Showing papers on "Biotic stress published in 2000"

Dual action of the active oxygen species during plant stress responses.

Abstract: Adaptation to environmental changes is crucial for plant growth and survival. However, the molecular and biochemical mechanisms of adaptation are still poorly understood and the signaling pathways involved remain elusive. Active oxygen species (AOS) have been proposed as a central component of plant adaptation to both biotic and abiotic stresses. Under such conditions, AOS may play two very different roles: exacerbating damage or signaling the activation of defense responses. Such a dual function was first described in pathogenesis but has also recently been demonstrated during several abiotic stress responses. To allow for these different roles, cellular levels of AOS must be tightly controlled. The numerous AOS sources and a complex system of oxidant scavengers provide the flexibility necessary for these functions. This review discusses the dual action of AOS during plant stress responses.

Adaptations of endophyte-infected cool-season grasses to environmental stresses : Mechanisms of drought and mineral stress tolerance

Abstract: Cool-season grasses infected with Neotyphodium spp. endophytes have an extraordinary impact on the ecology and economy of pasture and turf. A range of adaptations of endophyte-infected grasses to biotic and abiotic stresses has been identified but mechanisms of these adaptations are not clearly understood. In this review, we present recent research progress on endophyte-related mechanisms affecting abiotic (drought, mineral) and selected aspects of biotic stress tolerance in cool-season grasses. Endophytes induce mechanisms of drought avoidance (morphological adaptations), drought tolerance (physiological and biochemical adaptations), and drought recovery in infected grasses. Mineral nutrition (nitrogen, phosphorus, calcium) affects production of ergot alkaloids, thus understanding mechanisms involved in mineral economy of endophyte-infected grasses will help in developing management practices to reduce forage toxicity to livestock. Previous research resolved the role of endophyte in nitrogen (N) economy of tall fescue. We identified two endophyte-related mechanisms in tall fescue operating in response to phosphorus (P) deficiency. The mechanisms are altered root morphology (reduced root diameters and longer root hairs) and chemical modification of the rhizosphere resulting from exudation of phenolic-like compounds. These mechanisms were shown to benefit endophyte-infected plants grown under P deficiency. We also report a mechanism of aluminum (Al) sequestration on root surfaces in endophyte-infected tall fescue, which appears to be related to exudation of phenolic-like compounds with Al-chelating activity. Understanding mechanisms of abiotic stress tolerance in endophyte-infected grasses is essential for continued improvement and persistence of grasses for a range of applications, e.g., forage for semi-arid areas or cover plants for soil renovation.

The physiology of plants under stress : soil and biotic factors

Abstract: SOIL PROCESSES AND PLANT STRESS PHYSIOLOGY. Introduction and General Concepts. Soil/Plant Relationships. Nutrient Deficiency Stress and Plant Growth and Development. Mycorrhizae, special contribution by Shawn Semones. Salinity Stress. BIOTIC FACTORS AND PLANT STRESS PHYSIOLOGY. Influence of Plant Pathogens on Host Physiology. Herbivory and Plant Stress. Allelochemistry as a Plant Stress, special contribution by Thomas Ting Lei. Weeds and Other Competitors, special contribution by Cynthia Lipp. Parasitic Vascular Plants. ANTHROPOGENIC-INDUCED STRESSES. Soil Pollutants: Heavy Metals and Pesticides. Atmospheric Pollution: SO-2, O-3, NO-x, and "Greenhouse Gases". CONCLUSION. Generalities, Trends, and Future Directions. Appendices. Index. About the Authors.

The involvement of hydrogen peroxide in plant responses to stresses

Abstract: The role of reactive oxygen species, especially H2O2, in plant response to stresses has been the focus of much attention. Hydrogen peroxide has been postulated to play multiple functions in plant defence against pathogens. (1) H2O2 may possess direct microbicidal activity at the sites of pathogen invasion. (2) It is used for cell-wall reinforcing processes: lignification and oxidative cross-linking of hydroxyproline-rich proteins and other cell-wall polymers. (3) It was found to be necessary for phytoalexin synthesis. (4) H2O2 may trigger programmed plant cell death during the hypersensitive response that restricts the spread of infection. (5) H2O2 has been suggested to act as a signal in the induction of systemic acquired resistance and (6) it induces defence genes. Recently H2O2 has been proposed to be involved in the signal transduction pathways leading to acclimation and protection from abiotic stresses. The present review discusses new insights into the function of H2O2 in plant responses to biotic and abiotic stresses.

Genetic engineering for abiotic stress resistance in crop plants.

Abstract: Drought, extreme temperatures and high salinity are major limiting factors for plant growth and crop productivity In their quest to feed the ever-increasing world population, agricultural scientists have to contend with these adverse environmental factors If crops can be redesigned to better cope with abiotic stress, agricultural production can be increased dramatically Recent advances in understanding crop abiotic stress resistance mechanisms and the advent of molecular genetic technology allow us to address these issues much more efficiently than in the past This paper reviews the most significant achievements of the genetic engineering approach to improving plant abiotic stress resistance and discusses future prospects in transgenic research Improved resistance to drought, salinity and extreme temperatures has been observed in transgenic plants that express/overexpress genes regulating osmolytes, specific proteins, antioxidants, ion homeostasis, transcription factors and membrane composition Although the results are not always consistent, these studies collectively foretell a scenario where biotechnology will arm our future crops with new tactics to survive in hostile environments Further experiments are needed to determine if the achieved increases in stress tolerance are applicable to agriculture

Molecular markers for ozone stress isolated by suppression subtractive hybridization: specificity of gene expression and identification of a novel stress-regulated gene

Abstract: Suppression subtractive hybridization was used to identify genes regulated by ozone (100 nmol mol -1 ) in Pisum sativum One novel gene (named PsUod1) was found In addition, mRNA levels for four genes (encoding lipid transfer protein, pre-hevein-like protein, leucine-rich repeat protein, and disease-resistance response protein 230), which previously were shown to be regulated by biotic stress, increased Finally, mRNA species for two genes (encoding extensin and pathogenesis-related protein 4A), previously shown to be regulated by ozone in other species, were found to increase in abundance The ozone-specificity of the expression of these genes was studied by using UV-B radiation PsUod1 and the genes encoding extensin, leucine-rich repeat protein, and disease-resistance response protein 230, were differentially regulated when comparing ozone and UV-B Moreover, the mRNA levels for extensin, leucine-rich repeat protein and disease-resistance response protein 230 all increased under NaCl and aluminium stress and after wounding, whereas the message abundance for PsUodl was unchanged under these stresses Thus, in general, ozone caused changes similar to wounding, salt stress and aluminium stress, whereas UV-B radiation regulated gene expression differently

Responses of some crops to various abiotic stress factors and its physiological and biochemical basis of resistances: a review.

Abstract: The present paper reviews the physiological, biophysical and biochemical mechanisms developed by various crops against various abiotic stress factors such as salinity, high temperatures and drought. Special emphasis is givpen to Phaseolus bean. These abiotic stress factors greatly affect the growth and development and physiological functions of the crops. They affect different phenological stages starting from the seedling to the maturity of the crops thereby redUcing yields. Crop cultivars differ in their responses to these stress factors. In general, growth rate and photosynthesis are reduced. The cultivars offer different mechanisms for resistance to these stress factors: phenological manipulation, morphological and ultrstructural characteristics, the accumulation of biochemical components for osmotic adjustment, minor leakage of osmolites may be mentioned. The resistant lines show less disorganisation of thylakoids, more accumulation of starch grains, mitochondria and lipids acting as high energetic materials. Accumulation of HCN, proline, abscisic acids, soluble sugars, total proteins and the de novo synthesis of specific proteins are some mechanisms that resistant plants have to adapt to abiotic stress factors. A concrete knowledge of these mechanisms of resistance will help the breeders and biotechnologists to manipulate their techniques for the genetic improvement of crops for resistance to various stress factors.

Biotic stress limiting durum wheat production in Morocco - Hessian fly and the Russian wheat aphid: surveys, loss assessment, and identification of sources of resistance

Abstract: Article available on line / Article disponible en ligne à l’adresse : -------------------------------------------------------------------------------------------------------------------------------------------------------------------------http://om.ciheam.org/article.php?IDPDF=600061 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Dynamics of Defoliation, Biotic and Abiotic Damage During 1986–1998

Abstract: The estimation of tree defoliation, widely used to depict forest condition, has, despite its practicality, several disadvantages. Needle or leaf biomass in the crown is strongly affected by tree age, climatic and genetic factors, shading and a variety of abiotic or biotic stresses. Very little empirical information is available about the natural variation in leaf biomass (Westman and Lesinski 1986, McKay 1988). The reasons for an increase in defoliation must therefore be elucidated separately, e.g. with the help of statistical analysis. According to the ICP Forests recommendations, abiotic and biotic damage (especially that caused by snow, wind, ice, game, defoliating insects, needle cast and decay fungi) should be recorded in the forest health surveys (Manual on... 1994). In the reports from some countries, a rapid deterioration in forest vitality has been attributed to abiotic or biotic damage (Strelezki 1985, Roloff 1985, Hutte 1986, Innes et al. 1986, Keane et al. 1989, Innes and Schwyzer 1994). It has even been suggested that, apart from some special years when the growing conditions have been extremely poor, the results of forest health surveys merely reflect the effects of abiotic and biotic damage (Kandier 1989).