Growth and physiological activity in <Emphasis Type="Italic">Larix kaempferi</Emphasis> seedlings inoculated with ectomycorrhizae as affected by soil acidification

To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H⁺ kg⁻¹). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H⁺ added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H⁺ kg⁻¹ but was significantly reduced in soil treated with 60 and 90 mmol H⁺ kg⁻¹. The concentrations of Al and Mn in needles or roots increased with increasing H⁺ added to the soil. The total N in seedlings significantly increased with increasing H⁺ in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO₂ saturation (P _max) was greater in soil treated with 10 mmol H⁺ kg⁻¹ than in controls, and was less is soils treated with greater than with 30 mmol H⁺ kg⁻¹, especially with 60 and 90 mmol H⁺ kg⁻¹. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased the values of P _max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120% greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall growth.     

The growth and phosphorus utilisation of plants in sterile media when supplied with inositol hexaphosphate, glucose 1-phosphate or inorganic phosphate

Seedlings of six temperate pasture species, three grasses and three legumes, were grown for 19–24 days in sterile agar or sand-vermiculite media, in the presence of inorganic phosphate (P_i), glucose 1-phosphate (G1P) or inositol hexaphosphate (IHP). Agar (pH 5.0) had a low IHP-sorbing capacity while IHP was almost completely sorbed in sand-vermiculite. P_i and G1P were relatively available in both media. Growth of each species was measured in relation to phosphorus (P) supply and levels of P_i supply at which shoot yields reached 90% of maximum yield (P_crit) were determined. P_crit values were generally higher for the legume species than for the grasses, and were six-fold higher for Trifolium subterraneum L. seedlings when grown in sand-vermiculite relative to agar. When supplied with G1P, seedlings of the six species grew as well as plants supplied with P_i. By contrast, IHP was a poor source of P for plant growth, even when supplied in agar at levels up to 40-fold greater than P_crit. Using the growth of T. subterraneum in the presence of IHP, it was calculated that roots released approximately 0.09 nkat phytase g^-1 root dry wt per day, over 20 days of growth. By supplementing agar containing IHP with phytase from Aspergillus niger (E.C. 3.1.3.8; 0.012 nkat plant^-1, or _∼1.3 nkat g^-1 root dry wt), sufficient P became available to enable T. subterraneum seedlings to grow as well as P_i-supplied plants. These results indicate that while pasture plants can quite effectively use P from some organic P sources (e.g. G1P), the acquisition of phytate-P is limited both by availability of substrate and the capacity of plant roots to hydrolyse available IHP. This revised version was published online in June 2006 with corrections to the Cover Date.     

Responses of Wheat Roots to Exogenous Selenium Supply Under Enhanced Ultraviolet-B

Effects of selenium (Se) on growth and some physiological traits of roots in wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress are reported. Responses of roots were different depending on the Se concentration. Compared with the control, root weight of wheat seedlings treated with 1.0 and 2.0 mg Se kg⁻¹ soil increased by 39.47% and 16.28%, respectively. The lower amount Se (0.5 mg kg⁻¹) and the higher amount Se treatments (3.0 mg kg⁻¹) did not significantly affect on root weight. Se treatments significantly increased root activity, flavonoids and proline content, and activities of peroxidase and superoxide dimutase in wheat roots exposed to enhanced UV-B. In addition, the treatments with 0.5, 1.0, and 2.0 mg Se kg⁻¹ significantly reduced malondialdehyde content and the rate of superoxide radical (O₂⁻) production of roots, whereas the higher amount Se treatment only induced a decrease in the rate of O₂⁻ production. The results of this study demonstrated that optimal Se supply promoted roots growth of wheat seedlings, and that optimal Se supply could reduce oxidative stress in wheat roots under enhanced UV-B radiation.     

Influence of aluminum and phosphorus on growth and xylem sap composition in Melastoma malabathricum L.

Melastoma (Melastoma malabathricum L.) is an aluminum-accumulating woody plant that accumulates more than 10 000 mg kg^–1 of aluminum (Al) in mature leaves. The influence of Al and phosphorus (P) applications on plant growth and xylem sap was examined in the present study in order to elucidate the interaction between Al-induced growth enhancement and P nutrition, and to determine the form of Al for translocation from roots to shoots. Although the Al application significantly increased the growth of Melastomaseedlings with the high P pre-treatment, and P concentrations in the leaves and Pi concentrations in the xylem sap regardless of the P pre-treatment, we could not come to the conclusion that a primary cause of the Al-induced growth enhancement in Melastoma is the stimulation of P uptake. The degree of Al-induced growth enhancement corresponded not with the P concentrations but with the Al concentrations in the plant tissue, suggesting that the Al-induced growth enhancement in Melastoma is primarily caused by Al itself in the plant tissue rather than by the stimulation of P uptake. Through the analysis of organic acids and Al in the xylem sap and plant tissue, the form of Al for translocation from roots to shoots was shown to be an Al-citrate complex that was transformed into Al-oxalate complex for Al storage in the leaves. In addition, the xylem sap of Melastoma seedlings grown in the absence of Al contained higher concentrations of malate. In the presence of Al, however, higher concentrations of citrate were found, indicating that Melastoma changes its organic acid metabolism in the presence or absence of Al; more specifically, it increases the synthesis of citrate.     

Contrasting species responses to continued nitrogen and phosphorus addition in tropical montane forest tree seedlings

Global changes in nutrient deposition rates are likely to have profound effects on plant communities, particularly in the nutrient‐limited systems of the tropics. We studied the effects of increased nutrient availability on the seedlings of six tree species in montane forests of southern Ecuador in situ. After five years of continued N, P, or N+P addition, naturally grown seedlings of each of the two most common species at each elevation (1000, 2000, and 3000 m asl) were harvested for analyses of leaf morphology, nutrient content, herbivory, and tissue biomass allocation. Most species showed increased foliar N and P concentrations after addition of each respective element. Leaf tissue N:P ratios of >20 in the control plants of all species suggest that P is more growth‐limiting in these forests than N. Leaf morphological responses to nutrient addition were species and nutrient specific, with some species (Hedyosmum purparescens, Graffenrieda emarginata) exhibiting increased specific leaf area (SLA), and others (Graffenrieda harlingii) increased leaf area ratios (LAR). Pouteria torta (1000 m) had lower SLA and LAR after P addition. Increased herbivory was only evident in G. emarginata (after N and N+P addition). Only the species from 3000 m asl modified biomass allocation after nutrient addition. In general, N and N+P addition more strongly affected the species studied at the upper elevations, whereas P addition had a similar range of effects on the species at all elevations. We conclude that the responses of the studied tropical montane forest tree seedlings to chronic N and P addition are highly species‐specific and that successful adaptation to increased nutrient availability will depend on species‐specific morphological and physiological plasticity.     

A simple and efficient protocol for cryopreservation of embryogenic calli of the medicinal plant <Emphasis Type="Italic">Anemarrhena asphodeloides</Emphasis> Bunge by vitrification

Somatic embryogenesis and whole plant regeneration was achieved in callus cultures derived from immature zygotic embryos of Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst., recently identified as chromium (Cr), cadmium (Cd), lead (Pb) and nickel (Ni) accumulator. Embryogenic calli were induced on Murashige and Skoog (MS) medium added with a mixture of organic components plus N-6 benzyladenine (BA) (6.62 μM) and 2,4-dichlorophenoxyacetic acid (2,4-D) (2.26 μM) or thidiazuron (4.54–9.08 μM) and indole-3-acetic acid (1.42 μM). Embryogenic calli transferred onto half-strength MS medium without plant growth regulators developed globular embryos, of which 20% matured when treated with 3.75% (w/v) polyethylene glycol (PEG), and of these 50% fully differentiated into plantlet embryo. Regenerated plants were successfully acclimatized (90%), while in vitro seedlings transferred to MS medium containing 0.5 mM Cd, Cr, Ni or Pb, exhibited high heavy metals accumulation (627 mg Cr kg⁻¹, 5,688 mg Cd kg⁻¹, 1,148 mg Ni kg⁻¹, and 3,037 mg Pb kg⁻¹ dry weight) and efficient roots to shoots translocation (42–73%).     

Silicate-Mediated Alleviation of Pb Toxicity in Banana Grown in Pb-Contaminated Soil

Silicate (Si) can enhance plant resistance or tolerance to the toxicity of heavy metals. However, it remains unclear whether Si can ameliorate lead (Pb) toxicity in banana (Musa xparadisiaca) roots. In this study, treatment with 800 mg kg⁻¹ Pb decreased both the shoot and root weight of banana seedlings. The amendment of 800 mg kg⁻¹ Si (sodium metasilicate, Na₂SiO₃·9H₂O) to the Pb-contaminated soil enhanced banana biomass at two growth stages significantly. The amendment of 800 mg kg⁻¹ Si significantly increased soil pH and decreased exchangeable Pb, thus reducing soil Pb availability, while Si addition of 100 mg kg⁻¹ did not influence soil pH. Results from Pb fractionation analysis indicated that more Pb were in the form of carbonate and residual-bound fractions in the Si-amended Pb-contaminated soils. The ratio of Pb-bound carbonate to the total Pb tended to increase with increasing growth stages. Treatment with 100 mg kg⁻¹ Si had smaller effects on Pb forms in the Si-amended soils than that of 800 mg kg⁻¹ Si. Pb treatment decreased the xylem sap greatly, but the addition of Si at both levels increased xylem sap and reduced Pb concentration in xylem sap significantly in the Si-amended Pb treatments. The addition of Si increased the activities of POD, SOD, and CAT in banana roots by 14.2% to 72.1% in the Si-amended Pb treatments. The results suggested that Si-enhanced tolerance to Pb toxicity in banana seedlings was associated with Pb immobilization in the soils, the decrease of Pb transport from roots to shoots, and Si-mediated detoxification of Pb in the plants.     

The ability of 16 ectomycorrhizal fungi to increase growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell.

The effectiveness of 16 fungal isolates in forming ectomycorrhizas and increasing the growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell. seedlings was examined in the glasshouse. Seedlings were grown in yellow sand at 2 phosphorus levels (4 and 12 mg P kg^-1 sand). At the time of harvest (100 days), the non-inoculated seedlings and seedlings inoculated with Paxillus muelleri (Berk.) Sacc. and Cortinarius globuliformis Bougher had a low level of contamination from an unknown mycorrhizal fungi. Seedlings inoculated with Thaxterogaster sp. nov. and Hysterangium inflatum Rodway had developed mycorrhizas of the superficial type whereas Hydnangium carneum Wallr. in Dietr., Hymenogaster viscidus Massee & Rodway, Hymenogaster zeylanicus Petch, Setchelliogaster sp. nov., Laccaria laccata (Scop. ex. Fr.) Berk., Scleroderma verrucosum (Vaillant) Pers., Amanita xanthocephala (Berk.) Reid & Hilton, Descolea maculata Bougher and Malajczuk and Pisolithus tinctorius (Pers.) Coker & Couch formed typical pyramidal ectomycorrhizas. The dry weight of non-inoculated and inoculated E. globulus seedlings at 12 mg P kg^-1 sand did not differ, whereas several isolates caused growth depression of E. diversicolor. By contrast, at 4 mg P kg^-1 sand growth increases ranged from 0–13 times above that of non-inoculated seedlings. P. tinctorius produced the largest growth increase on both eucalypt species. In general, isolates which developed more extensive mycorrhizas on roots produced the largest growth responses to inoculation. Isolates which increased plant growth also increased phosphorus uptake by the plant. Seedlings inoculated with L. laccata and S. verrucosum retained more phosphorus in their roots than plants inoculated with the other fungal isolates.     

Mechanisms for tolerance of very high tissue phosphorus concentrations in Ptilotus polystachyus

Study of plants with unusual phosphorus (P) physiology may assist development of more P‐efficient crops. Ptilotus polystachyus grows well at high P supply, when shoot P concentrations ( [P] ) may exceed 40 mg P g^?1 dry matter (DM). We explored the P physiology of P. polystachyus seedlings grown in nutrient solution with 0–5 mM P. In addition, young leaves and roots of soil‐grown plants were used for cryo‐scanning electron microscopy and X‐ray microanalysis. No P‐toxicity symptoms were observed, even at 5 mM P in solution. Shoot DM was similar at 0.1 and 1.0 mM P in solution, but was ～14% lower at 2 and 5 mM P. At 1 mM P, [P] was 36, 18, 14 and 11 mg P g^?1 DM in mature leaves, young leaves, stems and roots, respectively. Leaf potassium, calcium and magnesium concentrations increased with increasing P supply. Leaf epidermal and palisade mesophyll cells had similar [P]. The root epidermis and most cortical cells had senesced, even in young roots. We conclude that preferential accumulation of P in mature leaves, accumulation of balancing cations and uniform distribution of P across leaf cell types allow P. polystachyus to tolerate very high leaf [P].     

Metabolic responses in cucumber (Cucumis sativus L.) roots under Fe-deficiency: a 31P-nuclear magnetic resonance in-vivo study

The metabolic responses occurring in cucumber (Cucumis sativus L.) roots (a strategy-I plant) grown under iron-deficiency conditions were studied in-vivo using ³¹P-nuclear magnetic resonance spectroscopy. Iron starvation induced activation of metabolism leading to the consumption of stored carbohydrates to produce the NAD(P)H, ATP and phosphoenolpyruvate necessary to sustain the increased activity of the NAD(P)H:Fe³⁺-reductase, the H⁺-ATPase (EC 3.6.1.35) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Activation of catabolic pathways was supported by the enhancement of glycolytic enzymes and concentrations of the metabolites glucose-6-phosphate and fructose-6-phosphate, and by enhancement of the respiration rate. Moreover, Fe-deficiency induced a slight increase in the cytoplasmic (pH_c) and vacuolar (pH_v) pHs as well as a dramatic decrease in the vacuolar phosphate (Pi) concentration. A comparison was done using fusicoccin (FC), a fungal toxin which stimulates proton extrusion. Changes in pH_c and pH_v were measured after addition of FC. Under these conditions, a dramatic alkalinization of the pH_v of −Fe roots was observed, as well as a concomitant Pi movement from the vacuole to the cytoplasm. These results showed that Fe starvation was indeed accompanied by the activation of metabolic processes useful for sustaining the typical responses occurring at the plasma-membrane level (i.e. increases in the NAD(P)H:Fe³⁺-reductase and H⁺-ATPase activities) as well as those involved in the homeostasis of pH_c. The decrease in vacuolar Pi levels induced by Fe-deficiency and FC and movement of Pi from the vacuole to the cytoplasm suggest a possible involvement of this compound in the cellular pH-stat system. Received: 30 July 1999 / Accepted: 11 November 1999     

Intermittent lead‐induced stress on antioxidant enzyme activity and subcellular distribution of Pb in Pogonatherum crinitum seedlings

• Pogonatherum crinitum is a promising lead (Pb) hyperaccumulator due to its high Pb tolerance and accumulation ability. However, the mechanisms that support Pb accumulation and tolerance in P. crinitum are not yet clearly understood.
• An indoor hydroponic experiment was conducted by cultivating P. crinitum seedlings exposed to intermittent Pb stress for 60 days, divided into four stages (T1, T2, T3 and T4), with a 15‐day duration per stage. The following concentrations of Pb were used: 0, 500, 0, 500 mg·l^?1 and 0, 1000, 0, 1000 mg·l^?1). Antioxidant enzyme activity, Pb concentration and subcellular distribution of Pb were measured at each of the above stages.
• The results showed that superoxide dismutase (SOD) activity in shoots, and SOD, peroxidase (POD) and malondialdehyde (MDA) activity in shoots and roots significantly increased from T1 (no Pb stress) to T2 (Pb stress) in both 500 mg·l^?1 and 1000 mg·l^?1 treatments; however, no significant difference was noted between stages T3 (no Pb stress) and T4 (Pb stress). There was no obvious effect of Pb stress on catalase (CAT) activity in shoots and roots among different stages. The Pb concentration in shoots was up to 5090.90 mg·kg^?1 and 7573.57 mg·kg^?1, and the bioconcentration factor (BFC) was 10.18 and 7.57 for the 500 mg·l^?1 and 1000 mg·l^?1 treatments, respectively, which confirmed the Pb hyperaccumulator characteristics of P. crinitum. For plants under Pb stress, most of the Pb was fixed in the cell walls, with a smaller amount in leaves and root vacuoles.
• Both SOD and POD scavenging of reactive oxygen radicals and fixing and compartmentalisation of Pb in the cell wall might play important roles in detoxification of P. crinitum seedlings in response to Pb stress. There was no phased response of P. crinitum to intermittent Pb stress and the physiological response to Pb stress may be contiguous.

     

Preferential utilization of organic and inorganic sources of phosphorus by wheat plant

On soils of low P supply organic P (Po) makes up a similar or even larger part in soil solution than inorganic P (Pi). The ability of wheat (Triticum aestivum L., cv. Star) plants to hydrolyze and absorb this Po in comparison to similar concentrations of Pi was studied. Four concentration levels of Pi and Po were obtained by extracting two soils with deionized water in a ratio of 1:1 and concentrating the resulting filtrate by freeze drying to different degrees. The concentration of Pi varied between 5 and 36 μM and Po between 3 and 22 μM. Wheat seedlings were grown in these solutions for 12 and 24 h and acid and alkaline phosphatase activity determined. The reduction of Po concentration in solution expressed on a root length basis gave the rate of Po hydrolysis and the reduction in concentration of Pi and Po gave the P inflow into the roots. No alkaline phosphatase activity was detected. The activity of wheat root acid phosphatase increased with Po concentration in solution. Phosphorus uptake was 2 to 6 fold higher from Pi than from Po at similar concentrations of both. The rate of uptake from Pi, the inflow, as well as the rate of hydrolysis of Po increased linearly with concentration but at similar concentration the inflow was 2 to 4 times higher than the rate of Po hydrolysis. Results suggest that plants can utilize Po after hydrolysis by phosphatase, but Pi is more important and preferentially used by plants; Po may be essential for plant nutrition especially in high P-fixing soils.     

Involvement of soluble proteins in growth and metabolic adjustments of drought‐stressed Calligonum mongolicum seedlings under nitrogen addition

• The planting of seedlings is the most effective measure for vegetation restoration. However, this practice is challenging in desert ecosystems where water and nutrients are scarce. Calligonum mongolicum is a sand‐fixing pioneer shrub species, and its adaptive strategy for nitrogen (N) deposition and drought is poorly understood.
• Thus, in a pot experiment, we studied the impacts of four N levels (0, 3, 6, 9 gN·m^?2·year^?1) under drought or a well‐watered regime on multiple eco‐physiological responses of 1‐year‐old C. mongolicum seedlings.
• Compared to well‐watered conditions, drought considerably influenced seedling growth by impairing photosynthesis, osmolyte accumulation and activity of superoxide dismutase and enzymes related to N metabolism. Nitrogen addition improved the productivity of drought‐stressed seedlings, as revealed by increased water use efficiency, enhanced superoxide dismutase and nitrite reductase activity and elevated N and phosphorus (P) levels in seedlings. Nevertheless, the addition of moderate to high levels of N (6–9 gN·m^?2·year^?1) impaired net photosynthesis, osmolyte accumulation and nitrate reductase activity. N addition and water regimes did not markedly change the N:P ratios of aboveground parts; while more biomass and nutrients were allocated to fine roots to assimilate the insufficient resources. Soluble protein in assimilating shoots might play a vital role in adaptation to the desert environment.
• The response of C. mongolicum seedlings to N addtion and drought involved an interdependency between soluble protein and morphological, physiological and biochemical processes. These findings provide an important reference for vegetation restoration in arid lands under global change.

     

Antioxidant Responses of Wheat Seedlings to Exogenous Selenium Supply Under Enhanced Ultraviolet-B

The paper reports the effects of selenium (Se) supply on growth and antioxidant traits of wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress. Antioxidant responses of seedlings were different depending on the Se concentration. Compared with the control, the lower amount used (0.5 mg Se kg⁻¹ soil) had no significant effect on biomass accumulation. The treatments with 1.0, 2.0, and 3.0 mg Se kg⁻¹ promoted biomass accumulation of wheat seedlings, and the increased amount in biomass was the most at 1.0 mg Se kg⁻¹ treatment. Se treatments with 1.0, 2.0, and 3.0 mg kg⁻¹ also significantly increased activities of peroxidase (POD) and superoxide dismutase (SOD) and reduced the rate of superoxide radical (O₂⁻) production and malondialdehyde (MDA) content of wheat seedlings. In addition, anthocyanins and phenolic compounds content in wheat seedlings evidently increased by the treatments with 1.0 and 2.0 mg Se kg⁻¹. The lower Se treatment had no significant effect on MDA content, although it increased activities of antioxidant enzymes (POD, SOD, and catalase activities) and reduced the rate of O₂⁻ production in wheat seedlings. These results suggest that optimal Se supply is favorable for the growth of wheat seedlings and that optimal Se supply can reduce oxidative stress of seedlings under enhanced UV-B radiation.     

Chickpea facilitates phosphorus uptake by intercropped wheat from an organic phosphorus source

Pot experiments were conducted to investigate interspecific complementation in utilization of phytate and FePO₄ by plants in the wheat (Triticum aestivum L.)/chickpea (Cicer arietinum L.) intercropping under sterile and non-sterile conditions. The pots were separated into two compartments by either a solid root barrier to eliminate root contact and solute movement, by a nylon mesh (30 M) to prevent root contact but permit solute exchange, or not separated between the compartments. Wheat plants were grown in one compartment and chickpea in the other. Two P sources were tested at 60 mg P kg^–1 soil (sodium phytate or FePO₄). Under non-sterile conditions, the biomass of wheat was significantly greater when the roots were intermingled with chickpea than when the roots were separated from chickpea roots by a solid root barrier or nylon mesh. When phytate–P was applied, P concentrations in wheat (2.9 g kg^–1 in shoots and 1.4 g kg^–1 in roots) without root barrier between the two species were higher than those in the treatments with nylon mesh or with the solid root barrier separation (1.9 g kg^–1 in shoots and 1.0 g kg^–1 in roots). In contrast, P concentrations in wheat supplied with FePO₄ were similar between the root separation treatments. There was no significant difference in P uptake by chickpea between the P sources or between the root separation treatments, except that P uptake was greater in the phytate treatment with the root barrier. Total P uptake from phytate was increased by 25% without root separation compared to the root separation treatments. Under sterile conditions and supply of phytate–P, the biomass of wheat was doubled when the roots were intermingled with chickpea and increased by a third with the nylon mesh separation compared to that with the solid root barrier. Biomass production in wheat at various treatments correlated with P concentration in shoot. Biomass production and P concentration in chickpea were unaffected by root separation. Total P uptake by plants was 68% greater with root intermingling and 37% greater with nylon mesh separation than that with the solid root barrier. The results suggest that chickpea roots facilitate P utilization from the organic P by wheat.     

Physiological adaptations to phosphorus deficiency during proteoid root development in white lupin

Release of large amounts of citric acid from specialized root clusters (proteoid roots) of phosphorus (P)-deficient white lupin (Lupinus albus L.) is an efficient strategy for chemical mobilization of sparingly available P sources in the rhizosphere. The present study demonstrates that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly restricted to mature root clusters in the later stages of P deficiency. Inhibition of citrate exudation by exogenous application of anion-channel blockers such as ethacrynic- and anthracene-9-carboxylic acids may indicate involvement of an anion channel. Phosphorus-deficiency-induced accumulation and subsequent exudation of citric acid seem to be a consequence of both increased biosynthesis and reduced metabolization of citric acid in the proteoid root tissue, indicated by increased in-vitro activity and enzyme protein levels of phosphoenolpyruvate carboxylase (EC 4.1.1.31), and reduced activity of aconitase (EC 4.2.1.3) and root respiration. Similar to citric acid, acid phosphatase, which is secreted by roots and involved in the mobilization of the organic soil P fraction, was released predominantly from proteoid roots of P-deficient plants. Also ³³Pi uptake per unit root fresh-weight was increased by approximately 50% in juvenile and mature proteoid root clusters compared to apical segments of non-proteoid roots. Kinetic studies revealed a K _m of 30.7 μM for Pi uptake of non-proteoid root apices in P-sufficient plants, versus K _m values of 8.5–8.6 μM for non-proteoid and juvenile proteoid roots under P-deficient conditions, suggesting the induction of a high-affinity Pi-uptake system. Obviously, P-deficiency-induced adaptations of white lupin, involved in P acquisition and mobilization of sparingly available P sources, are predominantly confined to proteoid roots, and moreover to distinct stages during proteoid root development. Received: 10 September 1998 / Accepted: 22 December 1998