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PubMed1994

Signaling among neighboring plants and the development of size inequalities in plant populations.

Transgenic tobacco plants that express an oat phytochrome gene (phyA) under control of the cauliflower mosaic virus (CaMV) 35S promoter and display altered photophysiology were used to test the role of light as a vehicle of information in dominance relationships between neighboring plants. Compared with the isogenic wild type, phyA-overexpressing plants showed dramatically reduced morphological responsivity to changes in the red/far red ratio of the incident light and to the proximity of neighboring plants in spacing experiments. In transgenic canopies an increase in stand density caused the small plants of the population to be rapidly suppressed by their neighbors. In wild-type canopies, plants responded to increased density with large morphological changes, and there appeared to be an inverse relationship between the magnitude of this morphological response and the ranking of the individual plant in the population size hierarchy. In these wild-type populations, size inequality increased only moderately with density within the time frame of the experiments. Our results suggest that, in crowded stands, the ability of individual plants to acquire information about their light environment via phytochrome plays a central role in driving architectural changes that, at the population level, delay the development of size differences between neighbors.

Avena↗
PubMed1999

Transgenic tobacco plants expressing the Drosophila Polycomb (Pc) chromodomain show developmental alterations: possible role of Pc chromodomain proteins in chromatin-mediated gene regulation in plants.

The chromodomain of the Drosophila Polycomb (Pc) protein has been introduced into tobacco nuclei to determine its location in the nucleus and its effect on plant development. Pc is a repressor of homeotic Drosophila genes that shares a well-conserved, although not identical, chromodomain with a structural heterochromatin component, Heterochromatin Protein 1. The chromodomains might therefore play a common role in chromatin repression. An analysis of transgenic plants expressing the Pc chromodomain, which was linked to the green fluorescent protein, suggested that the Pc chromodomain has distinct target regions in the plant genome. Transgenic plants expressing the Pc chromodomain had phenotypic abnormalities in their leaves and flowers, indicating a disruption in development. In axillary shoot buds of plants displaying altered leaf phenotypes, enhanced expression of a homeodomain gene, which is downregulated in wild-type leaves, was found. In Drosophila, Pc has been shown to possess distinct chromosome binding activity and to be involved in the regulation of development-specific genes. Our results support the assumptions that the heterologous chromodomain affects related functions in Drosophila and in plants, and that chromatin modification mechanisms are involved in the regulation of certain plant genes, in a manner similar to chromatin-mediated gene regulation in Drosophila.

Base Sequence↗
PubMed1998

A model for the lowering of plant ethylene concentrations by plant growth-promoting bacteria

It was previously shown that a number of plant growth promoting rhizobacteria contain an enzyme, 1-aminocyclopropane-1-carboxylate deaminase, that catalyses the cleavage of 1-aminocyclopropane-1-carboxylate, the immediate precursor of ethylene in plants. Moreover, experimental evidence indicated that the activity of this enzyme was the key factor in the ability of plant growth promoting rhizobacteria to stimulate the elongation of plant roots. In the model presented in this manuscript we address the question of how the bacterial enzyme 1-aminocyclopropane-1-carboxylate deaminase, with a low affinity for 1-aminocyclopropane-1-carboxylate, can effectively compete with the plant enzyme 1-aminocyclopropane-1-carboxylate oxidase, which has a high affinity for the same substrate, 1-aminocyclopropane-1-carboxylate, with the result that the plant's endogenous ethylene concentration is reduced. It is argued that the simplest explanation for the observed biological activity of plant growth promoting rhizobacteria relates to the relative amounts of 1-aminocyclopropane-1-carboxylate deaminase and 1-aminocyclopropane-1-carboxylate oxidase in the system under consideration. For plant growth promoting rhizobacteria to be able to lower plant ethylene levels, the 1-aminocyclopropane-1-carboxylate deaminase level should be at least 100- to 1000-fold greater then the 1-aminocyclopropane-1-carboxylate oxidase level. This is likely to be the case, provided that the expression of 1-aminocyclopropane-1-carboxylate oxidase has not been induced.Copyright 1998 Academic Press Limited Copyright 1998 Academic Press Limited

Journal Article↗
PubMed2006

Plant age, communication, and resistance to herbivores: young sagebrush plants are better emitters and receivers.

Plants progress through a series of distinct stages during development, although the role of plant ontogeny in their defenses against herbivores is poorly understood. Recent work indicates that many plants activate systemic induced resistance after herbivore attack, although the relationship between resistance and ontogeny has not been a focus of this work. In addition, for sagebrush and a few other species, individuals near neighbors that experience simulated herbivory become more resistant to subsequent attack. Volatile, airborne cues are required for both systemic induced resistance among branches and for communication among individuals. We conducted experiments in stands of sagebrush of mixed ages to determine effects of plant age on volatile signaling between branches and individuals. Young and old control plants did not differ in levels of chewing damage that they experienced. Systemic induced resistance among branches was only observed for young plants. Young plants showed strong evidence of systemic resistance only if airflow was permitted among branches; plants with only vascular connections showed no systemic resistance. We also found evidence for volatile communication between individuals. For airborne communication, young plants were more effective emitters of cues as well as more responsive receivers of volatile cues.

Animals↗
PubMed2003

Multiple mediators of plant programmed cell death: interplay of conserved cell death mechanisms and plant-specific regulators.

Programmed cell death (PCD) is a process aimed at the removal of redundant, misplaced, or damaged cells and it is essential to the development and maintenance of multicellular organisms. In contrast to the relatively well-described cell death pathway in animals, often referred to as apoptosis, mechanisms and regulation of plant PCD are still ill-defined. Several morphological and biochemical similarities between apoptosis and plant PCD have been described, including DNA laddering, caspase-like proteolytic activity, and cytochrome c release from mitochondria. Reactive oxygen species (ROS) have emerged as important signals in the activation of plant PCD. In addition, several plant hormones may exert their respective effects on plant PCD through the regulation of ROS accumulation. The possible plant PCD regulators discussed in this review are integrated in a model that combines plant-specific regulators with mechanisms functionally conserved between animals and plants.

Apoptosis↗
PubMed2001

Latrunculin B-induced plant dwarfism: Plant cell elongation is F-actin-dependent.

Marine macrolides latrunculins are highly specific toxins which effectively depolymerize actin filaments (generally F-actin) in all eukaryotic cells. We show that latrunculin B is effective on diverse cell types in higher plants and describe the use of this drug in probing F-actin-dependent growth and in plant development-related processes. In contrast to other eukaryotic organisms, cell divisions occurs in plant cells devoid of all actin filaments. However, the alignment of the division planes is often distorted. In addition to cell division, postembryonic development and morphogenesis also continue in the absence of F-actin. These experimental data suggest that F-actin is of little importance in the morphogenesis of higher plants, and that plants can develop more or less normally without F-actin. In contrast, F-actin turns out to be essential for cell elongation. When latrunculin B was added during germination, morphologically normal Arabidopsis and rye seedlings developed but, as a result of the absence of cell elongation, these were stunted, resembling either genetic dwarfs or environmental bonsai plants. In conclusion, F-actin is essential for the plant cell elongation, while this F-actin-dependent cell elongation is not an essential feature of plant-specific developmental programs.

Actins↗
PubMed2006

Ubiquitin fusion enhances cholera toxin B subunit expression in transgenic plants and the plant-expressed protein binds GM1 receptors more efficiently.

Developing plant based systems for the production of therapeutic recombinant proteins requires the development of efficient expression strategies and characterization of proteins made in heterologous cellular environment. In this study, the expression of cholera toxin B subunit (CtxB) was examined in the leaves of transgenic tobacco plants. A synthetic gene encoding CtxB was designed for high level expression in plant cells and cloned as ubiquitin (Ub) fusion in a plant expression vector. Tobacco plants were genetically engineered by nuclear transformation to express the CtxB or Ub-CtxB fusion proteins under the control of CaMV35S duplicated enhancer promoter. Functionally active CtxB accumulated in tobacco leaves at 2.5-fold higher level in the Ub-CtxB plants. In the best expressors, CtxB accumulated at 0.9% of the total soluble leaf protein. In both the constructs, molecular mass of the plant-expressed CtxB was 14.6 kDa in contrast to 11.6 kDa for the authentic CtxB. Schiff's test, retention on concanavalin A column and chemical and enzymatic deglycosylation established that the higher molecular mass was due to glycosylation of the CtxB expressed in plant cells. The glycosylated CtxB made in tobacco leaves had higher affinity of binding to the GM1 receptors.

Artificial Gene Fusion↗
PubMed2003

Distinguishing plant and fungal sequences in ESTs from infected plant tissues.

Expressed sequence tags (ESTs) from fungal-infected plant tissues are composed of a mixture of plant and fungal sequences. Using freely available software and tools, a novel procedure is described for distinguishing plant and fungal DNA sequences. Although the GenBank non-redundant (NR) database is larger and therefore one would presume that BLASTX analysis of it would be more accurate, superior resolution of 700 randomly selected fungal ESTs was found with Standalone TBLASTX analyses with a local matching database composed of a plant and a fungal genome. Standalone TBLASTX analyses of 3,983 ESTs from nine different fungal-infected plant EST libraries also proved to be superior in identifying the origin of sequences as either plant or fungal compared to GenBank BLASTX analysis. Standalone TBLASTX with a matching database comprised of a single plant and a single fungal genome appears to be a faster and more accurate method than BLASTX searches of the GenBank non-redundant database to distinguish fungal and plant sequences in mixed EST collections.

DNA, Fungal↗
PubMed2006

Fate of pentabrominated diphenyl ethers in soil: abiotic sorption, plant uptake, and the impact of interspecific plant interactions.

Polybrominated diphenyl ethers (PBDEs) are potentially harmful and persistent environmental pollutants. Despite evidence that soils are a major sink for PBDEs, little is known regarding their behavior in this medium. An environmentally relevant level of a commercial penta-BDE mixture (75 microg kg(-1)) was added to topsoil, and the extractability of three congeners (BDE-47, -99, and -100) was monitored over 10 weeks in planted and unplanted treatments. The extractability of each congener decreased rapidly in the experimental soil due largely to abiotic sorption to soil particles, which was demonstrated by low PBDE recovery from sterilized and dry soils. Monoculture plantings of zucchini and radish did not affect the recovery of PBDEs from soil. However, PBDE recovery from mixed species plantings was nearly 8 times higher than that of unplanted and monoculture treatments, indicating that interspecific plant interactions may enhance PBDE bioavailablity in soil. Evidence for competitive interactions between the two species was revealed by reduced shoot biomass of zucchini plants in mixed treatments relative to pots containing only zucchini. Both plant species accumulated PBDEs in root and shoot tissue (<5 microg kg(-1) plant tissue). PBDE uptake was higher in zucchini, and translocation of PBDEs to zucchini shoots was congener-specific. Our results suggest that although abiotic sorption may limit the potential for human exposure to PBDEs in soil, plants may increase the exposure risk by taking up and translocating PBDEs into aboveground tissues and by enhancing bioavailability in soil.

Adsorption↗
PubMed1996

Acetyl-CoA carboxylase in higher plants: most plants other than gramineae have both the prokaryotic and the eukaryotic forms of this enzyme.

The presence and the absence of a prokaryote type and a eukaryote type of acetyl-CoA carboxylase (EC 6.4.1.2; ACCase) were examined in members of 28 plant families by two distinct methods: the detection of biotinylated subunits of ACCase with a streptavidin probe, and the detection of the accD gene, which encodes a subunit of the prokaryotic ACCase, by Southern hybridization analysis. The protein extracts of all the plants studied contained a biotinylated polypeptide of 220 kDa, which was probably the eukaryotic ACCase. All the plants but those belonging to Gramineae also contained a biotinylated polypeptide of ca. 35 kDa, which is a putative subunit of the prokaryotic ACCase. In all plants but those in Gramineae, the ca. 35 kDa polypeptide was found in the protein extracts of plastids, while the 220 kDa polypeptide was absent from these plastid extracts. The plastid extracts of the plants in Gramineae contained the 220 kDa polypeptide, as did the homogenates of the leaves. Southern hybridization analysis demonstrated that all the plants but those in the Gramineae contained the accD gene. These findings suggest that most higher plants have the prokaryotic ACCase in the plastids and the eukaryotic ACCase in the cytosol. Only Gramineae plants might contain the eukaryotic ACCases both in the plastids and in the cytosol. The origin of the plastid-located eukaryotic ACCase in Gramineae is discussed as the first possible example of substitution of a plastid gene by a nuclear gene for a non-ribosomal component.

Acetyl-CoA Carboxylase↗
PubMed2004

Endophytic bacterial communities of field-grown potato plants and their plant-growth-promoting and antagonistic abilities.

To study the effect of plant growth on potato-associated bacteria, the composition and properties of bacteria colonizing the endosphere of field-grown potato were analyzed by a multiphasic approach. The occurrence and diversity of potato-associated bacteria were monitored by a cultivation-independent approach, using terminal restriction fragment length polymorphism analysis of 16S rDNA. The patterns obtained revealed a high heterogeneity of community composition and suggested the existence of plant-specific communities. However, endophytic populations correlated to a certain extent with plant growth performance. Endophytes were also isolated from plants that grew well or grew poorly and were identified by partial sequencing of the 16S rRNA genes. A broad phylogenetic spectrum was found among isolates and differently growing plants hosted different bacterial populations. In an approach to investigate the plant-growth-promoting potential of potato-associated bacteria, a total of 35 bacteria were screened by dual testing for in vitro antagonism towards (i) the fungal pathogens Verticillium dahliae, Rhizoctonia solani, Sclerotinia sclerotiorum, and Phytophthora cactorum and (ii) the bacterial pathogens Erwinia carotovora, Streptomyces scabies, and Xanthomonas campestris. The proportion of isolates with antagonistic activity was highest against Streptomyces sp. (43%) followed by those against Xanthomonas sp. (29%). As all plants showed more or less severe disease symptoms of scab disease caused by Streptomyces scabies, we assume that the presence of the pathogen induced the colonization of antagonists. The antifungal activity of the isolates was generally low. The biotechnological potential of endophytic isolates assessed by their antagonistic activity and by in vitro production of enzymes, antibiotics, siderophores, and the plant growth hormone indole-1,3-acetic acid was generally high. Overall, seven endophytes were found to antagonize fungal as well as bacterial pathogens and showed a high production of active compounds and were therefore considered promising biological control agents.

Antibiosis↗
PubMed1996

Unifying plant molecular data and plants.

Located at a botanical department at an Agricultural University, our taxonomical and genetic research is mainly directed towards cultivated plants and their wild relatives. The investigations are usually under a common heading 'experimental taxonomy', and include basic systematics, cytogenetics, biodiversity, population dynamics, conservation and evolutionary questions correlating the wild species and the cultivated forms. Our point of initiation is the plants and questions/problems raised regarding these plants. Our way of approaching the problems is usually by applying different sets of data and testing them. Experimental taxonomy covers classical cytogenetics (chromosome counting and karyotyping) as well as molecular cytogenetic methods (RAPD, RFLP, in situ hybridization), and includes also chemical data on isoenzymes and anthocyanins. We have had good collaborations with other laboratories and found their expertise on the plants in question very helpful. The aim is always to unify various data on the same set of problems, in order to get a more complete understanding of the plants. At present the department is working on several, quite different plant genera, comprising herbs, aquatic plants, and trees. The methods vary, depending on the plants and the problems in question. Some of the current investigations concern the horticultural genera Lilium and Crocus, in which the main point of interest is the study of chromosome evolution using fluorescence in situ hybridization; preliminary investigations into the composition of anthocyanins in Crocus look very promising. In the tropical starch tuber crop Pachyrhizus (Fabaceae), molecular analyses of relationships between existing cultivars, landraces and wild material have been carried out. A genus which we, in cooperation with a number of other laboratories, have been working with for many years is Hordeum (Poaceae) with one cultivated species (barley) and 31 wild species. Here the main areas of investigation have been field studies and collecting, followed by a taxonomical treatment, hybridization experiments, cytogenetic analysis and isoenzyme studies. Within the field of forestry, we have used population genetics as a tool in the management of natural and domesticated populations and for conservation of genetic diversity. We have also ventured into the identification and use of DNA markers that are suited for genome mapping in Picea abies (Norway Spruce).

Cytogenetics↗
PubMed1996

The plant oncogene rolD stimulates flowering in transgenic tobacco plants.

The Agrobacterium rhizogenes T-DNA oncogene rolD under the control of its own 5' regulatory region was transferred to day-neutral tobacco plants. The main trait induced by rolD in transgenic plants is a striking precocity in flower setting and a strong enhancement of the flowering potential. In rolD plants, early flowering is followed by the very rapid growth of numerous lateral inflorescences. The analysis of several morphological and histological parameters suggests that some characteristic morphological abnormalities observed in rolD plants can be accounted for by their early reproductive phase transition and points to the involvement in the transition of a greater portion of the plant body than is the case for untransformed tobacco. The in vitro morphogenic potential of tissues from rolD plants was also tested. Superficial thin cell layer explants from rolD plants show an earlier and much enhanced flower organogenesis, compared to controls, both on flowering and on hormone-free medium.

Cells, Cultured↗
PubMed2003

Preferential induction of 20S proteasome subunits during elicitation of plant defense reactions: towards the characterization of "plant defense proteasomes".

Plants have evolved efficient mechanisms to resist pathogens. The earliest defense response is the hypersensitive response (HR) considered as the main step leading to plant systemic acquired resistance (SAR) that protects the whole plant against a large spectrum of pathogens. We showed previously that elicitation of defense reactions in tobacco cells by cryptogein, a proteinaceous elicitor of plant defense reactions, leads to a rapid and differential accumulation of transcripts corresponding to genes encoding defense-induced (din) subunits of 20S proteasome: beta1din, alpha3din and alpha6din.Here, expression of these three subunits was investigated by Northern blotting and by Western blotting using specific antibodies synthesized against two peptides deduced from the beta1din, alpha3din or alpha6din encoding sequence. Kinetics of mRNA and protein accumulation in various defense models showed a simultaneous accumulation of beta1din, alpha3din and alpha6din corresponding mRNAs and proteins only in plants developing a systemic acquired resistance. Inhibition by diphenyleneiodonium of the oxidative burst induced in defense reactions blocked the expression of beta1din, alpha3din and alpha6din. Using 2D gel electrophoresis and Western blotting, we showed multiple spots for each induced subunit suggesting the possible existence of multigenic families confirmed by genomic DNA analysis. These results suggest a complex regulation of induced subunits tightly correlated with the activation of plant defense reactions. beta1din, alpha3din and alpha6din subunits could probably replace the corresponding constitutive subunits in 20S proteasome leading to "plant defense proteasomes" which could play an important role in plant defense reactions.

Algal Proteins↗
PubMed2002

Transgenic 14-3-3 isoforms in plants: the metabolite profiling of repressed 14-3-3 protein synthesis in transgenic potato plants.

14-3-3 proteins are abundant eukaryotic proteins that interact with many other proteins, thereby modulating their function and thus cell metabolism. The data from mRNA analysis confirm the developmental regulation of 14-3-3 isoform expression in potato plants. In order to test whether or not 14-3-3 protein expression affects plant phenotype and metabolism, transgenic potato plants either overexpressing Cucurbita pepo 14-3-3 or underexpressing endogenous 14-3-3 isoforms were analysed. An increase in tuber number and a decrease in tuber size in the overexpressed transformant was observed; the transgenic plants contain more chlorophyll than the control and they lose it more slowly than the control when transferred to the dark. The 14-3-3-repressed transgenic plants showed a decrease in tuber number and an increase in tuber size; an increase in the fresh weight of the transgenic tubers was also detected. The increased catecholamine level was accompanied by an increased ratio of soluble sugars to starch in overexpressed transformant. The opposite effect was detected in 14-3-3-repressed transgenic plants. All the repressed plants showed significant increases in nitrate reductase (NR) activity, suggesting that the regulation of NR occurs in vivo, and is not isoform-dependent. The increase in NR activity resulted in a significant decrease in nitrate level. The level of sucrose phosphate synthase activity was also significantly increased in all 14-3-3-underexpressed transgenes, and remarkably the increase in enzyme activity was accompanied by respective changes in sucrose levels in the tubers. The most intriguing finding was the significant (2-3-fold) increase in ethylene content in all the 14-3-3-repressed transgenic lines, which probably resulted from a methionine level increase. The substantial increase of ethylene level in the repressed forms might explain the significant shortening of the vegetation period of the analysed transgenic plants.

14-3-3 Proteins↗