Effect of ammonium on uptake of phosphorus,potassium, calcium and magnesium by intact soybean plants

Summary The effect of a wide range of ammonium concentrations (1.78×10^–5 to 3.57×10^–3 M) on the uptake and tissue content of P, K, Ca and Mg in intact soybean (Glycine max (L.) Merr. Cv. Amsoy) plants at different growth stages was studied. A stimulatory effect of ammonium on the uptake and content of P was observed over the entire concentration range, whereas this effect was observed only up to 500 M of ammonium with respect to K. At higher levels (>500 M), ammonium suppressed the uptake and content of K. Inhibition by high levels (>357 M) of ammonium was also found for the uptake and content of Ca and Mg. Inhibition of uptake of K, Ca and Mg by high levels of ammonium may be an important factor in the mineral nutrition of soybean plants. re]19760420     

Regulation of ammonium and potassium uptake by glutamine and asparagine in Pisum arvense plants

Pisum arvense plants were subjected to 5 days of nitrogen deprivation. Then, in the conditions that increased or decreased the root glutamine and asparagine pools, the uptake rates of 0.5 mM NH₄ ⁺ and 0.5 mM K⁺ were examined. The plants supplied with 1 mM glutamine or asparagine took up ammonium and potassium at rates lower than those for the control plants. The uptake rates of NH₄ ⁺ and K⁺ were not affected by 1 mM glutamate. When the plants were pre-treated with 100 μM methionine sulphoximine, an inhibitor of glutamine synthesis, the efflux of NH₄ ⁺ from roots to ambient solution was enhanced. On the other hand, exposure of plants to methionine sulphoximine led to an increase in potassium uptake rate. The addition of asparagine, glutamine or glutamate into the incubation medium caused a decline in the rate of NH₄ ⁺ uptake by plasma membrane vesicles isolated from roots of Pisum arvense, whereas on addition of methionine sulphoximine increased ammonium uptake. The results indicate that both NH₄ ⁺ and K⁺ uptake appear to be similarly affected by glutamine and asparagine status in root cells. The research was supported by grant of KBN No. 6PO4C 068 08     

Mycorrhiza of plants in different vegetation types in tropical ecosystems of Xishuangbanna,southwest China

We examined plants growing in four tropical vegetation types (primary forest, secondary forest, limestone forest and a slash and burn field) in Xishuangbanna, southwest China for mycorrhizal associations. Of the 103 plant species examined (belonging to 47 families), 81 had arbuscular mycorrhizal (AM) associations, while three species possessed orchid mycorrhiza. AM colonization levels ranged between 6% and 91% and spore numbers ranged between 1.36 spores and 25.71 spores per 10 g soil. Mean AM colonization level was higher in primary and secondary forest species than in plant species from limestone forests and a slash and burn field. In contrast, mean AM fungal spore numbers of the primary and limestone forest were lower than in the secondary forest or the slash and burn field. AM fungal spores belonging to Glomus and Acaulospora were the most frequent in soils of Xishuangbanna. AM fungal colonization and spore numbers were significantly correlated to each other and were significantly influenced by vegetation type.     

标题双胚苗水稻中单倍体和二倍体不同器官的cDNA- AFLP分析

SARII-628是四川农业大学水稻研究所的一个双胚苗自然群体, 每年都能定期分离出单倍体与二倍体(n:2n)。文章对单倍体和对应的二倍体进行了cDNA-AFLP分析。合成了3个单倍体和1个二倍体的根、茎、穗和叶的cDNA, 用EcoR I/ Msp I酶切组合, 通过cDNA-AFLP技术统计这16个样本的表达差异。共选用30对引物, 在633条扩增位点上筛选出49个有差异表达的序列。结果:(1)单倍化后cDNA-AFLP总体水平虽然在各单株间略有差异但变化不大, 表达变化的位点所占比例平均为5.14%, 高于二倍体的3.93%; (2)根据样本在根、茎、穗和叶中表达出带的有无, 在扩增出的14种带型中, 有4种只出现在单倍体中, 其对应位点的表达具有单倍体的特异性; (3)对这3个单倍体在不同器官的激活和沉默位点进行汇总, 发现在根和穗中, 发生沉默的位点多于激活的位点数, 而在茎和叶中的结果正好与之相反, 但是在单倍体的所有器官中发生激活变化的位点多于沉默变化的位点; (4)对不同器官中的发生表达变化(激活+沉默)位点分析, 发现根中的变化位点最多, 在穗中的变化最少, 说明位点的表达变化具有器官特异性。     

Structure, function and regulation of ammonium transporters in plants

Ammonium is an important source of nitrogen for plants. It is taken up by plant cells via ammonium transporters in the plasma membrane and distributed to intracellular compartments such as chloroplasts, mitochondria and vacuoles probably via different transporters in each case. Ammonium is generally not used for long-distance transport of nitrogen within the plant. Instead, most of the ammonium transported into plant cells is assimilated locally via glutamine synthetases in the cytoplasm and plastids. Ammonium is also produced by plant cells during normal metabolism, and ammonium transporters enable it to be moved from intracellular sites of production to sites of consumption. Ammonium can be generated de novo from molecular nitrogen (N(2)) by nitrogen-fixing bacteria in some plant cells, such as rhizobia in legume root nodule cells, and at least one ammonium transporter is implicated in the transfer of ammonium from the bacteria to the plant cytoplasm. Plant physiologists have described many of these ammonium transport processes over the last few decades. However, the genes and proteins that underlie these processes have been isolated and studied only recently. In this review, we consider in detail the molecular structure, function and regulation of plant ammonium transporters. We also attempt to reconcile recent discoveries at the molecular level with our knowledge of ammonium transport at the whole plant level.     

Leaf and canopy photosynthesis of four desert plants: considering different photosynthetic organs

Photosynthesis Research - Desert plants evolve different photosynthetic organs to adapt to the extreme environment. We studied the leaf and canopy gas exchange, chlorophyll content, fluorescence...     

Transport,signaling, and homeostasis of potassium and sodium in plants

Potassium （K＋） is an essential macronutrient in plants and a lack of K＋ significantly reduces the potential for plant growth and development. By contrast, sodium （Na＋）, while beneficial to some extent, at high concentrations it disturbs and inhibits various physiological processes and plant growth. Due to their chemical similarities, some functions of K＋ can be undertaken by Na＋ but K＋ homeostasis is severely affected by salt stress, on the other hand. Recent advances have highlighted the fascinating regulatory mechanisms of K＋ and Na＋ transport and signaling in plants. This review summarizes three major topics： （i） the transport mechanisms of K＋ and Na＋ from the soil to the shoot and to the cellular - compartments; （ii） the mechanisms through which plants sense and respond to K＋ and Na＋ availability; and （iii） the components involved in maintenance of K＋/Na＋ homeostasis in plants under salt stress.     

Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture

The biomass concentration extant in potassiumlimited cultures of either Klebsiella pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pH-dependent decrease in the cells' minimum K⁺ requirement. Significantly, this effect of pH was not eviden with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH₄Cl were added to the glutamate-containing medium. This suggested a functional replacement of K⁺ by NH ₄ ⁺ , a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 Å) and the ammonium ion (1.43 Å). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH₄Cl (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h^-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassiumlimited medium containing initially 0.5 mM K⁺. Qualitatively similar findings were made with cultures of K. pneumoniae; and whereas one may not conclude that NH ₄ ⁺ can totally replace K⁺ in the growth of these bacteria, it can clearly do so very extensively.     

Transport,signaling, and homeostasis of potassium and sodium in plants

Potassium(Kt) is an essential macronutrient in plants and a lack of Ktsignificantly reduces the potential for plant growth and development. By contrast, sodium(Nat),while beneficial to some extent, at high concentrations it disturbs and inhibits various physiological processes and plant growth. Due to their chemical similarities, some functions of Kt can be undertaken by Natbut Kthomeostasis is severely affected by salt stress, on the other hand. Recent advances have highlighted the fascinating regulatory mechanisms of Kt and Nattransport and signaling in plants. This review summarizes three major topics:(i) the transport mechanisms of Ktand Natfrom the soil to the shoot and to the cellular compartments;(ii) the mechanisms through which plants sense and respond to Ktand Natavailability; and(iii) the components involved in maintenance of Kt/Nathomeostasis in plants under salt stress.     

Uptake of potassium by rice plants at different stages of growth

Uptake of potassium by rice plants at different stages of growth can be described by a biphasic isotherm in the range of 5 × 10^?5 M and is probably mediated bya multiphasic mechanism in the plasmalemma.     

Calcium, potassium, and magnesium cycling in aMexican tropical dry forest ecosystem

We estimated the fluxes, inputs and outputs of Ca, K,and Mg in a Mexican tropical dry forest. The studywas conducted in five contiguous small watersheds(12–28 ha) gauged for long-term ecosystem research. A total of five 80 × 30 m plots were used for thestudy. We quantified inputs from the atmosphere,dissolved and particulate-bound losses, throughfalland litterfall fluxes, and standing crop litter pools. Mean cation inputs for a six-year period were 3.03 kg/ha for Ca, 1.31 kg/ha for K, and 0.80 kg/ha for Mg. Mean outputs in runoff were 5.24, 2.83, and 1.79 kg/ha, respectively. Calcium, K, and Mgconcentrations increased as rainfall moved through thecanopy. Annual Ca return in the litterfall (11.4 g/m²) was much higher than K (2.3 g/m²)and Mg (1.6 g/m²). Litterfall represented 99%of the Ca, 84% of the Mg, and 53% of the K, totalaboveground return to the soil. Calcium concentrationin standing litter (3.87%) was much higher than K(0.38%) and Mg (0.37%). These concentrations werehigher (Ca), lower (K), or similar (Mg) to those inlitterfall. Residence times on the forest floor were0.86, 1.17, and 1.77 yr for K, Mg, and Carespectively. Compared to the residence time fororganic matter at the site (1.31 yr), these resultssuggest slow mineralization for Ca in this ecosystem. Budget estimates were calculated for a wet and a dryyear. Results indicated that nutrients accumulated inthe dry but that nutrients were lost during the wetyear. Comparison of Ca, K, and Mg losses in streamwater with the input rates from the atmosphere for thesix-year period show that inputs are lower thanoutputs in the Chamela tropical dry forestecosystem.     

The alleviation of ammonium toxicity in plants

Nitrogen(N) is an essential macronutrient for plants and profoundly affects crop yields and qualities.Ammonium(NH4+) and nitrate(NO₃^-) are major inorganic N forms absorbed by plants from the surrounding environments.Intriguingly,NH₄⁺ is usually toxic to plants when it serves as the sole or dominant N source.It is thus important for plants to coordinate the utilization of NH₄⁺ and the alleviation of NH₄⁺ toxic...     

The regulation of ammonium translocation in plants

Much controversy exists about whether or not NH(+)(4) is translocated in the xylem from roots to shoots. In this paper it is shown that such translocation can indeed take place, but that interference from other metabolites such as amino acids and amines may give rise to large uncertainties about the magnitude of xylem NH(+)(4) concentrations. Elimination of interference requires sample stabilization by, for instance, formic acid or methanol. Subsequent quantification of NH(+)(4) should be done by the OPA-fluorometric method at neutral pH with 2-mercaptoethanol as the reducing agent since this method is sensitive and reliable. Colorimetric methods based on the Berthelot reaction should never be used, as they are prone to give erroneous results. Significant concentrations of NH(+)(4), exceeding 1 mM, were measured in both xylem sap and leaf apoplastic solution of oilseed rape and tomato plants growing with NO(-)(3) as the sole N source. When NO(-)(3) was replaced by NH(+)(4), xylem sap NH(+)(4) concentrations increased with increasing external concentrations and with time of exposure to NH(+)(4). Up to 11% of the translocated N was constituted by NH(+)(4). Glutamine synthetase (GS) incorporates NH(+)(4) into glutamine, but root GS activity and expression were repressed when high levels of NH(+)(4) were supplied. Ammonium concentrations measured in xylem sap sampled just above the stem base were highly correlated with NH(+)(4) concentrations in apoplastic solution from the leaves. Young leaves tended to have higher apoplastic NH(+)(4) concentrations than older non-senescing leaves. The flux of NH(+)(4) (concentration multiplied by transpirational water flow) increased with temperature despite a decline in xylem NH(+)(4) concentration. Retrieval of leaf apoplastic NH(+)(4) involves both high and low affinity transporters in the plasma membrane of mesophyll cells. Current knowledge about these transporters and their regulation is discussed.     

Effects of ammonium ions on spontaneous action potentials and on contents of sodium, potassium, ammonium and chloride ions in brain in vitro

The effects of ammonium ions on the frequency of spontaneous action potentials in guinea-pig cerebellar slices, recorded with an extracellular microelectrode, and on the contents of sodium, potassium and chloride ions in incubated guinea-pig cerebellar, and rat brain cortex, slices have been investigated. The frequencies of the spontaneous action potentials are partially suppressed by concentrations of NH₄Cl less than 2 mm and completely abolished by concentrations exceeding 2 mm . The amplitudes of the spike discharges are unaffected. A lag period of at least 15 s precedes the inhibition. The suppressing action of NH on the spike frequency is reversible, as shown by complete recovery on removal of NH after short time intervals. Deficiency of Cl^? in the superfusion medium causes conversion of inhibition by NH to excitation. Reduction of [K⁺], or of [Na⁺], causes increase of inhibition by NH in a normal [Cl¹], and reduction of excitation in a low [Cl¹], medium. The inhibitory effects of NH on spike frequency are unaffected by picrotoxin or strychnine. NH₄Cl, even at 1 or 2 mm , causes a significant increase of aerobic glycolysis. It is suggested that the lag period preceding the suppression of the frequency of spike discharges by NH is partly due to a metabolic change induced by NH, perhaps a transient lowering of pH in the responsible neurons, causing changed permeability to Cl^? and possibly to K⁺ and Na⁺, NH promotes, in guinea-pig cerebellar slices, an inward flow of Na⁺ and an outward flow of K⁺, the latter being greater than that due to exchange of K⁺ for NH. NH₄Cl at 1 or 2 mm causes an outward flow of K⁺ and an inward flow of Cl^? in rat brain cortex slices. The movement of Cl^? is biphasic, the first phase, seen with low [NH], consisting of an increase of tissue content of Cl^? with little or no fluid uptake and a second phase, seen with high (> 5 mm ) concentrations of NH, in which the uptake of Cl^? is directly proportional to the fluid uptake. It is suggested that the first phase is largely neuronal in location whilst the second is largely glial. In infant rat brain cortex slices, there seems to be predominantly an equal exchange of NH for K^+. There is little evidence of energy assisted concentrative uptake of NH by brain slices and this is thought to be due largely to the rapid diffusion of undissociated NH₃ across cell membranes. It is suggested that some NH (amounting to about 2 mequiv/1) may be bound in the brain. It is concluded that changes in ionic permeabilities, particularly that of Cl^?, partly due to a metabolic action, may be responsible for some of the acute cerebral effects of NH administration.     

The distribution of potassium in plants

Summary Recalculation of some literature data on potassium contents of plants revealed that potassium, like chloride, should be reported on a rational basis such as normality or percentage in plant sap. This would remove the necessity to explain large apparent differences in composition between adjacent plant parts. Potassium closely resembles chloride in its manner of distribution within the plant.     

Molecular mechanisms of ammonium transport and accumulation in plants

The integral membrane proteins of the ammonium transporter (AMT/Rh) family provide the major route for shuttling ammonium (NH(4)(+)/NH(3)) across bacterial, archaeal, fungal and plant membranes. These proteins are distantly related to the Rh (rhesus) glycoproteins, which are absent in higher plants, but are present in many species, including bacteria and mammals. It appears that the large nitrogen requirement of plants resulted in unique strategies to acquire, capture and/or release ammonium. The biological function of plant ammonium transporters will be discussed and compared to other AMT/Rh proteins.