Plant growth in elevated CO2 alters mitochondrial number and chloroplast fine structure.
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With increasing interest in the effects of elevated atmospheric CO(2) on plant growth and the global carbon balance, there is a need for greater understanding of how plants respond to variations in atmospheric partial pressure of CO(2). Our research shows that elevated CO(2) produces significant fine structural changes in major cellular organelles that appear to be an important component of the metabolic responses of plants to this global change. Nine species (representing seven plant families) in several experimental facilities with different CO(2)-dosing technologies were examined. Growth in elevated CO(2) increased numbers of mitochondria per unit cell area by 1.3-2.4 times the number in control plants grown in lower CO(2) and produced a statistically significant increase in the amount of chloroplast stroma (nonappressed) thylakoid membranes compared with those in lower CO(2) treatments. There was no observable change in size of the mitochondria. However, in contrast to the CO(2) effect on mitochondrial number, elevated CO(2) promoted a decrease in the rate of mass-based dark respiration. These changes may reflect a major shift in plant metabolism and energy balance that may help to explain enhanced plant productivity in response to elevated atmospheric CO(2) concentrations. (+info)
Gene silencing: fleshing out the bones.
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Genetic studies are revealing the pathway for RNA-mediated gene silencing. Short RNA molecules are the key, giving sequence specificity for RNA degradation and mediating communication within and between cells; these short RNAs are common to transcriptional and post-transcriptional silencing pathways. (+info)
Prediction of colonization by macrophytes in the Yacireta reservoir of the Parana River (Argentina and Paraguay).
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The potential colonization by anchored plants (PCAP) and the potential areas for initial colonization of free floating plants were estimated during the early filling phase for the Yacireta reservoir. In order to obtain the PCAP, the observed maximum depth of colonization of the anchored macrophytes before impoundment and the hypsographic curves were used. The species inhabiting the pre-impoundment area were classified according to the different bioforms before the inclussion in the analysis. The areal extent of PCAP (from depths between 0-4 m) could reach 275 km2 at 76 m above sea level (current water level), whereas at 82 m above sea level (final filling level) the littoral zone will be increased by about 21.5%. The potential area for geophytes was estimated to be 99 km2; 131 km2 for root-floating leaved plants and 120 km2 for submerged plants, at 76 m above sea level. At 82 m above sea level, the geophytes could reach 271 km2. The data for wind frequency, velocity and fetch, together with depth were used to calculate shallow and sheltered areas in which free floating plants could find favourable conditions to initial colonization. Physical and chemical features recorded at eight stations during the early filling phase are discussed in relation to potential plant development. (+info)
Advances in phytoremediation.
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Phytoremediation is the use of plants to remedy contaminated soils, sediments, and/or groundwater. Sorption and uptake are governed by physicochemical properties of the compounds, and moderately hydrophobic chemicals (logarithm octanol--water coefficients = 1.0--3.5) are most likely to be bioavailable to rooted, vascular plants. Some hydrophilic compounds, such as methyl-tert-butylether and 1,4-dioxane, may also be taken up by plants via hydrogen bonding with transpiration water. Organic chemicals that pass through membranes and are translocated to stem and leaf tissues may be converted (e.g., oxidized by cytochrome P450s), conjugated by glutathione or amino acids, and compartmentalized in plant tissues as bound residue. The relationship between metabolism of organic xenobiotics and toxicity to plant tissues is not well understood. A series of chlorinated ethenes is more toxic to hybrid poplar trees (Populus deltoides x nigra, DN-34) than are the corresponding chlorinated ethanes. Toxicity correlates best with the number of chlorine atoms in each homologous series. Transgenic plants have been engineered to rapidly detoxify and transform such xenobiotic chemicals. These could be used in phytoremediation applications if issues of cost and public acceptability are overcome. (+info)
Centrin is necessary for the formation of the motile apparatus in spermatids of Marsilea.
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During spermiogenesis in the water fern, Marsilea vestita, basal bodies are synthesized de novo in cells that lack preexisting centrioles, in a particle known as a blepharoplast. We have focused on basal body assembly in this organism, asking what components are required for blepharoplast formation. Spermiogenesis is a rapid process that is activated by placing dry microspores into water. Dry microspores contain large quantities of stored protein and stored mRNA, and inhibitors reveal that certain proteins are translated from stored transcripts at specific times during development. Centrin translation accompanies blepharoplast appearance, while beta-tubulin translation occurs later, during axonemal formation. In asking whether centrin is an essential component of the blepharoplast, we used antisense, sense, and double-stranded RNA probes made from the Marsilea centrin cDNA, MvCen1, to block centrin translation. We employed a novel method to introduce these RNAs directly into the cells. Antisense and sense both arrest spermiogenesis when blepharoplasts should appear, and dsRNA made from the same cDNA is an effective inhibitor at concentrations at least 10 times lower than either of the single-stranded RNA used in these experiments. Blepharoplasts are undetectable and basal bodies fail to form. Antisense, sense, and dsRNA probes made from Marsilea beta-tubulin permitted normal development until axonemes form. In controls, antisense, sense, and dsRNA, made from a segment of HIV, had no effect on spermiogenesis. Immunoblots suggest that translational blocks induced by centrin-based RNA are gene specific and concentration dependent, since neither beta-tubulin- nor HIV-derived RNAs affects centrin translation. The disruption of centrin translation affects microtubule distributions in spermatids, since centrin appears to control formation of the cytoskeleton and motile apparatus. These results show that centrin plays an essential role in the formation of a motile apparatus during spermiogenesis of M. vestita. (+info)
Oil-bodies as substrates for lipolytic enzymes.
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Plant seeds store triacylglycerols (TAGs) in intracellular organelles called oil-bodies or oleosomes, which consist of oil droplets covered by a coat of phospholipids and proteins. During seed germination, the TAGs of oil-bodies hydrolysed by lipases sustain the growth of the seedlings. The mechanism whereby lipases gain access to their substrate in these organelles is largely unknown. One of the questions that arises is whether the protein/phospholipid coat of oil-bodies prevents the access of lipase to the oil core. We have investigated the susceptibility of almond oil-bodies to in vitro lipolysis by various purified lipases with a broad range of biochemical properties. We have found that all the enzymes assayed were capable of releasing on their own free fatty acids from the TAG of oil-bodies. Depending on the lipase, the specific activity measured on oil-bodies using the pH-stat technique was found to range from 18 to 38% of the specific activity measured on almond oil emulsified by gum arabic. Some of these lipases are known to have a dual lipase/phospholipase activity. However, no correlation was found to exist between the ability of a lipase to readily and efficiently hydrolyse the TAG content of oil-bodies and the presence of a phospholipase activity. Kinetic studies indicate that oil-bodies behave as a substrate as other proteolipid organelles such as milk fat globules. Finally we have shown that a purified water-soluble plant lipase on its own can easily hydrolyse oil-bodies in vitro. Our results suggest that the lipolysis of oil-bodies in seedlings might occur without any pre-hydrolysis of the protein coat. (+info)
Biospheric primary production during an ENSO transition.
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The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) provides global monthly measurements of both oceanic phytoplankton chlorophyll biomass and light harvesting by land plants. These measurements allowed the comparison of simultaneous ocean and land net primary production (NPP) responses to a major El Nino to La Nina transition. Between September 1997 and August 2000, biospheric NPP varied by 6 petagrams of carbon per year (from 111 to 117 petagrams of carbon per year). Increases in ocean NPP were pronounced in tropical regions where El Nino-Southern Oscillation (ENSO) impacts on upwelling and nutrient availability were greatest. Globally, land NPP did not exhibit a clear ENSO response, although regional changes were substantial. (+info)
Light and brassinosteroid signals are integrated via a dark-induced small G protein in etiolated seedling growth.
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Plant growth and development are regulated through coordinated interactions between light and phytohormones. Here, we demonstrate that a dark-induced small G protein, pea Pra2, regulates a variant cytochrome P450 that catalyzes C-2 hydroxylation in brassinosteroid biosynthesis. The cytochrome P450 is dark-induced and predominantly expressed in the rapidly elongating zone of etiolated pea epicotyls, where Pra2 is also most abundant. Transgenic plants with reduced Pra2 exhibit a dark-specific dwarfism, which is completely rescued by exogenous brassinolide. Overexpression of the cytochrome P450 results in enhanced hypocotyl growth even in the light, which phenocopies the etiolated hypocotyls. We therefore propose that Pra2 and its orthologs are molecular mediators for the cross-talk between light and brassinosteroids in the etiolation process in plants. (+info)