Root to shoot translocation of macronutrients in relation to shoot demand in maize (Zea mays L.) grown at different root zone temperatures

Root growth and nutrient uptake rates of maize (Zea mays L.) are decreased at low root zone temperatures (RZT) and thus, shoot growth may be limited by nutrient deficiency. The objectives of this research were to characterize the shoot demand for nutrients per unit root at suboptimal RZT and to relate net translocation rates of N, P, K, and Ca from the roots to the shoot to shoot demand. Maize plants were grown for 11 days in soil or 8 days in nutrient solution at uniform shoot (24°/20°C, day/night) but different RZT (12°, 18°, and 24°C). The shoot base of the plants (apical shoot meristem and zone of leaf extension) was either kept within or above the cooled root zone. Shoot and root growth were significantly reduced at suboptimal RZT (12°, 18°). Lifting the shoot base above the cooling zone increased shoot growth markedly, whereas root growth was not significantly influenced. Thus, the shoot fresh weight increment day^?1 g^?1 root fresh weight (i.e. the shoot demand per unit root) was increased by a factor of up to 9 for plants with their shoot base above as compared to within the cooling zone. At suboptimal RZT, translocation rates of N, K, and Ca to the shoot remained low in plants with the shoot base in the cooling zone but were higher than in 24°C-grown plants, when the shoot base was above the cooling zone. In both nutrient solution- and soil-grown plants translocation rates of N, K, and Ca were closely correlated with the shoot demand per unit root but less to RZT. In contrast, the translocation rate of P was mainly affected by RZT but insensitive to shoot demand and, therefore, was always higher at a RZT of 24° than of 12°C. From these results it is suggested, that at low RZT the root-to-shoot translocation rates of N, K, and Ca are mainly determined by the shoot demand, whereas the translocation rate of P, regardless of the shoot demand, is reduced by a direct effect of low temperature on the roots.     

Cycling of nitrogen and potassium between shoot and roots in maize as affected by shoot and root growth

In nitrate-fed plants cycling of nitrogen (N) and potassium (K) may serve several functions including supply of the roots with nutrients needed for growth, signalling of the growth-related shoot demand for nutrients to the roots, and removal of excess K from the shoot. In the present study, cycling and recycling of N and K were estimated in plants showing different rates of shoot and root growth. To induce these variations in growth, the plants were cultured with the same optimal nutrient supply but with the root zone temperature (RZT) at 12°C or 24°C. Additionally at both RZT, the plants were grown with their shoot base including apical shoot meristem at high or low temperature (SBT). Decreasing the RZT to 12°C drastically diminished root growth and accumulation of N and K in the roots. Cycling of N and K were less reduced by low RZT. At both RZT, N and K cycling were markedly reduced at low in comparison to high SBT although root growth was not affected by the SBT. Obviously, N and K cycling from shoot to roots were more affected by shoot growth than by the growth related demand of the roots for nutrients. At both RZT, N and K cycling exceeded accumulation in the roots. It was estimated that at least 20—33% of the N, and 24—51% of the K translocated from the roots to the shoot in the xylem is not directly derived from root uptake but from cycling. Plant culture at low shoot base temperature (SBT) drastically diminished shoot growth, and the accumulation of N and K in the shoot to less than 50% of the values measured in plants grown at high SBT. The low SBT-induced decrease of N accumulation in the shoot, at both RZT was associated with a reduction of K circulation and recirculation rates to less than 50% of those found in plants grown at high SBT. These findings are in accordance with the suggested role of K⁺ for charge balance facilitating the transport of NO₃^— in the xylem and disposal of the negatively charged products of NO₃^— assimilation from shoot to roots in the phloem. In plants cultured at low SBT, net uptake and translocation rates of N and K were diminished to less than 50% of those measured in plants grown at high SBT. This repression was associated with reduced rates of N and K cycling from the shoot to the roots. Obviously, low rates of N and K cycling from the shoot to the roots are not necessarily signals to increase uptake in the roots. It is suggested that for plants adequately supplied with N, high rates of N cycling and recycling might be the consequence of an apparent lack in control of phloem loading of amino acids in the leaves.     

MODELING GROWTH AND ION CONCENTRATION OF LILIUM IN RESPONSE TO NITROGEN:POTASSIUM:CALCIUM MIXTURE SOLUTIONS

Nutrient solution composition plays an important role in root uptake rate due to interactions among nutrients and internal regulation. Studies to determine the optimum nutrient solution concentration are focused on individual ions, ignoring the adaptation mechanisms triggered by plants when growing in a varying external nutrient concentration. The objective of the present study was to determine the response in growth and tissue ion concentration of lilium cv. ‘Navona’ to nutrient mixtures of varying proportions of nitrogen (N), potassium (K⁺), and calcium (Ca²⁺) in solution using mixture experiments methodology in order to determine the optimum concentration. Bulbs of lilium were transplanted in plastic crates and drip-irrigated with the treatment solutions, which consisted of a mixture of N, K⁺, and Ca²⁺ whose total concentration was 340 mg L^?1 and minimum concentrations of each ion was 34 mg L^?1. Chlorophyll concentration (SPAD), shoot fresh weight (FW), leaf FW, and leaf area were measured 60 days after transplanting and ion analysis was performed on shoot tissues from selected treatments. Lilium exhibited a moderate demand for N and K⁺ (136–170 mg L^?1 N and 116–136 mg L^?1 K⁺) and a very low demand for Ca²⁺ (34–88 mg · L^?1). This low demand may be due to the remobilization of the nutrients stored in the bulbs. Integrating the predictions of the models estimated to produce >90% of maximum growth, the optimum nutrient solution should contain Ca²⁺ at a concentration between 34 and 126 mg · L^?1, K⁺ between 119 and 211 mg · L^?1, and N between 92 mg · L^?1 and 211 mg · L^?1. Increasing external N concentration affected internal N concentration but not internal K⁺ or Ca²⁺ concentrations, despite that the increase in external N was associated with a decrease in external K⁺ and Ca²⁺. Similar trends were observed for external K⁺ and Ca²⁺ concentration. In conclusion, lilium was able to maintain a relatively constant K⁺ and Ca²⁺ concentration regardless of the lower concentration in the nutrient solution when N was increased (similar response was observed for K⁺ and Ca²⁺) and it has a low Ca²⁺ demand and moderate N and K⁺ supply.     

Response of oilseed rape plant to low root temperature and nitrate: Ammonium ratios

Oilseed rape (Brassica napus L.) response to root temperature regimes (20/20, 16/8 and 12/12°C day/night) at constant 20°C air temperature was studied. At each regime, three NO₃ ^‐:NH₄ ⁺ ratios (10:0, 8:2, or 6:4), at constant 10 mM N, in the irrigation solution were tested. Plant growth, transpiration, ionic composition and level of cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 12/12 and 16/8°C, reduced rape shoot growth by 28 and 22%, and increased the accumulation of soluble carbohydrates by 42 and 26% in the roots, respectively, as compared to the 20/20°C regime. Low root temperatures reduced plants transpiration. The NO₃ ^‐:NH₄ ⁺ ratios had no effect on rape growth. At low root temperatures NO₃ ^‐contents increased in the shoot and decreased in the roots. The sum of cations and that of anions at 12/12 and 16/8°C root temperatures decreased significantly as compared to 20/20°C. The presence of NH₄ ⁺ in the irrigation solution decreased the concentrations of Ca²⁺ and Mg²⁺ in the shoots and roots and increased that of Cl^‐ in the shoots and of H₂PO₄ ^‐ in the roots at all root temperatures. Cytokinins and gibberellins contents in the xylem exúdate decreased at the low root temperature regimes. Low root temperature reduced total upward transport of the mineral nutrients and phytohormones, most probably because of reduced water flow through the plant.     

Alleviation of Manganese Phytotoxicity in Barley with Calcium

In order to clarify the mechanism by which calcium (Ca) alleviates manganese (Mn) phytotoxicity, barley plants were grown under the following conditions: (1) nutrient solution alone (control), (2) nutrient solution + 25 μM Mn (Mn-toxic), and (3) nutrient solution + 25 μ M Mn + 20 mM Ca (Ca-alleviated). Feeding experiments using ⁵⁴Mn and ⁵⁹Fe (iron) with 2.0 or 20 mM Ca to the plant roots were also conducted. The absorption and translocation of ⁵⁴Mn in the control plants were lowered by the high-Ca (20 mM) feeding condition. The translocation of ⁵⁴Mn to shoots of Mn-toxic or Ca-alleviated plants was also lowered by the high-Ca feeding condition, but ⁵⁴Mn absorption by roots of the plants was unaffected. The absorption and translocation of ⁵⁹Fe in the plants was unaffected by the high-Ca feeding condition. Calcium alleviation of Mn phytotoxicity in barley may be induced mainly by the inhibition of Mn translocation to shoots.     

Heavy Metal and Nutrient Ion Accumulation by Two Black Gram Cultivars Treated with Copper and Lead

ABSTRACT

A pot experiment was conducted to examine the uptake of nutrients (K⁺ (potassium) and Ca²⁺ (calsium)) and heavy metal (Cu²⁺ (copper) and Pb²⁺ (lead)) ions by leaves, seeds, and roots of two black gram [Vigna mungo (L.) Hepper] cultivars, ‘Mash-95018’(V₁) and ‘Mash-97’(V₂) treated with copper (Cu) and lead (Pb) at 25mg L^?1 and 50mg L^?1. This study was conducted in a greenhouse in the Botanical Garden, University of Agriculture, Faisalabad, Pakistan, during the spring of 2003. Heavy-metal treatments were applied 30 d after germination, and nutrient and heavy-metal ion uptake data were collected 10 d after treatment application. Both heavy metals in both cultivars substantially reduced nutrient ion accumulation and its translocation to seeds. Leaves had proportionately more K⁺ and Ca²⁺ than that recorded for roots and seeds after heavy-metal treatments. Nevertheless, both heavy metal (Cu²⁺ and Pb²⁺) ions ware predominantly sequestered in the roots, rather than in leaves and seeds, under their respective treatments. As the external concentrations of heavy metals increased, their uptake by the respective treated plants also increased, but nutrient ion (K⁺ and Ca²⁺) uptake was gradually reduced. This result suggests a concentration-dependent phenomenon. Overall, lead (Pb²⁺) showed more toxic effects on the uptake of essential nutrients compared with Ca²⁺, while ‘Mash-97’proved more sensitive to heavy metals than ‘Mash-95018.'     

硅对植物体中某些营养物质穿细胞及质外体吸收的影响

The positive effects of silicon（Si） on growth of plants have been well documented;however,the impact of Si on plant nutrient uptake remains unclear.The growth,nutrient content and uptake of wheat（Triticum aestivum L.）,canola（Brassica napus L.） and cotton（Gossypium hirsutum L.） plants were evaluated with or without application of 1.5 mmol L^-1 Si.Application of Si increased dry weights by 8%,30%and 30%and relative growth rate（RGR） by 10%,13%and 17%in the cotton,canola and wheat plants,respectively.The plant relative water content（RWC） was also increased,but the plant transpiration was decreased by Si application.The uptake and content of Ca²⁺ were 19%and 21%lower in the cotton and wheat plants with Si than those without Si,respectively;however,Si application increased both K⁺ and Fe uptake and contents in all plant species.Silicon application reduced B uptake and content only in cotton and increased P and Zn²⁺ contents in all three plant species.The decrease in Ca²⁺ uptake by Si application was sustained even in the presence of metabolic inhibitors 2,4-dinitrophenol and sodium cyanide.Uptake of Ca²⁺ by Si application was enhanced or did not change when plant shoots were saturated with water vapor or their roots were exposed to low temperature.Thus,Si application increased the uptake of transcellularly transported elements like K⁺,P,Zn²⁺ and Fe.In contrast,Ca2+ uptake which occurred via both apoplastic and transcellular pathways was decreased by Si application,possibly through reduction of apoplastic uptake.More efficient nutrient uptake might be another promoting effect of Si on plant growth.     

Growth and ion accumulation responses of four grass species to salinity

Ion inclusion or ion exclusion are the two main strategies developed by plants to tolerate saline environments. Shoot sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺) in four perennial grass species (tall wheatgrass, Nuttall's alkaligrass, creeping foxtail, and switchgrass) treated with nutrient solution salinity levels ranging from 2 to 32 dS m^?1 were measured. As the nutrient solution salinity was increased from 2 to 10 dS m^?1, tall wheatgrass, creeping foxtail and Nuttall's alkali grass had increased shoot Na⁺ and decreased Ca²⁺ concentration while maintaining growth suggesting that these species tolerated these changes in shoot ion concentration. In contrast, switchgrass excluded Na⁺ from the shoot and maintained K⁺ and Ca²⁺ concentrations but suffered dramatic shoot dry weight reduction. Thus, the Na⁺ exclusion mechanisms present in switchgrass were less efficient in maintaining growth under the 10 dS m^?1 nutrient solution treatment than the Na⁺ inclusion mechanisms used by the other three species.     

Einfluß von Chelatoren auf die Calcium-Verlagerung im Sproß höherer Pflanzen

Influence of chelating agents on calcium translocation in the shoots of higher plants Using 28-day-old plants and shoots of bush beans as well as isolated haulms of barley taken from the field 24-hour experiments were carried out to investigate how equimolar additions of the chelating agents Na₂H₂ EDTA (EDTA) or citric acid to the ⁴⁵CaCl₂ uptake solution (0.5–1.0 mM/l) influenced Ca-translocation in the shoot. The following results were obtained:

• 1 If Ca²⁺ was taken up by the intact root system, equimolar additions of EDTA to the CaCl₂-uptake solution reduced Ca-uptake, and therefore the translocation of Ca to and within the shoot was also lowered.
• 2 Chelating agents favoured Ca-translocation in the shoots only when Ca-uptake as a chelate by the plasmalemma of the root cells was prevented using DNP or when the roots were by-passed by injecting chelates or by removing the roots themselves.
• 3 Additions of MgCl₂ (0.5 mM/l) or DNP (10^?5-10^?4 M/l) to the ⁴⁵CaCl₂ uptake solution (0.5 mM/l) of isolated shoots reduced the favourable effect of equimolar EDTA-levels on Ca-translocation because Mg²⁺ and DNP themselves increased Ca-translocation.
• 4 From the effects of Mg²⁺ and DNP it was concluded that the favourable influence of chelating agents on Ca-translocation within the shoot can be explained on the one hand by the reduction in adsorption of Ca²⁺ on negatively charged cell walls of the xylem and on the other hand by the diminished accumulation and precipitation of Ca in the xylem-surrounding tissue.
• 5 On the basis of the results obtained here, stem injections of chelating agents or treatments which influence the content of native chelating agents in the plants appear to be possible starting points for the improvement of Ca-translocation within the shoot.

     

Effect of Calcium and Potassium Nutrition on Yield,Ion Content,and Salt Tolerance of Brassica campestris (rapa)

When plants encounter salinity, growth is reduced initially by water stress and subsequently by toxic levels of ions and by interference with nutrient acquisition and translocation. Calcium (Ca^{2 +}) in particular seems to have an important role in salt tolerance and there are reports of a beneficial effect of increasing Ca^{2 +} availability. Higher potassium (K⁺) concentrations in plants may also improve salinity tolerance as sodium (Na)⁺/K⁺ ratios have been shown to be important. Previous work with a range of Acacia species has suggested that endogenous seed Ca^{2 +} and K⁺ concentrations might influence salinity tolerance at germination, but this has not previously been tested with a single species. The objectives of this investigation were thus to determine whether (1) altered Ca^{2 +} and K⁺ nutrition of Brassica campestris (rapa) L. plants affects the yield and ion content of their seeds, and (2) seeds with different Ca^{2 +} and K⁺ contents differ in their salinity tolerance. Plants were grown in a growth room or greenhouse in (1) Gem® horticultural sand (2) Silvaperl® perlite and sand (2:1), or (3) Shamrock® Medium General Purpose Irish Sphagnum Peat and Vermiperl® vermiculite (1:1). Plants in each growth substrate were supplied with nutrient solutions based on a modified Hoagland's solution as a control, low Ca^{2 +} and low K⁺ solutions containing those elements at half the control strength, but all other mineral elements as far as possible at control strength, and high Ca^{2 +} and high K⁺ solutions containing those elements at double control strength but all other mineral elements, as far as possible, at control strength. An increase in substrate available Ca^{2 +} and K⁺ resulted in increased Ca^{2 +} and K⁺ concentration in seeds, respectively, and was accompanied by a reduction in seed K⁺ and Ca^{2 +}, respectively. The Ca^{2 +} and K⁺ concentrations of seeds affected their salinity tolerance. Increases in seed Ca^{2 +}, K⁺ or Ca^{2 +}+ K⁺ concentrations decreased salinity tolerance at germination. The results, especially in terms of Ca^{2 +} nutrition, contradict previous results of an increased salinity tolerance with increased Ca^{2 +} and/or K⁺ concentrations.     

Two cultivars of peanut (Arachis hypogaea) seedlings show different tolerance to calcium deficiency

The objectives were to determine whether two peanut cultivars show different tolerance to calcium (Ca) deficiency. The seedlings of cultivars LH11 and YZ9102 at first trifoliate leaf stage were transplanted in nutrient solution for 28 days with 0.01 and 2.0 mmol/L Ca treatments. Low Ca supply did not affect plant growth, root length and surface area of YZ9102, whereas decreased plant biomass, root length and surface area of LH11 seedlings that appeared necrosis in shoot tip. YZ9102 plant had higher Ca concentration and more Ca distribution to leaves than LH11. Under limited Ca condition, LH11 appeared net Ca²⁺ effluxes in the zones of 0.2 ～ 1.5 mm from root apex, while YZ9102 roots maintained net Ca²⁺ influxes. Peanut cultivar YZ9102 seedlings had longer roots and higher capacities of Ca uptake and Ca translocation to shoots than LH11, which might be account for higher tolerance to Ca deficiency compared with LH11.     

Einfluß von Ca2+ und pH auf das Fettsäuremuster von Phospholipiden der Rapswurzel (Brassica napus L.)

Effect of Ca²⁺ and pH upon the fatty acid composition of phospholipids from roots of rape plants (Brassica napus L.) The influence of Ca²⁺ and pH upon the dry matter of the shoot and the root of rape plants (Brassica napus L.) as well as upon the accumulation of nutrients in the shoot and the fatty acid composition of phosphatidyl ethanolamine (PÄ) and phosphatidyl choline (PC) from rape plant roots was tested by means of a water culture experiment. The experiment was designed with two concentrations of Ca-nutrition (3 mM and 0,03 mM CaCl₂ · 6 H₂O) and with three levels of pH (3,5; 5; 8) on the basis of four replications. The amounts and percentages of macro nutrients in the shoot indicated a specific effect on ion uptake by the treatments. K and Mg absorbed as cations were accumulated most intensively in the shoot at pH 5 whereas P absorbed as an anion was accumulated independent of pH at the same Ca-concentration. The fatty acid composition of PÄ and PC was distinctly dependent on the treatments. With regard to linolenic acid it appeared that Ca-nutrition may soften the harmful effect of a high H⁺-concentration. The results were discussed in relation to membrane functions.     

Comparison of the response of ion distribution in the tissues and cells of the succulent plants Aloe vera and Salicornia europaea to saline stress

There exists a great variability among plant species regarding their sensitivity and resistance to high salinity in soil, and most often this variability is related with the ability of a particular plant species to regulate ion homeostasis and transport. In this study, we have investigated the effects of NaCl on growth rate, water status, and ion distribution in different cells and tissues of two succulent plants, Aloe vera and Salicornia europaea. Our results showed that the growth of A. vera seedlings was significantly decreased in response to salinity. However, the growth of S. europaea seedlings was greatly stimulated by high concentrations of NaCl. Under saline conditions, S. europaea seedlings maintained K⁺ and Ca²⁺ uptake in roots and showed a higher root‐to‐shoot flux of Na⁺ and Cl^– as compared to A. vera. Despite great accumulation of Na⁺ and Cl^– in photosynthetically active shoot cells in S. europaea, its growth was enhanced, indicating S. europaea is capable of compartmentalizing salt ions in the vacuoles of shoot cells. Aloe vera seedlings, however, showed a low transport rate of Na⁺ and Cl^– to leaves and suppressed uptake of K⁺ and Ca²⁺ in roots during NaCl treatment. Our results also implicate that A. vera may be able to accumulate Na⁺ and Cl^– in the metabolically inactive aqueous cells in leaves and, as a result, the plant can survive and can maintain growth under saline conditions.     

Growth,transpiration, root‐born cytokinins and gibberellins,and nutrient compositional changes in sesame exposed to low root‐zone temperature under different ratios of nitrate: Ammonium supply

The growth of sesame (Sesamum indicum L.) was studied at three root temperature regimes (25/25, 20/10 and 15/15°C day/night) factorially combined with three NO₃ ^‐: NH₄ ⁺ ratios (mM ratios, 10:0, 8:2, or 6:4), as a source of nitrogen (N), in the irrigation solution. The air temperature was kept constant at 30°C. Transpiration, nutrient composition, and level of root‐born cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 15/15 and 20/10°C, restricted the growth of sesame, reduced transpiration and increased the accumulation of soluble carbohydrates in the shoot and in the roots compared to the 25/25°C regime. The NO₃:NH₄ ⁺ ratios had no effect on growth. Nutrient contents in the shoot at low root temperatures, particularly K⁺, NO₃ ^‐, and H₂PO₄ ^‐ were decreased markedly, but Na⁺ increased relative to it's content in the 25/25°C regime. Increasing NH₄ ⁺ proportion in the irrigation solution raised total N concentration in the plant tissues at all root temperatures. The amounts of cytokinins and gibberellins in the xylem exudate decreased at the low root temperature regimes relative to the 25/25°C regime. Low root temperature reduced xylem transport of nutrients and root born‐phytohormones, most probably because of reduced water flow through the plant relative to the 25/25°C regime.     

52Mn translocation in barley monitored using a positron-emitting tracer imaging system

Abstract

Until now, the real-time uptake and movement of manganese (Mn), an essential plant nutrient, has not been documented in plants. In this study, the real-time translocation of Mn in barley (Hordeum vulgare L. cv. Ehimehadaka no. 1) was visualized using the positron-emitting tracer ⁵²Mn and a positron-emitting tracer imaging system (PETIS). PETIS allowed the non-destructive monitoring of Mn translocation in barley under various conditions. In all cases, ⁵²Mn first accumulated in the discrimination center (DC) at the basal portion of the shoot, suggesting that this region may play an important role in Mn distribution in graminaceous plants. Manganese-deficient barley showed greater translocation of ⁵²Mn from roots to shoots than did Mn-sufficient barley, demonstrating that Mn deficiency causes enhanced Mn uptake and loading into vascular bundles. In contrast, the translocation of ⁵²Mn from roots to shoots was suppressed in Mn-excess barley. In these plants, the uptake of Mn may be suppressed or Mn may accumulate in the intercellular organelles of root cells, resulting in low rates of Mn translocation to shoots. In Mn-sufficient barley, the dark treatment did not suppress the translocation of ⁵²Mn to the youngest leaf, suggesting that the translocation of Mn to the youngest leaf is independent of the transpiration stream. When ⁵²Mn was supplied to the cut end of an expanded leaf, ⁵²Mn was transported to the DC within 27 min and then retranslocated to roots and other leaves. Our results show that the translocation of Mn from the roots to the DC depends passively on water flow, but actively on the Mn transporter(s).     

The role of free space calcium in the basipetal transport of indole‐3‐acetic acid in sunflower hypocotyls 1

Calcium has been reported to be involved in the basipetal transport of indole‐3‐acetic acid (IAA). It has been suggested that basipetal transport of IAA requires the influx of Ca²⁺ into the cytoplasm from the cell wall free space and that Ca²⁺ acts as a second messenger. Experiments were conducted to determine the interaction of free space Ca²⁺ with the basipetal transport of IAA. Four day old sunflower (Helianthus annus L. cv ‘Russian Mammoth') seedlings grown in 0.20 strength Hoagland's solution were either left intact or excised below the cotyledonary node to remove the meristem, the source of IAA in the shoot. After removal of the node, the plants were treated with or without 500 μM IAA in lanolin paste. After 24 h, 3 mm segments were cut from the hypocotyls and incubated in KCl. Solution Ca²⁺ concentration, representing free space Ca²⁺, increased when the source of IAA was removed. Plants which were provided a source of IAA, either endogenously or exogenously, had low levels of free space Ca²⁺. In a separate experiment, segments of sunflower hypocotyls were incubated in KCl solutions with or without 10 μM IAA. Free space Ca²⁺ was lower when the segments were incubated in solutions containing IAA. It was concluded that basipetal IAA transport resulted in low levels of Ca²⁺ in the free space, which supports the hypothesis that basipetal IAA transport has a requirement for the influx of Ca²⁺ from the free space into the cytoplasm.     

Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

Cesium uptake of field-grown Amaranthus species in Fukushima focusing on Cs concentration in xylem exudate and root distribution

ABSTRACT

Radiocesium (RCs) discharged by the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Co., Inc.) accident has extensively contaminated agricultural land in Fukushima Prefecture and its neighboring areas. Many studies have demonstrated that Cs (RCs and ¹³³Cs) uptake of plants is affected by the exchangeable K (Ex-K) concentration in soil. However, the precise plant–soil interaction in relation to Cs uptake is still unclear. The aim of this study was to investigate Cs uptake of plant in field by focusing on xylem exudate and roots because nutrients in xylem exudate reflect medium (soil) conditions and affect nutrient accumulation in shoots. Two varieties of amaranth, K4 (Amaranthus caudatus L.) and Mexico type (A. hypochondriacus L.), which have different Cs uptake abilities, were grown in four fields and in pots (750 to 3440 Bq kg^?1 of RCs) in Fukushima Prefecture. Cs concentrations in xylem exudate, shoot, and soil; Ex-K concentration in soil; and root distribution in soil were determined. RCs concentration in xylem exudate varied from 0.04 to 164 Bq kg^?1 and ¹³³Cs concentration in xylem exudate ranged from 0.01 to 33.7 μg kg^?1. The Cs concentrations were decreased by the high Ex-K concentration and the large amount of 2:1 type clay minerals in soil. The average of the ratios of Cs concentration in shoot to Cs concentration in xylem exudate for all samples was 127 ± 112 (mean ± standard deviation), although no clear correlation was found between them. The correlations betwee\n RCs and ¹³³Cs concentrations in xylem exudate and shoot were strong in pot and in the field with low Ex-K concentration. Eighty-five percent of the total root length was distributed in the topsoil (0–20 cm soil layer). The positions where roots take up Cs were estimated from the differences in the vertical distribution of RCs and ¹³³Cs concentrations in soil. The estimated Cs uptake ratios of topsoil to total soil layer ranged from 7% to 91% and varied with the concentration and the vertical distribution of Ex-K in soil.     

Effects of salt stress on distribution of Na+ and some other cations in two soybean varieties differing in salt tolerance

In the course of investigations on the impact of salinity on mineral ion transport in differentially salt susceptible soybeans (“Lee” and “Jackson”) short-term experiments were conducted to elucidate the distribution pattern of Na⁺ and some other cations. The results showed that low salinity (7.5 mM NaCl) did not induce varietal differences in Na⁺ content during a 30 hrs uptake period. At 66.5 mM NaCl, however, the Na⁺ contents increased more in the leaves of the salt sensitive variety “Jackson” than in “Lee”. Both soybean varieties retained Na⁺ in the proximal root and stem. Furthermore, they extruded considerable amounts of Na⁺ from the roots to the medium. Increasing the level of salinity in the solution substantially reduced the Ca²⁺ uptake of both soybean varieties. In an experiment with the salt sensitive variety under constant salinity but increasing Ca²⁺ concentration in the medium, the plants showed a reduction in Na⁺ uptake and translocation to stem and leaves and an enhanced Ca²⁺ uptake and translocation to the shoots. It is suggested that the injury observed in “Jackson” after salt treatment is not only related to the insufficient control of Cl^? transport. At higher salinity levels the increasing accumulation of Na⁺ in the leaves and the varietally independant depression of Ca²⁺ uptake and translocation may enhance the development of leaf necrosis.     

Wirkung einer Abscisinsäure-Applikation auf die Cl−Translokation in Sojabohnen bei niedriger und hoher Besalzung des Nährmediums

Effect of abscisic acid in the root medium on Cl^? translocation in soybeans under low and high salt conditions With soybeans of the varieties ?Lee”? and ?Jackson”? the effect of abscisic acid (ABA) applied to the root medium in different concentrations (10^?4, 10^?5 and 10^?6M) on Cl^? translocation was investigated. Under low salt conditions (0,5 mM NaCl) ABA, depending on its concentration, strongly decreased Cl^? translocation to the shoot. At the highest ABA concentration, within 24 h the Cl^? content of the shoots was reduced to about 40 % of the control, the Cl^? accumulation within the roots was reduced about 25 %. However, the 10^?5 and the 10^?6M ABA treatment increased Cl^? accumulation in the roots but decreased Cl^? translocation to the shoot. Under high salt conditions (75 mM NaCI) ABA had no measureable effect on CI- translocation to the shoot. It was found that the genetic mechanism responsible for high CI- accumulation within the roots of ?Lee”? and high CI- translocation to the shoot of ?Jackson”? was not affected by ABA. ABA strongly inhibited transpiration. High ABA concentration in combination with low salt treatment decreased the transpiration rate up to 50 % of the control. ABA also inhibited transpiration under high salt conditions. This result is discussed considering the fact, that ABA added to the highly saline nutrient solution did not decrease the CI- translocation to the shoot. An investigation using ¹⁴C-ABA showed, the radioactive substance was taken up by the roots and translocated to the shoot independently from the salt treatment. The metabolism of the radioactive substance was different for roots and leaves. However, no difference could be observed by comparing the two soybeans varieties with or without salt treatment.