Sodium and Potassium Compartmentation and Transport across the Roots of Intact Spergularia marina

The Na⁺ and K⁺ transport characteristics of Spergularia marina (L.) Griseb. were considered in order to compare the systems by which these two physiologically different cations are managed during initial acquisition and subsequent partitioning in midvegetative plants. Uptake of ²²Na⁺ and ⁴²K⁺ and redistribution of labels in pulse-chase studies were compared under steady state growth conditions or with the concentration of one of the ions elevated. At high external concentrations, the initial ⁴²K⁺ accumulation and transport to the shoot was associated with a small, rapidly exchanging, cellular compartment similar to that previously indicated for Na⁺ (D Lazof, JM Cheeseman 1986 Plant Physiol 81: 742-747). At 1 mol m⁻³, K⁺ was conducted to the shoot through a root compartment, the specific activity of which rose much more slowly than the rapidly exchanging compartment. After a lag of approximately 5 minutes, ⁴²K⁺ translocation approached a constant rate with a half-time of 14 minutes compared to 5 minutes for ²²Na⁺ or for ⁴²K⁺ at higher external levels. At all external levels, prolonged translocation of ⁴²K⁺ was measured when a 10 minute pulse was followed by an unlabeled chase, again suggesting a conducting compartment distinct from that for Na⁺. It is suggested that the K⁺ conducting compartment, possibly the `bulk cytoplasm,' is associated with the active K⁺ transport system generally found in higher plants.     

Coordination of AtHKT1;1 and AtSOS1 facilitates Na+ and K+ homeostasis in Arabidopsis thaliana under salt stress

Reducing Na⁺ accumulation and maintaining K⁺ stability in plant is one of the key strategies for improving salt tolerance. AtHKT1;1 and AtSOS1 are not only the salt tolerance determinants themselves, but also mediate K⁺ uptake and transport indirectly. To assess the contribution of AtHKT1;1 and AtSOS1 to Na⁺ homeostasis and K⁺ nutrition in plant, net Na⁺ and K⁺ uptake rate, Na⁺ and K⁺ distributions in Arabidopsis thaliana wild type (WT), hkt1;1 mutant (athkt1;1) and sos1 mutant (atsos1) were investigated. Results showed that under 2.5 mM K⁺ plus 25 or 100 mM NaCl, athkt1;1 shoot concurrently accumulated more Na⁺ and less K⁺ than did WT shoot, suggesting that AtHKT1;1 was critical for controlling Na⁺ and K⁺ distribution in plant; while atsos1 root accumulated more Na⁺ and absorbed lower K⁺ than did WT root, implying that AtSOS1 was determiner of Na⁺ excretion and K⁺ acquisition. Under 0.01 mM K⁺, athkt1;1 absorbed lower Na⁺ than did WT with 100 mM NaCl, suggesting that AtHKT1;1 is involved in Na⁺ uptake in roots; while atsos1 shoot accumulated less Na⁺ than did WT shoot no matter with 25 or 100 mM NaCl, implying that AtSOS1 played a key role in controlling long-distance Na⁺ transport from root to shoot. We present a model in which coordination of AtHKT1;1 and AtSOS1 facilitates Na⁺ and K⁺ homeostasis in A. thaliana under salt stress: under the normal K⁺, the major function of AtHKT1;1 is Na⁺ unloading and AtSOS1 is mainly involved in Na⁺ exclusion, whereas under the low K⁺, AtHKT1;1 may play a dominant role in Na+ uptake and AtSOS1 may be mainly involved in Na⁺ loading into the xylem.     

NaCl胁迫下沙枣幼苗生长和阳离子吸收、运输与分配特性

沙枣(Elaeagnus angustifolia L.)耐盐性强,是我国北方生态脆弱地区造林绿化的一个先锋树种。为探讨沙枣的盐适应机制,研究了不同浓度NaCl(0、100和200 mmol/L)胁迫30d对其水培幼苗生物量累积以及不同组织(根、茎、叶)K+、Na+、Ca2+和Mg2+吸收、运输与分配的影响。结果表明:盐胁迫不同程度地促进了沙枣苗根系生长;100 mmol/L NaCl胁迫对幼苗生物量累积无明显影响,而200 mmol/L则显著抑制了生物量累积;盐胁迫幼苗根、茎、叶中Na+含量以及K+-Na+选择性运输系数(S K,Na)和Ca2+-Na+选择性运输系数(S Ca,Na)显著或大幅度增加,而K+、Ca2+、Mg2+含量以及K+/Na+、Ca2+/Na+和Mg2+/Na+比值则显著或大幅度下降;200 mmol/L NaCl胁迫沙枣根Na+含量和根Na+净累积量分别为22.15 mg/g干重和1.87 mg/株(是对照的16.20倍和20.06倍),根成为Na+净累积量增加幅度最大的组织和Na+含量最高的组织;200 mmol/L NaCl胁迫沙枣茎、叶中的Na+含量以及冠组织Na+净累积量分别高达5.15、7.71 mg/g干重和3.29 mg/株(是对照的7.22倍、9.58倍和5.45倍),但幼苗仍能正常生长。综合分析认为,沙枣的盐适应机制是根系拒盐和冠组织耐盐,主要通过根系的补偿生长效应、根系对Na+的聚积与限制作用以及冠组织对Na+的忍耐来实现的,同时也与根、茎和叶对K+、Ca2+选择性运输能力显著增强有关。     

Responses of Atriplex spongiosa and Suaeda monoica to Salinity

The growth and tissue water, K⁺, Na⁺, Cl⁻, proline and glycinebetaine contents of the shoots and roots of two Chenopodiaceae, Atriplex spongiosa and Suaeda monoica have been measured over a range of external NaCl salinities. Both species showed some fresh weight response to low salinity mainly due to increased succulence. S. monoica showed both a greater increase in succulence (at low salinities) and tolerance of high salinities than A. spongiosa. Both species had high affinities for Na⁺ and maintained constant but low shoot K⁺ contents with increasing salinity. These trends were more marked with S. monoica in which Na⁺ stimulated the accumulation of K⁺ in roots. An association between high leaf Na⁺ accumulation, high osmotic pressure, succulence, and a positive growth response at low salinities was noted. Proline accumulation was observed in shoot tissues with suboptimal water contents. High glycinebetaine contents were found in the shoots of both species. These correlated closely with the sap osmotic pressure and it is suggested that glycinebetaine is the major cytoplasmic osmoticum (with K⁺ salts) in these species at high salinities. Na⁺ salts may be preferentially utilized as vacuolar osmotica.     

Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na⁺, Cl^?, K⁺, Ca²⁺, Mg²⁺) accumulation in different root tissues, and maintained lower Na⁺/K⁺ and Ca²⁺/Mg²⁺ ratios and a higher Na⁺/Ca²⁺ ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na⁺, K⁺, Mg²⁺ and Cl^?) concentrations of different root tissues, and correlated negatively with Na⁺/K⁺ ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na⁺/Ca²⁺ ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na⁺, K⁺, Mg²⁺ and Cl^? in different root tissues, and maintenance of lower root Na⁺/K⁺ and higher Na⁺/Ca²⁺ ratios when salinity is within acceptable limits.     

The K<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter <Emphasis Type="Italic">AhNHX1</Emphasis> improved tobacco tolerance to NaCl stress by enhancing K<Superscript>+</Superscript> retention

High salinity is the one of important factors limiting plant growth and crop production. Many NHX-type antiporters have been reported to catalyze K⁺/H⁺ exchange to mediate salt stress. This study shows that an NHX gene from Arachis hypogaea L. has an important role in K⁺ uptake and transport, which affects K⁺ accumulation and plant salt tolerance. When overexpressing AhNHX1, the growth of tobacco seedlings is improved with longer roots and a higher fresh weight than the wild type (WT) under NaCl treatment. Meanwhile, when exposed to NaCl stress, the transgenic seedlings had higher K⁺/H⁺ antiporter activity and their roots got more K⁺ uptake. NaCl stress could induce higher K⁺ accumulation in the roots, stems, and leaves of transgenic tobacco seedlings but not Na⁺ accumulation, thus, leading to a higher K⁺/Na⁺ ratio in the transgenic seedlings. Additionally, the AKT1, HAK1, SKOR, and KEA genes, which are involved in K⁺ uptake or transport, were induced by NaCl stress and kept higher expression levels in transgenic seedlings than in WT seedlings. The H⁺-ATPase and H⁺-PPase activities were also higher in transgenic seedlings than in the WT seedlings under NaCl stress. Simultaneously, overexpression of AhNHX1 increased the relative distribution of K⁺ in the aerial parts of the seedlings under NaCl stress. These results showed that AhNHX1 catalyzed the K⁺/H⁺ antiporter and enhanced tobacco tolerance to salt stress by increasing K⁺ uptake and transport.     

Sodium and potassium fluxes and compartmentation in roots of atriplex and oat

K⁺ and Na⁺ fluxes and ion content have been studied in roots of Atriplex nummularia Lindl. and Avena sativa L. cv Goodfield grown in 3 millimolar K⁺ with or without 3 or 50 millimolar NaCl. Compartmental analysis was carried out with entire root systems under steady-state conditions.

Increasing ambient Na⁺ concentrations from 0 to 50 millimolar altered K⁺, in Atriplex, as follows: slightly decreased the cytoplasmic content (Q_c), the vacuolar content (Q_v), and the plasma membrane influx and efflux. Xylem transport for K⁺ decreased by 63% in Atriplex. For oat roots, similar increases in Na⁺ altered K⁺ parameters as follows: plasma membrane influx and efflux decreased by about 80%. Q_c decreased by 65%, and xylem transport decreased by 91%. No change, however, was observed in Q_v for K⁺. Increasing ambient Na⁺ resulted in higher (3 to 5-fold) Na⁺ fluxes across the plasma membrane and in Q_c of both species. In Atriplex, Na⁺ fluxes across the tonoplast and Q_v increased as external Na⁺ was increased. In oat, however, no significant change was observed in Na⁺ flux across the tonoplast or in Q_v as external Na⁺ was increased. In oat roots, Na⁺ reduced K⁺ uptake markedly; in Atriplex, this was not as pronounced. However, even at high Na⁺ levels, the influx transport system at the plasma membrane of both species preferred K⁺ over Na⁺.

Based upon the Ussing-Teorell equation, it was concluded that active inward transport of K⁺ occurred across the plasma membrane, and passive movement of K⁺ occurred across the tonoplast in both species. Na⁺, in oat roots, was actively pumped out of the cytoplasm to the exterior, whereas, in Atriplex, Na⁺ was passively distributed between the free space, cytoplasm, and vacuole.

     

Na+ and K+ transport in excised soybean roots

Uptake, accumulation and xylem transport of K⁺ and Na⁺ in excised roots of soybean were investigated by use of a perfusion technique. This technique permitted independent quantification of, on the one hand, entry of ions into the roots and their transport through the cortex to the xylem vessels, and on the other hand reabsorption from the xylem vessels to the neighbouring cells and the external medium. Data are consistent with a low degree of selective uptake of K⁺ over Na⁺. However, Na⁺ depletion of the xylem stream by reabsorption limits, although weakly, its translocation to the shoots. Na⁺ reabsorbed is for a great part reexcreted into the external medium. The low efficiency of these processes is discussed in relation to the Na⁺ sensitivity of soybean.     

A strategy of Ca2+ alleviating Na+ toxicity in salt-treated Cyclocarya paliurus seedlings: photosynthetic and nutritional responses

Cyclocarya paliurus seedlings were subjected to 85?mM NaCl and 0, 6, 12 or 18?mM Ca(NO₃)₂ treatments to study changes in plant growth, photosynthetic parameters and distribution and/or accumulation of organic and inorganic solutes. Na⁺ toxicity symptoms were observed in plants non-treated with Ca(NO₃)₂, while 12?mM Ca(NO₃)₂ supplementation produced a significant promotion of shoot growth; meanwhile chlorophyll content, photosynthetic rate and optimum quantum yield of photosystem II (PSII), represented by the F_v/F_m ratio and pigments content as well as proline and soluble sugars, significantly increased. Ca(NO₃)₂ supply increased K⁺ and Ca²⁺ concentration, whereas the Na⁺ transport to the shoot was inhibited. There was a strong increase in the K⁺/Na⁺ ratio in shoot of Ca(NO₃)₂-treated plants. X-Ray microanalysis of roots showed that K⁺, Ca²⁺ and Na⁺ accumulated mainly in the epidermal cells and cortical cells of roots with 12?mM Ca(NO₃)₂ supply, and low accumulation was observed in stelar parenchyma, indicating exogenous Ca²⁺ possibly induced or strengthened effects of Casparian bands on ion transport. These results suggest that Ca(NO₃)₂ supplement increased inorganic and organic solutes accumulation in shoot and leaf, and restricted Na⁺ transport to the shoot by reinforcing barrier effects for attenuating salt injuries in plants, which could be a strategy of Ca²⁺ alleviating Na⁺ toxicity in C. paliurus seedlings subjected to salt stress.     

Change in uptake, transport and accumulation of ions in Nerium oleander (rosebay) as affected by different nitrogen sources and salinity

Background and Aims

The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants.

Methods

Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined.

Key Results

Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na⁺ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1·8, 1·9 and 2·7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na⁺ accumulated in roots in nitrate-fed plants was about 1·5 times higher than that in ammonium-fed plants. Similarly, Cl⁻ transport via the xylem to the shoot and its retranslocation via the phloem (Cl⁻ cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K⁺ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K⁺ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants.

Conclusions

The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na⁺ and Cl⁻ in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na⁺ and Cl⁻ in shoots probably caused harmful effects and reduced growth of plants.Key words: Mineral cycling, Nerium oleander, nitrogen source, salinity, xylem and phloem transport     

Oxygen-Dependent Exclusion of Sodium Ions from Shoots by Roots of Zea mays (cv Pioneer 3906) in Relation to Salinity Damage

Using radio-tracers, we measured Na⁺ and K⁺ accumulation in roots and transport to shoots in Zea mays (cv Pioneer 3906) as a function of NaCl concentration and O₂ partial pressure in the nutrient solution. Under fully aerobic conditions, roots partially excluded Na⁺ from the shoots over a wide range of NaCl concentration (0.2-200 millimolar). With root anoxia, the exclusion mechanism broke down so that much greater amounts of Na⁺ reached the shoots, with simultaneous inhibition of K⁺ transport. The ratio Na⁺/K⁺ entering the shoot consequently increased 90 to 200 times. Increases in Na⁺ transport were first detected when the O₂ partial pressure was reduced from ambient (21% v/v) to 15%, whereas K⁺ transport was not inhibited until O₂ concentrations were <5%. Since soil O₂ deficiency can often accompany high salinity in irrigation agriculture, failure of the Na⁺ exclusion mechanism may be a contributory factor in salinity damage of salt-sensitive glycophytes.     

Control of Na+ and K+ transport in Spergularia marina. III. Relationship between ion uptake and growth at moderate salinity

In this paper, we continue our analysis of Na⁺ and K⁺ uptake by mid-vegetative Spergularia marina (L.) Griseb. plants growing on 0.2x sea water medium, with attention to the relationship of ion uptake and growth. In the first part of the paper, growth analysis techniques are used to compare relative growth rates (RGR) and relative accumulation rates (RAR) for Na⁺ and K⁺. Under constant growth conditions, a high correlation between RGR and RAR indicated that growth and accumulation of both ions were well balanced, resulting in Na⁺ and K⁺ concentrations within the plants which were stable after adjustement to the saline medium. The analysis confirmed the existence of a Na⁺ -related growth stimulation in S. marina and an associated increase in the efficiency of K⁺ utilization for growth. When plants were subjected to more rapid salinization and step changes in the light intensity of the growth chamber, RGR and RAR were again similar, even through the discontinuities in growth conditions, suggesting that growth and ion accumulation were co-regulated rather than simply correlated. The growth analysis data were then transformed to give net uptake rates for Na⁺ and K⁺ and the results were compared to those of isotope studies under similar growth conditions. In roots, the rates estimated by the two techniques differed substantially; net uptake rates reflected primarily growth, while isotope studies indicated a substantial ion exchange rate between mature cells and the growth medium. The rates of transport of either Na⁺ or K⁺ to the shoot were very similar using the two estimation techniques. As the rates measured with isotopes were taken from studies lasting at most a few hours, this suggested a very rapid turnover of the upwardly mobile Na⁺ and K⁺ pools in the roots.     

Salt resistance in two cashew species is associated with accumulation of organic and inorganic solutes

This study establishes relationships between salt resistance and solute accumulation in roots and leaves of two contrasting cashew species. The sensitive (Anacardium microcarpum) and resistant (A. occidentale) species showed maximum root LD₅₀ values (the external NaCl concentration required for a 50% reduction in dry weight) of 63 and 128?mM NaCl, whereas the shoot LD₅₀ values were 90 and 132?mM, respectively. The salt sensitivity was directly associated with Na⁺ accumulation and especially with the Cl^? content in leaves and to a minor extent in roots. The accumulation of saline ions was associated with higher net uptake rates by roots and transport rates from root to shoot in the sensitive cashew species. The K⁺/Na⁺ ratios were not associated with salt resistance either in roots or leaves. Proline and free amino acid concentrations were strongly increased by salinity, especially in the leaves of the resistant species. The soluble sugar concentrations were not influenced by NaCl treatments in leaves of both species. In contrast, the root soluble sugar content was significantly decreased by salinity in the sensitive species only. In conclusion, the higher salt sensitivity of A. microcarpum is associated to an inefficient salt exclusion system of the leaves, especially for Cl^?. On the other hand, the resistant species displays higher concentrations of organic solutes especially a salt-induced accumulation of proline and free amino acids in leaves.     

Male poplars have a stronger ability to balance growth and carbohydrate accumulation than do females in response to a short‐term potassium deficiency

Potassium (K) deficiency influences plant performance, such as ion uptake and carbohydrate transport. However, little is known about differences between males and females in response to K deficiency. In this study, dry matter accumulation, photosynthetic capacity, allocation patterns of K⁺, Na⁺ and carbohydrates, and ultrastructural changes in males and females of Populus cathayana exposed to K deficiency were investigated. The results indicated that males maintained a significantly higher K⁺ content and K⁺/Na⁺ ratio in leaves and stems than did females under K deficiency. Moreover, K deficiency significantly increased the sucrose content of females, whereas no significant effect on males was detected. In addition, a comparative analysis showed that males allocated more resources to roots, while females allocated more to leaves, which resulted in sexually different root/shoot (R/S) ratios. Transmission electron microscopic (TEM) observations showed that males suffered fewer injuries than did females. These results suggested that males have a better ability to cope with K deficiency. In addition, the combined effects of salinity and K deficiency on poplars were studied. The results indicated that salt stress aggravates the negative effects caused by K deficiency. Taken together, our study provided evidence for gender‐specific strategies in ion and carbohydrate allocation in poplars exposed to a short‐term K deficiency. In leaves and stems, the lower K⁺ accumulation inhibited sucrose translocation and resulted in a decreased R/S ratio, which may contribute to males having a stronger ability to balance growth and carbohydrate accumulation when compared with females.     

Long-term effects of plant hormones on K+ levels and transport in young wheat plants of different K+ status

Long-term effects of 1-naphtaleneacetic acid (NAA), benzyladenine (BA), gibberellic acid (GA₃), abscisic acid (ABA) and ethylene on K⁺ levels, K⁺ uptake and translocation to the shoot were studied in young wheat plants (Triticum aesticum L. cv. Martonvásári-8) grown at different K⁺ supplies. Na⁺ levels and K⁺/Na⁺ selectivity were also investigated. Both in shoots and roots, NAA, BA and ABA decreased K⁺ and Na⁺ levels more effectively in high-K⁺ plants than in low-K⁺ plants. GA, and ethylene did not influence K⁺ and Na⁺ levels. K⁺/Na⁺ selectivity in roots of low-K⁺ plants was increased in favour of K⁺ by BA, NAA and to a lesser extent by ABA. In high-K⁺ plants only BA increased the K⁺/Na⁺ ratio, whereas the effects of the other hormones were the opposite (NAA) or less pronounced (ABA). K⁺(⁸⁶Rb) uptake was inhibited by NAA and BA in low-K⁺ plants but not in high-K⁺ plants. K⁺(⁸⁶Rb) uptake was inhibited throughout by 10 μM ABA. K⁺(⁸⁶Rb) translocation to the shoot was influenced by the hormones similarly to the uptake patterns, with the exception of ABA, which inhibited translocation in low-K⁺ plants but not in high-K⁺ plants. The results show that hormonal effects may quantitatively and qualitatively be modified by K⁺ levels in the plant and that internal K⁺ concentration may play a role in the mechanisms regulating the effects of NAA, BA and ABA but probably not in those of GA₃ or ethylene.     

Physiological adjustment to salt stress in Jatropha curcas is associated with accumulation of salt ions,transport and selectivity of K+, osmotic adjustment and K+/Na+ homeostasis

This study assessed the capacity of Jatropha curcas to physiologically adjust to salinity. Seedlings were exposed to increasing NaCl concentrations (25, 50, 75 and 100 mm ) for 15 days. Treatment without NaCl was adopted as control. Shoot dry weight was strongly reduced by NaCl, reaching values of 35% to 65% with 25 to 100 mm NaCl. The shoot/root ratio was only affected with 100 mm NaCl. Relative water content (RWC) increased only with 100 mm NaCl, while electrolyte leakage (EL) was much enhanced with 50 mm NaCl. The Na⁺ transport rate to the shoot was more affected with 50 and 100 mm NaCl. In parallel, Cl^? transport rate increased with 75 and 100 mm NaCl, while K⁺ transport rate fell from 50 mm to 100 mm NaCl. In roots, Na⁺ and Cl^? transport rates fell slightly only in 50 mm (to Na⁺) and 50 and 100 mm (to Cl^?) NaCl, while K⁺ transport rate fell significantly with increasing NaCl. In general, our data demonstrate that J. curcas seedlings present changes in key physiological processes that allow this species to adjust to salinity. These responses are related to accumulation of Na⁺ and Cl^? in leaves and roots, K⁺/Na⁺ homeostasis, transport of K⁺ and selectivity (K–Na) in roots, and accumulation of organic solutes contributing to osmotic adjustment of the species.     

Effect of tentoxin on K+transport in winter wheat seedlings of different K+-status

Klotz, M. G. and Erdei, L. 1988. Effect of tentoxin on K⁺ transport in winter wheat seedlings of different K⁺-status. The influence of the phytoeffective mycotoxin, tentoxin, [cyclo-(L-leucyl-N-methyltrans-dehydronhenyl-alanyl-glycyl-N-methyl-L-alanyl)] (in K⁺ uptake and on translocation of K⁺ from roots to shoot was studied in 14-day-old winter wheat plants (Triticum aestivum L. cv. Martonvásári-8) grown at different levels of K⁺ supply. For comparison, the effects of 2,4-dinilrophcnol and valinomycin were also investigated. In I-h experiments I pM tentoxin reduced K⁺ influx in the routs over the external K⁺ concentration range 0.1 to 1 m^M (low-K⁺ plants), whereas stimulation was observed al lower and higher K⁺ concentrations. On the other hand, in plants grown at 0.3 m^M K⁺, tentoxin stimulated the translocation of K⁺ from roots to shoots in 5-h experiments. Valinomycin affected K⁺ transport only al high K⁺-status (slight stimulation). In low-K⁺ plants 2,4-dinitrophenol (DNP) caused drastic inhibition of K⁺ uptake, but in high-K⁺ plants uptake was only slightly inhibited and translocation slightly stimulated, It is concluded that the opposite effects of tentoxin on K⁺ uptake and translocation agree1 with the directions of the H⁺-ATPases pumping H⁺ towards the apoplast and located at the cortex plasmalemma and the xylem parenchyma plasma-membrane, respectively. These effects should probably be attributed to the interaction between tentoxin and the K⁺-carrier protein rather than to a direct influence of tentoxin on H⁺-ATPase.     

短期NaCl胁迫对不同小麦品种幼苗K+吸收和Na+、K+积累的影响

为研究盐胁迫下小麦幼苗生长及Na⁺、K⁺的吸收和积累规律,以中国春、洲元9369和长武134等3种耐盐性不同小麦品种为材料,采用非损伤微测技术检测盐胁迫2 d后的根系K⁺离子流变化,并对植株体内的Na⁺、K⁺含量进行测定。结果表明:短期(2d)盐胁迫对小麦生长有抑制作用,且对根系的抑制大于地上部,耐盐品种下降幅度小于盐敏感品种。盐胁迫下,小麦根际的 K⁺大量外流,盐敏感品种中国春K⁺流速显著高于耐盐品种长武134,最高可达15倍。小麦幼苗地上部分和根系均表现为Na⁺积累增加,K⁺积累减少,Na⁺/K⁺比随盐浓度增加而上升。中国春限Na⁺能力显著低于长武134,Na⁺/K⁺则显著高于长武134。综上所述,盐胁迫下造成小麦组织器官中Na⁺/K⁺比上升的主要原因是根系K⁺大量外流和Na⁺的过量积累,耐盐性不同的小麦品种间差异显著,并认为根系对K⁺的保有能力可能是作物耐盐性评价的一个重要指标。     

Significance of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> for Sustained Hydration of Organ Tissues in Ecologically Distinct Halophytes of the Family Chenopodiaceae

The contents of Na⁺, K⁺, water, and dry matter were measured in leaves and roots of euhalophytes Salicornia europaea L. and Climacoptera lanata (Pall.) Botsch featuring succulent and xeromorphic cell structures, respectively, as well as in saltbush Atriplex micrantha C.A. Mey, a halophyte having bladder-like salt glands on their leaves. All three species were able to accumulate Na⁺ in their tissues. The Na⁺ content in organs increased with elevation of NaCl concentration in the substrate, the concentrations of Na⁺ being higher in leaves than in roots. When these halophytes were grown on a NaCl-free substrate, a trend toward K⁺ accumulation was observed and was better pronounced in leaves than in roots. Particularly high K⁺ concentrations were accumulated in Salicornia leaves. There were no principal differences in the partitioning of Na⁺ and K⁺ between organs of three halophyte species representing different ecological groups. At all substrate concentrations of NaCl, the total content of Na⁺ and K⁺ in leaves was higher than in roots. This distribution pattern persisted in Atriplex possessing salt glands, as well as in euhalophytes Salicornia and Climacoptera. The physiological significance of such universal pattern of ion accumulation and distribution among organs in halophytes is related to the necessity of water absorption by roots, its transport to shoots, and maintenance of sufficient cell water content in all organs under high soil salinity.