Showing papers on "Biotic stress published in 2001"

Signal Interactions in Induced Resistance to Pathogens and Insect Herbivores

Abstract: Plants are often simultaneously challenged by pathogens and insects capable of triggering an array of responses that may be beneficial or detrimental to the plant. The efficacy of resistance mechanisms can be strongly influenced by the mix of signals generated by biotic stress as well as abiotic stress such as drought, nutrient limitation or high soil salinity. An understanding of their biochemical nature, and knowledge of the specificity and compatibility of the signaling systems that regulate the expression of inducible responses could optimize the utilization of these responses in crop protection. Signaling conflicts and synergies occur during a plant's response to pathogens and insect herbivores, and much of the research on defense signaling has focused on salicylate- and jasmonate-mediated responses. We will review our results using tomato (Lycopersicon esculentum) in greenhouse and field studies that illustrate a trade-off between salicylate- and jasmonate-mediated signaling, and discuss research on strategies to minimize the trade-off that can occur following the application of chemical elicitors of resistance. In addition, there is evidence of another signaling system that mediates endogenous levels of ceramide in the plant. This signal is associated with programmed cell death and protection of tomato against the fungal pathogen Alternaria alternata f. sp. lycopersici.

Accumulation of plastid lipid‐associated proteins (fibrillin/CDSP34) upon oxidative stress, ageing and biotic stress in Solanaceae and in response to drought in other species

Abstract: Plastid lipid-associated proteins, also termed fibrillin/CDSP34 proteins, are known to accumulate in fibrillar-type chromoplasts such as those of ripening pepper fruit, and in leaf chloroplasts from Solanaceae plants under abiotic stress conditions. It is shown here that treatments generating active oxygen species (high light combined with low temperature, gamma irradiation or methyl viologen treatment) result in potato CDSP34 gene induction and protein accumulation in leaves. Using transgenic tomato plants containing the pepper fibrillin promoter, a significant increase in promoter activity in leaves subjected to biotic stress, namely bacterial infections, was observed. In WT, a higher level of the endogenous fibrillin/CDSP34 protein is also observed after infection by E. chrysanthemi strain 3739. In addition to stress-related induction, a progressive increase in the fibrillin promoter activity is noticed during ageing in various tomato photosynthetic tissues and this increase correlates with a higher abundance of the endogenous protein in WT leaves. It is proposed that a mechanism related to oxidative events plays an essential role in the regulation of fibrillin/CDSP34 genes during stress and also during development. Using a biolistic transient expression assay, the pepper fibrillin promoter is found to be active in various dicot species, but not in monocots. Further, substantially increased levels of fibrillin/ CDSP34 proteins are shown in various dicotyledonous and monocotyledonous plants in response to water deficit.

Plant Stress Physiology

Abstract: ‘Stress’ in plants can be defined as any external factor that negatively influences plant growth, productivity, reproductive capacity or survival. This includes a wide range of factors which can be broadly divided into two main categories: abiotic or environmental stress factors, and biotic or biological stress factors. Keywords: abiotic; stress; metabolism; signalling; resistance

Biosynthesis of secondary metabolites in sugarcane

Abstract: A set of genes related to secondary metabolism was extracted from the sugarcane expressed sequence tag (SUCEST) database and was used to investigate both the gene expression pattern of key enzymes regulating the main biosynthetic secondary metabolism pathways and the major classes of metabolites involved in the response of sugarcane to environmental and developmental cues. The SUCEST database was constructed with tissues in different physiological conditions which had been collected under varied situation of environmental stress. This database allows researchers to identify and characterize the expressed genes of a wide range of putative enzymes able to catalyze steps in the phenylpropanoid, isoprenoid and other pathways of the special metabolic mechanisms involved in the response of sugarcane to environmental changes. Our results show that sugarcane cDNAs encoded putative ultra-violet induced sesquiterpene cyclases (SC); chalcone synthase (CHS), the first enzyme in the pathway branch for flavonoid biosynthesis; isoflavone synthase (IFS), involved in plant defense and root nodulation; isoflavone reductase (IFR), a key enzyme in phenylpropanoid phytoalexin biosynthesis; and caffeic acid-O-methyltransferase, a key enzyme in the biosynthesis of lignin cell wall precursors. High levels of CHS transcripts from plantlets infected with Herbaspirillum rubri or Gluconacetobacter diazotroficans suggests that agents of biotic stress can elicit flavonoid biosynthesis in sugarcane. From this data we have predicted the profile of isoprenoid and phenylpropanoid metabolism in sugarcane and pointed the branches of secondary metabolism activated during tissue-specific stages of development and the adaptive response of sugarcane to agents of biotic and abiotic stress, although our assignment of enzyme function should be confirmed by careful biochemical and genetic supporting evidence.

Environmental and Developmental Regulation of the Wound-Induced Cell Wall Protein WI12 in the Halophyte Ice Plant

Abstract: A wounded gene WI12 was used as a marker to examine the interaction between biotic stress (wounding) and abiotic stress (high salt) in the facultative halophyte ice plant (Mesembryanthemum crystallinum). The deduced WI12 amino acid sequence has 68% similarity to WUN1, a known potato (Solanum tuberosum) wound-induced protein. Wounding, methyl jasmonate, and pathogen infection induced local WI12 expression. Upon wounding, the expression of WI12 reached a maximum level after 3 h in 4-week-old juvenile leaves, whereas the maximum expression was after 24 h in 8-week-old adult leaves. The temporal expression of WI12 in salt-stressed juvenile leaves was similar to that of adult leaves. The result suggests that a salt-induced switch from C3 to Crassulacean acid metabolism has a great influence on the ice plant's response to wounding. The expression of WI12 and the accumulation of WI12 protein were constitutively found in phloem and in wounded mesophyll cells. At the reproductive stage, WI12 was constitutively found in petals and styles, and developmentally regulated in the placenta and developing seeds. The histochemical analysis showed that the appearance of WI12 is controlled by both environmental and developmental factors. Immunogold labeling showed WI12 preferentially accumulates in the cell wall, suggesting its role in the reinforcement of cell wall composition after wounding and during plant development.

Adaptations to biotic and abiotic stress: Macaranga-ant plants optimize investment in biotic defence

Abstract: Obligate ant plants (myrmecophytes) in the genus Macaranga produce energy- and nutrient-rich food bodies (FBs) to nourish mutualistic ants which live inside the plants. These defend their host against biotic stress caused by herbivores and pathogens. Facultative, 'myrmecophilic' interactions are based on the provision of FBs and/or extrafloral nectar (EFN) to defending insects that are attracted from the vicinity. FB production by the myrmecophyte, M. triloba, was limited by soil nutrient content under field conditions and was regulated according to the presence or absence of an ant colony. However, increased FB production promoted growth of the ant colonies living in the plants. Ant colony size is an important defensive trait and is negatively correlated to a plant's leaf damage. Similar regulatory patterns occurred in the EFN production of the myrmecophilic M. tanarius. Nectar accumulation resulting from the absence of consumers strongly decreased nectar flow, which increased again when consumers had access to the plant. EFN flow could be induced via the octadecanoid pathway. Leaf damage increased levels of endogenous jasmonic acid (JA), and both leaf damage and exogenous JA application increased EFN flow. Higher numbers of nectary visiting insects and lower numbers of herbivores were present on JA-treated plants. In the long run, this decreased leaf damage significantly. Ant food production is controlled by different regulatory mechanisms which ensure that costs are only incurred when counterbalanced by defensive effects of mutualistic insects.

Severity of root rot on tomato plants caused by Phytophthora nicotianae under nutrient- and light-stress conditions

Abstract: Abiotic stress induced by three concentrations of nutrients in solution, and biotic stress caused by three inoculum densities of Phytophthora nicotianae, were imposed on tomato plants grown hydroponically under natural light in the glasshouse. The pathogen causes stem and root rot, thereby inducing water deficiency symptoms. The progress of the disease, as measured serologically by DAC–ELISA, was markedly accelerated by enhanced concentrations of nutrients. Significant differences in proline content of infected and noninfected plants were observed at a nutrient concentration equivalent to 5·0 dS m−1. Higher nutrient concentrations increased further proline concentration in leaves. Inoculation of tomatoes under two light regimes in a phytotron produced significantly more affected roots with increasing inoculum density, but disease was not affected by different light treatments. However, higher light intensity accelerated the appearance of symptoms and produced higher proline contents in tomato leaves. It is suggested that the proline content of tomato leaves is a suitable marker for stress induced by both abiotic and biotic factors.

Calcium as a Messenger in Stress Signal Transduction

Abstract: Plant growth in the natural environment is often adversely affected by a number of factors. These include environmental factors such as low temperature, heat, drought, wind, ultraviolet light, anoxia, and high salinity and biological factors such as pathogens (bacteria, viruses, and fungi). Abiotic and biotic factors that limit growth and development of plants and eventually productivity are considered stress factors. Crop losses due to these various abiotic and biotic stresses are in the billions of dollars annually. It has been estimated that stress factors (abiotic and biotic) depress the yield of agronomically important crops in the United States by 78%, of which about 70% is due to unfavorable environmental conditions [1,2]. Plants possess built-in mechanisms to cope with the abiotic and biotic stress factors. Plant scientists have been studying the effects of various stresses on plants to better elucidate the mechanisms by which plants respond to stress signals. It is hoped that knowledge derived from the increased understanding of plant responses to biotic and abiotic stresses would eventually help in developing new plant varieties that are resistant to these stress factors. Advances in molecular and cellular biology are offering a variety of new approaches to investigate plant responses to stresses.

Flow Cytometry: Cell Cycle

Abstract: Quantitative analyses of cell cycle can give essential information about the response of plants to short- or long-term abiotic or biotic stress, as most species alter leaf expansion or root growth as one of the first responses to cope with adverse environmental conditions (Boyer 1982). Tardieu and Granier (2000) observed a reduction of leaf area under water and light deficits due to partial blockage of nuclei in G1, which increased cell cycle duration and decreased final cell number. This effect can be detected shortly after the application of the stress and, sometimes, does not alter the photosynthetic rate, as is independent of carbon metabolism.

Experimentation in biology of plant abiotic stress responses

Abstract: During the course of growth under natural field conditions, crop plants are exposed to a number of different abiotic stresses (such as water stress, temperature stress, salt stress, flooding stress, chemical stress and oxidative stress). These stresses exert adverse effects on metabolism, growth and yield of the crops. The intensity of the abiotic stresses is on the rise, implying that various possible solutions for mitigating the damage caused by such stresses must be combined for future increase in crop production. At the level of plant genetics, there are indications that it may be possible to improve plants against such stress factors. However, the practical success in this regard depends on how well we understand the biochemistry. physiology and molecular biology of the plant abiotic stress responses. The cellular response of plants to abiotic stresses is of complex nature involving simultaneous interplay of several mechanisms. Although there is a great deal of progress in cataloguing the biochemical reactions that are associated with plant abiotic stress responses, precise understanding of the defense reactions leading to acquisition of stress tolerance remains a challenge. A number of different experimental systems including lower and higher plants as well as microbes have been analyzed for examining the plant abiotic stress responses. The molecular analysis of the stress response has been carried out at the level of stress proteins, stress genes, stress promoters, trans-acting factors that bind to stress promoters and signal transduction components involved in mediation of stress responses. The functional relevance of the stress - associated genes is being tested in different trans-systems including yeast as well as higher plant species. In this article, we discuss selective features of experimentation in biology of plant abiotic stress responses.

Method for generating or increasing resistance to biotic or abiotic stress factors in organisms

Abstract: The invention relates to a method for generating or increasing resistance to biotic and abiotic stress in organisms, especially plants. The method is based on a modification of the distribution of ATP and/or ADP in the cells of organisms. This modification can be carried out using various methods.

Molecular Breeding for Improved Biotic Stress Resistance

Abstract: Molecular breeding of wheat in the sense of genetic engineering will be the subject of this paper It will review actual strategies for engineering fungal resistance in crops An efficient method for genetic transformation of wheat like the biolistic method using immature embryos as target tissue — together with genes that directly or indirectly inhibit the pathogen’s spread — form the basis for the development of transgenic wheat plants with improved fungal resistance

Inheritance of shoot and root characters and molecular markers in chickpea (Cicer arietinum L.)

Abstract: Chickpea, the third most important pulse crop, includes forty-three species, eight of which are annuals. It is used as a complement to cereal food and as snack food and sweets. Major loss in yield of chickpea is due to biotic stress (Ascochyta blight and fusarium wilt), abiotic stress (moisture stress, heat, cold) and also due to poor nutritional status of the soil and use of marginal lands. Early harvesting of chickpea as a result of reduced crop duration helps in avoiding most of the biotic and abiotic stresses which usually occur at flowering and podding time. Early developed prolific root system under water-limited environments is needed in chickpea. As molecular markers helped accelerating plant breeding in many crops. construction of intraspecitic linkage map is very important in chickpea. Hence, the present investigation was carried out with the following objectives to...