Effects of polyamines on the expression of antioxidant genes and proteins in citrus plants exposed to salt stress

Although there are accumulating reports that polyamines are involved in abiotic/oxidative stress responses, their role is not yet fully understood. Salt stress is one of the most devastating abiotic stresses which seriously interrupt plant growth and productivity. The present study attempts to examine the effects of root treatments with putrescine (Put, I mM), spermidine (Spd, ImM) and spermine (Spm, ImM) on polyamine homeostasis, as well as on several antioxidant-related genes and proteins in the leaves of citrus plants (Citrus aurantium L.) exposed to 150 mM NaCI for 15 d. Analysis of endogenous levels of free polyarnines in NaCl-stressed plant tissues reveals the existence of a polyamine transport system from roots to leaves. Real-time analysis of reactive oxygen species (ROS) by confocal laser scanning microscopy (CLSM) showed an over-accumulation of superoxide anion (02) and hydrogen peroxide (H202) in the stomata of citrus plants exposed to salt stress. Exogenously applied polyamines to salinized nutrient solution induced the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and ascrobic oxidase (AO) whereas it caused the opposite effect on peroxidase (POD), guaiacol peroxidase (GPO D) and ascorbate peroxidase (APX). The effect of polyamines was further examined by determining the plant's antioxidant gene expression profile following a quantitative real-time RT-PCR approach. The overall results indicate that the interaction between different polyamines can be dispersed throughout the citrus plant, and provide additional information suggesting that polyamines may act as a biological mediator allowing citrus plants to activate specific antioxidant responses against salinit

Parameterization of DGPS carrier phase errors over a regional network of reference stations

Bibliography: p. 168-178

An analysis on the optimal combination of geoid, orthometric and ellipsoidal height data

Bibliography: p. 224-23

UCGE Reports

The main objective of this research is to present a detailed analysis of the optimal combination of heterogeneous height data, with particular emphasis on (i) modelling systematic errors and datum inconsistencies, (ii) separation of random errors and estimation of variance components for each height type, and (iii) practical considerations for modernizing vertical control systems. Specifically, vertical control networks consisting of ellipsoidal, orthometric and geoid height data are investigated. Although the theoretical relationship between these height types is simple in nature, its practical implementation has proven to be quite challenging due to numerous factors that cause discrepancies among the combined height data. To address these challenges a general procedure involving empirical and statistical tests for assessing the performance of selected parametric models is developed. In addition, variance component estimation is applied to the common adjustment of the heterogeneous heights. This leads to an in-depth analysis of the effects of correlation among heights of the same type, provisions for computing non-negative variance factors, and the intrinsic connection between the proper modelling of systematic errors and datum inconsistencies with the estimated variance components. Additional numerical studies include the calibration of geoid error models (both regional and global), scaling the GPS-derived ellipsoidal height covariance matrix, and evaluating the accuracy of orthometric heights obtained from national/regional adjustments of levelling data. Ultimately, one of the main motivations for this work is embedded in the eminent need to introduce modern tools and techniques, such as GNSSlevelling, in establishing vertical control. Therefore, part of this researc..

Possible Orbit Scenarios for an InSAR Formation Flying Microsatellite Mission

Multistatic interferometric synthetic aperture radar (InSAR) is a promising future payload for a small satellite constellation, providing a low-cost means of augmenting proven “large” SAR mission technology. The Space Flight Laboratory at the University of Toronto Institute for Aerospace Studies is currently designing CanX-4 and CanX-5, a pair of formation-flying nanosatellites slated for launch in 2009. Once formation flight has been demonstrated, a future multistatic InSAR formation-flying constellation can exploit sub-centimeter inter-satellite baseline knowledge for interferometric measurements, which can be used for a myriad of applications including surface deformation, digital terrain modeling, and moving target detection. This study evaluates two commonly proposed InSAR constellation configurations, namely the Cartwheel and the Cross-Track Pendulum, and considers two ‘large’ (~kilowatt) SAR transmitters (C- and X-band) and one microsatellite transmitter (X-band, 150W). Each case is evaluated and assessed with respect to the available interferometric baselines and ground coverage. The microsatellite X-band transmitter is found to be technically feasible, although the lower available transmitter power limits the operating range. The selected transmit band determines the maximum allowable cross-track baseline between receiver satellites in the constellation. Additionally, the Cartwheel and Cross-Track Pendulum configurations offer different available baselines and ground coverage patterns, namely, the Cartwheel eliminates the near-zero cross-track baseline component that contributes to DEM height errors but adds a coupled along-track baseline, while the Cross-Track Pendulum offers the advantage of independent cross-track and along-track baseline components. Ultimately, the primary application for the InSAR data will dictate the transmit band used, the desired baselines, and the receiver constellation configuration

InSAR Microsatellite Constellations Enabled by Formation Flying and Onboard Processing Capabilities

The advancing development of low-cost small satellite platforms is a compelling driver for future remote sensing constellation missions. Multistatic interferometric synthetic aperture radar (InSAR) is a promising payload for such missions, potentially also in combination with additional remote sensing data. Significant challenges associated with using low-cost platforms for multistatic interferometric applications include the requirement of precise knowledge of the baseline distances between the spacecraft, and the high data volume generated (in the hundreds of megabytes per image), in light of the limited downlink capability of a microsatellite platform. To address these challenges, the Space Flight Laboratory (SFL) is making progress in a number of areas. CanX-4 and CanX-5 are a pair of identical nanosatellites designed by SFL, that will demonstrate formation flight in 2012 and enable future microsatellite constellation missions with sub-centimeter inter-satellite baseline knowledge. In regard to the data volume issue, it is observed that application-specific data requirements can be significantly smaller than the total amount of imagery collected. For example, the data required by a ground moving target indication (GMTI) mission may be limited to the position and velocity of targets, rather than entire images. Real-time image processing methods currently in development at SFL will enable onboard SAR focusing, automated image registration using precise orbit knowledge and frequency domain alignment methods, and interferometric image processing, allowing the downlink data volume to be reduced according to specific application needs. This paper discusses how CanX- 4&5 technology together with real-time image processing approaches can be used to enable high performance sparse aperture missions on low-cost, small platforms

Oxidative and Nitrosative-based Signaling and Associated Post-translational Modifications Orchestrate the Acclimation of Citrus Plants to Salinity Stress

Reactive oxygen and nitrogen species are involved in a plethora of cellular responses in plants; however, our knowledge on the outcomes of oxidative and nitrosative signaling is still unclear. To better understand how oxidative and nitrosative signals are integrated to regulate cellular adjustments to external conditions, local and systemic responses were investigated in the roots and leaves of sour orange plants (Citrus aurantium L.) after root treatment with hydrogen peroxide (H 2O 2) or sodium nitroprusside (a nitric oxide donor), followed by NaCl stress for 8 days. Phenotypic and physiological data showed that pre-exposure to these treatments induced an acclimation to subsequent salinity stress that was accompanied by both local and systemic H 2O 2 and nitric oxide (NO) accumulation. Combined histochemical and fluorescent probe approaches showed the existence of a vascular-driven long-distance reactive oxygen species and NO signaling pathway. Transcriptional analysis of genes diagnostic for H 2O 2 and NO signaling just after treatments or after 8 days of salt stress revealed tissue- and time-specific mechanisms controlling internal H 2O 2 and NO homeostasis. Furthermore, evidence is presented showing that protein carbonylation, nitration and S-nitrosylation are involved in acclimation to salinity stress. In addition, this work enabled characterization of potential carbonylated, nitrated and nitrosylated proteins with distinct or overlapping signatures. This work provides a framework to better understand the oxidative and nitrosative priming network in citrus plants subjected to salinity condition