Control of potassium influx in roots of birch (Betula pendula) seedlings exposed to cadmium

The nutrient status of the root may be a factor of vital importancefor plant tolerance to changes in the environment. In this studythe effect of Cd on the K+ uptake of birch plants, starved andnon-starved of potassium, was examined. Changes in potassiuminflux of birch [Betula pendula) roots, with time, were examinedin birch plants introduced to a nutrient solution containing125/jM K+ after a K+-starvation period. Cadmium was introducedduring the K+-recovery period and the effects of the heavy metalon the development of the uptake pattern was studied. When noCd was present K+ influx, in previously K+-starved plants, increasedwith time and reached a maximum after 6 h. When 2 or 5//M Cdwas supplied simultaneously with potassium to the root, K+ influxwas unchanged during an 8 h K+-recovery period, and the K concentrationin the roots did not increase as was the case when the plantswere given K+ without Cd. In another experiment Cd supply (2//M)to K+-fed plants gave an immediate 50% decrease in K+ influx.However, after prolonged exposure to Cd (up to 20 h), K+ influxrecovered to the control value. Key words: Birch, cadmium, influx, potassium, regulation     

The influence of potassium humate on 137Cs accumulation by barley growing on soil with different fertility

The changes studied in 137Cs uptake by plants and its distribution between vegetative and generative organs of barley cultivated with the application of potassium humate. A relationship has been found between 137Cs accumulation size in barley at various ontogenesis stages and way of potassium humate application (treatment of seeds or plants), as well as availability of mineral nutrients in the soil. Changes in K+ and NH4+ concentrations in soil solution are shown to be of prevailing importance in regulating 137Cs uptake by plants compared with potassium humate effects.     

High-affinity potassium and sodium transport systems in plants

All living cells have an absolute requirement for K+, which must be taken up from the external medium. In contrast to marine organisms, which live in a medium with an inexhaustible supply of K+, terrestrial life evolved in oligotrophic environments where the low supply of K+ limited the growth of colonizing plants. In these limiting conditions Na+ could substitute for K+ in some cellular functions, but in others it is toxic. In the vacuole, Na+ is not toxic and can undertake osmotic functions, reducing the total K+ requirements and improving growth when the lack of K+ is a limiting factor. Because of these physiological requirements, the terrestrial life of plants depends on high-affinity K+ uptake systems and benefits from high-affinity Na+ uptake systems. In plants, both systems have received extensive attention during recent years and a clear insight of their functions is emerging. Some plant HAK transporters mediate high-affinity K+ uptake in yeast, mimicking K+ uptake in roots, while other members of the same family may be K+ transporters in the tonoplast. In parallel with the HAK transporters, some HKT transporters mediate high-affinity Na+ uptake without cotransporting K+. HKT transporters have two functions: (i) to take up Na+ from the soil solution to reduce K+ requirements when K+ is a limiting factor, and (ii) to reduce Na+ accumulation in leaves by both removing Na+ from the xylem sap and loading Na+ into the phloem sap.     

Effects of potassium deficiency on water relations and photosynthesis of the tomato plant

Potassium deficient (−K) and potassium sufficient (+K) plants were exposed to four days of water stress. Well watered −K and +K plants had comparable rates of transpiration. But +K plants had a larger leaf area and depleted the soil moisture to a greater extent on day 1 of stress. For days 2 and 3 their transpiration rate, leaf water potential and relative water content fell below those of −K plants. Well watered −K plants had a significantly lower rate of photosynthesis than +K plants. Photosynthesis of −K plants was more sensitive to reduction in plant water potential than that of +K plants. Reduction of photosythesis in −K leaves was due to impairment of photosynthetic capacity and not to stomatal closure. Growth was significantly reduced in −K plants.     

Research on potassium in agriculture: needs and prospects

This review highlights future needs for research on potassium (K) in agriculture. Current basic knowledge of K in soils and plant physiology and nutrition is discussed which is followed by sections dealing specifically with future needs for basic and applied research on K in soils, plants, crop nutrition and human and animal nutrition. The section on soils is devoted mainly to the concept of K availability. The current almost universal use of exchangeable K measurements obtained by chemical extraction of dried soil for making fertilizer recommendations is questioned in view of other dominant controlling factors which influence K acquisition from soils by plants. The need to take account of the living root which determines spatial K availability is emphasized. Modelling of K acquisition by field crops is discussed. The part played by K in most plant physiological processes is now well understood including the important role of K in retranslocation of photoassimilates needed for good crop quality. However, basic research is still needed to establish the role of K from molecular level to field management in plant stress situations in which K either acts alone or in combination with specific micronutrients. The emerging role of K in a number of biotic and abiotic stress situations is discussed including those of diseases and pests, frost, heat/drought, and salinity. Breeding crops which are highly efficient in uptake and internal use of K can be counterproductive because of the high demand for K needed to mitigate stress situations in farmers’ fields. The same is true for the need of high K contents in human and animal diets where a high K/Na ratio is desirable. The application of these research findings to practical agriculture is of great importance. The very rapid progress which is being made in elucidating the role of K particularly in relation to stress signalling by use of modern molecular biological approaches is indicative of the need for more interaction between molecular biologists and agronomists for the benefit of agricultural practice. The huge existing body of scientific knowledge of practical value of K in soils and plants presents a major challenge to improving the dissemination of this information on a global scale for use of farmers. To meet this challenge closer cooperation between scientists, the agrochemical industry, extension services and farmers is essential.     

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.     

Plants use alternative strategies to utilize nonexchangeable potassium in minerals

Plant species differ in their capacity to use nonexchangeable potassium (NEK) in soils. In this study two typical plants with high K use efficiency, ryegrass and grain amaranth, were compared with regard to their capacity to use K from five K-bearing minerals. Biomass relative yield and K uptake data indicated that ryegrass was much more efficient than grain amaranth at using NEK in minerals. Root exudates of grain amaranth collected under hydroponic culture contained considerable amounts of oxalic and citric acids, while these acids were not detected in ryegrass root exudates. Compared with grain amaranth, the kinetic parameters of K uptake by ryegrass roots were characterized by a significantly higher K uptake rate (V_max) and a significantly lower C_min, the minimum external K concentration at which K is taken up. The dynamic release of NEK from minerals in various solutions showed that the release rate of NEK was largely K-concentration dependent and some thresholds of K concentration prevented further NEK release from minerals. The K thresholds were related to mineral type and increased in the presence of Ca²⁺ or Na⁺ in solutions. The positive effect of H⁺ (20 mmol L^?1) on NEK release was also mainly attributed to elevating the thresholds of K concentration, rather than to the effects of weathering. The results indicated that the main mechanism by which plant species efficiently use NEK in minerals was to the capacity of plants to absorb K at low concentrations. The lower the C_min for the root K uptake, the higher the expected NEK use efficiency of the plant.     

植物钾营养性状的遗传潜力v

钾是植物生长发育所必需的大量元素,是与氮、磷并列的植物营养的“三大要素”之一。不同植物种类或同种类植物的不同品种之间钾营养效率的差异非常显著,这为植物钾营养性状的遗传改良提供了科学依据     

Potassium uptake by Chinese cabbage (Brassica pekinensis Rupy.) from fused potassium silicate,a slow-releasing fertilizer

Fused potassium silicate (FPS), which contains K₂Ca₂Si₂O₇, has been prepared as a slow-releasing potassium fertilizer. Moreover, it is difficult to estimate the proportion of nutrients utilized by plants that come from the soil versus the slow-releasing fertilizer applied. To trace the uptake of potassium (K) by plants from FPS supplied to the soil, the fertilizer K was partially replaced with rubidium (Rb). The growth and K+Rb uptake (moles) of Chinese cabbage (Brassica pekinensis Rupy. cv. Kekkyu) plants in sand culture experiments were not affected by the replacement of K with Rb. In pot experiments using a volcanic ash Ando soil, Chinese cabbage was grown with no application of K, with K and Rb salts, or with Rb-containing FPS for three cycles of 40 days each. The amounts of fertilizer-derived K in the shoots estimated by the Rb-tracer method were smaller than those estimated by the difference of K accumulation between K fertilized and unfertilized plants. Such result suggests the involvement of `K priming', a process by which the addition of K fertilizers enhances plant K uptake from the soil. The amount of K absorbed from FPS, calculated by the Rb-tracer method, indicated that the sparingly soluble K, that is soluble in 0.2 g L^–1 citric acid solution but not in water, was absorbed at least partly through direct contact with the roots without prior exchange with soil K. Moreover, the plant absorption of sparingly soluble K from FPS was also confirmed by the difference method in K uptake.     

Potassium deficiency induces the biosynthesis of oxylipins and glucosinolates in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Background  

Mineral fertilization and pest control are essential and costly requirements for modern crop production. The two measures go hand in hand because plant mineral status affects plant susceptibility to pests and vice versa. Nutrient deficiency triggers specific responses in plants that optimize nutrient acquisition and reprogram metabolism. K-deficient plants illustrate these strategies by inducing high-affinity K-uptake and adjusting primary metabolism. Whether and how K deficient plants also alter their secondary metabolism for nutrient management and defense is not known.     

Cytosolic potassium homeostasis revisited: <Superscript>42</Superscript>K-tracer analysis in<Emphasis Type="Italic"> Hordeum vulgare</Emphasis> L. reveals set-point variations in [K<Superscript>+</Superscript>]

Current models of potassium acquisition and cytochemical processes in plants assume that potassium concentrations in the cytosol ([K+]cyt) are maintained homeostatically at approximately 100 mM. Here, we use 42K radiotracer data in the model plant species Hordeum vulgare L. (barley) to show that this assumption is incorrect. Our study reveals that [K+]cyt in root cells of intact barley seedlings is held at a minimum of two physiological set points, coinciding with two fundamentally distinct modes of K+ transport, each of which is characterized by a unique network of fluxes to and from the cytosol, and reflects variations in mechanisms and energetics of K+ transport, cytosolic K+ turnover, flux partitioning, and sensitivity to NH4+. Increased external potassium or ammonium concentrations caused a substantial drop in [K+]cyt, as well as a switch from a transport mode dominated by high-affinity, energy-dependent, influx to a mode dominated by channel-mediated fluxes in both directions across the plasma membrane. Our study provides the first subcellular demonstration of the flexibility, rather than strict homeostasis, of cellular K+ maintenance, and of the dynamic interaction between plant membrane fluxes of the two major nutrient cations K+ and NH4+.     

寄主钾营养对烟粉虱发育、存活和寄主选择的影响

为了探讨寄主钾营养对烟粉虱发育、存活和寄主选择的影响,设置了K0（0 mg/L）、K30（30 mg/L）、K60（60 mg/L）、K120（120 mg/L）和K240（240 mg/L）5种不同钾浓度,研究了烟粉虱在不同处理黄瓜上的发育历期、存活率、体形以及成虫的寄主选择。结果表明：在温度（26±1）℃,相对湿度80%±5%的条件下,取食不同钾营养水平黄瓜的烟粉虱在发育历期、存活率、体形上均有差异,其中在K240处理黄瓜上烟粉虱若虫发育最慢,从卵到成虫的时间最长,为21.4天,而在K60处理黄瓜上最快,为18.3天。在不同钾浓度处理寄主上从卵到成虫存活率以K30处理黄瓜上最高（84.7%）,其次依次为K60（83.8%）、K120（76.2%）、K0（71.4%）和K240（64.8%）。在体形上以K30处理黄瓜上最大,K240处理黄瓜上最小。寄主选择性试验结果表明,在温室条件下,烟粉虱成虫喜欢在K60处理黄瓜上取食和产卵。这些结果提示在一定范围内可以通过调节寄主钾营养状况来调控烟粉虱种群。     

Nitrogen deficiency increases volicitin-induced volatile emission,jasmonic acid accumulation,and ethylene sensitivity in maize

Insect herbivore-induced plant volatile emission and the subsequent attraction of natural enemies is facilitated by fatty acid-amino acid conjugate (FAC) elicitors, such as volicitin [N-(17-hydroxylinolenoyl)-L-glutamine], present in caterpillar oral secretions. Insect-induced jasmonic acid (JA) and ethylene (E) are believed to mediate the magnitude of this variable response. In maize (Zea mays) seedlings, we examined the interaction of volicitin, JA, and E on the induction of volatile emission at different levels of nitrogen (N) availability that are known to influence E sensitivity. N availability and volicitin-induced sesquiterpene emission are inversely related as maximal responses were elicited in N-deficient plants. Plants with low N availability demonstrated similar volatile responses to volicitin (1 nmol plant(-1)) and JA (100 nmol plant(-1)). In contrast, plants with medium N availability released much lower amounts of volicitin-induced sesquiterpenes compared with JA, suggesting an alteration in volicitin-induced JA levels. As predicted, low N plants exhibited greater sustained increases in wound- and volicitin-induced JA levels compared with medium N plants. N availability also altered volicitin-E interactions. In low N plants, E synergized volicitin-induced sesquiterpene and indole emission 4- to 12-fold, with significant interactions first detected at 10 nL L(-1) E. Medium N plants demonstrated greatly reduced volicitin-E interactions. Volicitin-induced sesquiterpene emission was increased by E and was decreased by pretreatment the E perception inhibitor 1-methylcyclopropene without alteration in volicitin-induced JA levels. N availability influences plant responses to insect-derived elicitors through changes in E sensitivity and E-independent JA kinetics.     

Glutathione and the gated potassium channels of Escherichia coli

Glutathione-deficient mutants of Escherichia coli were found to require high potassium concentrations for growth, unless supplemented with glutathione. The unsupplemented mutants exhibited a rapid leak of potassium when transferred to a K+-free medium and a fast K+ turnover at the steady state of K+ accumulation, contrasting with the slow rate of the same processes in the wild-type. The steady-state level of K+ accumulation in low potassium medium increased immediately upon addition of glutathione, even in the absence of protein synthesis. K+-independent revertants were found to possess restored glutathione synthesis. Many properties of the glutathione-deficient mutants were identical with those of the potassium leaky K-B- and K-C- mutants, which, however, have a normal glutathione content. Both types of mutants differ from the wild-type in their response to thiol reagents in that no rapid loss of K+ is observed: they have, however, clear-cut differences under these circumstances. These results suggest that the products of trkB and trkC genes are essential for the formation of the potassium channel and glutathione plays an important role in the gating process.     

Carbon dioxide exchange rates in soybeans during podfilling as a function of potassium supply

Photosynthetic and dark respiration rates of single leaflets and whole plant canopies were measured during podfilling of soybean plants that were grown under low and high K regimes. Dark respiration rates of detached seed from these plants were also determined during the latter part of seed development. The study was carried out to test the hypothesis that low oil/protein ratios of seed from K-deficient plants resulted from the reduction in carbon availability within the plant, as a result of lower carbon assimilation rates and higher rates of respiratory carbon loss. Photosynthetic rates of upper canopy leaflets during early podfilling were depressed under K deficiency but this effect did not occur with whole plant canopies. In fact, towards the latter part of the podfilling period canopy photosynthetic rates were higher in K-deficient plants as nitrogen was exported earlier from the leaves in high-K plants, resulting in earlier leaf senescence in these plants. The level of K supply had no consistent effect on dark respiration rates of single leaflets or plant canopies, and had no effect on CO₂ evolution rates from detached, developing seed. The findings do not substantiate the hypothesis that reduced photosynthetic efficiency or enhanced respiratory carbon loss are responsible for lower oil/protein ratios in seed from K-deficient soybean plants.     

Optimized potassium nutrition improves plant-water-relations of barley under PEG-induced osmotic stress

Aims

Water use efficiency (WUE) of crop plants is an important plant trait for maintaining high yield in water limited areas. By influencing osmoregulation of plants, potassium (K) plays a critical role in stress avoidance and adaptation. However, whole plant physiological mechanisms modulated by K supply in respect of plant drought tolerance and water use efficiency are not well understood. In the present study, growth, development and transpiration dynamics of two barley cultivars were evaluated with and without PEG-induced osmotic stress using an automated balance system and image based leaf area determination.

Methods

Experiments were conducted to study the effects of varied K supply under different osmotic stress treatments on a wide range of morphological, biochemical and physiological characteristics of barley plants such as leaf area development, daily whole plant transpiration rate (DTR), stomatal conductance (g_s), assimilation rate (A_N), biomass and leaf water use efficiency (WUE) as well as foliar abscisic acid (ABA) concentrations. Two barley cultivars (cv. Sahin-91 and cv. Milford) were treated with two K supply levels (0.04 and 0.8 mM K) and osmotic stress induced by polyethylene glycol 6000 (PEG) for a period of 9 days (in total 48 days experiment) in the hydroponic plant culture (non-PEG and + 20% PEG ).

Results

Without PEG, low-K supply depressed dry matter (DM) by almost 60% averaged across both cultivars. Under osmotic stress (+PEG), total leaf area was reduced by almost 70% in low-K compared to adequate-K plants. Low K concentration under PEG stress was correlated with higher ABA concentration and was correlated with lower leaf- and whole plant transpiration rate. Biomass-WUE under low K supply decreased significantly in both barley cultivars, to a greater extent in cv. Milford under osmotic stress. However, leaf-WUE was not affected by K supply in the absence of osmotic stress.

Conclusions

It was suggested that reduced biomass-WUE in low-K treated barley plants was not related to inefficient stomatal control under K deficiency, but instead due to reduced assimilation rate. It was further hypothesized that under low K supply, a number of energy consuming activities reduce biomass-WUE, which are not distinguished by measuring leaf-WUE. This study showed that low K supply under osmotic stress increases foliar ABA concentration thereby decreasing plant transpiration.

     

Simple empirical intensity and buffering capacity measurements to predict potassium uptake by white clover

Summary This experiment examined the feasibility of predicting K uptake in white clover by the use of simple and relatively rapid tests that would dispense with the need of knowing the quantity of plant available potassium. Potassium uptake was found to correlate highly (R=>0.9) in linear bivariate regressions using K concentration in the soil solution displaced by centrifuging and an empirical estimate of potassium retention. There was no advantage in determining activity ratios because in at least some of the soils used the ratio law did not apply. Exchangeable potassium alone correlated rather poorly with uptake except at very low soil potassium status. This was not because nonexchangeable potassium was an important source of this nutrient to white clover but because of the large differences in the retention of K amongst the soils used.     

Phosphate sensing in higher plants

Phosphate (Pi) plays a central role as reactant and effector molecule in plant cell metabolism. However, Pi is the least accessible macronutrient in many ecosystems and its low availability often limits plant growth. Plants have evolved an array of molecular and morphological adaptations to cope with Pi limitation, which include dramatic changes in gene expression and root development to facilitate Pi acquisition and recycling. Although physiological responses to Pi starvation have been increasingly studied and understood, the initial molecular events that monitor and transmit information on external and internal Pi status remain to be elucidated in plants. This review summarizes molecular and developmental Pi starvation responses of higher plants and the evidence for coordinated regulation of gene expression, followed by a discussion of the potential involvement of plant hormones in Pi sensing and of molecular genetic approaches to elucidate plant signalling of low Pi availability. Complementary genetic strategies in Arabidopsis thaliana have been developed that are expected to identify components of plant signal transduction pathways involved in Pi sensing. Innovative screening methods utilize reporter gene constructs, conditional growth on organophosphates and the inhibitory properties of the Pi analogue phosphite, which hold the promise for significant advances in our understanding of the complex mechanisms by which plants regulate Pi-starvation responses.     

拟南芥钾离子吸收、转运及低钾胁迫的分子机理研究进展

钾(K)作为植物所需的3种大量元素之一,参与体内诸多的生理和生化过程,对于植物的生长和发育极其重要。目前,国内外学者对植物吸收、运输和利用K⁺的研究已有一定深度,尤其以模式植物拟南芥(Arabidopsis thaliana(L.) Heynh.)为研究对象。其中,与K⁺吸收、转运相关的离子通道和转运蛋白一直都是研究热点。本文综合近年来国内外相关研究进展,主要阐述K⁺通道和转运蛋白,K⁺的吸收和运输,类钙调磷酸酶(Calcineurin B-Like, CBL)-CBL相互作用蛋白激酶(CBL-Interacting protein kinase, CIPK)信号途径,参与该信号转导的一些小信号分子,对K⁺研究方面存在的问题进行了总结,并对未来的研究方向进行了展望。