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1.
Phosphate uptake by excised roots of sunflower (Helianthus annuus)was determined by the disappearance of phosphate from the externalsolution and by the accumulation of phosphate labelled with32P. Over a 24 h period it was observed that net phosphate uptakedeclined to zero whilst uptake of 32P continued unabated. Theelectrical PD of the cortical cell membranes declined in parallelwith net phosphate uptake and it was found that both could berestored by creating a pH gradient across the plasmalemma. Itwas concluded that net phosphate uptake was responsible fora component of the membrane PD of the root cortical cells. Key words: Roots, Phosphate, Membranes  相似文献   

2.
High rates of phosphate uptake into phosphate-starved Lemna gibba L. G1 were correlated with a high membrane potential (pd = −220 millivolts). In plants maintaining a low pd (−110 millivolts), the uptake rate was only 20% of that of high-pd plants. At the onset of phosphate transport, the membrane of high-pd plants was transiently depolarized. This effect was much smaller in low-pd plants. Light stimulated phosphate uptake and the repolarization upon phosphate-induced depolarization, especially in plants grown without sucrose. The phosphate uptake rate was optimal at pH 6 and decreased with increasing pH, corresponding to the phosphate-induced pd changes. Phosphate starvation stimulated the uptake and increased the phosphate-induced depolarization, thus indicating that phosphate uptake depends on the intracellular phosphate level. It is suggested that uptake of monovalent phosphate in Lemna gibba proceeds by an H+ cotransport dependent on the proton electrochemical potential difference and, hence, on the activity of an H+ -extrusion pump.  相似文献   

3.
玉米幼苗种子根局部供磷可明显改变根系的形态。供磷区侧根生长增加,无磷区侧极生长减少。供磷区1次、2次侧根长度与2次侧根数量明显增加;而1次侧根数量则不增加。供磷区缩小时,根系生长加快,单位根区磷吸收速率增加,但单位根重磷吸收速率的增加不很明显。磷局部供应植株主要通过供磷区根系的生长来增加磷的吸收,以满足植株对磷的需求。局部供磷植株中转运到供磷根区的光合产物明显多于无磷根区。  相似文献   

4.
The Electrical Potential Difference Across the Tonoplast of Root Cells   总被引:1,自引:0,他引:1  
Changes in electrical potential, measured as a microelectrodewas advanced into epidermal cells and from cell to cell in rootsof Lolium multiflorum and Zea mays, are described. The recordingssuggest that the electrical potential difference between thecytoplasm and vacuole, Evc is of the order of a few millivolts,the vacuole tending to be the more positive. Evc appeared tobe approximately the same for epidermal, cortical, endodermal,and pericycle cells.  相似文献   

5.
The uptake of phosphate by aged beetroot discs was examinedunder a range of water deficits which were induced osmoticallywith mannitol or polyethylene glycol At low water potentialsthe absorption of labelled phosphate was enhanced when the ambientconcentration of phosphate was high (10–3 M) and the timefor absorption was short (30 mm): this occurred even when themetabolism was inhibited (by the water deficit), as indicatedby lowered oxygen consumption and incorporation of 33P intohexose-phosphate, phosphoglycenc acid, a liquid fraction, anda precipitate consisting mainly of cell walls. The Q10 of theuptake process approached unity at these low water potentials.Accompanying the enhanced uptake there was an increase in leakageof previously absorbed phosphate. It is postulated that thestimulation in uptake of phosphate in low osmotic potentialswas due to an increase in permeability Over long periods (6 h) uptake was inhibited by treatment atlow osmotic potentials. This is interpreted in terms of inhibitionof a metabolic component of phosphate uptake.  相似文献   

6.
The effect of changing the transpiration rate on leaf waterpotential and water balance has been examined to show if permeabilityof the plant (predominantly the roots) is constant or varieswith the transpiration rate. Measurements of leaf effectivethickness, water potential, transpiration, and uptake of waterby roots were made on sunflower, barley, and maize plants grownin solution culture and subjected to a range of atmosphericconditions and root treatments: cooling, low osmotic potential,and removal of part of the root system. Leaf water potential changed little under a wide range of atmosphericconditions and rates of water flux in the three species, sothat the root permeability to water increases as the rate oftranspiration, and therefore flow across the root surface, increases.Equality between uptake and loss of water and thereby maintenanceof constant leaf water potential is assisted by stomatal changes,which appear to be in response to conditions at or in the rootrather than a direct response to changes in bulk leaf waterpotential.  相似文献   

7.
Root Development and Nutrient Uptake   总被引:1,自引:0,他引:1  
Root system formation proceeds in close coordination with shoot growth. Accordingly, root growth and its functions are regulated tightly by the shoot through materials cycling between roots and shoots. A plant root system consists of different kinds of roots that differ in morphology and functions. The spatial configuration and distribution of these roots determine root system architecture in the soil, which in turn primarily regulates the acquisition of soil resources like nutrients and water. Morphological and physiological properties of each root and the concomitant tissues further affect nutrient uptake and transport, while the root traits that are related to such acquisition also depend on the kinds of nutrients and their mobility in the soil. In addition, mechanisms involved in the uptake and transport of mineral nutrients recently have been elucidated at the molecular level. A number of genes for acquisition and transport of various mineral nutrients have been identified in model plant systems such as Arabidopsis thaliana, and rice, and in other plant species. An integration of studies on nutrient behavior in soils and the morphological and physiological functions of root systems will further elucidate the mechanism of plant nutrient uptake and transport by roots, and offer a real possibility of genetically improving crop productivity in problem soils.

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8.
The extent of phosphate uptake measured by the relative changes in cytoplasmic Pi, vacuolar Pi, ATP, glucose-6-phosphate, and UDPG was determined using in vivo31P nuclear magnetic resonance spectroscopy. Maize (Zea mays) root tips were perfused with a solution containing 0.5 or 1.0 millimolar phosphate at pH ~6.5 under different conditions. In the aerated state, phosphate uptake resulted in a significant increase (>80%) in vacuolar Pi, but cytoplasmic Pi only transiently increased by 10%. Under N2, the cytoplasmic Pi increased ~150% which could be attributed to a large extent to the breakdown of ATP, sugar phosphates and UDPG. Vacuolar Pi increased but only to the extent of ~10% of that seen under aerobic conditions. 2-deoxyglucose pretreatment was utilized to decrease the level of cytoplasmic Pi. When pretreated with the 2-deoxyglucose, the excised maize roots absorbed phosphate from the perfusate with a significant increase in the cytoplasmic Pi. The increase could only be traced to external phosphate since the concentrations of other phosphorus containing species remained constant during the uptake period. With 2-deoxyglucose pretreatment, phosphate uptake under anaerobic conditions was substantially inhibited with only the vacuolar phosphate showing a slight increase. When roots were treated with carbonyl cyanide m-chlorophenyl hydrazone, no detectable Pi uptake was found. These results were used to propose a H+-ATPase related transport mechanism for phosphate uptake and compartmentation in corn root cells.  相似文献   

9.
Anaerobic Phosphate Uptake by Barley Plants   总被引:1,自引:0,他引:1  
Considerable uptake of phosphate by both the shoot and roothas been demonstrated for young barley plants with their rootsin anoxic culture solution at concentrations of 1 to 10 µMorthophosphate. Consideration of the free space and passivetranspirational uptake indicates an accumulatory process, andthe immediate efflux caused by respiratory inhibitors supportsthis. Shoot uptake is much less at higher external concentrationsof phosphate and at o.I mM was only 14 per cent of the control.The root accumulation process was unimpaired at an externalconcentration of 1 µM phosphate when the whole plant wassubjected to anaerobic conditions (shoot illuminated) but undersimilar conditions at a concentration of 100 µM a considerableefflux of phosphate occurred. Analysis of the fate of phosphatetaken up from anoxic solution of phosphate (10 µM) indicatedthat there was a reduction in the level of inorganic phosphateafter 4.5 h and steady rise in sugar phosphates up to 6 h witha marked increase in the levels of glucose-6-phosphate, fructose-6-phosphate,and the phosphoglycerate fraction.  相似文献   

10.
Interference of arsenate and vanadate with phosphate uptakein Lemna gibba L. was studied by measuring voltage changes and(32P)phosphate uptake. Arsenate proved to be competitive withthe high- and low-affinity phosphate uptake system. It inducedtransient membrane potential changes of up to 120 mV which weresimilar to those induced by phosphate and indicated a cotransportmechanism with at least 2H+/H2As. The amplitude of the transient arsenate-induced membrane depolarization wasstrongly influenced by phosphate starvation. A permanent membranedepolarization to the diffusion potential was achieved within2 to 6 h in P-starved plants. Thus, arsenate is indeed a stronglycompetitive physiological analogue of phosphate in higher plants. Vanadate was easily transported into L. gibba as concluded fromtransient Em changes of up to 110 mV. Vanadate interfered onlyslightly and non-specifically with the two phosphate transportmechanisms. Like phosphate, vanadate uptake seems to be an H+-cotransportmechanism, both with similar optima at pH 6.0. Unlike phosphateuptake, vanadate-linked membrane depolarization was not affectedby high intracellular phosphate concentrations. P-starvationdid not enhance the weak long-term effect on Em. Hence, vanadate,in contrast to arsenate, is not regarded as a physiologicalphosphate analogue. The distinct and rapid vanadate-inducedand permanent membrane depolarization of Avena sativa, Triticumaestivum and Glycine max leaves was not seen in Lemna nor inleaves of Gossypium hirsutum and Nicotiana tabacum. Plasmalemma-enrichedpreparations of L. gibba revealed, however, a high vanadate-sensitiveATPase activity (87%). As a possible explanation for these differencesit is suggested that the latter plant species have cytosolicvanadate-detoxifying properties, i.e. they can reduce vanadateto vanadyl ions, in contrast to the former group of plant species. Key words: Arsenate, vanadate, H+/solute cotransport, membrane potential, phosphate competition  相似文献   

11.
The effect of ringing the stem on the electrical potential difference(PD) in the root cortical cells of H. annuus was studied. PDand salt transport were followed simultaneously. By ringingit was possible to separate the PD from K+, , and Cl uptake and H+ efflux. The uptake of phosphatehowever was found to be closely connected with a component ofthe PD. It was concluded that there is an electrogenic pumpfor phosphate in these roots which generates 60–80 mV.  相似文献   

12.
Multiphasic Uptake in Plants I. Phosphate and Sulfate   总被引:2,自引:0,他引:2  
Uptake of phosphate and sulfate is shown by reanalysis of available data to be mediated by single, multiphasic mechanisms which may be fundamentally similar in a variety of plants and tissues.  相似文献   

13.
Root Density and Water Potential Gradients near the Plant Root   总被引:2,自引:1,他引:2  
The models of Gardner (1960) and Cowan (1965) for water transferto the plant root are used to estimate the differences in waterpotential between the root and the bulk soil for a wide rangeof root densities and water extraction rates at a series ofmatric potentials for a Yolo light clay. For root densities and extraction rates reported both in theliterature and in this paper there is good evidence to suggestthat the large potential gradients originally predicted by Gardnerand Cowan are restricted to situations involving very low rootdensities and high extraction rates in relatively dry soil.  相似文献   

14.
DIXON  R. O. D. 《Annals of botany》1967,31(1):179-188
Hydrogenase activity in pea root nodules was studied by followinggas exchanges of hydrogen and deuterium. It was found that thenodules did not evolve hydrogen but that hydrogen was takenup when it was provided in the gas mixture. When increasingpartial pressures of deuterium were supplied, hydrogen was evolvedat a rate which increased as the pressure of deuterium increased.Deuterium was taken up at the same time as this hydrogen wasevolved. Hydrogen evolution in the presence of deuterium wasinhibited by nitrogen, while the uptake of deuterium remainedunaffected. It was concluded that pea root nodules have at leasttwo separate hydrogenase system that are working in oppositedirections and must thus be situated in sites of different oxidation-reductionpotentials within the nodule.  相似文献   

15.
16.
Treating carrot (Daucus carota L.) discs with ice-cold NaCl solutions for 30 minutes caused three effects that appear to be functionally related: the exchange of tissue Ca2+ and Mg2+ for Na+, the release of protein, and the suppression of active uptake of glucose and orthophosphate. Cyclosis continued apparently unabated after treatment with NaCl at concentrations of up to 0.25 m, so the cells remained viable and energetically competent. The correlation between the release of Ca2+ and Mg2+ and release of protein, and between these effects and the suppression of glucose and orthophosphate uptake, supports the hypothesis that divalent cations maintain, and monovalent cations disrupt, linkages between the outer cell surface and proteins required for active solute uptake. Calcium preserved uptake activity only when it was added in time to prevent the release of protein. Cells gradually recovered some glucose uptake activity after it had been completely inactivated by treatment with 0.25 m NaCl. This recovery occurred in the absence of added Ca2+. It was inhibited by puromycin and so appears to require some protein synthesis. Beet (Beta vulgaris L.) discs were more resistant than carrot discs to treatment with NaCl solutions, thus reflecting the difference in tolerance of the two species to sodicity.  相似文献   

17.
植物根系向地性感应的分子机理与养分吸收   总被引:6,自引:0,他引:6  
植物根系向地性是决定根系空间生长趋势的主要因素之一,对于养分吸收具有重要影响.认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系,可为遗传改良根系性状、提高植物养分吸收效率提供理论依据.本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理,探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系,最后对根系向地性研究的若干问题进行了展望.  相似文献   

18.
19.
Root Architecture Responses: In Search of Phosphate   总被引:1,自引:0,他引:1  
Soil phosphate represents the only source of phosphorus for plants and, consequently, is its entry into the trophic chain. This major component of nucleic acids, phospholipids, and energy currency of the cell (ATP) can limit plant growth because of its low mobility in soil. As a result, root responses to low phosphate favor the exploration of the shallower part of the soil, where phosphate tends to be more abundant, a strategy described as topsoil foraging. We will review the diverse developmental strategies that can be observed among plants by detailing the effect of phosphate deficiency on primary and lateral roots. We also discuss the formation of cluster roots: an advanced adaptive strategy to cope with low phosphate availability observed in a limited number of species. Finally, we will put this work into perspective for future research directions.Plant embryogenesis generates a very primitive developmental blueprint with two apical meristems (shoot and root) that, unlike in animals, do not reflect the anatomy of the adult organism. The ability to form new organs is maintained throughout their lifecycle because of the sustained activity of these meristems as well as the presence of dedicated cells that dedifferentiate and generate new meristems. The continuous nature of plant development associated with their sessile lifestyle results in a strong dependency on their immediate environment. As a result, the study of plant development must not only focus on the fundamental molecular and cellular mechanisms but also, integrate their ability to perceive and respond to the environment. In this regard, plant root systems represent a good model, because they have a high level of developmental plasticity in response to water, nutrients, gravity, and mechanical characteristics of the soil as well as biotic interactions.Among the essential nutrients for plant growth and development, phosphorus is a key component of nucleic acids and phospholipids and present in soil in the form of either inorganic phosphate (Pi) or organophosphates. The former strongly interacts with divalent and trivalent cations. The latter has to be hydrolyzed to release phosphate for root uptake. The high sorption capacity of phosphate to soil particles results in a very low mobility and availability for uptake by plants. Therefore, the capacity of plants to find an adequate phosphate supply is directly correlated with their ability to explore the soil. Correspondingly, phosphorus deficiency induces changes in root system architecture as a key adaptive mechanism. A general strategy has been described under the term topsoil foraging that favors a shallower root system to explore the upper part of the soil, where phosphate tends to be more available because of the presence of organic matter and animal excrements. Although this term was first introduced to describe root system adaptation in bean (Phaseolus vulgaris; Lynch and Brown, 2001), the set of responses behind the topsoil foraging strategy has now been described in many other species (Panigrahy et al., 2009; Péret et al., 2011; Li et al., 2012; Shi et al., 2013). We will give an up-to-date overview of recent publications on developmental adaptations to low phosphate observed in diverse monocot and dicot species by focusing on the responses of the primary root (PR) and lateral roots. Finally, we will describe the evolutionarily advanced developmental adaptation to low phosphorus that has been found in several plant families’ (i.e. cluster or proteoid) root formation.  相似文献   

20.
植物根毛的发生、发育及养分吸收   总被引:9,自引:0,他引:9  
根毛是植物吸收养分的重要器官,认识根毛的发生、发育规律及其与养分吸收的关系,可为植物养分吸收效率的遗传改良提供依据.介绍了植物根毛的形态特性、发生和发育过程及其调控机制,并结合本实验室的工作,讨论了根毛对养分吸收的贡献、根毛受养分有效性的调节及其与其他根系形态构型性状间的关系,阐述了根毛中养分转运等植物营养过程及其生理和分子生物学基础.最后提出了关于根毛研究中的一些问题和研究前景.  相似文献   

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