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1.
Transfer Cells in Roots of Phaseolus coccineus: Ultrastructure and Possible Function in Exclusion of Sodium from the Shoot 总被引:4,自引:0,他引:4
A study was made of ultrastructural aspects and ion distributionin roots of Phaseolus coccineus as affected by NaCl and Na2SO4salinity. In the proximal region of the root, xylem parenchymacells are differentiated as transfer cells with well developedwall protuberances adjacent to the half-bordered pits of thevessels. The cytoplasm of these transfer cells contains cisternaeof rough endoplasmic reticulum, the number of which was increasedgreatly when the plants were grown in the presence of NaCl orNa2SO4. The cisternae of the endoplasmic reticulum are oftenassociated closely with the plasmalemma and interconnected withit by fibrillar bridges. Wall protuberances occur also in the exodermis and epidermisof the more apical region of the root. Their function is stillunknown. P. coccineus excludes Na, but not Cl, from the leaves by retainingit particularly in the proximal region of the root. X-ray microanalysisof unfixed, frozen, hydrated specimens revealed that the transfercell-type xylem parenchyma cells in salt-treated roots accumulatedNa relative to both the adjoining xylem vessels and the corticalcells and showed very high Na/K and Na/Cl ratios. It is suggestedthat the xylem parenchyma cells can reabsorb Na from the vessels,probably in exchange for K, and that Na exclusion from the shootis at least partly mediated by this process. The implicationof this for regulation of salt transport in salt sensitive glycophytesis discussed. 相似文献
2.
Ion Distribution in Salt-stressed Mature Zea mays Roots in Relation to Ultrastructure and Retention of Sodium 总被引:5,自引:0,他引:5
Ultrastructural features and the distribution of soluble ionshave been examined in mature roots of Zea mays plants grownin both NaCl and Na2SO4 salinities. When the plants were grown in either salt, the Na concentrationincreased proximally along the root with a concomitant declinein the K concentration. Both trends were reversed in the shoot. X-ray microanalysis of deep-frozen, fully hydrated specimensshowed that in salt-treated roots Na, and Cl, or S were distributedabout stoichiometrically in the cortex and endodermis. Na wasusually less concentrated than the anion in the lumens of thevessels, but was concentrated markedly relative to either Clor S in the adjoining xylem parenchyma cells. In the older, proximal parts of seminal roots of plants grownboth without salt (controls) and in the presence of either NaClor Na2SO4, wall developments occurred in xylem parenchyma cellsat the half-bordered pits in which the cell wall became markedlythicker and possessed a loosely packed fibrillar structure.These structures were not comparable with the transfer-celltype of protuberances reported in the roots of other species. In the xylem parenchyma of plants grown in the presence of Na2SO4there were dramatic increases in the quantities of rough endoplasmicreticulum, ribosomes, and mitochondria relative both to controlsand NaCl treatments. The results are discussed in relation to the possible functionof the xylem parenchyma of the mature root in the reabsorptionof Na from the xylem sap, which may mitigate adverse effectsof salinity in salt-sensitive glycophytes. 相似文献
3.
Using excised roots of Atriplex hortensis L., cv. Gelbe Gartenmelde, the uptake, accumulation and xylem transport of K+ and Na+ have been measured. Influx as well as xylem transport proved to discriminate little between K+ and Na+ , when considered in relation to the external solution. Both K+ and Na+ inhibited the uptake and xylem transport of each other to about the same degree. Measurements of intracel-lular Na+ fluxes by means of compartment analysis indicated that the low degree of K/Na discrimination during uptake was due to low influx selectivity. Moreover, K+ /Na+ exchange at the plasmalemma was not very efficient in Atriplex roots. In order to establish the basis of the low K/Na discrimination in xylem transport, the rates of K+ and Na+ transport were related to the cytoplasmic K+ and Na+ concentrations to yield the selectivity ratio of transport, S(transport) = (φcx (K) × [Na+ ]c )/(φcx (Na) × [K+ ]c ). Under all conditions this ratio was far below one indicating that Na+ was favoured during xylem release in excised roots of Atriplex at low external concentrations. The implications of this discrimination in favour of Na+ are discussed with respect to salt tolerance of A. hortensis . 相似文献
4.
Within its wide range across Canada, jack pine is exposed to salinity from both natural and anthropogenic sources. To compare the effects of Cl and SO4 on salt injury, sand and solution-culture grown jack pine ( Pinus banksiana Lamb.) seedlings were treated with nutrient solutions containing 60 or 120 m M NaCl, 60 m M Na2 SO4 , or a mixture of 60 m M NaCl and 30 m M Na2 SO4 . After 5 weeks of salt treatments, concentrations of Cl, K, Na, and SO4 were determined in roots, stem and needles of the current and previous years growth, and in necrotic needles. To determine the role of water uptake in the absorption and translocation of salts in plants, total transpiration was measured as the loss of water from a sealed system and related to total plant uptake of Cl, Na, and SO4 . Sodium uptake and root-to-shoot transport rates were greater in treatments containing Cl. A delay in root-to-shoot transport of both Na and Cl indicates retention of these ions in the roots. Electrolyte leakage of needles was more closely related to treatment Cl concentrations than treatment Na concentrations. The transport of Na ions to the shoot was related to the presence of Cl, but was not related to transpiration rate. 相似文献
5.
Bean plants, Phaseolus vulgaris L. cv. Contender, were grown in the spring and summer seasons to study the relationship between xylem Na+/Cl-, transpiration rate, and salt tolerance. Eight-day-old seedlings were transplanted to 50% modified Hoagland solution with 1 mM NaCl. Four days after transfer, one of two treatments was applied: a control of 1 mM NaCl or a treatment of 25 mM NaCl every two days to reach a final treatment concentration of 75 mM NaCl. Plants were sampled on the fourth day after the final salt concentration was reached, eight days after the salinisation treatment began. Relative growth rate was 2.6-fold greater in summer than in spring. However, while no differences were found between treatments in spring, summer salt-treated plants had growth rates that were 31% lower than those of controls. In summer, CO2 assimilation, stomatal conductance, and transpiration rate of salinised plants declined with respect to controls. Leaf Na+ and trifoliolate leaf Cl- were higher in salt-treated plants in summer, although root Na+ was significantly higher in spring. Moreover, in summer salinity inhibited Ca2+ and K+ uptake and changed its distribution. Summer salt-treated plants had an average of 17-fold higher xylem Na+ during the daily cycle, while xylem Cl-, only in the afternoon, showed higher values (1.5-fold) compared to spring-grown plants. Our results suggest that the faster growth response to salt in summer-grown bean was at least partly due to an increase in xylem Na+ independent of the transpiration rate and possibly related to an increase in xylem Na+ influx or/and Na+ recirculation. 相似文献
6.
Sodium exclusion from leaves is an important mechanism for salt tolerance in durum wheat. To characterize possible control points for Na(+) exclusion, quantitative cryo-analytical scanning electron microscopy was used to determine cell-specific ion profiles across roots of two durum wheat genotypes with contrasting rates of Na(+) transport from root to shoot grown in 50 mm NaCl. The Na(+) concentration in Line 149 (low transport genotype) declined across the cortex, being highest in the epidermal and sub-epidermal cells (48 mm) and lowest in the inner cortical cells (22 mm). Na(+) was high in the pericycle (85 mm) and low in the xylem parenchyma (34 mm). The Na(+) profile in Tamaroi (high transport genotype) had a similar trend but with a high concentration (130 mm) in the xylem parenchyma. The K(+) profiles were generally inverse to those of Na(+). Chloride was only detected in the epidermis. These data suggest that the epidermal and cortical cells removed most of the Na(+) and Cl(-) from the transpiration stream before it reached the endodermis, and that the endodermis is not the control point for salt uptake by the plant. The pericycle as well as the xylem parenchyma may be important in the control of net Na(+) loading of the xylem. 相似文献
7.
Na+-K+ Exchange at the Xylem/Symplast Boundary (Its Significance in the Salt Sensitivity of Soybean) 总被引:2,自引:0,他引:2
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We investigated the mechanism of Na+ reabsorption in exchange for K+ at the xylem/symplast boundary of soybean roots (Glycine max var Hodgson). The xylem vessels of excised roots were perfused with solutions of defined composition to discriminate between entry of ions into or reabsorption from the xylem vessels. In the presence of NaCl, the transport systems released K+ into the xylem sap and reabsorbed Na+. The Na+-K+ exchange was energized by proton-translocating ATPases, enhanced by external K+ concentration, and dependent on the anion permeability. Evidence was presented for the operation of H+/Na+ and H+/K+ antiporters at the xylem/symplast interface. 相似文献
8.
Stomatal limitation of photosynthesis and reduced growth of the halophyte, Plantago maritima L., at high salinity 总被引:2,自引:3,他引:2
Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m−3 NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m−3 NaCl was only 20% of that in plants at low salinity. Both the Na+ and K+ content of leaves and roots increased with external salinity. There was no change in the Na+ /K+ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na+ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO2 and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO2 concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity. 相似文献
9.
Atripiex spongiosa was grown in hydroponic culture with additionof 0, 50, 200, 400 and 600 mM NaCl. Frozen, hydrated cells ofthe roots were analysed by X-ray micro-analysis. Comparisonswere made of meristematic cells at the root apex and vacuolatedcells 5.0 mm from the apex. High selectivitiy for K relativeto Na was found for the cytoplasm of meristematic cells andthere was little effect of increasing salinity on the ratiosNa/K, Cl/K, Na/P and CI/P. In the cell vacuoles of the cortex,selective uptake of K relative to Na also occurred, but to alesser extent than in the meristematic cells. Gradients werefound of decreasing ratio of Na/K from the epidermis to thestele. Measurements of chemical content of the roots and shoots ofthese plants showed that the ratio of Na/K was higher in theshoot than in the cortical cell vacuoles and higher again thanin the stele or meristematic cytoplasm. It is suggested thattransport of ions to the shoot of Atripiex spongiosa involvesselective exclusion of Na from the xylem parenchyma into thexylem, and that this may be general to other halophytes. Key words: Micro-analysis, X-ray, Cells, Atripiex spongiosa 相似文献
10.
Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA3 ) on K+ (Rb+ ) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA3 was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K+ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb+ replaced K+ , the GA3 effects were evident also on Rb+ uptake and transport. In intact plants, GA3 increased the Rb+ transported to the shoot but did not affect Rb+ accumulation in the root. It is suggested that these GA3 effects can be explained if it is assumed that GA3 acts on the transport of ions to the xylem vessels. 相似文献
11.
SERGEY SHABALA JIAYIN PANG MEIXUE ZHOU LANA SHABALA TRACEY A. CUIN PETER NICK & LARS H. WEGNER 《Plant, cell & environment》2009,32(2):194-207
Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from −18 to −12 nmol m−2 s−1 ) and K+ uptake (∼2 nmol m−2 s−1 ) reverted to efflux (∼−3 nmol m−2 s−1 ). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m−2 s−1 ). Kinetin (2–4 µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed. 相似文献
12.
Wegner LH Stefano G Shabala L Rossi M Mancuso S Shabala S 《Plant, cell & environment》2011,34(5):859-869
Early events in NaCl-induced root ion and water transport were investigated in maize (Zea mays L) roots using a range of microelectrode and imaging techniques. Addition of 100 mm NaCl to the bath resulted in an exponential drop in root xylem pressure, rapid depolarization of trans-root potential and a transient drop in xylem K(+) activity (A(K+) ) within ~1 min after stress onset. At this time, no detectable amounts of Na(+) were released into the xylem vessels. The observed drop in A(K+) was unexpected, given the fact that application of the physiologically relevant concentrations of Na(+) to isolated stele has caused rapid plasma membrane depolarization and a subsequent K(+) efflux from the stelar tissues. This controversy was explained by the difference in kinetics of NaCl-induced depolarization between cortical and stelar cells. As root cortical cells are first to be depolarized and lose K(+) to the environment, this is associated with some K(+) shift from the stelar symplast to the cortex, resulting in K(+) being transiently removed from the xylem. Once Na(+) is loaded into the xylem (between 1 and 5 min of root exposure to NaCl), stelar cells become more depolarized, and a gradual recovery in A(K+) occurs. 相似文献
13.
Major nitrogen compounds transported in xylem vessels from roots to top in Citrus trees 总被引:1,自引:0,他引:1
Tadashi Kato 《Physiologia plantarum》1981,52(2):275-279
Four-year-old citrus trees ( Citrus unshiu Marcovitch) were fed via the roots with (15 NH4 )2sO4 or K15 NO3 as a nitrogen source. Nitrogenous compounds and their isotopic abundances in fine roots and xylem sap from trunks were assayed in order to obtain information on the species of nitrogen released by the root system into the ascending xyiem stream.
Arginine, asparagine, nitrate and proline in xylem sap accounted for 48, 21, 13 and 10%, respectively, of the total nitrogenous constituents tested in the sap. However, in the trees fed with labelled ammonium the main nitrogenous compound labelled with15 N in the xylem sap was asparagine and glutamine, which accounted for 79% and 18%, respectively, of total labelled nitrogen. In the xylem sap of trees fed with labelled nitrate, nitrate accounted for 94% of total labelled nitrogen. Nitrate and asparagine followed by glutamine showed the highest ratios of isotopic abundance in xylem sap as compared to fine roots. Proline and arginine had much lower ratios. These results indicate that nitrate, asparagine and glutamine are the main nitrogenous compounds released by the roots to the xylem stream, whereas arginine and proline are released into the xylern vessels by the trunk tissues. Furthermore, nitrate and asparagine are probably in steady movement upward in the trunk xylem, whereas glutamine is more easily taken up by the trunk tissues than nitrate and asparagine. 相似文献
Arginine, asparagine, nitrate and proline in xylem sap accounted for 48, 21, 13 and 10%, respectively, of the total nitrogenous constituents tested in the sap. However, in the trees fed with labelled ammonium the main nitrogenous compound labelled with
14.
Summary Roots of detopped tobacco plants (Nicotiana tabacum var. Virginia Gold) were exposed to Na, K, and Ca salts or to water, and cation transfer to xylem vessels was measured. In some cases plants had been exposed to Na in addition to regular nutrient solutions before detopping. Calcium in the external medium greatly depressed the transport of Na from the external medium to the xylem vessels and it often stimulated the transfer of K from the external medium to the xylem vessels. The K/Na ratio in the exudate thus was dependent upon the Ca content of the external medium under these conditions. In contrast, externally applied Ca or Ca deficiency had very little effect on the transfer of preaccumulated K and Na from compartments within roots to the xylem vessels. The K/Na ratio in the exudate under these conditions was not related to Ca levels nor to mild Ca deficiency. The ratios decreased with time after detopping regardless of Ca level. Intact plants accumulated more Na than did root systems of detopped plants in a 6-day period.Riverside University of CaliforniaSoil Science and Agricultural Engineering 相似文献
15.
Physiological function of water channels as affected by salinity in roots of paprika pepper 总被引:16,自引:0,他引:16
Micaela Carvajal Vicente Martínez Carlos Francisco Alcaraz 《Physiologia plantarum》1999,105(1):95-101
The sap flow (Jv) and the osmotic pressure-dependent hydraulic conductance (L0 ) of detached exuding root systems from paprika pepper plants (cv. Albar) were measured. Plants stressed with NaCl (30 m M ) and with six times the macronutrients of the Hoagland nutrient solution (6×HNS) were compared with controls grown in complete Hoagland nutrient solution. Jv of +NaCl and +6×HNS plants decreased markedly, but recovered to values similar to those of controls after removal of the treatments. Hydraulic conductance L0 was always less in NaCl plants than in controls and 6×HNS. A total increase in the ion concentration of the xylem (except Na+ and Cl− ) was observed with both treatments. In control and 6×HNS plants, HgCl2 treatment (50 μ M ) caused a sharp decline in L0 to values similar to those of NaCl-stressed roots, but were restored by treating with 5 m M dithiothreitol (DTT). However, in NaCl roots only a slight effect of Hg2+ and DTT was observed. In each treatment, there was no difference in the flux of K+ into the xylem after HgCl2 and DTT application. The results suggest that NaCl decreased L0 of the roots by reducing either the activity or abundance of Hg-sensitive water channels. The putative reduction in water-channel function of NaCl-treated plants did not seem to be due to the osmotic effect. 相似文献
16.
Bert P. Stok Otto Gy. Tànczos Monika Kähr C. E. E. Stuiver ers Kylin Pieter J. C. Kuiper 《Physiologia plantarum》1981,52(1):115-123
Mg2+ - and Ca2+ -uptake was measured in dark-grown oat seedlings ( Avena sativa L. cv. Brighton) cultivated at two levels of mineral nutrition. In addition the stimulation of the ATPase activity of the microsomal fraction of the roots by Mg2+ was measured. Ca2+ -uptake by the roots was mainly passive. Mg2+ -uptake mainly active; the passive component of Mg2+ -uptake was accompanied by Ca2+ -efflux up to 60% of the Ca2+ present in the roots.
In general Mg2+ -uptake of oat roots was biphasic. The affinity of the second phase correspond well with that of the Mg2+ -stimulation of the ATPase activity, in low-salt roots as well as in high-salt roots and in roots of plants switched to the other nutritional condition. Linear relationships were observed when [phase 2] Mg2+ -uptake was plotted against Mg2+ -stimulation of the ATPase activity of the microsomal fraction of the roots. In 5 days old high-salt plants 1 ATP (hydrolysed in the presence of Mg2+ J corresponded with active uptake of a single Mg2+ ion, but in older high-salt roots and in low-salt roots more ATP was hydrolysed per net uptake of a Mg2+ ion. The results are discussed against the background of regulation of the Mg2+ -level of the cytoplasm of root cells by transport of Mg2+ by a Mg2+ -ATPase to the vacuole, to the xylem vessels, and possibly outwards. 相似文献
In general Mg
17.
Translocation of NH4 + was studied in relation to the expression of three glutamine synthetase (GS, EC 6.3.1.2) isogenes and total GS activity in roots and leaves of hydroponically grown oilseed rape ( Brassica napus ). The concentration of NH4 + in the stem xylem sap of NO3 − -fed plants was 0.55–0.70 m M , which was ≈60% higher than that in plants deprived of external nitrogen for 2 days. In NH4 + -fed plants, xylem NH4 + concentrations increased linearly both with time of exposure to NH4 + and with increasing external NH4 + concentration. The maximum xylem NH4 + concentration was 8 m M , corresponding to 11% of the nitrogen translocated in the xylem. In the leaf apoplastic solution, the NH4 + concentration increased from 0.03 m M in N-deprived plants to 0.20 m M in N-replete plants. The corresponding values for leaf tissue water were 0.33 and 1.24 m M , respectively. The addition of either NO3 − or NH4 + to N-starved plants induced both cytosolic gs isogene expression and GS activity in the roots. In N-replete plants, gs isogene expression and GS activity were repressed, probably due to carbon limitations, thereby protecting the roots against the excessive drainage of photosynthates. Repressed gs isogene expression and GS activity under N-replete conditions caused enhanced NH4 + translocation to the shoots. 相似文献
18.
Manuel Diaz de la Guardia José M. Fournier Manuel Benlloch 《Physiologia plantarum》1985,63(2):176-180
Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K+ levels (0.25 and 2.5 m M ) were used to study the effect of K+ content in the root on uptake and transport of K+ to the exuding stream of decapitated plants. Roots of plants grown in low K+ gave higher exudation flux, higher K+ concentration in exudate and higher K+ flux than high K+ roots. After 6 h of uptake the K+ flux in low K+ roots was about three times that in high K+ roots. When the roots were kept in a nutrient solution in which Rb+ replaced K+ , low K+ roots exuded much more Rb+ than K+ after the first 2 h, whereas high K+ roots exuded about similar amounts of K+ and Rb+ . In intact plants grown at three different K+ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K+ level in the nutrient solution and the Rb+ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes. 相似文献
19.
Salinity and waterlogging interact to reduce growth of poorly adapted species by, amongst other processes, increasing the rate of Na(+) and Cl(-) transport to shoots. Xylem concentrations of these ions were measured in sap collected using xylem-feeding spittlebugs (Philaenus spumarius) from Lotus tenuis and Lotus corniculatus in saline (NaCl) and anoxic (stagnant) treatments. In aerated NaCl solution (200 mM), L. corniculatus had 50% higher Cl(-) concentrations in the xylem and shoot compared with L. tenuis, whereas concentrations of Na(+) and K(+) did not differ between the species. In stagnant-plus-NaCl solution, xylem Cl(-) and Na(+) concentrations of L. corniculatus increased to twice those of L. tenuis. These differences in xylem ion concentrations, which were not caused by variation in transpiration between the two species, contributed to lower net accumulation of Na(+) and Cl(-) in shoots of L. tenuis, indicating that ion transport mechanisms in roots of L. tenuis were contributing to better 'exclusion' of Cl(-) and Na(+) from shoots, compared with L. corniculatus. Root porosity was also higher in L. tenuis, due to constitutive aerenchyma, than in L. corniculatus, suggesting that enhanced root aeration contributed to the maintenance of Na(+) and Cl(-) 'exclusion' in L. tenuis exposed to stagnant-plus-NaCl treatment. Lotus tenuis also had greater dry mass than L. corniculatus after 56 d in NaCl or stagnant-plus-NaCl treatment. Thus, Cl(-) 'exclusion' is a key trait contributing to salt tolerance of L. tenuis, and 'exclusion' of both Cl(-) and Na(+) from the xylem enables L. tenuis to tolerate, better than L. corniculatus, the interactive stresses of salinity and waterlogging. 相似文献
20.
Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K+ and NO3 − uptake by roots, both uptake of K+ and NO3 − and secretion into the xylem of young sunflower plants ( Helianthus annuus L.) were measured after changes in light intensity.
No close correlation was observed between the uptake of NO3 − and that of K+ ; an increase in light intensity produced a much greater stimulation of NO3 − uptake than of K+ uptake. On the other hand, secretion of NO3 − into the xylem was tightly coupled to that of K+ , and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K2 -malate shuttle on the regulation by the shoot of K+ and NO3 − secretion in the xylem, which is linked to NO3 − uptake, while K+ uptake is independent of this regulation mechanism. 相似文献
No close correlation was observed between the uptake of NO