Paul Jensén

Variation among species and varieties in uptake and utilization of potassium

In uptake experiments from water cultures K+-influx in roots of sunflower (Helianthus annuus L.), cucumber (Cucumis sativus L.), birch (Betula verrucosa Ehrh.), lingonberry (Vaccinium vitis-idaea L.), and pine (Pinus silvestris L.) was related to the K+-contents of the roots. However, due to genotypic variation, no universal “optimum” K+-state of the roots for maximum K+-influx could be defined.

Growth and cation uptake in spruce (Picea abies Karst.) grown in sand culture with various aluminium contents

Three clones of spruce (Picea abies Karst.) were grown in sand culture for 9 weeks, whereafter they were transferred to water culture for 3 days. The plants were supplied with or grown in nutrient solution containing 0, 0.1, 1.0 respectively 10 mM AlCl3. The monomer Al fraction (including Al3+) and the Al3+ fraction were determined in the fresh nutrient solutions. The shoot/root dry weight ratio and the water content in shoots and roots were determined, and the main cationic composition (Al, K, Ca, Mg, Mn) in needles, stems and roots were analysed. A short term uptake experiment was performed 3 days after the plants were transferred from sand culture to water culture. The K+(86Rb+) and Ca2+(45Ca2+) uptake rates in the roots were determined in absence of external AlCl3.A high proportion of the supplied Al was taken up by the plants; 57% of total supply in the 0.1 mM Al treatment and 20% in the 1.0 mM Al treatment. Between 11% and 28% of the total Al taken up in the 0.1–10 mM Al treatments was exported to the shoot, indicating that Al not only was bound in the root free space, but also crossed the plasmalemma. Al decreased the Ca and Mg concentrations in the roots. The short term uptake experiment also showed that Ca2+(45Ca2+) uptake in the roots decreased with increasing external Al concentration. However, Ca and Mg concentrations were not lower in the shoots, except at the 10 mM Al treatment. This indicates that a higher percentage of the ions taken up was exported to the shoots in presence of Al. Concentrations of Mn and K in the roots were about the same in the Al treatments as for the control, except that the K concentration decreased at the 10 mM Al treatment. K levels in stems and needles increased with increasing Al treatment probably as a result of a decreased efflux from the roots combined with a higher export/uptake ratio. However, at the end of the cultivation period, K+(86Rb+) uptake, in the roots, decreased with increasing Al treatment, probably mainly due to a reduced ATP level. The shoot/root dry weight ratio was highest for the two highest Al treatments (1.0 and 10 mM) due to a reduced root growth.

Modifications of root geometry in winter wheat by phosphorus deprivation

Summary The effects of phosphorus (P) deprivation on root geometry in winter wheat ( Triticum aestivum ) were studied. In the first week the plants were grown in complete nutrient solutions at 2P levels (10 μM and 1000 μM phosphate), and in the second week both concentrations of P were omitted in the nutrient solution for half of the plants. The plants were harvested on days 7,9, 11,13 and 14, dried and analysed for P. Lateral and seminal root length and number were determined. The low P plants had lower dry weights and lower P contents in the dry matter than the high P plants. P was retranslocated from shoot to root in the P deprived plants. In the deprived high P plants, a high P level in the root could be sustained until day 11, whereafter it decreased to about the same level as in the root of the low P plants. P affected mainly the number of laterals. After two weeks most of the parameters (lateral root number and length, dry weight, P content) determined for the different categories of plants could be ranked in the order: deprived low P

Regulation of Phosphate Influx in Winter Wheat: Root-Shoot Phosphorus Interactions

Summary Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown at various external phosphate (Pi) levels for 10 days in order to investigate the effects of P nutritional status of roots and shoots on Pi influx and efflux measured at intervals the following 7 days. When external Pi was supplied to plants previously deprived of phosphate, P accumulated in the shoots to levels around four times that of controls due to high influx rates and proportionally large P-transport to the shoot. Efflux was, however, comparatively low. Split-root experiments with plants where one or two of the three seminal roots were pretreated with Pi for a period of up to 5 h showed increased phosphate influx in the non-treated root(s) when transferred to 32P-labelled Pi solution. Pretreatment with elevated light intensity for 5 h prior to split-root uptake experiments resulted in higher Pi influx in the part of the root system formerly exposed to Pi. The findings indicate that the shoot P concentration exerted a great effect in regulating the phosphate influx. The mechanisms involved are discussed.

Aluminium Effects on Vacuolar Phosphorus in Roots of Beech (Fagus sylvatica L.)

Summary Plants of beech ( Fagus sylvatica L.) were grown on nutrient solutions with various concentrations of phosphate (0, 0.01, 0.1, 1.0 mM) and aluminium (0, 0.1, 1.0 mM) and at low pH (usually 4.2). About half of the supplied Al occurred as Al 3+ under these conditions. The vacuolar inorganic phosphate concentrations, [P] vac , of excised fine roots were determined by 31 P NMR. In roots of plants treated with 0.1 mM AlCl 3 , [P] vac did not change over a period of 21 days. In contrast, plants treated with 1.0 mM AlCl 3 for about one day (18–29 h) generally contained somewhat higher [P] vac in the roots than did control plants. Longer treatments (3–21 days) at the high Al level caused a continuously decreasing [P] vac in the roots; [P] vac was 22 % of control after 21 days. In the presence of 1.0 mM AlCl 3 , plants with different P status showed about the same relative decrease of [P] vac . After transfer of control plants to a P- and Al-free nutrient solution, [P] vac , of roots decreased in a manner similar to that for the 1.0 mM Al treatment. The results show that exposure to 1.0 mM Al initially increases [P] vac , apparently due to a decrease in metabolic fixation of inorganic phosphate in the cytoplasm and subsequent transfer of inorganic phosphate to vacuoles. Al-P complex formation in substrate and root cell walls or specific effects on cell membranes may inhibit phosphate influx. Then, within 2–3 weeks most of the P reserves in the vacuoles are used to maintain growth. Our results are discussed in relation to effects by aluminium on P nutrition of trees growing on acid soils.

Uptake of 24Mg by excised pine roots: A preliminary study

Uptake of 24Mg by excised roots of Pinus sylvestris L. during up to 4 h long incubations in 99.9 atom % 24Mg (50 μM) was measured by ICP-MS. A rapid initial uptake phase (30 min) was followed by a slower uptake. This was interpreted as a shift from a phase dominated by saturable ion exchange (free space uptake), to a non-saturable phase, during which the rate of uptake was 0.077±0.0.012 μmol Mg g−1 (d.wt.) h−1. The metabolic uncoupler DNP (2,4-dinitrophenol) at 50 μM decreased the Mg uptake rate by 35% only, but the effect of DNP was significant (p<0.01). Several problems related to a high variability in the experimental material were encountered, and further refinement of this approach in studies of plant Mg uptake is suggested.

Vegetative adaptation to N stress regimes in two barley cultivars with different N requirement

Plants of two barley cultivars, differing in requirement for N, were grown in water culture at combinations of stressing and non-stressing rates of N supply. At all N regimes, Kajsa, the cultivar with the lowest N requirement. produced more dry matter and used N more efficiently than Hellas. For both cultivars the morphological development was strongly influenced by the N supply, mainly seen as effects on tillering. Under N stress, tillering was more inhibited in Kajsa than Hellas. At higher rates of N supply Kajsa formed fewer, but on average large tillers than Hellas.

Effects of Nettle Water on Growth and Mineral Nutrition of Plants. II. Pot- and Water-Culture Experiments

ABSTRACT Extract of nettles (Unica dioica) was evaluated for potential growth stimulating effects on wheat, tomato and barley. Approximately 10× dilution of nettle water gave the highest root fresh weight and adventitious root length in wheat in relation to more dilute or concentrated media. Plants of barley and tomato were grown in sand and a peat-sand mixture supplied with dilute nettle water or a nutrient solution with the same mineral composition. Use of nettle water resulted in about 20% higher shoot fresh weight and about 15% higher nitrogen levels in shoots compared with the nutrient solution treatment. Chlorophyll levels were also higher with the nettle water treatment. Soil respiration was approximately doubled in pots treated with nettle water compared with those receiving nutrient solution. Nettle water increased pH in the substrate by one to two units. No significant difference in growth effects was observed from use of fresh or dry nettles. Nettle water made from spring nettles usually gave h...

Uptake and transport of N, P and K in tomato supplied with nettle water and nutrient solution

Water extract of stinging nettle (Urtica dioica) has a growth stimulating effect on plants. This investigation elucidated effects of nettle water on uptake and transport of N, P and K. Tomato plants (Solanum lycopersicum L. cv. Dansk export) were grown in sand culture 6–8 weeks. Plants were supplied with nettle water and nutrient solution was used as a control medium. Uptake and transport of N, P and K+ were determined with isotopes (15N,32P and86Rb+ as a tracer for K+) and ion-selective electrodes and in exudation experiments.A 15% higher uptake of nitrogen (15N assay) was found after nettle water treatment compared with the nutrient solution control. The total amount of nitrogen was also higher in plants cultivated with nettle water. Transport of inorganic and organic nitrogen, measured in exudation experiments, was more than 50% higher for plants supplied with nettle water compared with plants supplied with nutrient solution. In contrast, nettle water had no effect on uptake, transport or total amount of phosphorus and potassium in the plants.Experiments in hydroculture showed that nettle water had a strong pH-elevating effect. Uptake of NH4+ was strongly stimulated by nettle water compared with nutrient solution. By holding pH at a constant level during the uptake period for 6 h, the uptake of NH4+ from nettle water was significantly lower when no adjustment of pH was made. Consequently a good deal of the NH4+ uptake enhancement by nettle water could be explained by pH-stimulation. Assays with the uncoupler/inhibitor 2,4-dinitrophenol (DNP) and dichlorophenyl-dimethyl-urea (DCMU) showed that uptake of nitrogen from nettle water was less metabolically-linked than uptake from a corresponding nutrient solution. All together, nettle water seems to stimulate the uptake of nitrogen, but not phosphorus or potassium.

Tiller expansion and retranslocation of previously absorbed nitrogen among main stems, tillers and roots of two barley cultivars

Barley plants (Hordeum vulgare L. cvs Hellas and Kajsa), grown in nutrient solutions, were supplied with15NO3− from day 12 to day 16. Changes in distribution of15N between different plant parts were followed during ageing, (days 16, 28 and 52) to study differences in redistribution of N induced by variation in NO3− supply and choice of cultivar.Main stems and tillers competed for previously absorbed N and their competitive strength depended on their growth rate. Inhibition of tillering during N stress protected the main stem from detrimental losses of a limiting resource. Tillers on Hellas received in most cases proportionally more15N from the rest of the plant than tillers on Kajsa.