Inayatullah Tahir

Flower Senescence-Strategies and Some Associated Events

Different strategies of petal senescence and some important events associated with it have been discussed. On the basis of sensitivity to ethylene and associated symptoms of senescence, petal senescence has been classified into five different classes; besides changes in membrane permeability, autophagy and involvement of VPEs (Vacuolar processing enzymes), degradation of nucleic acids, protein turn over and remobilization of essential nutrients during petal senescence have been discussed. Nucleus appears to play a central role in administrating the execution of the events associated with petal senescence. Protein turn over appears to be an important factor governing petal senescence in both ethylene-sensitive and ethylene-insensitive flower systems and that the loss of membrane integrity, vacuolar autophagy and remobilization of essential nutrients being its important consequences. Autophagy seems to be a main process responsible for cell dismantling and remobilization of macromolecules besides final disintegration of nucleus. A large number of senescence-associated genes have been found to be differentially expressed during petal senescence. On the basis of the available literature, a schematic model representing some important events associated with petal senescence has been constructed. The review recommends that more elaborate work is required at cellular and organelle level to understand the ethylene-independent pathway and its execution in both ethylene-sensitive and ethylene-insensitive flower systems. It also recommends that ethylene sensitivity should not be generally assigned to plants at the family level on the basis of response of a few species in a family.Résumésdes stratégies différentes de pétale senescence et certains événements importants associés ont été discutés. Sur la base d’une sensibilité d’éthylène et les symptômes associés de sénescence, pétale senescence ont été classé en cinq différentes classes ; outre les modifications dans la perméabilité de la membrane, Autophagie et l’implication des VPEs (Vacuolar traitement des enzymes), la dégradation des acides nucléiques, protéines tour sur re de nutriments essentiels au cours de la senescence pétale ont été discutés. Noyau semble jouer un rôle central dans l’administration de l’exécution des événements associés pétale senescence. Tour de protéines sur semble être un facteur important régissant pétale senescence dans les systèmes de fleur d’éthylène sensibles et éthylène-insensible et que la perte d’intégrité de la membrane, Autophagie vacuolar et re de nutriments essentiels à ses conséquences importantes. Autophagie semble être un processus principal responsable du démantèlement de la cellule et re de macromolécules outre finale désintégration du noyau. Un grand nombre de gènes associés senescence a été trouvé pour être exprimé différemment au cours de la senescence pétale. Sur la base de la documentation disponible, un modèle schematic représentant certains événements importants associés pétale senescence a été construit. L’examen recommande qu’un travail plus élaboré est nécessaire au niveau cellulaire et Organite pour comprendre la voie de l’éthylène-indépendante et son exécution dans les deux systèmes de fleur d’éthylène sensibles et éthylène-insensible. Elle recommande également que éthylène sensibilité ne doit pas être généralement affectée aux plantes au niveau familial sur la base de la réponse de quelques espèces dans une famille.

Flower senescence: some molecular aspects

Some molecular aspects of flower senescence have been reviewed. The isolation, identification and characterization of different genes from various flowers (mainly from petals) associated with senescence have been discussed. The isolated genes were divided into different groups. A large proportion of genes have been found to be upregulated during flower senescence while some genes were also found to be downregulated indicating that there exists a complex interplay between the expression patterns of various genes. The genes involved in petal expansion are found to be upregulated during normal flower development from anthesis to open flower stage, but XTH (Xyloglucan endotransglucosylase hydrolase) is found to be involved in petal expansion as well as abscission. Cysteine proteases or the genes encoding cysteine proteases (assigned a central role in protein degradation) have been identified from various flower systems, but no cysteine protease has been identified from senescing Mirabilis jalapa flowers. In addition to proteases, the genes encoding ubiquitin (exhibiting proteasomal degradation by 26S proteasomes) have also been identified suggesting the two alternate pathways for protein degradation. Genes encoding specific nucleases have also been identified, but they displayed an early increase in transcript abundance before the senescence symptoms become evident and characterize the involvement of PCD during flower senescence. A range of transcription factors are described and their possible role in flower senescence has been discussed. A detailed description of genes involved in ethylene synthesis and the components involved in ethylene signaling have been presented.

Grain composition in some buckwheat cultivars (Fagopyrum Spp.) with particular reference to protein fractions

A comparative study has been made of the chemical composition of grains in four buckwheat cultivarsviz. Fagopyrum esculentum Moench,F. sagittatum Gilib.,F. kashmirianum Munshi andF. tataricum Gaertn. Grains ofF. esculentum had the lowest content of phenolics, relatively low fat, free sugar and protein content but a higher starch content compared to other three cultivars.F. esculentum had a lower albuminglobulin content as also a lower glutelin content but a higher content of residual insoluble proteins. The content of prolamins was generally low in each of the four cultivars. Low content of phenolics in the groat fraction ofF. esculentum accounts for its better palatability compared to other three cultivars which possess astringent taste.

Physiological and biochemical changes associated with flower development and senescence in Dianthus chinensis L

Flowers of Dianthus chinensis growing in Kashmir University Botanic Garden (KUBG) were selected for the present study. Flower development and senescence was divided into six stages (I–VI), categorized as (I) tight bud stage, (II) mature bud stage, (III) paint brush stage, (IV) fully open/bloom stage, (V) partially senescent stage and (VI) senescent stage. Various physiological and biochemical changes associated with flower development and senescence were recorded. Fresh and dry mass, water content and flower diameter showed a continuous increase from bud to bloom, i.e., from stage I–IV and a significant decrease from stage V to VI. Scanning electron microscopic studies showed a clear degeneration of the cellular integrity and architecture with the onset of senescence in Dianthus chinensis. Soluble proteins, α-amino acids and sugar fractions increased with flower opening and showed a decrease as the senescence progressed. SDS-PAGE of the petal tissues revealed a decrease in both high and low molecular weight proteins. The present study suggests that the protein degradation is the key factor in regulating the process of flower senescence in this flower.

Plant signaling: Understanding the molecular crosstalk

Among abiotic factors, salinity and drought stress affect every aspect of plant from physiology to metabolic activities. Understanding of abiotic stress responses and signal transduction to control adaptive pathways is a crucial step in determining the plant resistance exposed to unfavorable environments. Molecular and genomic fi ndings have shown several changes in gene expression profi ling under drought and salt stresses in plants. Numbers of transcription factors which are accountable for inducing stress-responsive genes have been documented. To survive in adverse condition, plants have stress‐specifi c and adaptive responses which provide them necessary protection. Although, there are several signaling pathways and stress-responsive perceptions, some of which are defi nite in function, while others may have cross talk. Expressions of a large number of transcripts and genes are induced by these abiotic stresses in plants which facilitate stress tolerance and stress response. Recently, progress has been made in investigating the complex cascades of gene expression in stress responses. Knowledge about plant stress signaling is essential for the development of transgenic and improving breeding strategies in crops under stress environment. This chapter provides an outline of the common features of stress signaling in plants with some current studies on the functional analysis of signaling machineries under salt and drought stresses.

Recent Trends and Approaches in Phytoremediation

The current technique of remediation of heavy metal from contaminated soil is not cost-effective and eco-friendly. Besides, these heavy metals are recalcitrant and are not degraded like organic compounds, therefore effective clean-up requires their immobilization to reduce or remove toxicity. Phytoremediation in future will play an important role in attaining the goals towards sustainable development. The recent development in biotechnology has generated a large knowledge base and thus has opened many opportunities for research and development in the field of phytoremediation. In this chapter we summarize some recent approaches in phytoremediation and how genetic engineering plays an important role to improve the potential of phytoremediation.

Phytoremediation: An Eco-Friendly Green Technology for Pollution Prevention, Control and Remediation

Among the environmental concerns the accumulation of heavy metals is of prime importance. The factors that are generally responsible for deteriorating soil quality include geological and anthropogenic activities. Besides, due to constantly changing urbanization and industrialization patterns the quality of the soil has greatly been affected which ultimately poses a threat to the ecosystem, food safety and human health. Reclamation of these contaminated soils by engineering methods is expensive, time consuming and sometimes not eco-friendly. Researchers all over the world are focusing to exploit the potential of plants as phytoremediators, a technology which is cost-effective, sustainable and eco-friendly. Phytoremediation technology is emerging gradually and as one of the important components of green technology which aims to employ plants across various genera for restoring ecosystem health. Plants possess a natural ability to eliminate, detoxify or immobilize environmental contaminants in a growth matrix by means of various biological processes. The main significant points discussed in this chapter include the mechanisms of phytoremediation and factors affecting phytoremediation.

Sugar Signaling in Plant Growth and Development

Sugars are the primary energy sources produced by green plants via the life-sustaining process of photosynthesis. The metabolic role of sugars as energy compounds and essential metabolites in living organisms has long been recognized. However, genetic and molecular (mutational) studies during the last decade have highlighted the role of sugars as signaling molecules in controlling diverse aspects of plant growth and development. The review focuses on specific signaling roles of various sugars particularly hexoses (glucose and fructose), sucrose, trehalose, and small glycans. Moreover, the sugar-specific regulations of various genes and the diverse signaling cascades involved have been discussed. The role of hexokinase–kinase-dependent and hexokinase-independent signals (like G proteins) in sugar signal transduction pathways has also been documented. The evidences generated from the analyses of sugar-insensitive mutants and hormone-insensitive mutants have also demonstrated a complex interplay of factors regulating the common signaling capabilities of sugar/hormone interactions. Characterization of sugar-signaling mutants in Arabidopsis has unraveled a complex signaling network that links sugar responses to two plant stress hormones, abscisic acid and ethylene, in opposite ways. Similar cross talk between sugar and other plant hormones in their signaling capabilities has been discussed.

Plant Signaling: Response to Reactive Oxygen Species

It is noteworthy to mention how the last 20 years have modified the concept of signalling in plants, especially the molecular crosstalk associated with it. Plants have the ability to show remarkable developmental plasticity to sustain in a continually changing environment. In response to various environmental stresses such as drought, salinity, metal toxicity, temperature and pathogens, plants defend themselves by developing some special defence mechanisms. Plants recognise these environmental signals with the help of some membrane protein sensors and then transduce these signals to the nucleus which ultimately stimulates various transcription factors and genes to form the product that ultimately leads to plant adaptation and assists the plant to sustain and surpass the adverse conditions. Amongst the environmental factors which are involved in signalling is the reactive oxygen species (ROS) generated during cell metabolism. ROS are spontaneously produced in the cell enzymatically through the action of various soluble membrane-bound enzymes and nonenzymatically by autoxidation reactions. Some of these ROS (e.g. superoxide dismutase, hydrogen peroxide and nitric oxide) are physiologically useful and in fact necessary for life but can also be harmful if present in excess or in inappropriate amounts. Current research in this regard focuses more on the development of transgenic plants with enhanced tolerance to ROS by using genetic approaches and analytical techniques. In particular nitric oxide (NO), a reactive radical, may be involved in the defence mediated by the ROS such as defence gene activation, hypersensitive response cell death and phytoalexin biosynthesis. By using biotechnological approaches NO together with ROS activates a stronger response and tolerance to various stresses in plants.

Biomass Pellet Technology: A Green Approach for Sustainable Development

The supply of sustainable or green energy is the main challenge that mankind will face over the coming decades, especially because of the need to address climatic changes. Biomass being abundantly available in nature can make a substantial contribution to cater future energy demands in a sustainable way. Currently, it is the largest universal contributor of green energy and has significant potential to expand in the production of electricity, heat and fuels. However, handling as well as direct combustion of biomass is restrained due to peculiar properties of this kind of fuel. As raw biomass possesses low density (30–50 kg/m3) and high moisture content that limits its usage for energy purposes and it needs to be densified prior to its use. The compact and densified biomass possess a high magnitude of density as well as low moisture content which in turn helps to dwindle technical limitations associated with storage, handling and transportation. One immediate solution is the pelletisation of raw biomass that enhances its energy efficiency and enables the competition of biomass with other types of fuels. Besides, biomass pellet technology has gained a rapid momentum in many European countries. The future of the biomass pellet industry is greatly influenced by various environmental, economic, political as well as social aspects that create a multiplex relation among suppliers, producers and consumers. Therefore, the main aim of this chapter is to develop a comprehensive review of biomass processing that involves pellet production technology, energy efficiency of biomass pellet, current status, opportunities and challenges for the development of biomass pellet market.