Effects of sulfate and nitrate on K+ uptake and growth of wheat and cucumber

The uptake of K⁺ ion was studied in the roots of wheat ( Triuicum aestivum L. cv. GK Szeged) and cucumber ( Cucumis sativus L. cv. Budai csemege) seedlings grown in nutrient solution under nitrogen and sulfate stress conditions. Seedlings pretreated with 1 or 10 m M NaNO₃, absorbed more K⁺ than those treated with 0.1 m M NaNO₃. However, the posteffect of NaNO₃ was considerably influenced by the Na₂SO₄, treatment. The results suggest that, at least partly, a feed-back regulation of K⁺ uptake may occur. However, due to the high Na⁺ contents of the roots, a Na⁺ effect in this process cannot be excluded. The growth and dry matter yields of the roots and shoots were strongly influenced by the SO²⁻/₄ and NO⁻/₃ supply of the plants. Appreciable differences were experienced between wheat and cucumber seedlings. The optimum SO²⁻/₄ concentration of the growth solution for maximal growth varied considerably between the species, and was also different for the roots and the shoots in a given species.     

Ethylene-induced putrescine accumulation modulates K+ partitioning between roots and shoots in barley seedlings

We investigated the cause and effect relationships among ethylene, polyamines, and K⁺ in barley ( Hordeum vulgare L. cv. Amagi) seedlings. Application of 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene, to the growth medium caused a decrease in K⁺ concentration in roots and an increase in shoots. Addition of ACC induced putrescine accumulation in roots, while spermidine and spermine levels remained unchanged. Exogenous supply of putrescine led to putrescine accumulation and reduced K⁺ concentration. Application of Co²⁺, an inhibitor of ethylene biosynthesis, together with ACC, inhibited putrescine accumulation with a decrease in K⁺ concentration in roots. ACC-treated roots showed K⁺ uptake capacity equivalent to that of control roots, implying that the majority of K⁺ is translocated to shoots. These results suggest that ethylene regulates K⁺ partitioning between roots and shoots through the level of accumulation of putrescine in barley seedlings.     

Uptake and distribution of calcium, magnesium and potassium in cucumber of different age

Uptake and distribution of Ca⁺, Mg²⁺ and K²⁺ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca²⁺, 2.0 m M Mg²⁺ and 2.0 m M K⁺. The ⁺ concentration was about the same in roots and shoots, while the Ca²⁺ and Mg²⁺ concentrations were low in roots compared to shoots. The K⁺ concentration decreased with increasing leaf age, while the Ca²⁺ and Mg²⁺ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca²⁺ (⁴⁵Ca) uptake. Transport of Ca²⁺ increased to leaves above and below the excision point and total Ca²⁺ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca²⁺ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites.     

Sulphur accumulation and redistribution in wheat (Triticum aestivum): a study using stable sulphur isotope ratios as a tracer system

Wheat plants were grown hydroponically and fed with two sulphate sources differing in stable isotope composition, one having a δ ³⁴S of 13·7‰ and the other 4·1‰. Plant sulphur (S) isotope ratios were determined using an on-line continuous flow-isotope ratio mass spectrometer. This method greatly simplified the procedure for the measurement of S isotope ratios, and was found to be precise for samples containing > 1 mg S g^–1 dry weight. The δ ³⁴S values of plant shoots, which had been grown on a single sulphate source, were very close to the source values, suggesting little isotope fractionation during sulphate uptake and transport from roots to shoots. By changing the sulphate sources at different growth stages, it was possible to estimate S accumulation and redistribution within different plant parts. At maturity, wheat grain derived 14, 30, 6 and 50% of its S from the accumulation during the following successive growth stages: between emergence and early stem extension, between stem extension and flag leaf emergence, between flag leaf emergence and anthesis, and after anthesis, respectively. It was estimated that 39, 32 and 52% of the S present in the flag leaves, older leaves and stems, respectively, at anthesis, was exported during the postanthesis period. These results demonstrate considerable cycling of S within wheat plants, and highlight the importance of S uptake after anthesis to the accumulation of S in grain under the experimental conditions employed.     

Distribution and redistribution of sulphur taken up from nutrient solution during vegetative growth in barley

Barley plants were grown in a nutrient solution containing 25 μ M sulphate and the roots were pulsed with [³⁵S]sulphate for 48-h periods at 6 different times between the emergence of leaf 5 (L5) and the emergence of leaf 8 (L8). Growth was continued in unlabelled solution until the emergence of L10. Within the shoot system sulphur was directed principally into the leaf undergoing expansion. A large proportion of the ³⁵S-label delivered to young expanding leaves (> 40% of full expansion) did not occur at the time of the pulse, but subsequently during the ensuing chase indicating slow redistribution of sulphur from another site. During the later stages of leaf expansion (40–100%), most of the sulphur entered the leaf during the pulse, suggesting that sulphur was delivered more directly from the nutrient solution. Up to 75% of the sulphur delivered to L3–L6 at the time they approached or attained full expansion (70–100%) was re-exported. At least some of the sulphur exported from fully expanded leaves was redistributed to developing leaves.     

Translocation of NH4+ in oilseed rape plants in relation to glutamine synthetase isogene expression and activity

Translocation of NH₄⁺ was studied in relation to the expression of three glutamine synthetase (GS, EC 6.3.1.2) isogenes and total GS activity in roots and leaves of hydroponically grown oilseed rape ( Brassica napus ). The concentration of NH₄⁺ in the stem xylem sap of NO₃⁻-fed plants was 0.55–0.70 m M , which was ≈60% higher than that in plants deprived of external nitrogen for 2 days. In NH₄⁺-fed plants, xylem NH₄⁺ concentrations increased linearly both with time of exposure to NH₄⁺ and with increasing external NH₄⁺ concentration. The maximum xylem NH₄⁺ concentration was 8 m M , corresponding to 11% of the nitrogen translocated in the xylem. In the leaf apoplastic solution, the NH₄⁺ concentration increased from 0.03 m M in N-deprived plants to 0.20 m M in N-replete plants. The corresponding values for leaf tissue water were 0.33 and 1.24 m M , respectively. The addition of either NO₃⁻ or NH₄⁺ to N-starved plants induced both cytosolic gs isogene expression and GS activity in the roots. In N-replete plants, gs isogene expression and GS activity were repressed, probably due to carbon limitations, thereby protecting the roots against the excessive drainage of photosynthates. Repressed gs isogene expression and GS activity under N-replete conditions caused enhanced NH₄⁺ translocation to the shoots.     

Potassium transport in wheat seedlings grown with different potassium supplies.

The K⁺(⁸⁶Rb) uptake into the roots and the translocation to the shoots of 11-day-old intact wheat seedlings ( Triticum aestivum L. cv. Martonvásári 8) were investigated using plants grown with different K⁺ supplies. The effects of environmental conditions (darkness, humidity) and of metabolic and transport inhibitors (oligomycin, disalicylidene-propanediamine, 2,4-dinitriphenol, diethylstilbestrol, colchicine) were also studied. Plants with K content of about 0.2 mmol/g dry weight in the root and 0.5 mmol/g dry weight in the shoot (low K status) showed high K⁺ uptake into the roots and high translocation rates to the shoots. Both transport processes were very low in plants with K content of more than 1.5 and 2.2 mmol/g dry weight in the root and shoot, respectively (high K status).
Darkness and a relative humidity of the air of 100% did not influence K⁺ uptake by roots, but did inhibit upward translocation and water transport. Inhibition of photosynthesis and treatments with diethylstilbestrol (10⁻⁵ mol/dm³), as well as with colchicine resulted in inhibition of translocation in plants of low K status, but these inhibitors had little effect on K⁺ uptake by the roots. Oligomycin, 2,4-dinitrophenol and diethylstilbestrol (10⁻⁴ mol/dm³), however, inhibited K⁺ uptake by the roots. In general, K⁺ transport processes were almost unchanged in plants of high K status. It is concluded that only plants of low K status operating with active K⁺ transport mechanisms are responsive to environmental factors. In high K⁺ plants the transport processes are passive and are uncoupled from the metabolic energy flow.     

Effects of Cd2+ and EDTA on young sugar beets (Beta vulgaris). I. Cd2+ uptake and sugar accumulation

Sugar beets ( Beta vulgaris L. cv. Monohill) grown in a complete nutrient solution, were treated with Cd²⁺ (5 or 50 μ M ) and/or EDTA (10 or 100 μ M ) in different combinations. The Cd contents of five-week-old roots and shoots were determined by atomic absorption spectrophotometry, and the sucrose, glucose and fructose contents were measured enzymatically. The Cd²⁺ uptake in both roots and shoots shows a linear relationship to the concentration of free Cd²⁺ in the nutrient solution. This uptake is diminished in the presence of EDTA, suggesting that the Cd-EDTA complex is unable to penetrate the membranes. The contents of glucose, fructose and sucrose in both roots and shoots decrease with increasing uptake of free Cd²⁺. This may be a secondary effect caused by the inhibition of photosynthesis in the presence of Cd²⁺. EDTA reduces the inhibition of Cd²⁺ on sugar formation and accumulation. In the presence of EDTA alone the sugar content increases somewhat. EDTA slightly influences the dry weights of whole plants. The ratio roots:whole plants increases. Cd²⁺ (≤ 50 μ M ) increases the dry matter portion of roots by ca 30%, but not that of shoots.     

Time-course of uptake of dissolved inorganic carbon through willow roots in light and in darkness

Uptake of dissolved inorganic carbon (DIC) from a nutrient solution by willow roots was measured in light and darkness and the distribution in the plant of DIC taken up by the roots was determined. It was also studied whether the transport system could be activated by preincubation with dissolved inorganic carbon.
Willow plants ( Salix cv. Aquatica gigantea) grown in hydroponic culture media were preincubated for 2 days with or without 0.74 mM NaHCO₃. After preincubation, either unlabelled or [¹⁴C]-labelled NaHCO₃ was injected into the media and after 1, 5, 10 and 24 h either in light or in darkness the plants were harvested in pieces into liquid nitrogen, lyophilized and burned in a combustion chamber.
¹⁴C was transported through the roots to the shoots and leaves both in light and in darkness, although incorporation of ¹⁴C in darkness was only half of that in light at the end of the 24-h feeding period. Both in light and in darkness the amount of ¹⁴C increased in all parts of willow plants with time. In light the rate of labelling was highest into cuttings and shoots. In darkness more than half of the total label was detected in cuttings of both the non-activated and the activated treatments.
In the shoots the middle part was most strongly labelled after 5 and 10 h, but after 24 h ¹⁴C moved towards the base of the shoot. In the leaves at all feeding times most radioactivity was incorporated into the young, fully open leaves on the upper part of the shoots. Preincubation of plants with unlabelled NaHCO³ in growth media had no clear effect on the rate of DIC uptake either in light or in darkness.     

Effects of applying etnylene to the root system of Zea mays on growth and nutrient concentration in relation to flooding tolerance

Previous studies have shown increases in the concentration of ethylene in the soil and roots of plants when the soil is water saturated (flooded). In Zea mays L. this occurs in association with an overall reduction in growth but without extensive foliar senescence and in conjunction with the development of an adventitious root system. We have assessed the possibility that ethylene may be involved in these responses to flooding. Mixtures of the gas in air were therefore supplied to the roots and stem-base of Z. mays growing in nutrient solution.
Seven or 14 d exposure to ethylene (1 or 5 νl 1⁻¹) inhibited seminal root elongation and growth in dry weight and accelerated the emergence of adventitious roots, although their final length and dry weight were depressed. Leaf extension was inhibited by 0.1,1.0 or 5.0 μl 1⁻¹ ethylene around the roots; leaves extending rapidiy at the start of treatment were the most sensitive. Final shoot fresh and dry weights were depressed by the gas but tie shootrroot dry weighl ratio and percentage dry matter were not affected greatly. Leaf chlorosis was not observed but the concentration of phosphorus in the shoots was 26 to 31% below normal.
When aeration of the nutrient solution was stopped, the concentration of dissolved oxygen declined and the concentration of ethylene in the roots increased. Similar changes occur in response to soil flooding. Root and shoot growth was slowed by non-aeration although the shootroot dry weight ratio remained unchanged. The phosphorus concentration of the shoots was depressed but there was little chlorosis or leaf death. The similarity in these respects between the effects of ethylene and non-aeration suggests that in flooded Z. mays , ethylene contributes to their development by accelerating the emergence of adventitioos roots, inhibiting phosphorus accumulation in the shoots and by a non-toxic inhibition of plant growth.     

Inhibition of sulphur redistribution into new leaves of vegetative soybean by excision of the maturing leaf

When soybean plants are pulsed with [³⁵S]sulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants ( Glycine max [L.] Merr. cv. Stephens) were grown in 20 μ M sulphate and a small portion of the root system (donor root) was pulsed with [³⁵S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20→SO) or with 20 μ M sulphate (S20→20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20→20 plants, ³⁵S-label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20→SO plants except that export of label from L3 was more rapid. Excision of L3 from S20→S20 plants inhibited labelling of leaves L4-L6 but not total sulphur, whereas in S20→SO plants, excision of L3 inhibited the import of both total sulphur and ³⁵S-label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The ³⁵S-label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves.     

Diurnal pattern of acetaldehyde emission by flooded poplar trees

The emission of the tropospheric trace gas acetaldehyde was determined in leaves of 4-month-old poplar trees ( Populus tremula × P. alba ) grown under controlled environmental conditions in a greenhouse. Using a dynamic cuvette system together with a high sensitivity laser-based photoacoustic detection unit, rates of acetaldehyde emission were measured with the high time resolution of about 15 min. Submergence of the roots resulted in the emission of acetaldehyde by the leaves. The emission increased linearly before reaching more or less steady-state values (ca 350 nmol m⁻² min⁻¹; ca 470 ng g⁻¹ dry weight min⁻¹) after approximately 6 h. Prolonged flooding of poplar trees resulted in a clear diurnal rhythm of acetaldehyde emission. The emission rates decreased when the light was switched off in the evening and peaked in the morning after the light was turned on again. This pattern significantly correlated with diurnal rhythms of stomatal conductance, photosynthesis, transpiration and with the concentrations of ethanol, the assumed precursor of acetaldehyde, in the xylem sap of flooded poplar trees. It may be concluded that under conditions of diminished stomatal conductance, acetaldehyde emission declines because its diffusive flux is reduced. Alternatively, reduced transpiration may decrease ethanol transport from the roots to the shoots and appreciable amounts of the acetaldehyde precursor ethanol are lacking in the leaves. The present results support the view that acetaldehyde emitted by the leaves of plants is derived from ethanol produced by alcoholic fermentation in submerged roots and transported to the leaves with the transpiration stream.     

Effects of aluminium on growth and kinetics of K+(86Rb) uptake in two cultivars of wheat (Triticum aestivum) with different sensitivity to aluminium

Two cultivars of wheat (Triticum aestivum L. cvs Kadett and WW 20299) were grown for 9 days with 20% relative increase in nutrient supply per day at pH 4.1. Aluminium at 50 μ M retarded the growth of roots more than that of shoots in both cultivars, thus decreasing the root/shoot ratio. The inhibition was largest in WW 20299. With long term Al treatment (9 days), K_m for K⁺(⁸⁶Rb) influx increased five times in both cultivars and V_max decreased in WW 20299. Efflux of K⁺(⁸⁶Rb) was little affected. When the roots were treated with aluminium for two days, only relative growth rate of roots was retarded, while growth of shoots was unaffected and influx of K⁺(⁸⁶Rb) adjusted to the actual K⁺ demand of the plants. It is concluded that the effects of aluminium on K⁺ uptake in these wheat cultivars are not primary factors contributing to aluminium sensitivity. However, in soil with Al the demand for a comparatively high concentration of K⁺ to maintain an adequate K⁺ uptake rate, in combination with a slow growth rate of the roots, may secondarily lead to K⁺ deficiency in the plants.     

Calcium ion dependency of ethylene production in segments of primary roots of Zea mays

We investigated the effect of Ca²⁺ on ethylene production in 2-cm long apical segments from primary roots of corn ( Zea mays L., B73 × Missouri 17) seedlings. The seedlings were raised under different conditions of Ca²⁺ availability. Low-Ca and high-Ca seedlings were raised by soaking the grains and watering the seedlings with distilled water or 10 m M CaCl₂, respectively. Segments from high-Ca roots produced more than twice as much ethylene as segments from low-Ca roots. Indoleacetic acid (IAA; 1 μ M ) enhanced ethylene production in segments from both low-Ca and high-Ca roots but auxin-induced promotion of ethylene production was consistently higher in segments from high-Ca roots. Addition of I-aminocyclopropane-I-carboxylic acid (ACC) to root segments from low-Ca seedlings doubled total ethylene production and the rate of production remained fairly constant during a 24 h period of monitoring. In segments from high-Ca seedlings ACC also increased total ethylene production but most of the ethylene was produced within the first 6 h. The data suggest that Ca²⁺ enhances the conversion of ACC to ethylene. The terminal 2 mm of the root tip were found to be especially important to ethylene biosynthesis by apical segments and, experiments using ⁴⁵Ca²⁺ as tracer indicated that the apical 2 mm of the root is the region of strongest Ca²⁺ accumulation. Other cations such as Mn²⁺, Mg²⁺, and K⁺ could largely substitute for Ca²⁺. The significance of these findings is discussed with respect to recent evidence for gravity-induced Ca²⁺ redistribution and its relationship to the establishment of asymmetric growth during gravitropic curvature.     

Response of 19 cultivars of soybeans to ultraviolet-B irradiance

Nineteen soybean cultivars were grown for four weeks in controlled environmental chambers with artificial daylight supplemented by five UV-B irradiance regimes to determine the range of growth and development responses of seedlings. Data from nine plant characteristics were assessed: leaf area, dry weight of leaves, stems and roots, total plant dry weight, height, ratio of roots to shoots and leaf area to weight and rating of leaves for damage. Significant differences were observed in the responses noted. Stunting, leaf chlorosis and loss of apical dominance were three general symptoms apparent on all cultivars which received UV-B irradiance. Varying degrees of reduced leaf area and dry weight of the plants and altered ratios of weights of leaves per unit area and weight of roots to shoots were also found. It was concluded that different soybean cultivars demonstrate a marked difference in sensitivity to UV-B radiation under the artificial conditions of controlled environmental growth chambers and this may indicate a genetic basis for variability in sensitivity of soybean cultivars to this waveband. However, the sensitivity to UV-B radiation was increased by the lower than normal photon fluence of photosynthetically active radiation (225 μE m⁻² s⁻¹).     

Characterization of Na+ exclusion mechanisms of salt-tolerant reed plants in comparison with salt-sensitive rice plants

Salt-tolerant reed plants ( Phragmites communis Trinius) and salt-sensitive rice plants ( Oryza sativa L. cv. Kinmaze) were grown in salinized nutrient solutions up to 50 m M NaCl, and growth, Na⁺ contents and kinetics of ²²Na⁺ uptake and translocation were compared between the species to characterize the salt tolerance mechanisms operating in reed plants. When both plants were grown under the same salinity, Na⁺ contents of the shoots were lower in reed plants, although those of the roots were quite similar. The shoot base region of both species accumulated Na⁺ more than the leaf blades did. Sodium-22 uptake and pulse-chase experiments suggested that the lower Na⁺ transport rate from root to shoot could limit excessive Na⁺ accumulation in the reed shoot. There was a possibility that the apparently lower ²²Na⁺ transport rate to the shoot of reed plants was due to net downward Na⁺ transport from shoot base to root.     

Mobilization of sulphur in soybean cotyledons during germination

Soybean seeds ( Glycine max L. cv , Stephens) contain a large amount of sulphur (ca 40 μ mol seed⁻¹), mostly in the insoluble fraction in the cotyledons. During germination in nutrient solution lacking sulphur the amount of insoluble sulphur decreases to very low levels. This is accompanied by a transitory increase in the pool of soluble sulphur which then declines. All of the sulphur lost from the cotyledons is quantitatively recovered in the seedling. In the short term, the root and the stem are the most important sinks for sulphur from the cotyledons but as growth proceeds the shoot becomes the dominant sink for remobilized sulphur. Within the shoot most of the sulphur is recovered in leaves L1 and L2. The growth of L3 and, to a lesser extent, L2, was retarded due to sulphur insufficiency. The cotyledons of plants treated with 20 μ M sulphate also exhibited mobilization of sulphur from the insoluble fraction except that the maximum rate of loss of sulphur occurred somewhat later. Plants grown with sulphate exhibited a net gain of sulphur and did not exhibit sulphur insufficiency. In these plants, endogenous sulphur from the cotyledons was directed into L1–L3 and this sulphur remained within these leaves for the duration of the experiment. The delivery of exogenous sulphur (supplied as [³⁵S]sulphate via the roots) to the leaves increased with leaf number. In leaves L1–L3, the level of exogenous sulphur in any one leaf declined with time, indicating that this sulphur was remobilized and did not mix with the sulphur derived from the cotyledons. It was concluded that the cotyledons are an important source of sulphur to support early plant growth and development of soybean.     

Pea seedling growth and development regulated by cotyledons and modified by irradiance

Growth and development of hydroponically grown pea seedlings ( Pisum sativum L. cv. Alaska) were measured using stem and root length as well as number of leaves and lateral roots. The growth was dependent on the presence of cotyledons and was modulated by the irradiance. All plants were grown in a full nutrient solution. If grown at low irradiance (73 μmol m^-2s^-1) they depended more and for a longer time on the cotyledons than plants grown at high irradiance (220 μmol m^-2s^-1). Low irradiance caused stem elongation but decreased root length and number of lateral roots as compared to plants grown at high irradiance. The dark respiration of the leaves was measured as oxygen uptake. In plants grown at the low irradiance, excision of the cotyledons caused the rate of oxygen uptake to increase by a factor of three, and the increase was sensitive to cyanide. Decotyledonized plants showed a high respiration rate and a diminished leaf growth for their entire life cycle. CO₂ fixation also increased in decotyledonized pea seedlings grown at either irradiance. The mobilization of food reserves from the seeds was positively correlated to seed dry weight, but only if the plants were grown at 73 μmol m^-2s^-1. Increasing dry weight of the seed enhanced top growth, whereas root growth was depressed, so that top and root responds differently with regard to that part of growth which depends on mobilization of reserves from the seed.