Showing papers in "Advances in Botanical Research in 2000"
602 citations
324 citations
TL;DR: The new understanding of anchorage has thrown light on various aspects of root biology, such as their distribution of strength, lack of prestress, and their sensitivity to mechanical stimulation, and has helped point the way towards the development of more stable cereal crops and forestry trees.
Abstract: The past 20 years has seen the re-emergence of the study of root anchorage. The research has combined theory from composite materials and foundations technology with experimental observations and mechanical testing. This has shown that the mechanical role of roots is restricted to the basal root system, but that it nevertheless greatly influences both the size and shape of root systems. Procumbent and climbing plants, which must resist being uprooted vertically, are most efficiently anchored by a fibrous root system. In contrast, self-supporting plants require rigid elements in their anchorage systems to prevent them toppling. Small herbaceous dicots tend to possess tap root systems, larger herbaceous dicots and trees possess plate systems, and monocots possess coronal or prop root systems. The mechanics of anchorage of each system has been determined in a range of species, methods used including direct observations of the motions of roots systems, and measurements of the torque required and of surface strains around the root system as plants were pulled over. Serial destruction of elements of the anchorage system allowed the relative importance of the various components of anchorage to be estimated. The new understanding of anchorage has thrown light on various aspects of root biology, such as their distribution of strength, lack of prestress, and their sensitivity to mechanical stimulation. It has also helped point the way towards the development of more stable cereal crops and forestry trees. It is hoped that future work on the effect of soil properties and on the modelling of anchorage could help explain other observations. why, for instance, trees develop different root systems in different soil types; and why trees replace tap root systems with plate systems as they grow.
106 citations
92 citations
TL;DR: The present status of the molecular genetics of sulphate assimilation in plants is reviewed and the ability to manipulate these pathways is now possible and will allow the engineering of crops with improved sulphur acquisition and utilization traits.
Abstract: The importance of sulphur in promoting yield, quality and stress resistance parameters in plants has been highlighted by the recent increased problems of S-deficiency in agriculture. These deficiencies are in part a consequence of reduced atmospheric emissions from industry and the subsequent decreased deposition on agricultural land. Contributions from several laboratories, worldwide, have resulted in the cloning of almost all of the genes responsible for uptake, transport and assimilation of sulphate. This has led directly to the resolution of many outstanding questions regarding the control of uptake and of the pathways and intermediates involved in assimilation. Furthermore, the ability to manipulate these pathways is now possible and will allow the engineering of crops with improved sulphur acquisition and utilization traits. This paper reviews the present status of the molecular genetics of sulphate assimilation in plants.
86 citations
77 citations
TL;DR: Infection of cereal hosts is achieved by formation of multicellular plaques, and the colonization process is described, and recent advances in the molecular genetics of the pathogens will aid analysis of pathogenic variation in eyespot.
Abstract: Eyespot is an important stem-base disease of cereal crops in temperate regions. Cultural, genetic and molecular criteria have been used to separate the fungi responsible into two species, Tapesia yallundae (previously W-type) and T. acuformis (previously R-type). Discovery of the apothecial sexual stage (teleomorph) of Tapesia yallundae on straw stubble was a key factor in this change for a pathogen previously believed to be asexual (anamorph: Pseudocercosporella herpotrichoides ). Sexual reproduction is controlled by a two-allele heterothallic system in both species, although mating appears to be rare in T. acuformis . Infection of cereal hosts is achieved by formation of multicellular plaques, and the colonization process is described. The host range includes wild grass species as well as small-grain cereals, and new genetic sources of resistance to the disease have been identified in Triticum species and wild relatives. Recent advances in the molecular genetics of the pathogens will aid analysis of pathogenic variation in eyespot.
68 citations
TL;DR: Plant metabolites associated with trichomes were up to now consulted little for the investigation of taxonomic relationships, but were shown to be useful tools for recent trends in chemosystematics considering information from biosynthetic pathways in plants.
Abstract: Plant metabolites associated with trichomes were up to now consulted little for the investigation of taxonomic relationships. This is unexpected given the fact that plant trichomes provide a unique means of making biomolecules of specific pathways accessible at the plant surface in a concentrated form. In cases where compounds from glandular trichomes have been investigated, they have proved to be reliable taxonomic characters. In combination with microscopic studies, the presence or absence of metabolites in a plant or in specific organs is often predictable, thus avoiding unnecessary chemical analysis. The high resolution of modern chromatography allows the development of fingerprinting techniques for compound assignment of extracts gained directly from trichomes via microsampling. The previous inability of spectroscopic structure identification with analytical sample amounts is now adays partly compensated. On-line techniques such as GC-MS, LC-MS, CE-MS and LC-NMR require sample amounts adjusted to the concentrations found in trichomes. Trichomes were also shown to be useful tools for recent trends in chemosystematics considering information from biosynthetic pathways in plants. Enzymes extracted from living glandular cells were successfully employed to study the biosynthesis of terpenoids. Considering these circumstances, chemotaxonomy based on metabolites from glandular trichomes could become an interesting section of plant systematics – it just has to be attempted.
59 citations
TL;DR: This chapter focuses on calcium-dependent protein kinases as well as their close relatives the calcium- dependent protein kinase (CDPK)-related kinases (CRKs), which represent a novel group of kinases with a limited representation in eukaryotes.
Abstract: Publisher Summary This chapter focuses on calcium-dependent protein kinases as well as their close relatives the calcium-dependent protein kinase (CDPK)-related kinases (CRKs). Consistent with calcium's role as a signaling molecule, many cellular processes are known to require calcium. For calcium to function as a second messenger in transducing signals, the concentration of calcium in the cytoplasm under resting conditions must be maintained at low levels. Calcium fluxes through the cytoplasm can develop and then dissipate very rapidly, thereby allowing for specific responses to be initiated, followed by the resetting of the system in preparation for the next stimulus. In plants, the large calcium-dependent protein kinase (CDPK) family of enzymes may function as downstream targets of increased calcium levels. CDPKs are directly activated by calcium ions. Thus, CDPKs represent a novel group of kinases with a limited representation in eukaryotes.
53 citations
TL;DR: Protein phosphorylation for signal transduction is particularly suited for defense because it allows efficient amplification of the original signal, negative feedback for desensitization, and cross-talk and branching for the activation of diverse lines of defense.
Abstract: Publisher Summary Protein kinases of different families are involved in defense mechanisms at different cellular levels, including elicitor recognition, as extracellular or intracellular receptors, signal transduction, and the induction of transcriptional activation. However, only a few kinases participating in defense signaling have been isolated to date, and their molecular characterization is still very limited. The ability to induce defense mechanisms is a characteristic of incompatible (resistant) plant–pathogen interactions. Resistant plants are equipped with a molecular alert system that allows them not only to recognize pathogen intrusion but also to amplify very efficiently the initial alarm signal and to activate self-defense. Protein kinases and phosphatases in plants, as well as in animals, are implicated as key components in signaling mechanisms critical for responses to environmental stresses and attack by pathogens. The use of protein phosphorylation for signal transduction is particularly suited for defense because it allows efficient amplification of the original signal, negative feedback for desensitization, and cross-talk and branching for the activation of diverse lines of defense. In cellular signal transduction pathways, phosphorylation by protein kinases is antagonized by the dephosphorylation activity of protein phosphatases.
48 citations
TL;DR: This chapter focuses on members of two-component systems that have been identified in Arabidopsis, which gives the most complete picture currently available on the way these signaling systems are represented in plants and the way they function.
Abstract: Publisher Summary This chapter focuses on members of two-component systems that have been identified in Arabidopsis . Arabidopsis gives the most complete picture currently available on the way these signaling systems are represented in plants and the way they function. Histidine kinases and response regulators are collectively known as “two-component systems.” They confer upon bacteria the ability to sense and respond to environmental stimuli. The first component is a histidine kinase that autophosphorylates a conserved histidine residue in response to an environmental stimulus. This phosphate is then transferred to an aspartic acid residue on the second component referred to as the “response regulator.” In plants, proteins with homology to two-component systems are implicated in signaling by the hormones ethylene and cytokinin in sensing changes in osmotic pressure in responses to light and in the regulation of pyruvate dehydrogenase. Thus, all components needed for establishing a phosphorelay are represented in plants. In addition to two-component proteins implicated in specific signaling pathways, plants contain a number of two-component proteins whose functions in the plant are currently unknown.
TL;DR: This chapter discusses sucrose nonfermenting-1 (SNF1) and adenosine monophosphate-activated protein kinase (AMPK)—global regulators of carbon metabolism in their respective systems.
Abstract: Publisher Summary This chapter discusses sucrose nonfermenting-1 (SNF1) and adenosine monophosphate-activated protein kinase (AMPK)—global regulators of carbon metabolism in their respective systems. SNF1-related protein kinases (SnRKs) are a family of plant protein kinases with catalytic domains similar to that of SNF1) of yeast and AMPK of animals. The plant SnRK family comprises at least three subfamilies (SnRKs1, 2, and 3). Relatively little is known about the functions of SnRK2s and SnRK3s, but it is already clear that SnRK1s play an important role in the regulation of carbon metabolism and in the cross-talk between metabolic and other signaling pathways in plants. This role not only has some similarities with the roles of SNF1 and AMPK but also has some intriguing differences. The genetic modification of SnRK1 activity and function may be one way of improving this important trait in crop plants.
TL;DR: Structural features, biological and biochemical functions, and modes of action of the plant receptor tyrosine kinases (RLKs)—in particular, RLKs that play a crucial role in plant development are described.
Abstract: Publisher Summary This chapter describes structural features, biological and biochemical functions, and modes of action of the plant receptor tyrosine kinases (RLKs)—in particular, RLKs that play a crucial role in plant development. The latest progress in uncovering the components the RLK-mediated signal transduction pathways, including both potential ligands and downstream targets, is highlighted in the chapter. The chapter discusses the importance of such signaling mechanisms in plant cell–cell interaction. A common feature of plant RLKs is that each has a cytoplasmic protein kinase catalytic domain, a single membrane-spanning region, an N-terminal signal sequence, and an extracellular domain that varies in structure. In animals, growth factor receptors with an intrinsic protein tyrosine kinase activity, known as “RTKs,” play key roles in cellular processes to coordinate the development of multicellular organs. Because plant cells are encapsulated by cell walls, the idea of plant cell–cell communication via the recognition of polypeptide ligands and transmembrane receptors at the cell surface was once viewed with skepticism. Functional-genomic studies of RLKs, such as generating knockout lines for each RLK, may provide a comprehensive view in understanding the breadth of biological activities for RLKs.
TL;DR: Plant movements are adaptive strategies for enhancing the photosynthetic performance, water use efficiency and reproductive efficiency, and may be modified by environmental stresses.
Abstract: Terrestrial plants perform a variety of movements, by which they optimize their utilization of the existing environmental resources. Developing buds, flowers, inflorescences, fruits, leaves, leaflets, or even entire shoots, reorient by means of biophysical motors that subtend them. The motors operate by performing differential and anisotropic changes in the volume of tissues located in their opposite sides, resulting in increase, or decrease in the radius of curvature of the motor. These changes are either mediated by growth, or by turgor. The lifetime of the motor for growth-mediated movements is limited by the capacity of the tissue to grow. Turgor-mediated movement is characteristic of mature leaves and is accomplished by means of a special motor organ — the pulvinus — situated in strategic junctions within the leaf, principally at the base of the leaf let) lamina. The pulvinar motor remains operative throughout the active life of the leaf. Light is the major environmental requirement of the shoot. Consequently, most of these movements are driven by specific light signals. Photonastic movements take place in a predetermined direction and are independent of the direction of the light signals. In pulvinated leaves these signals are perceived in the pulvinus. Phototropic movements take place in a direction that is tightly coupled to the direction of light. The direction of light may be perceived either by differential of interception in opposite flanks of the motor itself, or as a vector. Some pulvinated leaves perceive the direction of light in the pulvinus, as a unilateral signal, and exhibit pulvinar phototropism. Other leaves perceive the direction of light in the lamina as a vectorial excitation, and exhibit laminar phototropism. The vectorial signal is transmitted to the subtending pulvinus. Heliotropic movements track the daily solar transit. After sunset, they reverse direction (in total darkness) to face the anticipated direction of the next sunrise. Phototropic movements of pulvinated leaves may be modified by environmental stresses. Plant movements are adaptive strategies for enhancing the photosynthetic performance, water use efficiency and reproductive efficiency.
TL;DR: The biochemical properties of protein phosphatases have been highly conserved among eukaryotic organisms and efforts need to be directed to the functional analysis of these enzymes in the context of plant cell and developmental biology.
Abstract: Publisher Summary The reversible phosphorylation of proteins is an essential component of almost all signaling pathways in a living cell. Changes in the phosphorylation state of a protein are conducted by two types of enzyme activities: protein kinases that catalyze the covalent attachment of a phosphate group to an amino acid side chain and protein phosphatases that reverse this process. Nearly all aspects of cell function involve reversible phosphorylation. Some examples include metabolism, cell-cycle progression, ion transport, developmental control, and stress responses. This diverse spectrum of cellular functions is reflected by a large number of intracellular proteins that are subject to reversible phosphorylation. Several approaches have already been taken in the study of plant protein phosphatases—for example, a genetic screening identified abscisic acid–insensitive (ABI) phosphatases in a pathway related to abscisic acid (ABA) signaling. The biochemical properties of protein phosphatases have been highly conserved among eukaryotic organisms. Efforts need to be directed to the functional analysis of these enzymes in the context of plant cell and developmental biology.
TL;DR: The more the insight gained into signal transduction pathways, the earlier protein kinases appear to have evolved and the more conserved they appear to be.
Abstract: Publisher Summary A protein kinase is only rigorously defined when its DNA and/or amino acid sequence is established. Therefore, the most logical method is to classify them on the basis of the similarities in amino acid sequences. Protein kinases can be classified by various biochemical criteria, such as by their substrate specificity or their regulatory properties. However, an inherent problem with a purely biochemical approach is the difficulty in comparing results obtained by different laboratories, especially when different species or tissues are used; it is often difficult to know whether the protein kinases under study correspond to the same molecular entities. Animal and yeast protein kinases provide good models for the functions of plant systems, particularly where they appear to be homologues. This approach has validity because the more the insight gained into signal transduction pathways, the earlier they appear to have evolved and the more conserved they appear to be.
TL;DR: The nature of endophytic fungal relationships of the Gymnospermae and factors affecting their colonization frequencies within Gymnosperm foliage are discussed and aspects of quiescent infection, latent pathogenesis and absolute endophytism are discussed.
Abstract: This review discusses the nature of endophytic fungal relationships of the Gymnospermae and factors affecting their colonization frequencies within Gymnosperm foliage. The roles of fungal foliar endophytes in insect herbivory, biological control, latent pathogenesis and other associations are addressed. Specific mention is made of host and fungal diversity, ecology of endophytic colonization, and the physiology of endophytic associations. Aspects of quiescent infection, latent pathogenesis and absolute endophytism are also discussed.
TL;DR: The yeast two-hybrid system and the functional complementation tests with yeast mutants will be powerful tools for the isolation of regulators and substrates of the protein kinases and phosphatases.
Abstract: Publisher Summary This chapter discusses the biological roles of protein phosphorylation and dephosphorylation in environmental stress responses and explains the role of mitogen-activated protein (MAP) kinase in environmental stress signal transduction in higher plants. Protein kinases are essential for cellular activities. Genetic, biochemical, and pharmacological analyses have shown that protein kinases and protein phosphatases play important roles in environmental stress responses, including responsiveness to stress-induced phytohormones in plants. Protein phosphorylation/dephosphorylation has been shown to regulate diverse cellular processes in eukaryotes. Thousands of protein kinases have been reported and classified into several groups based on their structures, substrate specificities, and regulatory ligands. Recently, forward and reverse genetic approaches have led to the isolation of genes encoding protein kinases and protein phosphatases that play important roles in stress signaling in plants. The yeast two-hybrid system and the functional complementation tests with yeast mutants will be powerful tools for the isolation of regulators and substrates of the protein kinases and phosphatases.
TL;DR: This chapter focuses on the regulation of activity of several enzymes involved in carbon- and nitrogen-metabolisms that are phosphorylated by either calmodulin-like domain protein kinases (CDPKs) or sucrose nonfermenting-1 (SNF1)-related protein.
Abstract: Publisher Summary This chapter focuses on the regulation of activity of several enzymes involved in carbon- and nitrogen-metabolisms that are phosphorylated by either calmodulin-like domain protein kinases (CDPKs) or sucrose nonfermenting-1 (SNF1)-related protein. Coordination between carbohydrate metabolism and nitrogen assimilation is essential to avoid direct competition, and it potentially involves control at several levels including gene expression, membrane transport, and enzyme activity. One important mechanism that may impact all three levels is reversible protein phosphorylation. Recent studies have also identified several other enzymes, including trehalose-6-phosphate synthase and glutamine synthetases, as phosphoproteins because they interact with 14-3-3 proteins in a phosphorylation-dependent manner. Several transport activities that may impact metabolism either directly or indirectly may also be controlled by phosphorylation. Of particular importance is the possible regulation by phosphorylation of ion and solute transport, for example, the plasma membrane H + -adenosine triphosphate (ATP)ase, plasma membrane K + channel, and the sucrose transporter.
TL;DR: There is a substantial body of evidence to show that light causes rapid changes in protein phosphorylation and in the expression of protein kinase genes, consistent with the notion that protein kinases play a role in transducing light signals.
Abstract: Publisher Summary This chapter focuses on the role that protein kinases play in the perception and transduction of light signals. There is a substantial body of evidence to show that light causes rapid changes in protein phosphorylation and in the expression of protein kinase genes. These types of data are consistent with the notion that protein kinases play a role in transducing light signals. Protein kinases are often mentioned as potential components of signaling pathways activated by the photoreceptors. Light alters the phosphorylation status of several proteins, including phytochromes and phototropin. Light regulates the expression of genes encoding protein kinases; in most cases, the signaling function of these kinases remains to be elucidated, although clear hints exist on where to begin. From a protein phosphorylation perspective, the most profound recent advance is perhaps the identification of phytochrome and phototropin as protein kinases.
TL;DR: This chapter discusses a few model mitogen-activated protein (MAP) kinase pathways in well-developed nonplant systems and reviews the information currently available on plant MAP kinase signaling pathways, including recent data.
Abstract: Publisher Summary This chapter discusses a few model mitogen-activated protein (MAP) kinase pathways in well-developed nonplant systems and reviews the information currently available on plant MAP kinase signaling pathways, including recent data. This allows detailing conserved features within the MAP kinase module. Additional data should be obtained from the Protein Kinase Resource. MAP kinase cascade components constitute families of protein kinases that participate in cascades ubiquitously observed from yeast to vertebrates and plants. MAP kinase modules are highly conserved and extremely versatile. Most MAP kinase-mediated signal transduction pathways channel various extracellular or intracellular stimuli and activate signal transmission from membrane receptors to intracellular targets, thus generating specific cellular responses. Currently, investigators studying plant MAP kinase signaling pathways benefit greatly from the advances made in other model organisms. Research will lead to the identification of plant-specific sequences and mechanisms that will contribute to the elucidation of the complex picture currently emerging on the way eukaryotic development is controlled.
TL;DR: The chapter discusses the nature of the male component, the putative ligand for the S-locus receptor-like kinase (SRK) receptor, and how a combination of biochemical and map-based approaches will lead to the identification of this gene in the near future.
Abstract: Publisher Summary The majority of flowering plant species are hermaphrodites and possess flowers in which the male and female organs are in close proximity. Despite this proximity, outcrossing is favored in a large number of these species because of the action of self-incompatibility (SI) systems that permit the pistil to reject self-pollen. The chapter discusses the nature of the male component, the putative ligand for the S-locus receptor-like kinase (SRK) receptor. This is important with regard to the mechanism of SI because it would provide a means of testing the hypothesis that the members of the receptor tyrosine kinase (RLK) superfamily function as receptors. A major advantage of the SI system is that the male component of the SI response is predicted to be encoded by a gene located at the S locus. A combination of biochemical and map-based approaches will lead to the identification of this gene in the near future.
TL;DR: This chapter focuses on the specificity, reversibility, and rapidity (minutes or even seconds) of protein phosphorylation, which provides an efficient means for the regulation of complex and highly controlled and coordinated processes such as stomatal movement.
Abstract: Publisher Summary This chapter focuses on the specificity, reversibility, and rapidity (minutes or even seconds) of protein phosphorylation, which provides an efficient means for the regulation of complex and highly controlled and coordinated processes such as stomatal movement. Protein phosphorylation regulates proteins involved in a range of cellular processes, from membrane channels and pumps through metabolic enzymes and cytoskeletal proteins to transcription factors. Even protein kinases and phosphatases themselves are subject to modulation by phosphorylation. The chapter discusses a case study of guard cell proteins modulated by phosphorylation. Phosphorylation of a number of proteins from guard cells is stimulated by abscisic acid (ABA), cyclic adenosine monophosphate (cAMP), or Ca 2+ . However, the identities of almost all of these guard cell phosphoproteins are to be determined. Another approach to assess the role of protein phosphorylation in stomatal regulation is to examine the effects of inhibitors of protein kinases/phosphatases or purified protein kinases/phosphatases on the activity of a key guard cell protein whose activity can be assayed—for example, an ion channel monitored by the patch clamp technique.
TL;DR: Structural genomics is an interesting area, which, along with the rest of bioinformatics, will see much development over the next 10 years as database sizes and numbers increase and programs evolve.
Abstract: Publisher Summary This chapter focuses on using bioinformatics to discover functional relationships between genes and proteins. These techniques are used to examine gene and species evolution. With the availability of whole genome sequences and sequences from several different genomes, new approaches in bioinformatics can answer new questions. To further the understanding of the common and unique characteristics of the plant kingdom, discoveries need to be extended beyond the specific organism or gene. Structural genomics is an interesting area, which, along with the rest of bioinformatics, will see much development over the next 10 years as database sizes and numbers increase and programs evolve. This development will encompass new methods, as well as the sequence alignment and the phylogenetic tree making discussed in the chapter. This and greater structural knowledge may make the applications of specific biochemical investigations to groups of homologous proteins more accurate and useful.