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1.
Rice OsHKT2;1 transporter mediates large Na+ influx component into K+-starved roots for growth 总被引:3,自引:0,他引:3
Horie T Costa A Kim TH Han MJ Horie R Leung HY Miyao A Hirochika H An G Schroeder JI 《The EMBO journal》2007,26(12):3003-3014
Excessive accumulation of sodium in plants causes toxicity. No mutation that greatly diminishes sodium (Na+) influx into plant roots has been isolated. The OsHKT2;1 (previously named OsHKT1) transporter from rice functions as a relatively Na+-selective transporter in heterologous expression systems, but the in vivo function of OsHKT2;1 remains unknown. Here, we analyzed transposon-insertion rice lines disrupted in OsHKT2;1. Interestingly, three independent oshkt2;1-null alleles exhibited significantly reduced growth compared with wild-type plants under low Na+ and K+ starvation conditions. The mutant alleles accumulated less Na+, but not less K+, in roots and shoots. OsHKT2;1 was mainly expressed in the cortex and endodermis of roots. (22)Na+ tracer influx experiments revealed that Na+ influx into oshkt2;1-null roots was dramatically reduced compared with wild-type plants. A rapid repression of OsHKT2;1-mediated Na+ influx and mRNA reduction were found when wild-type plants were exposed to 30 mM NaCl. These analyses demonstrate that Na+ can enhance growth of rice under K+ starvation conditions, and that OsHKT2;1 is the central transporter for nutritional Na+ uptake into K+-starved rice roots. 相似文献
2.
Sodium transport and HKT transporters: the rice model 总被引:30,自引:0,他引:30
Garciadeblás B Senn ME Bañuelos MA Rodríguez-Navarro A 《The Plant journal : for cell and molecular biology》2003,34(6):788-801
3.
Rice potassium transporter OsHAK1 is essential for maintaining potassium‐mediated growth and functions in salt tolerance over low and high potassium concentration ranges
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Guang Chen Qingdi Hu Le Luo Tianyuan Yang Song Zhang Yibing Hu Ling Yu Guohua Xu 《Plant, cell & environment》2015,38(12):2747-2765
Potassium (K) absorption and translocation in plants rely upon multiple K transporters for adapting varied K supply and saline conditions. Here, we report the expression patterns and physiological roles of OsHAK1, a member belonging to the KT/KUP/HAK gene family in rice (Oryza sativa L.). The expression of OsHAK1 is up‐regulated by K deficiency or salt stress in various tissues, particularly in the root and shoot apical meristem, the epidermises and steles of root, and vascular bundles of shoot. Both oshak1 knockout mutants in comparison to their respective Dongjin or Manan wild types showed a dramatic reduction in K concentration and stunted root and shoot growth. Knockout of OsHAK1 reduced the K absorption rate of unit root surface area by ~50–55 and ~30%, and total K uptake by ~80 and ~65% at 0.05–0.1 and 1 mm K supply level, respectively. The root net high‐affinity K uptake of oshak1 mutants was sensitive to salt stress but not to ammonium supply. Overexpression of OsHAK1 in rice increased K uptake and K/Na ratio. The positive relationship between K concentration and shoot biomass in the mutants suggests that OsHAK1 plays an essential role in K‐mediated rice growth and salt tolerance over low and high K concentration ranges. 相似文献
4.
Improving rice tolerance to potassium deficiency by enhancing OsHAK16p:WOX11‐controlled root development
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Guang Chen Huimin Feng Qingdi Hu Hongye Qu Aiqun Chen Ling Yu Guohua Xu 《Plant biotechnology journal》2015,13(6):833-848
Potassium (K) deficiency in plants confines root growth and decreases root‐to‐shoot ratio, thus limiting root K acquisition in culture medium. A WUSCHEL‐related homeobox (WOX) gene, WOX11, has been reported as an integrator of auxin and cytokinin signalling that regulates root cell proliferation. Here, we report that ectopic expression of WOX11 gene driven by the promoter of OsHAK16 encoding a low‐K‐enhanced K transporter led to an extensive root system and adventitious roots and more effective tiller numbers in rice. The WOX11‐regulated root and shoot phenotypes in the OsHAK16p:WOX11 transgenic lines were supported by K‐deficiency‐enhanced expression of several RR genes encoding type‐A cytokinin‐responsive regulators, PIN genes encoding auxin transporters and Aux/IAA genes. In comparison with WT, the transgenic lines showed increases in root biomass, root activity and K concentrations in the whole plants, and higher soluble sugar concentrations in roots particularly under low K supply condition. The improvement of sugar partitioning to the roots by the expression of OsHAK16p:WOX11 was further indicated by increasing the expression of OsSUT1 and OsSUT4 genes in leaf blades and several OsMSTs genes in roots. Expression of OsHAK16p:WOX11 in the rice grown in moderate K‐deficient soil increased total K uptake by 72% and grain yield by 24%–32%. The results suggest that enlarging root growth and development by the expression of WOX11 in roots could provide a useful option for increasing K acquisition efficiency and cereal crop productivity in low K soil. 相似文献
5.
Summary The uptake of Na and K by perennial ryegrass from flowing solution culture with monitored concentrations of Na and K was followed
in two experiments. In the first, when only 50 and 10 per cent of the K uptake by one set of plants, grown with K held constant
at 2.5 μeq 1−1, was supplied to two other linked sets of plants and the balance supplied as Na, there was a rapid decrease in K, and an
increase in Na, concentration in the shoots over a 20-day period. However, when compared with the plants grown in K in solution
held constant, there was not a complete replacement of Na for K. In the second experiment the concentration of K in the culture
solution was held constant at 2 μeq 1−1 and Na at 0, 5, 25, 50 and 100 μeq 1−1. Although uptake of Na increased with increasing concentration in solution the contents in the plants were low,i.e. less than 0.19 per cent and decreased with time. There was an increase in the yield of both shoots and roots with increasing
Na in the solution; it was suggested that, during the early stages of growth there may have been an inadequate supply of K
and that Na may have substituted for K in some of the non-specific roles of K in the plants. There was evidence in both experiments
that a flux of H-ions was involved in the uptake of Na. 相似文献
6.
We examined the capacity of several Old-World lupin species (Lupinus luteus L., L. hispanicus Boiss. et Reuter and L. angustifolius L.) and one species of a New-World lupin (L. mutabilis Sweet) to form cluster roots under a range of conditions in solution culture. The effect of the synthetic auxin, IBA (indole-3-butyric acid), on cluster-root development in L. luteus and L. albus L. provided with an adequate phosphorus (P) supply was also investigated. In addition, the effect of a high nitrate-N (NO3-N) supply on the efflux of citrate and malate from roots of L. angustifolius was examined to determine if specific regions of the root system exuded these organic anions. When P-deficient, L. hispanicus, L. luteus and L. mutabilis formed cluster roots that secreted organic anions. Citrate was generally the dominant organic anion exuded, although succinate was also exuded in large quantities from L. luteus. Citrate efflux by L. hispanicus and L. luteus was at least comparable to that reported for P-deficient L. albus[up to 1.092 nmol g–1 fresh weight (FW) s–1], but was over an order of magnitude lower in L. mutabilis (0.036 nmol g–1 FW s–1). Citrate and malate were not detected in significant amounts from either the lateral roots or the root tips of any species grown under P-sufficient or -deficient conditions. Citrate efflux from cluster roots of L. luteus showed a diurnal pattern, similar to that reported for L. albus, with maximum efflux during the day, and declining to a minimum before dawn. IBA added to the nutrient solution induced cluster-root formation on both L. albus and L. luteus at concentrations of P that would normally suppress the production of these roots. However, the IBA-induced cluster roots did not exude significant amounts of citrate. Although L. angustifolius did not produce cluster roots when P-deficient, it produced cluster-like root structures that exuded citrate (0.053 nmol g–1 FW s–1) when grown at a high nitrate-N (NO3-N) supply. L. angustifolius did not exude significant citrate or malate from lateral roots or root tips when grown at either high or low NO3-N supply. Our findings for L. hispanicus and L. luteus are the first reports of cluster-root formation in response to P deficiency for these Old-World species, and for L. mutabilis, it is the first report of cluster roots for a New-World lupin species. These reports indicate that evolutionary and biogeographical aspects of cluster-root formation in the genus Lupinus need to be revised. Furthermore, investigation is warranted to determine the capacity of species of the large group of New-World lupins to form cluster roots in soils of their native habitats. 相似文献
7.
Miniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3–4 mm) in the undisturbed soil of a mature beech–oak–spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (Js) for individual fine root systems of 0.5–1.0 m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of Js, and (ii) to investigate the relationship between uptake and soil moisture θ, atmospheric saturation deficit D, and radiation I. On most days, water uptake followed the diurnal course of D with a mid-day peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of Js (<100–2000 g m−2 d−1) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and θ on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots <2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48–205 g m−2 h−1 (i.e. 0.7–3.2 mmol m−2 s−1), oak of 12–160 g m−2 h−1 (0.2–2.5 mmol m−2 s−1). Maximal transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m−2 s−1 for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered. 相似文献
8.
9.
Joni Esrom Lima Vagner Augusto Benedito Antonio Figueira Lázaro Eustáquio Pereira Peres 《Plant cell reports》2009,28(8):1169-1177
We analyzed the impact of ethylene and auxin disturbances on callus, shoots and Agrobacterium rhizogenes-induced hairy root formation in tomato (Solanum lycopersicum L.). The auxin low-sensitivity dgt mutation showed little hairy root initiation, whereas the ethylene low-sensitivity Nr mutation did not differ from the control Micro-Tom cultivar. Micro-Tom and dgt hairy roots containing auxin sensitivity/biosynthesis rol and aux genes formed prominent callus onto media supplemented with cytokinin. Under the same conditions, Nr hairy roots did not form callus. Double mutants combining Rg1, a mutation conferring elevated shoot formation capacity, with either dgt or Nr produced explants that formed shoots with little callus proliferation. The presence of rol + aux genes in Rg1 hairy roots prevented shoot formation. Taken together, the results suggest that although ethylene does not affect hairy root
induction, as auxin does, it may be necessary for auxin-induced callus formation in tomato. Moreover, excess auxin prevents
shoot formation in Rg1. 相似文献
10.
11.
Characterization of the growth and auxin physiology of roots of the tomato mutant,diageotropica 总被引:7,自引:0,他引:7
Roots of the tomato (Lycopersicon esculentum, Mill.) mutant diageotropica (dgt) exhibit an altered phenotype. These roots are agravitropic and lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots are less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a reduction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated naphthylphthalamic acid ([3H]NPA), to root microsomal membranes, NPA-sensitive IAA uptake by root segments, and uptake of [3H]NPA into root segments are all similar in mutant and wild-type roots. We speculate that the reduced sensitivity of dgt root growth to auxin-transport inhibitors and ethylene is an indirect result of the reduction in sensitivity to auxin in this single gene, recessive mutant. We conclude that dgt roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin perception or action.Abbreviations BCA
bicinchoninic acid
- IAA
indole 3-acetic acid
-
dgt
diageotropica
- IC50
concentration for 50% inhibition of growth
- NPA
N-1-naphthylphthalamic acid
- SCB-1
semicarbazone 1
This research was supported by grants from Sandoz Agro, Inc. (G.K.M), the National Aeronautics and Space Administration (NASA) and the National Science Foundation (T.L.L), and NASA (D.L.R.). 相似文献
12.
Two types of HKT transporters with different properties of Na+ and K+ transport in Oryza sativa 总被引:3,自引:0,他引:3
Horie T Yoshida K Nakayama H Yamada K Oiki S Shinmyo A 《The Plant journal : for cell and molecular biology》2001,27(2):129-138
It is thought that Na+ and K+ homeostasis is crucial for salt-tolerance in plants. To better understand the Na+ and K+ homeostasis in important crop rice (Oryza sativa L.), a cDNA homologous to the wheat HKT1 encoding K+-Na+ symporter was isolated from japonica rice, cv Nipponbare (Ni-OsHKT1). We also isolated two cDNAs homologous to Ni-OsHKT1 from salt-tolerant indica rice, cv Pokkali (Po-OsHKT1, Po-OsHKT2). The predicted amino acid sequence of Ni-OsHKT1 shares 100% identity with Po-OsHKT1 and 91% identity with Po-OsHKT2, and they are 66-67% identical to wheat HKT1. Low-K+ conditions (less than 3 mM) induced the expression of all three OsHKT genes in roots, but mRNA accumulation was inhibited by the presence of 30 mM Na+. We further characterized the ion-transport properties of OsHKT1 and OsHKT2 using an expression system in the heterologous cells, yeast and Xenopus oocytes. OsHKT2 was capable of completely rescuing a K+-uptake deficiency mutation in yeast, whereas OsHKT1 was not under K+-limiting conditions. When OsHKTs were expressed in Na+-sensitive yeast, OsHKT1 rendered the cells more Na+-sensitive than did OsHKT2 in high NaCl conditions. The electrophysiological experiments for OsHKT1 expressed in Xenopus oocytes revealed that external Na+, but not K+, shifted the reversal potential toward depolarization. In contrast, for OsHKT2 either Na+ or K+ in the external solution shifted the reversal potential toward depolarization under the mixed Na+ and K+ containing solutions. These results suggest that two isoforms of HKT transporters, a Na+ transporter (OsHKT1) and a Na+- and K+-coupled transporter (OsHKT2), may act harmoniously in the salt tolerant indica rice. 相似文献
13.
Alteration of nutrient allocation and transporter genes expression in rice under N,P, K,and Mg deficiencies 总被引:2,自引:0,他引:2
Nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) have essential physiological functions in plants. Their interactions
in plants are not fully understood especially at the molecular level. In this study, we detected the physiological and molecular
responses of rice plants at the vegetative growth phase to N, P, K, and Mg starvations. Deficiencies of N and P resulted in
accumulation of soluble sugar and starch in the leaves. The root to shoot ratio increased under N and P deficiencies, but
decreased under K and Mg deficiencies. In addition, deficiency of either K or Mg resulted in accumulation of the other cation
in shoots. Moreover, K starvation decreased both K and soluble sugar contents in the roots pronouncedly. RT-PCR analysis showed
that several sugar transporter genes in the leaves orchestrated with sugar accumulation induced by the nutrient shortages.
Expression of a high affinity K transporter gene (OsHAK1) and a putative Mg transporter gene (OsMGT) showed opposite down- and up-regulation in the roots by K starvation. These findings suggest that deficiencies of the major
nutrients suppressed the export of carbohydrates from source leaves. The regulated sugar and nutrient transporter genes investigated
in this study could be used for elucidating the molecular mechanism of plants in their adaptation to varied nutrient supply. 相似文献
14.
Influence of external zinc and phosphorus supply on Cd uptake by rice (Oryza sativa L.) seedlings with root surface iron plaque 总被引:1,自引:0,他引:1
Rice seedlings were grown in hydroponic culture to determine the effects of external Zn and P supply on plant uptake of Cd
in the presence or absence of iron plaque on the root surfaces. Iron plaque was induced by supplying 50 mg l−1 Fe2+ in the nutrient solution for 2 day. Then 43-day-old seedlings were exposed to 10 μmol l−1 Cd together with 10 μmol l−1 Zn or without Zn (Zn–Cd experiment), or to 10 μmol l−1 Cd with 1.0 mmol l−1 P or without P (P–Cd experiment) for another 2 day. The seedlings were then harvested and the concentrations of Fe, Zn, P
and Cd in dithionite–citrate–bicarbonate (DCB) extracts and in roots and shoots were determined. The dry weights of roots
and shoots of seedlings treated with 50 mg l−1 Fe were significantly lower than when no Fe was supplied. Adsorption of Cd, Zn and P on the iron plaque increased when Fe
was supplied but Cd concentrations in DCB extracts were unaffected by external Zn or P supply levels. Cd concentrations in
shoots and roots were lower when Fe was supplied. Zn additions decreased Cd concentrations in roots but increased Cd concentrations
in shoots, whereas P additions significantly increased shoot and root Cd concentrations and this effect diminished when Fe
was supplied. The percentage of Cd in DCB extracts was significantly lower than in roots or shoots, accounting for up to 1.8–3.8%
of the plant total Cd, while root and shoot Cd were within the ranges 57–76% and 21–40% respectively in the two experiments.
Thus, the main barrier to Cd uptake seemed to be the root tissue and the contribution of iron plaque on root surfaces to plant
Cd uptake was minor. The changes in plant Cd uptake were not due to Zn or P additions altering Cd adsorption on iron plaque,
but more likely because Zn or P interfered with Cd uptake by the roots and translocation to the shoots. 相似文献
15.
Growth and arsenic uptake by Chinese brake fern inoculated with an arbuscular mycorrhizal fungus 总被引:2,自引:0,他引:2
Yu Liu Peter Christie Junling Zhang Xiaolin Li 《Environmental and Experimental Botany》2009,66(3):435-441
A split-root experiment investigated the effects of inoculation with the arbuscular mycorrhizal fungus Glomus mosseae and arsenic (As) addition on As uptake by Pteris vittata L. Either part or all of the root system was inoculated with G. mosseae or exposed to As addition (50 ml 1000 μmol L−1 As 1 week before harvest). Mycorrhizal colonization substantially increased frond and root dry weight and P and As contents irrespective of As addition. Frond As contents in mycorrhizal plants were highest when the whole root system was exposed to As. Frond As concentrations and contents were higher when inoculation and As addition were in the same parts of the root system than when spatially separate. There were positive effects of arbuscular mycorrhiza inoculation on plant growth and As uptake, and inoculation of part of the roots seemed to be as effective as inoculation of the whole root system. 相似文献
16.
To examine the mechanisms of earlier reported alleviation of fluoride injury in ectomycorrhizal plants by NaCl, jack pine
(Pinus banksiana) and white spruce (Picea glauca) seedlings were subjected to 1 mM and 5 mM KF in the presence of either 60 mM NaCl or 10% polyethylene glycol 3350 (PEG)
for 2 weeks. Before the treatments, seedlings had either been inoculated with the ectomycorrhizal fungus Suillus tomentosus or remained non-inoculated. The inoculation with S. tomentosus reduced Na uptake by shoots and roots of jack pine seedling and by roots of white spruce that were treated with 60 mM NaCl.
Mycorrhizal associations also drastically decreased fluoride uptake by jack pine seedlings, but did not affect shoot fluoride
concentrations in white spruce. When NaCl was replaced by PEG in the 5 mM KF treatment solution, shoot fluoride concentrations
were reduced by more than twofold without corresponding reductions in transpiration rates in mycorrhizal and non-mycorrhizal
white spruce seedlings. When fluoride was present in the treatment solution, Na concentrations were lower in shoots and roots
of both jack pine and white spruce mycorrhizal and non-mycorrhizal seedlings. The results suggest that Suillus tomentosus may help alleviate the effects of soil fluoride and salinity in jack pine and that fluoride uptake in white spruce is sensitive
to osmotic stress. 相似文献
17.
The influence of carbohydrates on ammonium uptake and ammonium transporter (AMT1) expression was investigated in roots of
field pea (Pisum arvense) and rutabaga (Brassica napus var. rapifera). Ammonium transport into field pea seedlings diminished markedly following cotyledon removal, which indicated that uptake
of ammonium was under control of reserves stored in the cotyledons. Excision of cotyledons decreased also the level of some
amino acids, glucose and total reducing sugars in field pea roots. To investigate the importance of the sugar supply for the
regulation of ammonium uptake at low external NH
4
+
level, 1 mM glucose or sucrose was supplied for several hours to the field pea seedlings deprived cotyledons or to intact
rutabaga plants. Supply of both sugars resulted in a substantial increase in ammonium uptake by both plant species and enhanced
markedly the expression of AMT1 in rutabaga roots. The results indicate that sugars may regulate ammonium transport at the
genetic level. 相似文献
18.
Fe uptake in dicotyledonous plants is mediated by a root plasma membrane-bound ferric reductase that reduces extracellular Fe(III)-chelates, releasing Fe2+ ions, which are then absorbed via a metal ion transporter. We previously showed that Fe deficiency induces an increased capacity to absorb Fe and other micronutrient and heavy metals such as Zn2+ and Cd2+ into pea (Pisum sativum L.) roots [Cohen et al. (1998) Plant Physiol 116:1063–1072). To investigate the molecular basis for this phenomenon, an Fe-regulated transporter that is a homologue of the Arabidopsis IRT1 micronutrient transporter was isolated from pea seedlings. This cDNA clone, designated RIT1 for root iron transporter, encodes a 348 amino acid polypeptide with eight putative membrane-spanning domains that is induced under Fe deficiency and can functionally complement yeast mutants defective in high- and low-affinity Fe transport. Chelate buffer techniques were used to control Fe2+ in the uptake solution at nanomolar activities representative of those found in the rhizosphere, and radiotracer methodologies were employed to show that RIT1 is a very high-affinity 59Fe2+ uptake system (K
m =54–93 nM). Additionally, radiotracer (65Zn, 109Cd) flux techniques were used to show that RIT can also mediate a lower affinity Zn and Cd influx (K
m of 4 and 100 M, for Zn2+ and Cd2+, respectively). These findings suggest that, in typical agricultural soils, RIT1 functions primarily as a high-affinity Fe2+ transporter that mediates root Fe acquisition. This is consistent with recent findings with Arabidopsis IRT1 knockout mutants that strongly suggest that this transporter plays a key role in root Fe uptake and nutrition. However, the ability of RIT1 to facilitate Zn and Cd uptake when these metals are present at elevated concentrations suggests that RIT1 may be one pathway for the entry of toxic metals into the food chain. Furthermore, the finding that plant Fe deficiency status may promote heavy metal uptake via increased expression of this transporter could have implications both for human nutrition and also for phytoremediation, the use of terrestrial plants to sequester toxic metals from contaminated soil. 相似文献
19.
Phytostabilization strategies may be suitable to reduce the dispersion of uranium (U) and the overall environmental risks
of U-contaminated soils. The role of Glomus intraradices, an arbuscular mycorrhizal (AM) fungus, in such phytostabilization of U was investigated with a compartmented plant cultivation
system facilitating the specific measurement of U uptake by roots, AM roots and extraradical hyphae of AM fungi and the measurement
of U partitioning between root and shoot. A soil-filled plastic pot constituted the main root compartment (CA) which contained a plastic vial filled with U-contaminated soil amended with 0, 50 or 200 mg KH2PO4−P kg–1soil (CB). The vial was sealed by coarse or fine nylon mesh, permitting the penetration of both roots and hyphae or of just hyphae.
Medicago truncatula plants grown in CA were inoculated with G. intraradices or remained uninoculated. Dry weight of shoots and roots in CA was significantly increased by G. intraradices, but was unaffected by mesh size or by P application in CB. The P amendments decreased root colonization in CB, and increased P content and dry weight of those roots. Glomus intraradices increased root U concentration and content in CA, but decreased shoot U concentrations. Root U concentrations and contents were significantly higher when only hyphae could
access U inside CB than when roots could also directly access this U pool. The proportion of plant U content partitioned to shoots was decreased
by root exclusion from CB and by mycorrhizas (M) in the order: no M, roots in CB > no M, no roots in CB > M, roots in CB > M, no roots in CB. Such mycorrhiza-induced retention of U in plant roots may contribute to the phytostabilization of U contaminated environments. 相似文献
20.
Effects of defoliation and atmospheric CO2 depletion on nitrate acquisition,and exudation of organic compounds by roots of Festuca rubra 总被引:1,自引:1,他引:0
The aim of this study was to investigate the physiological basis of increased root exudation from Festuca rubra, in response to defoliation. The hypothesis, that assimilate supply to roots is a key determinant of the response of root exudation to defoliation was tested by imposing CO2-deplete (< 50 mol mol–1) atmospheres to F. rubra. This was done as a non-destructive means of preventing supply of new assimilate to roots of intact and defoliated plants. F. rubra was grown in axenic sand systems, with defoliation and CO2-depletion treatments applied to plants at 14 and 35 days after planting. Root exudation and NO3
– uptake were quantified throughout, and post-treatment uptake and allocation of N were determined from the distribution of 15N label, supplied as 15NO3
–. Defoliation of F. rubra resulted in significantly (P <0.01) increased root exudation, CO2-depletion did not result in increased exudation from plants of either age. When treatments were applied to F. rubra after 14 days, defoliation and CO2-depletion each reduced NO3
– uptake significantly (P <0.05). However, in older plants, uptake of NO3
– was less sensitive to defoliation and CO2-depletion. The results indicate that increased root exudation following defoliation is not related directly to reduced assimilate supply to roots. This was evident from the lack of effect of CO2-depletion on root exudation, and the absence of correlation between root-C efflux and the rate of NO3
– uptake. The physiological basis of increased exudation following defoliation remains uncertain, but may be dependent on physical damage, either directly or as a consequence of systemic responses to wounding. 相似文献