Showing papers in "Critical Reviews in Plant Sciences in 1998"
TL;DR: Four major lectin families, namely, the legume lectins, the chitin-binding lectins composed of hevein domains, the type 2 ribosome-inactivating proteins, and the monocot mannose- binding lectins comprise the majority of all currently known plant lectins.
Abstract: Many plants contain carbohydrate-binding proteins that are commonly designated as lectins, agglutinins, or hemagglutinins. Due to the obvious differences in molecular structure, biochemical properties, and carbohydrate-binding specificity, plant lectins are usually considered a complex and heterogeneous group of proteins. Recent advances in the structural analysis of lectins and molecular cloning of lectin genes enable subdividision of plant lectins in a limited number of subgroups of structurally and evolutionary related proteins. Four major lectin families, namely, the legume lectins, the chitin-binding lectins composed of hevein domains, the type 2 ribosome-inactivating proteins, and the monocot mannose-binding lectins comprise the majority of all currently known plant lectins. In addition to these four large families the jacalin-related lectins, the amaranthin family, and the Cucurbitaceae phloem lectins are now recognized as separate subgroups. Each of the above-mentioned lectin families is discussed...
640 citations
TL;DR: On-site effects of erosion on agronomic productivity are assessed with a wide range of methods, which can be broadly grouped into three categories: agronomics/soil quality evaluation, economic assessment, and knowledge surveys.
Abstract: Soil erosion is a global issue because of its severe adverse economic and environmental impacts. Economic impacts on productivity may be due to direct effects on crops/plants on-site and off-site, and environmental consequences are primarily off-site due either to pollution of natural waters or adverse effects on air quality due to dust and emissions of radiatively active gases. Off-site economic effects of erosion are related to the damage to civil structure, siltation of water ways and reservoirs, and additional costs involved in water treatment. There are numerous reports regarding the on-site effects of erosion on productivity. However, a vast majority of these are from the U.S., Canada, Australia, and Europe, and only a few from soils of the tropics and subtropics. On-site effects of erosion on agronomic productivity are assessed with a wide range of methods, which can be broadly grouped into three categories: agronomic/soil quality evaluation, economic assessment, and knowledge surveys. Agronomic me...
597 citations
TL;DR: Agriculturally important grasses such as sugar cane (Saccharum sp.), rice (Oryza sativa), wheat (Triticum aestivum) sorghum (Sorghum bicolor), maize (Zea mays), Panicum maximum, Brachiaria spp.
Abstract: Agriculturally important grasses such as sugar cane (Saccharum sp.), rice (Oryza sativa), wheat (Triticum aestivum) sorghum (Sorghum bicolor), maize (Zea mays), Panicum maximum, Brachiaria spp., and Pennisetum purpureum contain numerous diazotrophic bacteria, such as, Acetobacter diazotrophicus, Herbaspirillum spp., Azospirillum spp. These bacteria do not usually cause disease symptoms in the plants with which they are associated and the more numerous of them, for example, Herbaspirillum spp. and A. diazotrophicus, are obligate or facultative endo-phytes that do not survive well (or at all) in native soil; these are thought to be spread from plant generation to plant generation via seeds, vegetative propagation, dead plant material, and possibly by insect sap feeders. By contrast, Azospirillum spp. are not wholly endophytic but are root-associated, soil-dwelling bacteria that are also often found within plants, probably entering host plants via seeds or via wounds/cracks at lateral root junctions. Endophy...
425 citations
TL;DR: Progress in the knowledge of the lignin biosynthesis pathway has been obtained and it is now clear that the pathway is more complex than initially thought and there is evidence for alternative pathways.
Abstract: Lignin, a complex heteropolymer of cinnamyl alcohols, is, second to cellulose, the most abundant biopolymer on Earth. Lignification has played a determining role in the adaptation of plants to terrestrial life. As all extracellular polymers, lignin confers rheological properties to plant tissues and participates probably in many other functions in cell and tissue physiology or in cell-to-cell communication. Economically, lignin is very important because it determines wood quality and it affects the pulp and paper-making processes as well as the digestibility of forage crops. For all these reasons the lignin biosynthesis pathway has been the subject of many studies. At present, most genes encoding the enzymes involved in the biosynthesis of lignin have been cloned and characterized. Various recent studies report on the alteration of the expression of these genes by genetic engineering, yielding plants with modified lignin. In addition, several mutants have been analyzed with changes in lignin content or lignin composition resulting in altered properties. Thanks to these studies, progress in the knowledge of the lignin biosynthesis pathway has been obtained. It is now clear that the pathway is more complex than initially thought and there is evidence for alternative pathways. A fine manipulation of the lignin content and/or composition in plants is now achievable and could have important economical and environmental benefits.
390 citations
TL;DR: This review summarizes current methods to identify endophytes and to characterize the colonization of plants by endophytic bacteria and discusses how to study their functions and metabolism in association with plants.
Abstract: Nitrogen-fixing bacteria colonize the roots of many gramineous plants from different geographic regions. The discovery that diazotrophs can be isolated from surface-sterilized roots or other plant material led to studies of their potential to inhabit plant tissue. For some diazotrophs, their endophytic character has been documented. This review summarizes current methods to identify endophytes and to characterize the colonization of plants by endophytic bacteria. Taxonomy, occurrence, diversity, and mechanisms of plant infection of Azoarcus spp. is discussed in relation to Herbaspirillum spp. and Acetobacter diazotrophicus. Perspectives how to study their functions and metabolism in association with plants are discussed.
171 citations
TL;DR: Polyamines are small, positively charged aliphatic amines that play a variety of roles in plant physiology and are collectively meant by the term polyamines.
Abstract: Polyamines are small, positively charged aliphatic amines that play a variety of roles in plant physiology. Putrescine, spermidine, and spermine are usually what are collectively meant by the term ...
125 citations
TL;DR: It is now realized that protein phosphorylation/dephosphorylation has a very important role in signal transduction and also in regulating metabolic activities.
Abstract: Plants respond very efficiently to changes in the external environment and accordingly regulate their growth and development. They also have the ability to sense stress conditions and pathogen presence and subsequently activate stress or defense-related functions. Lately, progress has been made in identification of cis- and trans-acting factors that mediate gene expression induced by variable external factors. However, in most of the cases our understanding is limited in relation to the molecular signal transduction events that couple perception of the signal and changes in the gene expression. It is now realized that protein phosphorylation/dephosphorylation has a very important role in signal transduction and also in regulating metabolic activities. During the last decade, a large number of serine/threonine protein kinases have been isolated from plants. Some of these belong to the same category as reported in animal systems, like MAP kinases, receptor kinases, cell division controlling kinases, whereas...
83 citations
TL;DR: This article summarizes the latest development in the isolation and characterization of nodule-specific and -enhanced transcripts isolated from actinorhiza and shows that gene products are involved in nitrogen, carbon, and oxygen metabolism.
Abstract: Infection of actinorhizal plants roots by the actinomycete Fmnkia leads to the formation of a nitrogen-fixing root nodule (actinorhiza) consisting of multiple lobes, each of which is a modified lateral root. Actinorhiza development involves several specific steps, for example, root hair infection, prenodule formation, and initiation of lobe primordia from root pericycle. This article summarizes the latest development in the isolation and characterization of nodule-specific and -enhanced transcripts isolated from actinorhiza. The amino acid sequence derived from the nucleotide sequence of the cDNAs, in combination with localization data, showed that gene products are involved in nitrogen, carbon, and oxygen metabolism. Furthermore, some transcripts represented encoded gene products that might be part of infection and senescence mechanisms in actinorhiza. The article also reviews experiments designed to establish genetic transformation systems for actinorhizal plants. This research has led to the obtain-men...
63 citations
TL;DR: Light plays a crucial role throughout the life cycle of higher plants modulating various aspects of their growth and development, such as seed germination, leaf differentiation, flowering, and sene...
Abstract: Light plays a crucial role throughout the life cycle of higher plants modulating various aspects of their growth and development, such as seed germination, leaf differentiation, flowering, and sene...
51 citations
TL;DR: It was shown that in continuous cropping of rye, despite the decrease of crop yields, no significant difference was observed in annual primary production rates compared with estimates found for rye fields cultivated in diversified crop rotation patterns.
Abstract: Long-term studies on the ecological effects of continuous rye cultivations carried out in Poland are summarized. It was shown that in continuous cropping of rye, despite the decrease of crop yields...
31 citations
TL;DR: The interaction among data, model structure, parameter sets, and predictive uncertainty will lead to important progress in the development of dynamic biosphere models.
Abstract: There is a widespread perception that the atmosphere and the climate are beginning to change, and that these changes could have profound impacts on the primary productivity of the terrestrial biosphere. The terrestrial biosphere is a dynamic system that interacts with the atmosphere and climate principally through the exchanges of energy, water, and elements. Due to the limitations of equilibrium terrestrial biosphere models, new generation models-dynamic biosphere models, are critically needed for assessing and predicting the primary production and biogeochemical cycles of the terrestrial biosphere in changing global environment. The goal of dynamic biosphere modeling is to model terrestrial ecosystem dynamics induced by natural and anthropogenic disturbances, as well as the interactions of energy, water, and carbon cycles within the terrestrial biosphere and between the terrestrial biosphere and the atmosphere. The critical gaps in developing such a terrestrial biosphere model are not our inability to construct model code but instead the poorly developed links between empiricism and the concepts we used to construct our models, especially a lack of data that would help to make our models mechanistic, an incomplete fundamental knowledge about how complex terrestrial ecosystems work, a poor understanding of how to scale up what we do know and of how to validate such a model. The interaction among data, model structure, parameter sets, and predictive uncertainty will lead to important progress in the development of dynamic biosphere models.
TL;DR: Evidence is given that infecting bacteria follow a ‘crack entry’ invasion at sites where developing tumors have emerged through the root cortex and epidermis and establish with high cell numbers inside intercellular spaces of cortical and meristematic spaces.
Abstract: Gramineous crops such as wheat (triticum oestivum), maize (zea mays), and rice (oryza sativa) develop tumorous structures (para-nodules) along primary and secondary roots when treated with low concentrations of various auxins. Rice forms additional tumors along its hypocotyle. Histologically, auxin-induced tumors appear as cancerous grown out root meristems and thus are comparable in origin and structure to stem nodules of the legume sesbania rostrata. Auxin-affected root meristems do not recover and develop further to large nodule-like organs. Introduced diazotrophs (Azospirillum spp., Azorhizobium caulinodans, Rhizobium spp.) potentially inhabit tissues of both stem and root tumors with the central meristem as a major colonization niche. Evidence is given that infecting bacteria follow a ‘crack entry’ invasion at sites where developing tumors have emerged through the root cortex and epidermis. Bacteria are shown to establish with high cell numbers inside intercellular spaces of cortical and meristematic...
TL;DR: This article deals with the hypothesis, first put forward in the late 1980s, that rhodopsin-like proteins are responsible for photo-detection and that the paraxial rod is involved in the control of flagellar movements.
Abstract: For over 100 years, a major focus of photobiological studies has been the unicellular flagellate, Euglena gracilis, an organism well suited for such investigations by its special complement of organelles that may be considered an ancient, yet complete “visual” system. The possible photoreceptive roles of the cytoplasmic stigma and the photoreceptor (paraflagellar swelling) of E. gracilis are still under debate, because of conflicting interpretations of the results produced so far by the different research groups working on this microorganism. This article deals with our hypothesis, first put forward in the late 1980s, that rhodopsin-like proteins are responsible for photo-detection and that the paraxial rod is involved in the control of flagellar movements. This hypothesis uses oriented dipole and electroconformational coupling mechanisms as the physical phenomena that produce signal transduction. A model for phototaxis is presented.