GROWTH AND POTASSIUM TRANSPORT IN COMMON AND DURUM WHEAT AS AFFECTED BY ALUMINUM AND NITRITE STRESS

Aluminum (Al) toxicity has been identified as one of the most important factors limiting plant growth in acid soil. Besides Al, nitrite (NO₂ ^?) may also be a significant stress factor in an acid environment. The objective of this study was to examine the effects of Al and NO₂ ^? stress on the growth and potassium (K⁺) uptake of roots and their transport toward the shoots of an Al-resistant common wheat (Triticum aestivum L. cv. Jubilejnaja 50) and an Al-sensitive durum wheat (T. durum Desf. cv. GK Betadur) grown in 0.5 mM CaSO₄ solution at pH 4.1 or 6.5. Root elongation of durum wheat was inhibited with 30% at 10 μM AlCl₃ treatment, while this low Al-concentration did not show a significant effect on root growth of common wheat. In all cases shoot growth was not influenced under low-salt conditions by 10 μ M AlCl₃, but exposure to 100 μM KNO₂ (alone or in combination with Al) had a definite stimulatory effect on growth. Aluminum was found to stimulate the K⁺(⁸⁶Rb) influx in short-term (6 h) experiments, but to inhibit it in long-term (3 days) experiments. This treatment was thought to damage the plasma membrane. When 10 μM 2,4-dinitrophenol was present in the uptake solution the Al-stimulated K⁺ uptake stopped even in short-term experiments. In the case of nitrite and nitrite + Al treatment combinations, however, a striking inhibition was observed in the K⁺(⁸⁶Rb) influx and the K⁺ concentration of the roots and shoots of both species.     

Puccinellia tenuiflora Exhibits Stronger Selectivity for K+ over Na+ than Wheat

Abstract

The characteristics of selectivity for K⁺ over Na⁺ by the roots of the halophyte Puccinellia tenuiflora were investigated in comparison with the glycophyte wheat (Triticum aestivum). Under various NaCl concentrations, the concentrations of K⁺ in the shoots of P. tenuiflora were 16–24% lower than those of wheat, whereas the concentrations of K⁺ in Puccinellia roots were 2.8–4.0 times higher than those of wheat. In 200 mM NaCl, the concentrations of Na⁺ in shoots of P. tenuiflora and wheat were similar under high K⁺ levels, but the concentrations of Na⁺ in wheat were 1.6 times higher than those in Puccinellia under low K⁺ levels. The concentrations of K⁺ in roots of P. tenuiflora were 1.5–2.0 times higher than those of wheat under low K⁺ levels. Formulas are given for calculating net selective absorption (SA) capacity and selective transport (ST) capacity by roots for K⁺ over Na⁺. We interpret SA as the net capacity of selectively absorbing K⁺ over Na⁺ by epidermal and cortical cells of whole plant roots into the root symplast. ST could reflect the net capacity of selection for K⁺ over Na⁺ transport from whole root stelar symplast to the xylem vessels. The lower ST value of P. tenuiflora might be the reason for accumulation of K⁺ in its roots. The SA values of P. tenuiflora and wheat were approximately equivalent in the low-affinity K⁺ uptake range. The SA values of the former were about two times higher than that of the latter in the high-affinity K⁺ uptake range, showing the root high-affinity K⁺ uptake system of the halophyte P. tenuiflora has a stronger capacity for K⁺ uptake.     

钾营养对不同基因型小麦幼苗NaCl胁迫的缓解作用

在温室砂培条件下,研究了钾营养对NaCl胁迫下不同基因型小麦幼苗生长、植株可溶性糖、丙二醛(MDA)含量及几种抗氧化酶活性的影响。结果表明,100.mmol/L.NaCl胁迫下,施入5～10.mmol/L.K+可提高小麦幼苗茎叶及根的生长及含水量;耐盐品种DK961可溶性糖含量随外界K+浓度的提高出现先升高后降低的趋势,而盐敏感品种JN17则随溶液K+浓度的提高一直降低;两品种电解质外渗量及MDA含量都比对照增加,但随外界K+浓度的升高呈现先降低后升高的趋势,以10.mmol/L.K+时最接近对照;两品种超氧物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性随外界K+浓度升高都是先升高后降低,以Na+/K+比值为10∶1最好,并且对POD活性的影响更显著。表明根据NaCl胁迫程度不同,按Na+/K+比值为10∶1的比例施用钾肥可最大限度地降低NaCl胁迫对小麦幼苗造成的伤害,促进小麦生长。     

Inoculating wheat seedlings with exopolysaccharide-producing bacteria restricts sodium uptake and stimulates plant growth under salt stress

A pot experiment was conducted to elucidate the effects of inoculating five exopolysaccharide- (EPS-) producing bacterial strains on the dry matter yield and the uptake of K⁺, Na⁺, and Ca²⁺ by wheat seedlings grown in a moderately saline soil. The bacteria were isolated from the rhizosphere soil (RS) of wheat grown in a salt-affected soil and included Aeromonas hydrophila/caviae (strain MAS-765), Bacillus insolitus (strain MAS17), and Bacillus sp. (strains MAS617, MAS620 and MAS820). The inoculation substantially increased the dry matter yield of roots (149–527% increase) and shoots (85–281% increase), and the mass of RS (176–790% increase). All the strains, except MAS617, also increased the RS mass/root mass ratio as well as the population density of EPS bacteria on the rhizoplane, and both these parameters were significantly correlated with the content of water-insoluble saccharides in the RS. Inoculation restricted Na⁺ uptake by roots, which was not attributable to the binding of Na⁺ by the RS, or to the ameliorative effects of Ca²⁺ under salinity. The decreased Na⁺ uptake by roots of inoculated than uninoculated plants was probably caused by a reduced passive (apoplasmic) flow of Na⁺ into the stele due to the higher proportion of the root zones covered with soil sheaths in inoculated treatments. Among the strains tested, MAS820 was the most efficient in all respects, whereas MAS617 was the least effective. Results suggested that inoculating selected EPS-producing bacteria could serve as a useful tool for alleviating salinity stress in salt-sensitive plants.     

Effects of nitrogen fertilization on pot‐grown wheat photosynthate partitioning within intensively farmed soil determined by 13C pulse‐labeling

Understanding rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha^?1 was pulse‐labeled with ¹³CO₂ at tillering, elongation, anthesis, and grain‐filling stages. The ¹³C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO₂ was measured 28 d after each ¹³C labeling. The proportion of net‐photosynthesized ¹³C recovered (shoots + roots + soil + soil respired CO₂) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the ¹³C respired CO₂ allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of ¹³C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment.     

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.     

Aufnahme und Verlagerung von 42K und 86Rb bei jungen Gerstenpflanzen in Abhängigkeit von einer Calcium-Behandlung der Wurzeln

Uptake and translocation of ⁴² and ⁸⁶Rb by young seedlings in relation to different calcium levels in the root medium The uptake of ⁴²K and ⁸⁶Rb by 8-d.-old barley seedlings was studied after 4 h period in solutions containing either ⁴²K or ⁸⁶Rb (1 mmol ⁴²KNO₃ + 1 mmol KCl; 1 mmol ⁸⁶RbCl + 1 mmol RbNO₃). The amount of ⁴²K was 56% and 20% higher than that of ⁸⁶Rb in the roots and shoots respectively (Pict. 1). Increasing the level of Ca in the root medium enhanced ^{42 86}Rb uptake. However the translocation rate of ⁸⁶Rb in the shoot was relatively lower than that of ⁴²K. In view of the content in the roots both elements were translocated to the shoot in a similar percentage (Table 1).     

Influence of phosphate and hydroxyl ions on aluminum toxicity in soybeans and wheat

Aluminum (Al) toxicity to plants in complete nutrient solutions is difficult to relate to Al activity in solution because of precipitation and complexation. Aluminum toxicity was studied for two seedling crops, sorghum (Sorghum bicolor L. Moench) and wheat (Triticum aestivum L. em Thell), at low levels (≤10 μM) in two incomplete nutrient solutions to study plant response to Al alone, Al+PO₄ ^3‐, Al+OH^‐, and Al+PO₄ ³‐+OH^‐. Relative root length was the bioassay for Al toxicity. ‘Monomeric’ Al was measured using Aluminon and both root length and measured Al were compared to the theoretical Al in solution predicted by the MINTEQA2 equilibrium model.

Low levels of Al were toxic to plant roots with sorghum showing a decrease in relative root length from 1 to 10 μM Al, and wheat showing a decrease from 4 to 10 μM. A mono‐salt background solution (400 μM CaCl₂) and a more complex base solution (CaCl₂, KNO₃, and MgCl₂) gave similar root lengths and measured Al values. Phosphate and hydroxyl ameliorated Al toxicity and lowered measured Al in solution, but not to the extent predicted by the model. Adding phosphate (PO₄ ^3‐) or hydroxyl (OH^‐) raised the pH, but again not as high as the model predicted. The difference in toxicity and measured Al were most likely the result of polymers (Al⁺³) which are toxic, but not measured by the procedure used, or included in the model which showed the Al as being removed from solution by precipitation.     

环境因素对小麦根系非选择性阳离子通道(NSCCs)转运钾的影响

以石家庄8号小麦作为研究对象,通过添加钾载体抑制剂和钾专性通道抑制剂的方法,探讨了温度变化和重金属镉、铜对植物根系的非选择性阳离子通道(NSCCs)转运钾离子的影响。结果显示,NSCCs转运钾的最适温度在35℃左右,低温和高温都会使NSCCs的吸钾速率下降。较高的温度(40℃)对NSCCs转运钾的影响大于对专一性钾通道的影响;而较低温度(20℃)对专一性钾通道活性的抑制比对NSCCs的抑制更强。重金属镉和铜均对小麦的钾吸收速率产生影响,浓度越大,抑制作用越强。其中,根系NSCCs对镉的敏感度相对于专一性钾通道来说要低,而对铜的敏感度相对较高。说明不同重金属对两类通道蛋白的影响机制不一样。     

Comparison of the early response to aluminum stress between tolerant and sensitive wheat cultivars: Root growth,aluminum content and efflux of K+

In order to characterize the mechanism of Al tolerance (Atlas 66) and Al sensitivity (Scout 66) in two cultivars of wheat (Triticum aestivum L.), the early responses to Al stress under acidic conditions were investigated. Marked inhibition of root elongation of Scout was observed upon treatment with 10 μM AlCl₃ for less than 3 h. The inhibition of root elongation of Scout was reversed within 3 days when the treated samples were transferred to a solution without Al. However, treatment for 6 h with AlCl₃ repressed root elongation almost completely and irreversibly. Root elongation of Atlas was only partially inhibited by the treatment with 10 μM AlCl₃ for more than 6 h. Levels of Al in two portions of roots, namely, portions 0–5 mm and 5–10 mm from the tip, were lower in Atlas than those in Scout. In Atlas the levels of Al on a fresh weight basis in both portions were very similar, while the level of Al in the portion 0–5 mm from the tip was almost double than that in the 5–10 mm portion in Scout. A distinct increase in levels of Al in the 0–5 mm portion over that in the 5–10 mm portion of Scout was observed even after 3 h of treatment with AlCl₃.

Both Atlas and Scout were preloaded with K⁺ at pH 5.5 and transferred to distilled water at various pH values to monitor the efflux of K⁺. A reduction in the pH induced increases in the efflux of K⁺ in both cultivars, and the rate of efflux in Scout was twice that in Atlas at pH 4.2. AlCl₃ at concentrations as low as 5 μM markedly repressed K⁺efflux at pH 4.2 and this effect was more pronounced in Scout. Ca²⁺ also had a repressive effect on K⁺ efflux, while EGTA increased K⁺ efflux. Vanadate increased K⁺ efflux, a result that suggests the involvement of a H⁺ pump in K⁺ efflux. Ca²+ failed to repress the increased efflux of K⁺ caused by vanadate while Al repressed the K⁺ efflux even in the presence of vanadate. These results suggest that a low extracellular pH may cause an increase in the cytoplasmic concentration of H⁺ that is followed by depolarization of the plasma membrane, which may be modified by the efflux of K⁺ and H⁺. The characteristic difference in terms of K⁺ efflux between Atlas and Scout at low pH may be caused by differences associated with plasma membrane potentials, as follows. The net influx of H+ at low pH, which causes depolarization of the plasma membrane, is higher in Scout than in Atlas. The difference in the net influx of H⁺ may be regulated in part by Ca2⁺, that either repress the influx of H⁺ or the activate of the H⁺ pump. Inhibition of K⁺ efflux by Al, which tends to depolarize the plasma membrane at low pH, may be an important factor in determining sensitivity and/or tolerance to Al.     

Methionine sulfoximine suppressed the stimulation of dark carbon fixation by ammonium nutrition in wheat roots

To evaluate the role of NH₄ ⁺ assimilates in dark carbon fixation in roots in providing carbon skeletons expended for NH₄ ⁺ assimilation, the rate of dark carbon fixation in roots was measured using NaH¹⁴CO₃. The ¹⁴C-metabolites were analyzed in wheat (Triticum aestivum L.) plants grown in NH₄ ⁺ media for various periods of time with or without methionine sulfoximine (MSX) treatment. The dark carbon fixation rate in the roots of wheat plants that had been grown with NH₄ ⁺ for 1 d was approximately 6-fold higher than the rate in control roots. The stimulation of dark carbon fixation in NH₄ ⁺-grown plants, however, was not observed in MSX-treated roots. In the roots of NH₄ ⁺-grown plants, the concentration and ¹⁴C-Iabeling of acidic metabolites such as citrate and malate considerably decreased whereas those of basic metabolites, especially asparagine, increased noticeably. With MSX treatment, the incorporation of ¹⁴C into basic metabolites was negligible. In response to NH₄ ⁺, phosphoenolpyruvate carboxylase (PEPC) activity increased, and PEPC proteins accumulated in wheat roots. Neither activity nor amounts of PEPC in roots increased in the presence of MSX. These findings suggest that primary assimilation of NH₄ ⁺ in roots is essential for the stimulation of dark carbon fixation, which coincides with the increased activity of root PEPC, to sufficiently replenish carbon skeletons necessary for NH₄ ⁺ assimilation.     

Silicon-induced changes in growth,ionic composition,water relations,chlorophyll contents and membrane permeability in two salt-stressed wheat genotypes

We investigated the effect of exogenously applied silicon (Si) on the growth and physiological attributes of wheat grown under sodium chloride salinity stress in two independent experiments. In the first experiment, two wheat genotypes SARC-3 (salt tolerant) and Auqab 2000 (salt sensitive) were grown in nutrient solution containing 0 and 100 mM sodium chloride supplemented with 2 mM Si or not. Salinity stress substantially reduced shoot and root dry matter in both genotypes; nonetheless, reduction in shoot dry weight was (2.6-fold) lower in SARC-3 than in Auqab 2000 (5-fold). Application of Si increased shoot and root dry weight and plant water contents in both normal and saline conditions. Shoot Na⁺ and Na⁺:K⁺ ratio also decreased with Si application under stress conditions. In the second experiment, both genotypes were grown in normal nutrient solution with and without 2 mM Si. After 12 days, seedlings were transferred to 1-l plastic pots and 150 mM sodium chloride salinity stress was imposed for 10 days to all pots. Shoot growth, chlorophyll content and membrane permeability were improved by Si application. Improved growth of salt-stressed wheat by Si application was mainly attributed to improved plant water contents in shoots, chlorophyll content, decreased Na⁺ and increased K⁺ concentrations in shoots as well as maintained membrane permeability.     

Silicon-Induced Growth and Yield Enhancement in Two Wheat Genotypes Differing in Salinity Tolerance

Silicon (Si) is known to alleviate a number of abiotic stresses in higher plants including salinity stress. Two independent experiments were conducted to evaluate the role of Si in alleviating salinity stress in two contrasting wheat (Triticum aestivum L.) genotypes, Auqab-2000' (salt sensitive) and SARC-3 (salt tolerant). In the first experiment, genotypes were grown in hydroponics with two levels of salinity (0 and 60 mM NaCl) with and without 2 mM Si in a completely randomized design with four replications. Salinity stress significantly (P < 0.01) decreased all of the growth parameters, increased sodium (Na⁺) concentration, and decreased potassium (K⁺) concentration in shoots of both genotypes grown in hydroponics. Silicon significantly improved growth of both genotypes. The increase in growth was more prominent under salt stress (75%) than under normal condition (15%). In the second experiment, both genotypes were grown in normal [electrical conductivity (EC) = 1.23 d Sm^–1] and natural saline field (EC = 11.92 d Sm^–1) conditions with three levels of Si (0, 75, and 150 g g^–1 Si) with three replications in a randomized complete block design. Silicon significantly (P < 0.05) decreased growth reduction in both genotypes caused by salinity stress. The grain yield under salt stress decreased from 62% to 33% and from 44% to 20% of the maximum potential in Auqab-2000 and SARC-3, respectively, when 150 g g^–1 Si was used. Auqab-2000 performed better in normal field conditions, but SARC-3 produced more straw and grain yield in saline field conditions. Addition of Si significantly (P < 0.05) improved K uptake and reduced Na⁺ uptake in both of wheat genotypes and increased the K⁺/Na⁺ ratio in shoot. Enhanced salinity tolerance and improved growth in wheat by Si application was attributed to decreased Na⁺ uptake, its restricted translocation toward shoots, and enhanced K⁺ uptake.     

Adjustment of mineral ratio and composition in rice genotypes under varied salinity regimes

A study of the salinity effect on mineral content in rice genotypes differing in salt tolerance was conducted in a factorial Completely Randomized Design experiment. The results indicated that the genotypes developed differently by mutation conventional breeding. NS15 represented as salt-sensitive, Pokkali was included as an internationally salt-tolerant check and Iratom24 was moderately tolerant. The content of Na⁺, Ca²⁺, Mg²⁺ and Cl^? followed an increasing pattern in roots and shoots of all the rice genotypes due to increasing salinity levels except Ca²⁺ and Mg²⁺ in the root. However, the concentration of K⁺ showed more or less an increasing pattern in root and a decreasing pattern in shoot. The concentration of Na⁺ and Ca²⁺ sharply increased with increasing the salinity levels in both the roots and shoots of NS15. The concentration of K⁺ sharply decreased in shoot and increased in the root of susceptible genotype NS15 with increasing salinity over 6 dS m^?1 salinity levels, where the transformation of K⁺ from root to shoot was disrupted by Na⁺. The Cl^? content sharply increased with increasing salinity in the root of NS15 as compared to shoot. The effect of different salinity levels on Na⁺/K⁺ ratio in the shoots of the selected rice genotypes sharply increased in susceptible genotype NS15 as compared to the other genotypes.     

Genotypic differences in effects of cadmium on growth and nutrient compositions in wheat

Abstract

A solution culture study was conducted to determine the genotypic difference in the effects of cadmium (Cd) addition on growth and on the uptake and distribution of Cd and other 11 nutrients in wheat plants. Cadmium addition at a rate of 1 mg L^?1 significantly reduced root and shoot dry matter production, shoot height, root length, chlorophyll content, and tillers per plant. On the average of 16 wheat genotypes used in study, Cd concentrations of Cd‐treated plants were 48.1 and 459 μg g^?1 dry weight (DW) in shoots and roots, respectively, and retained 77.91% of total Cd taken up in the roots. On the whole, Cd addition reduced the concentration of sulfur (S), phosphorus (P), magnesium (Mg), molybdenum (Mo), manganese (Mn), and boron (B), and increased iron (Fe), irrespective of the plant parts. The effect of Cd on the concentration of potassium (K), calcium (Ca), and copper (Cu) differed in shoots and roots. The significant difference existed among 16 wheat genotypes in their response to Cd in terms of growth and nutrient concentrations. Genotype E81513, which showed relatively less inhibition in growth, had the lowest shoot Cd concentration and more Cd accumulation in roots, while Ailuyuang had the highest Cd concentration and accumulation in shoot with lower Cd concentration in root. The significant interaction was found between Cd treatment and genotype for all nutrient concentrations in both shoot and root, except S and Zn in root.     

Effects of Supplemental Calcium on Ion Accumulation,Transport and Plant Growth of Salt Sensitive Brassica Rapa Landrace

ABSTRACT

Effects of three supplemental calcium (Ca⁺⁺; 2.5, 5.0, and 10 mole m^?3) concentrations on ion accumulation, transport, selectivity, and plant growth of salt-sensitive species, Brassica rapa ‘Sani’ in saline medium were investigated. Supplemental Ca⁺⁺ in the presence of 125 mol m^?3 sodium chloride (NaCl) did not improve the dry weight and leaf area indicating no role played by Ca⁺⁺ in the alleviation of salinity induced growth inhibition. However, calcium chloride (CaCl₂) did significantly affect sodium (Na⁺), potassium (K⁺), and Ca⁺⁺ contents of roots and shoots. The ion contents of shoots were significantly greater than those of roots per g dry weight, indicating ion transportation to shoots is greater than ion accumulation in roots. Use of CaCl₂ in 125 mol m^?3 NaCl reduced the Na⁺ content but increased K⁺ and Ca⁺⁺ contents in shoots. Sodium contents in shoots differed among the supplemental Ca⁺⁺ treatments indicating the role of CaCl₂ in Na⁺ ions transportation. Calcium content in shoots declined significantly in the control treatment (0 CaCl₂) but increased significantly in 10 mol m^?3 CaCl₂. The root also showed the effects of Ca⁺⁺ on the reduction of Na⁺ content and the increase of K⁺ and Ca⁺⁺ content. Unexpectedly, 5 mol m^?3 CaCl₂ induced the highest Na⁺ content in roots at 16 days after treatment. Supplemental CaCl₂ application influenced the K⁺ or Ca⁺⁺ selectivity over Na⁺ in two ways, ion accumulation at roots and transport to shoots. However, high CaCl₂ treatments allowed greater Ca⁺⁺ selectivity over Na⁺ than low CaCl₂. Likewise, high supplemental CaCl₂ showed higher K⁺ selectivity over Na⁺ than low CaCl₂. A marked increase in K⁺ versus Na⁺ selectivity for the transport process occurred at 10 mol m^?3 CaCl₂ treatments. The roots and shoots exhibited higher K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios in high CaCl₂ treatment than in low. The results are discussed in context to supplemental Ca⁺⁺ concentrations, ions accumulation, transportation and selectivity of salt sensitive Brassica rapa cultivar.     

Compensatory root growth in winter wheat: Effects of copper exposure on root geometry and nutrient distribution

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown for seven days in split‐root chambers containing nutrient solutions with various copper chloride (CuCl₂) concentrations [0.5/0.5 (controls), 0.5/2, 0.5/5, 0.5/7 and 0.5/10 μM]. At harvest (day 11), shoot dry weights were about the same in the different copper (Cu) treatments. Dry weights of the root parts exposed to 2–10 μM Cu (Cu‐fed) decreased while they increased for the control roots. A Cu exposure of 2–10 μM severely retarded lateral root initiation and average lateral root length. Average seminal root length was also reduced. The control roots compensated for the retarded growth of the Cu‐fed roots by increasing chiefly in lateral root number, but their average length remained similiar. Phosphorus (P) concentration decreased gradually in all determined plant parts (shoots, Cu‐control and Cu‐fed roots) with increased external Cu concentration. The potassium (K) concentration in the shoots was similarly affected, but it did not decrease in the Cu‐fed roots until the external Cu concentration reached 10 μM. The Cu concentration in the Cu‐fed roots increased proportionally to the external Cu concentration, but Cu was not exported to the other plant parts. The reasons for changes in root geometry and nutrient balance are discussed.     

Effect of potassium on uptake and translocation of sodium and potassium in Chinese cabbage under NaCl stress

To investigate the influence of potassium (K⁺) on the salinity tolerance of Chinese cabbage (Brassica pekinensis Rupr.) seedlings, the plants were cultured at three K⁺ levels (0, 5, or 10?mM), under normal (0?mM NaCl) and high-salt (100?mM NaCl) conditions. The results indicated that the dry weight of Chinese cabbage increased with the application of K⁺ under salt stress. Addition of K⁺ increased K⁺ concentrations and suppressed sodium (Na⁺) concentration, which eventually increased the K⁺/Na⁺ ratios in roots or shoots. Application of K⁺ enhanced the uptake of K⁺ and suppressed the uptake of Na⁺. Moreover, the ratios of shoot-K⁺/root-K⁺ increased considerably, but the ratios of shoot-Na⁺/root-Na⁺ decreased in response to K⁺ application. It was concluded that the application of K⁺ could enhance the salt stress tolerance in Chinese cabbage because more K⁺ than Na⁺ was absorbed and translocated from roots to shoots.     

Responses of barley to hypoxia and salinity during seed germination,nutrient uptake,and early plant growth in solution culture

The resistance of most plants to salt can be impaired by concurrent waterlogging. However, few studies have examined this interaction during germination and early seedling growth and its implications for nutrient uptake. The aim of the study was to examine the response of germination, early growth, and nutrient uptake to salt (NaCl) and hypoxia applied to barley (Hordeum vulgare L. cv. Stirling), in solution culture. Hypoxia, induced by covering seeds with water, lowered the germination from 94% to 28% but salinity and hypoxia together lowered it further to 13% at 120 mM NaCl. While the germination was 75% at 250 mM NaCl in aerated solution, it was completely inhibited at this NaCl concentration under hypoxia. Sodium ion (Na⁺) concentrations in germinated seedlings increased with increasing salinity under both aerated and hypoxic conditions during germination, while K⁺ and Mg⁺ concentrations were decreased with increasing salinity in 6 d old seedlings. After 20 d, control seedlings had the same dry weights of the roots and shoots with and without hypoxia but at 10 mM NaCl and higher, shoot and root dry weight was depressed with hypoxia. Sodium ion increased in roots and shoots with increased NaCl under both aerated and hypoxic conditions while K⁺ was depressed when salinity and hypoxia were applied together and Ca²⁺ was mostly decreased by NaCl. In general, hypoxia had greater effects on nutrient concentrations than NaCl by decreasing N, P, S, Mg, Mn, Zn, and Fe in shoots and by increasing B concentrations. The threshold salinity levels decreased markedly for germination, uptake of a range of nutrients, and for seedling growth of barley under hypoxic compared to well‐aerated conditions.     

不同矿化度咸水灌溉对小麦产量和生理特性的影响

为充分利用河北低平原区蕴藏丰富的咸水资源,缓解淡水资源匮乏的矛盾,在连续定位灌溉田间试验的基础上,采用裂区设计,以灌溉水矿化度作为主处理,以不同小麦品种作为副处理,研究了不同矿化度梯度咸水灌溉对小麦产量、叶片相对电导率、丙二醛(MDA)含量、脯氨酸(Pro)含量以及叶片Na+、K+、Ca2+及K+/Na+等指标的影响及其与品种耐盐性的关系。研究结果表明,随灌溉水矿化度的增加叶片的细胞膜透性增强,同时膜脂氧化产物MDA增加、渗透调节物质脯氨酸增多、叶片中Na+累积增多,而高矿化度下Ca2+和K+/Na+比值明显降低;从品种的产量和耐盐指数来看,"石家庄8号"较"衡4399"表现较强的耐盐特性。从生理指标来看,"石家庄8号"较"衡4399"细胞膜更稳定,"衡4399"用2 g.L 1以上咸水灌溉其膜透性显著增加,而"石家庄8号"需要4 g.L 1以上咸水灌溉膜透性才显著提高。另外"石家庄8号"的耐盐性还与其维持较高的K+和较低的脯氨酸水平以及较高的K+/Na+比值有关,而与Na+、Ca2+绝对含量关系不明显。从MDA来看,返青期和孕穗期"石家庄8号"较"衡4399"水平低,但到抽穗期和灌浆期其积累量较"衡4399"反而要高。灌溉水的矿化度超过4 g.L 1时,两个小麦品种产量明显降低但耐盐性强的"石家庄8号"减产幅度相对较小。因此咸水灌溉小麦品种选择十分重要,从作物耐盐性和产量考虑,多年连续灌溉咸水的矿化度不宜超过4 g.L 1。