ozone. Ozone causes elevations in [Ca2+]cyt in a dose dependent manner inducing a characteristic ‘calcium signature’. This consists of an initial peak in calcium of short duration followed by a second prolonged increase. The amplitude and duration of the second phase of [Ca2+]cyt elevations increase with ozone concentration. Ozone and other oxidative stresses initiate plant defence responses, however the signalling pathways involved are poorly understood. Here a pharmacological analysis of the initiation of the calcium signature and subsequent induction of antioxidant gene glutathione-S-transferase tau 5 (GSTU5) in response to ozone has been undertaken. The calcium specific inhibitors lanthanum and ruthenium red and the calcium chelator EGTA have been used prior to fumigation with ozone. In each case the calcium signature was altered, with a reduction in the first and second phase of calcium release. Inhibitors of other signalling molecules and components of signalling pathways have also been used. Additionally to further our understanding of the sources of calcium involved in the adaptive response of plants to ozone a mutagenic approach has also been undertaken. The calcium transport mutant ACA3, also transformed with apoaequorin, was treated with ozone to establish whether disruption of calcium transport within the plasma membrane affects the plant’s ability to respond to ozone.

Calcium is well established as a key signalling molecule in plant and animals systems. Stimuli such as heat, cold, touch and ozone (O3) cause an increase in cytosolic calcium concentration [Ca2+]cyt in plants. O3 is a reactive oxygen species (ROS) and acts as a pollutant in the troposphere, whereas stratospheric ozone protects the earth from damaging ultra violet radiation. ROS are able to cause damage to plant cell components, effects include lipid peroxidation, reduced transpiration, a decrease in photosynthesis and a reduction in productivity. We have been studying the early molecular events in the response of Arabidopsis thaliana to O3 focusing on the role of calcium ions. Arabidopsis thaliana transformed with the photoprotein apoaequorin have been used to measure changes in [Ca2+]cyt during fumigation with O3. Elevations in [Ca2+]cyt occur in a dose dependent manner and a ‘calcium signature’ characteristic of O3 exposure is seen. Increases in antioxidant defences also occur following O3 exposure, however the signal transduction pathways leading from the perception of O3 stress and adaptation to the stress are poorly understood. The ozone induced increase in [Ca2+]cyt has been implicated in the induction of the antioxidant gene glutathione-S-transferase tau 5 (GSTU5) (Clayton et al. (1999) The Plant Journal 17(5) 575-579) . This study provides a continuation of this work. A pharmacological analysis of the calcium signature in response to O3 has been undertaken. Two inhibitors of calcium release pathways, lanthanum, a plasma membrane channel blocker and ruthenium red, an intracellular calcium channel blocker, have been used, as has the calcium chelator EGTA. The calcium response following treatment with inhibitors of other signalling molecules and components of signal transduction pathways has also been investigated. These include the cADPR inhibitor nicotinamide and the phospholipase C inhibitor 2-APB. The research has been extended to include an analysis of the