Influence of phosphate-stress on phosphate absorption and translocation by various parts of the root system of Hordeum vulgare L. (barley)

Plants of Hordeum vulgare (barley) were grown initially in a solution containing 150 M phosphate and then transferred on day 6 to solutions with (+P) and without (-P) phosphate supplied. After various times plants from these treatments were supplied with labelled phosphate. Analysis of plant growth and rates of labelled phosphate uptake showed that a general enhancement of uptake and translocation was found, in plants which had been in the-P solution, several days before the rate of dry matter accumulation was affected. Subsequently a detailed analysis of phosphate uptake by segments of intact root axes showed that the enhancement of phosphate uptake by P-stress occurred first in the old and mature parts of the seminal root axis and last in the young zones 1 cm from the root apex. During this transition period there were profound changes in the pattern of P absorption along the length of the root. Most of the additional P absorbed in response to P-stress was translocated to the shoot, particularly in older zones of the axis. Enhancement of phosphate uptake in young zones of nodal axes occurred at an earlier stage than in seminal axes. The results are related to the P-status of shoots and root zones and discussed in relation to the general control by the shoot of phosphate transport in the root.     

31P NMR Measurements of the Cytoplasmic and Vacuolar Pi Content of Mature Maize Roots: Relationships with Phosphorus Status and Phosphate Fluxes

The vacuolar and cytoplasmic inorganic phosphate (Pi) contentof the mature regions of maize roots was measured by a ³¹P NMRtechnique which used an external standard to avoid the needfor tissue extraction and which exploited the relatively rapidrelaxation of cytoplasmic Pi in order to improve the detectionof this pool in fully-vacuolated cells. In mature roots of maize growing with abundant external phosphate,the concentration of Pi in the cytoplasm was approximately 6.5mol m^–3. When these plants were deprived of external phosphate,the vacuolar Pi content of the roots decreased rapidly, butthe cytoplasmic Pi concentration initially remained constantand did not begin to decline until P-stress became severe. Calculationsshow that withdrawal of Pi from the vacuoles into the cytoplasmunder these conditions would be against an electrochemical gradient. During P-starvation, an increased capacity for Pi influx developed,preceding any detectable change in the cytoplasmic Pi contentof the roots. This response is considered in terms of paralleleffects on transport sites for phosphate at the plasmalemmaand at the tonoplast. Comparisons of simultaneous rates of influxand net uptake implied that phosphate efflux accounted for <10% of influx in plants of a steady or declining P-status. However,direct measurements of efflux suggested that this process maybe temporarily accelerated when plants are recovering from P-stress. Key words: P-nutrition, subcellular compartmentation     

The bacterial wilt,uptake of phosphate,and phosphate ester levels in the resistant and susceptible alfalfa plants

7 days or 7 weeks old alfalfa plants (Medicago sativa L.), susceptible (S) and resistant (R) to bacterial wilt, were inoculated withCorynebacterium michiganense pv.insidiosum and on day 8 and 15 after inoculation the levels of acid-soluble phosphate esters (P-esters) were determinated by means of³²P labelling in the shoots or roots. The most significant changes were recorded in the roots of the older R plants grown in full Knop nutrient solutions on day 8 after inoculation. The marked reduction of inorganic phosphate (P₁) uptake by whole R plants is accompanied by a decrease in the levels of fructose-l, 6-bisphosphate (Fru-P₂), glucose-6-phosphate (Glc-6-P), fructose-6-phosphate (Fru-6-P), adenosine mono-, and diphosphate (AMP and ADP), phosphorylcholine (P-choline) and a proportional increase in the level of P₁. In the S plants, infection affected neither P₁ uptake nor P₁ proportions. In the plants grown after inoculation in diluted Knop’s solutions (0.147 mM KH₂PO₄), infection induced a reduction of the radial transport of P₁ to the segments of R roots whereas a reduction of the levels was only recorded in some P-esters [AMP, ADP, dihydroxyacetone phosphate (DHAP), and P-choline, but no decrease of Fru-P₂, Glc-6-P and Fru-6-P]. In the S plants, P₁ transport and the levels of P-esters were increased by the infection. P₁ transport exhibited considerable metabolic dependence (DNP, DCCD). Bacterial infection probably had no influence on the activity of the plasma membrane ATPases.     

Growth, nitrate uptake and respiration rate in bean roots under phosphate deficiency

The decrease in inorganic phosphate concentration in bean (Phaseolus vulgaris L. cv. Złota Saxa) roots induced decrease in respiration rate. The decrease observed in ATP pool in phosphate deficient (-P) roots was greater than it would result from the decline in respiration and possible involvement of alternative pathway, suggesting an increased energy utilization for growth and ion uptake. Indeed, relative growth rate was higher in -P plants until 12 d of culture and later dropped to the rate similar to the control. Net nitrate uptake rate was higher in -P plants than in +P plants at the beginning of phosphate starvation, then during the prolonged culture it decreased rapidly in -P plants and after 19 d it was 8 times lower than that in the control. The decline in ATP production during prolonged phosphate starvation influenced NO₃ ^- uptake more than root growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Translocation and loss of phosphate along roots of wheat seedlings

Summary Sites of phosphate uptake, translocation and loss along sterile roots of 5-day-old wheat seedlings were obtained using an automatic scanning method. Highest uptake occurred in the apical centimetre of the primary root and in the lateral root zone although appreciable uptake occurred along the whole of the root. 68% of absorbed phosphate was translocated from the apex, 84% from the midroot portion and 87% from the lateral root zone after 24 hr. Profuse production of lateral roots is seen as important in phosphate uptake and translocation.Losses of absorbed phosphate from root to solution were small and the patterns of such losses along the root corresponded with the patterns of uptake by the root. Patterns of net flux of phosphate along the root are likely to be identical with those for influx. Patterns of phosphate loss along the root are in marked contrast to those reported for chloride efflux and loss of organic materials.     

The influence of phosphate nutrition on H ion efflux from the roots of young rape plants

Changes in pH around the roots of young rape plants were studied using a nutrient film technique which allowed either part or all of the root system to be subjected to specific nutrient treatments. The rapidity and direction of change of pH was assessed by embedding absorbing roots in a thin layer of agar containing bromocresol purple. Measurements were also made with a pH microelectrode placed next to the roots. Phosphate-fed plants were deprived of phosphate when 14 days old. Patterns of pH changes round the deprived roots were the same as with phosphate-fed plants until the plants had been deprived of P for three days, when H ion efflux started in the terminal portions of the roots. The lengths of root producing acid and amounts of H ion both increased as the plants became more P deficient. Both P fed and P deprived roots produced HCO₃ ions but the net amount of HCO₃ ion produced by the P deficient roots fell as did nitrate uptake rates. Cation-anion balances measured at the end of the experiment showed that uptake of all anions and K decreased in the P deprived plants but uptake of Ca and Mg were little altered. This resulted in a smaller ratio of anions to cations absorbed which was reflected in the reduced HCO₃ ion efflux.     

Nitrate uptake by bean (Phaseolus vulgaris L.) roots under phosphate deficiency

Bean (Phaseolus vulgaris L.) plants were cultured for 19 d on complete or on phosphate deficient culture media. Low inorganic phosphate concentration in the roots decreased ATP level and nitrate uptake rate. The mechanisms which may control nitrate uptake rate during phosphate deficiency were examined. Plasma membrane enriched fractions from phosphate sufficient and phosphate deficient plants were isolated and compared. The decrease in total phospholipid content was observed in plasma membranes from phosphate deficient roots, but phospholipid composition was similar. No changes in ATPase and proton pumping activities measured in isolated plasma membrane of phosphate sufficient and phosphate deficient bean roots were noted. The electron microscope observations carried out on cortical meristematic cells of the roots showed that active ATPases were found in plasma membrane of both phosphate sufficient and phosphate deficient plants. The decrease in inorganic phosphate concentration in roots led to increased nitrate accumulation in roots, accompanied by a corresponding alterations in NO₃ distribution between shoots and roots. Nitrate reductase activity in roots of phosphate deficient plants estimated in vivo and in vitro was reduced to 50–60% of the control. The increased NO₃ concentration in root tissue may be explained by decreased NR activity and lower transport of nitrate from roots to shoots. Therefore, the reduction of nitrate uptake during phosphate starvation is mainly a consequence of nitrate accumulation in the roots.     

Growth and Phosphate Transport in Barley and Tomato Plants During the Development of, and Recovery from, Phosphate-stress

Barley and tomato plants were cultured in nutrient solutionsincluding 0.15 mol m^–3 H²PO^–₄. The phosphate supplywas discontinued and the subsequent effects on growth, internalphosphorus concentrations, phosphate absorption and translocationwere measured at frequent intervals. Growth rates were at firstunchanged and the internal phosphorus concentration decreased.During this phase the rate of phosphate transport by the rootssometimes increased significantly. Growth slowed more in shootsthan in roots during a second phase of stress development andvisual symptoms of deficiency appeared in tomato but not inbarley. During this phase, enhancement of phosphate uptake capacityreached a maximum in both species. The subsequent decline inuptake capacity was associated with visible symptoms of deficiencydeveloping in barley and intensifying in tomato. When stressedplants were returned to a solution containing 0.15 mol m^–3H₂PO^–₄ rapid absorption continued for several days afterthe internal phosphorus concentration had returned to the levelof the controls. Phosphate toxicity may have been the causeof leaf lesions and necrosis during the ‘recovery’phase. Stomatal conductance in tomato was decreased at an early stageof stress development. Foliar-applied phosphate was absorbedmore rapidly by P-stressed barley leaves than by their controlsand much larger amounts were translocated from the leaves tothe roots.     

Enriched rhizosphere CO2 concentrations can ameliorate the influence of salinity on hydroponically grown tomato plants

Our previous work indicated that salinity caused a shift in the predominant site of nitrate reduction and assimilation from the shoot to the root in tomato plants. In the present work we tested whether an enhanced supply of dissolved inorganic carbon (DIC, CO₂+ HCO₃) to the root solution could increase anaplerotic provision of carbon compounds for the increased nitrogen assimilation in the root of salinity-stressed Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were grown in hydroponic culture with 0 or 100mM NaCl and aeration of the root solution with either ambient or CO₂-enriched air (5000 μmol mol^?1). The salinity-treated plants accumulated more dry weight and higher total N when the roots were supplied with CO₂-enriched aeration than when aerated with ambient air. Plants grown with salinity and enriched DIC also had higher rates of NO^?₃ uptake and translocated more NO^?₃ and reduced N in the xylem sap than did equivalent plants grown with ambient DIC. Incorporation of DIC was measured by supplying a 1 -h pulse of H¹⁴CO^?₃ to the roots followed by extraction with 80% ethanol. Enriched DIC increased root incorporation of DIC 10-fold in both salinized and non-salinized plants. In salinity-stressed plants, the products of dissolved inorganic ¹⁴C were preferentially diverted into amino acid synthesis to a greater extent than in non-salinized plants in which label was accumulated in organic acids. It was concluded that enriched DIC can increase the supply of N and anaplerotic carbon for amino acid synthesis in roots of salinized plants. Thus enriched DIC could relieve the limitation of carbon supply for ammonium assimilation and thus ameliorate the influence of salinity on NO^?₃ uptake and assimilation as well as on plant growth.     

The influence of salinity on phosphate uptake and distribution in lupin roots

Treeby, M. T. and van Steveninck, R. F. M. 1988. The influence of salinity on phosphate uptake and distribution in lupin roots. - Physiol. Plant. 72: 617–622.
The uptake and distribution of phosphate in lupin ( Lupinus luteus L. cv. Weiko III) roots under moderate salt (NaCl) stress was studied. Vacuolar inorganic phosphate (PJ concentrations in high phosphate plants were decreased by salt, although whole root P| was unaffected. In low phosphate plants, vacuolar P_i was unaffected by salt while whole root P_i was increased. Phosphate uptake was not altered by salt in high phosphate plants, but was depressed in low phosphate plants. These observations lead to the conclusion that in high phosphate plants P_i accumulates in cytoplasm and/or stele, ultimately giving rise to phosphate toxicity in shoots. Increasing phosphate supply had no effect on Na⁺ accumulation in root cell vacuoles in the epidermis or cortex, but the concentration of Cl⁻ in endodermal vacuoles was lowered.     

Nitrate Absorption and Acetylene Reduction by Soybeans during Reproductive Development

Nodulated and unnodulated soybeans (Glycine max [L.] Merr.) were grown in N-free or N-containing nutrient solutions, respectively. Starting at the initial flowering stage, and throughout reproductive growth, the NO₃- absorption capacity of roots of intact plants from both treatments was determined in short-term uptake experiments. Acetylene reduction activity was determined for nodulated plants. Nitrate absorption rate, expressed on a root dry weight basis, was greatest at early flowering for both nodulated and unnodulated plants. At 33 days after germination, the NO₃^- absorption rate of unnodulated plants was twice as great as that of nodulated plants. During the remainder of the sampling period, NO₃^- absorption rates of both nodulated and unnodulated plants decreased progressively and similarly. Maximum nodule specific activity occurred 30 days after germination, or initial flowering. However, maximum total C₂H₂ reduction activity, oner plant basis, was observed during the early stages of pod-filling. Compared to unnodulated plants dependent on NO₃^- assimilation, nodulated plants were smaller, had less N in vegetative tissues, and produced less seed per plant. We suggest that the higher NO₃^- absorption rate of unnodulated soybean roots, particularly during early reproductive growth, may have reflected a more favorable supply of photosynthate translocated to the roots from larger, more vigorous, non-N-stressed shoots.     

Citrate, Malate, and Succinate Concentration in Exudates from P-Sufficient and P-Stressed Medicago sativa L. Seedlings

Under certain stress conditions roots exude organic molecules, which may facilitate the uptake of nutrients. The objective of this research was to identify and measure the effect of low P upon the exudation of organic acids by roots of alfalfa (Medicago sativa L.) seedlings. Surface-sterilized alfalfa seeds were grown aseptically in sterile sand using an apparatus specially designed for the addition of ±P nutrient solutions and for the collection of root exudates. Citric, malic, and succinic acids were detected in the root exudates of 24-day-old alfalfa seedlings. Citrate exudation from the roots of P-stressed alfalfa was 182% that of plants receiving a complete nutrient solution. The increased release of citrate may provide a mechanism by which P-stressed plants enhance the availability of P in the rhizosphere.     

Role of iron plaque in Cd uptake by and translocation within rice (Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L⁻¹) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L⁻¹) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L⁻¹ Fe were exposed to ¹⁰⁹Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe₀ at Cd_0.1, and at Cd_1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of ¹⁰⁹Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to ¹⁰⁹Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.     

Uptake and transport of foliar applied zinc (65Zn) in bread and durum wheat cultivars differing in zinc efficiency

Using two bread wheat (Triticum aestivum) and two durum wheat (Triticum durum) cultivars differing in zinc (Zn) efficiency, uptake and translocation of foliar-applied ⁶⁵Zn were studied to characterize the role of Zn nutritional status of plants on the extent of phloem mobility of Zn and to determine the relationship between phloem mobility of Zn and Zn efficiency of the used wheat cultivars. Irrespective of leaf age and Zn nutritional status of plants, all cultivars showed similar Zn uptake rates with application of ⁶⁵ZnSO₄ to leaf strips in a short-term experiment. Also with supply of ⁶⁵ZnSO₄ by immersing the tip (3 cm) of the oldest leaf of intact plants, no differences in Zn uptake were observed among and within both wheat species. Further, Zn nutritional status did not affect total uptake of foliar applied Zn. However, Zn-deficient plants translocated more ⁶⁵Zn from the treated leaf to the roots and remainder parts of shoots. In Zn-deficient plants about 40% of the total absorbed ⁶⁵Zn was translocated from the treated leaf to the roots and remainder parts of shoots within 8 days while in Zn-sufficient plants the proportion of the translocated ⁶⁵Zn of the total absorbed ⁶⁵Zn was about 25%. Although differences in Zn efficiency existed between the cultivars did not affect the translocation and distribution of ⁶⁵Zn between roots and shoots. Bread wheats compared to durum wheats, tended to accumulate more ⁶⁵Zn in shoots and less ⁶⁵Zn in roots, particularly under Zn-deficient conditions. The results indicate that differences in expression of Zn efficiency between and within durum and bread wheats are not related to translocation or distribution of foliar-applied ⁶⁵Zn within plants. Differential compartementation of Zn at the cellular levels is discussed as a possible factor determining genotypic variation in Zn efficiency within wheat.     

Nature of the calcium effect in phosphate uptake by barley roots

Summary The rates of phosphate uptake of young intact plants were measured in solution at concentrations between 3.2×10^–7 M and 3.2×10^–5 M KH₂PO₄. The addition of 0.005 to 0.01M CaCl₂ increased the uptake rates to values of up to 4 times those of controls. The increases in uptake relative to the controls were most marked at the lowest phosphate concentrations. The addition of KCl also increased the uptake rates, but to a much smaller extent. The results are analyzed by the enzyme kinetic theory, and it is concluded that the uptake of phosphate at low ionic strengths is impeded by negative potentials at the root surface.The experimental results in this letter have appeared in a thesis.     

Effects of defoliation and atmospheric CO2 depletion on nitrate acquisition,and exudation of organic compounds by roots of Festuca rubra

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.     

Effect of Ophiobolus graminis infection on the assimilation and distribution of 14C in wheat

The uptake of ¹⁴C and movement of ¹⁴C-labelled assimilates in wheat plants inoculated with Ophiobolus graminis was examined following exposure of the second youngest leaf to ¹⁴CO₂. Autoradiographs of plants with infected seminal roots showed that assimilates were not translocated past the sites of root infection but accumulated in the undamaged portions of infected root systems, in particular the developing crown roots. There was no evidence that assimilates accumulated in the vicinity of O. graminis lesions. The net assimilation of ¹⁴CO₂ by wheat plants over a 5 h feeding period was not significantly affected by O. graminis infection. However, infection reduced the amount of ¹⁴C lost through respiration. Infection delayed the transfer of labelled assimilates from the fed leaf to the remainder of the plant but increased the proportion translocated to the roots. The latter effect was not apparent when infected plants were continuously irrigated during, and for 20 h following, the feeding period.     

Salinity and flooding stress effects on mycorrhizal and non-mycorrhizal citrus rootstock seedlings

Seedlings of the rootstocks Pineapple sweet orange (SwO), Carrizo citrange (CC), and sour orange (SO) were grown in low phosphorus (P) sandy soil and either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus intraradices, or were non-mycorrhizal (NM) and fertilized with P. VAM and NM seedings of similar shoot size and adequate P-status were selected for study of salinity and flooding stress. One-third of each of the VAM and NM plants were given 150 mM NaCl for a period of 24 days. One-third of the plants were placed into plastic bags and flooded for 21 days while the remaining third were non-stressed controls. In general, neither stress treatment affected mycorrhizal colonization. Salinity stress reduced the hydraulic conductivity of roots, leaf water potential, stomatal conductance and net assimilation of CO₂ (ACO₂) of mycorrhizal and non-mycorrhizal seedlings to a similar extent. VAM plants of CC and SO accumulated more Cl in leaves than NM plants. Cl was higher in non-mycorrhizal roots of SwO and CC than in mycorrhizal roots. Flooding the root zone for 3 weeks did not produce visible symptoms in the shoot but did influence plant water relations and reduce ACO₂ of all 3 rootstocks. VAM and NM plants of each rootstock were affected similarly by flooding. Comparable reduction in nitrogen and P content of both mycorrhizal and non-mycorrhizal plants suggested that flooding stress was primarily affecting root rather than hyphal nutrient uptake. Florida Agricultural Experimental Station Journal Series No. 7773.     

Uptake and transfer of nutrients in ectomycorrhizal associations: interactions between photosynthesis and phosphate nutrition

Energy-dispersive X-ray microanalytical investigations and microautoradiographic studies were carried out to examine whether the uptake and transfer of phosphate (P) by an ectomycorrhizal fungus is affected by the carbohydrate supply of its host plant. For this purpose, non-mycorrhizal seedlings of Pinus sylvestris L. and plants inoculated with the ectomycorrhizal basidiomycete Suillus bovinus (L. ex Fr.) Kuntze were placed in the dark for 7 days in advance of a P supply. The subcellular element distribution and the uptake and distribution of (33)P was analyzed in non-mycorrhizal and mycorrhizal roots of these plants and compared with plants kept constantly under normal light conditions (control plants). The results show that placing non-mycorrhizal plants in the dark in advance of the nutrient supply led to (1) a reduction of the subcellular contents of P, S and K, but to an increase in the cytoplasmic Na content, and (2) an increase of (33)P absorption and translocation to the shoot. It can be assumed that this increased inflow of (33)P in non-mycorrhizal plants was due to P starvation after suppressed photosynthesis and reduced respiration of these plants. The suppression of photosynthesis by an ectomycorrhizal host plant and the resulting lower carbohydrate supply conditions for the ectomycorrhizal fungus led to (1) a decrease of P absorption by the mycobiont, (2) a change of the P allocation in the fungal cell compartments of an ectomycorrhizal root, and (3) a reduction of P transfer to the host plant. However, microautoradiographic studies revealed that, under these conditions, P was also absorbed by the mycorrhizal fungus and translocated via the Hartig net to the host plant. In mycorrhizal roots of plants placed in the dark in advance of the nutrient supply, the cytoplasmic P content of the Hartig net was reduced and, instead, a high number of polyphosphate granules could be detected within the hyphae. The results indicate that the exchange processes between the symbionts in a mycorrhiza are possibly linked and that P uptake and translocation by an ectomycorrhizal fungus is also regulated by the carbohydrate supply of its host plant.