Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of aerobic metabolism. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Whereas plants are surfeited with mechanisms to combat increased ROS levels during abiotic stress conditions, in other circumstances plants appear to purposefully generate ROS as signaling molecules to control various processes including pathogen defense, programmed cell death, and stomatal behavior. This review describes the mechanisms of ROS generation and removal in plants during development and under biotic and abiotic stress conditions. New insights into the complexity and roles that ROS play in plants have come from genetic analyses of ROS detoxifying and signaling mutants. Considering recent ROS-induced genome-wide expression analyses, the possible functions and mechanisms for ROS sensing and signaling in plants are compared with those in animals and yeast.

REACTIVE OXYGEN SPECIES: Metabolism, Oxidative Stress, and Signal Transduction

http://paymanhassibi.persiangig.com/document/mittler%20oxidative.pdf

Oxidative stress, antioxidants and stress tolerance

To cope with environmental fluctuations and to prevent invasion by pathogens, plant metabolism must be flexible and dynamic. Active oxygen species, whose formation is accelerated under stress conditions, must be rapidly processed if oxidative damage is to be averted. The lifetime of active oxygen species within the cellular environment is determined by the antioxidative system, which provides crucial protection against oxidative damage. The antioxidative system comprises numerous enzymes and compounds of low molecular weight. While research into the former has benefited greatly from advances in molecular technology, the pathways by which the latter are synthesized have received comparatively little attention. The present review emphasizes the roles of ascorbate and glutathione in plant metabolism and stress tolerance. We provide a detailed account of current knowledge of the biosynthesis, compartmentation, and transport of these two important antioxidants, with emphasis on the unique insights and advances gained by molecular exploration.

ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control

▪ Abstract Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to t...

Plant cellular and molecular responses to high salinity.

Antioxidants, Oxidative Damage and Oxygen Deprivation Stress: a Review

One of the major forces driving the birth of the field of cell biology was the application of electron microscopy to cells. Today, virtual nanoscopy has brought electron microscopy and the cell biology community to a new frontier in biological imaging and cell biological inquiry. The Journal of Cell Biology is pleased to announce that the JCB DataViewer is “going big” to host electron microscopy data at a whole new scale.

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The JCB DataViewer scales up

In this paper we review the current state of the art and key open problems in the development of predictive, adaptive user interfaces for mobile devices. Mobile interfaces that are dynamic and adapt to each user pose a challenge to developers, as a user's context is constantly changing, and the interface must continually adapt to accommodate changes in the user's activity and environment. We first introduce this problem of creating a truly context-aware interface. We then analyze the state-of-the-art in both research and practice. We conclude by discussing key open problems in the area of adaptive mobile interfaces, as well as future research directions.

Predictive, adaptive mobile user interfaces: state of the art and open problems

While traditional search engines can often provide useful knowledge, some information that is more temporal and contextual can be found more easily or exclusively on social media. However, the number of posts on many social media platforms is too large to manage without a method for clustering posts into distinct topics. In this paper, we compare two approaches for the topical clustering of Twitter posts to discover various subjects that users are talking about. The first approach is GeoContext, our tool for clustering a social media stream into topics that uses a unique approach for calculating the similarity between posts. We compare GeoContext against Latent Dirichlet Allocation (LDA), a commonly used topic modeling algorithm. LDA has been used as a basis in several different approaches for clustering social media posts.

A comparison of two methods for the topical clustering of social media posts

Social media is often useful for discovering contextual information that is difficult to find on traditional query-based search engines such as Google. For example, temporal events such as traffic incidents are often posted on social media due to the wide-reaching and real-time nature of social media platforms. Social media can also be used to model the sentiments and opinions of different geographical regions, as well as provide a platform for organizing social movements. In this paper, we give an overview of our system, GeoContext, which models a stream from Twitter into topics and analyzes the geographical locations of the topics. GeoContext includes methods for filtering a social media stream by keywords and location coordinates in order to provide more specific topics. GeoContext includes a geolocation module, called GeoContext Locator, for predicting the locations of tweets that are not associated with explicit coordinates, in order to model topics in different locations.

Geocontext: discovering geographical topics from social media

Social media can provide an insight into different contextual and temporal events that are not easily discovered with traditional search engines. In this paper, we evaluate different configurations for creating a social media analysis engine. We briefly describe our system, GeoContext, for analyzing a Twitter stream. GeoContext creates clusters of tweets that have the same topic, and then analyzes the topic clusters to determine if each cluster is centered in a geographical location. In this paper, we present our evaluation of four threshold values present in GeoContext: the threshold value of GeoContexts similarity score calculation by which two tweets are considered to have similar topics, the time between pruning sessions, at which old irrelevant clusters of tweets are removed, the time at which a cluster is considered to be irrelevant, or stale, and the threshold value of GeoContexts geographical analysis algorithm, by which a cluster of tweets is considered to be centered at a location. We posit that these types of threshold values are likely to be present in any system for clustering and analyzing a social media stream.

Elizabeth H. Williams

Papers

The JCB DataViewer scales up

Predictive, adaptive mobile user interfaces: state of the art and open problems

A comparison of two methods for the topical clustering of social media posts

Geocontext: discovering geographical topics from social media

Evaluating GeoContext: A system for creating geographical topics from a social media stream