Mechanism for Cd2+ inhibition of (K++ Mg2+)ATPase activity and K+ (86Rb+) uptake join roots of sugar beet (Beta vulgaris)

Steady state kinetics were used to examine the influence of Cd²⁺ both on K⁺ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K⁺(⁸⁶Rb⁺) uptake in intact or excised beet roots. The in vitro effect of Cd²⁺ was studied both on a 12000–25000 g root fraction of the (Na⁺+K⁺+Mg²⁺)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd²⁺ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd²⁺ at concentrations <100 μM inhibits the specific K⁺ activation at both high and low affinity sites for K⁺. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K⁺ <5 mM, the inhibition by Cd²⁺ with respect to K⁺ is uncompetitive. In the presence of MgATP and K⁺ >10 μM, the inhibition by Cd²⁺ is competitive. 3) At the low concentrations of K⁺, Cd²⁺ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K⁺(⁸⁶Rb⁺) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K⁺(⁸⁶Rb⁺) uptake is little influenced by Cd²⁺. As Cd²⁺ inhibits the metabolic uptake of K⁺(⁸⁶Rb⁺) and the K⁺ activation of the ATPase in the same way at low concentrations of K⁺, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K⁺ is low, the presence of Cd²⁺ could be disadvantageous.     

Effects of saponin extracts from Solanum elaeagnifotium fruits on ion uptake by clover seedlings

Solanum elaeagnifolium Cav. fruits contain high concentrations of steroidal saponins. Treatment of 3-day-old clover seedlings with aqueous fruit extracts modified Ca²⁺ uptake without significantly altering K⁺ and H₂PO₄⁻ uptake. The extracts increased Ca²⁺ uptake in the concentration range of 0.2 to 20 m M Ca²⁺. Uptake curves could be represented by two phases. In the lower phase (0.2-1.0 m M Ca²⁺), this change could be related to an increase in V_max. Pretreatment of seedlings with saponin extracts significantly reduced ATP-dependent Ca²⁺ uptake and Ca²⁺-dependent ATPase activity in a fraction isolated from root homogenates by centrifugation at 1500 g for 15 min. Saponins purified from S. eleagnifolium extracts by thin-layer chromatography modified in vitro the Ca²⁺-ATPase activity of this fraction, indicating that the steroid may act directly on Ca²⁺ transport across membranes.     

Distribution and recovery of15N after fertilization of Douglas-fir saplings with different nitrogen sources

Summary Four-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) saplings planted in pots with a sand and peat mix (11) were fertilized at the rate of 200 kg N/ha of (¹⁵NH₂)₂CO (U-15),¹⁵NH₄NO₃ (A-15) and NH₄ ¹⁵NO₃(An-15). They were placed in a shadehouse and watered regularly to maintain soil moisture at field capacity over periods of one and two years. Quantity of¹⁵N in foliage generally increased from old to current growth, irrespective of the nitrogen source. Utilization of¹⁵N fertilizers by saplings after the first and second growing seasons following fertilization was greatest with nitrate labelled ammonium nitrate AN-15, and nearly equal for urea U-15 and ammonium labelled ammonium nitrate A-15. The soil immobilized more fertilizer nitrogen-15 from U-15 and A-15 than from AN-15. Data from the present study, in which leaching losses of fertilizer were minimized, demonstrated that in terms of nitrogen uptake by the saplings the nitrate fertilizer was superior to ammonium fertilizer.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

Relationships between EUF-N fractions,N uptake and quality of sugar beet in deep loess soils of Southern Lower Saxony

Summary In field experiments conducted in 1981 on deep loess soils a significant correlation was obtained between EUF-N content in the topsoil and N in sugar beet roots as well as in whole plants. A very close correlation was found to exist between EUF-N values in June 1981 and -amino N in sugar beet roots at harvest. Also other quality criteria such as the contents of sugar, K and Na in roots and yield parameters correlated with EUF-N contents in topsoils.The inorganic and organic EUF-N fractions changed during the vegetation period due to both N uptake by the crop and mineralization. Therefore it appears to be expedient to use both fractions when calculating N fertilizer requirements.The correlation between EUF-N (topsoil samples drawn in the year preceding sugar beet) and sugar yield increases obtained by N fertilization that was found in Austria¹² was confirmed in our experiments with soils from Southern Lower Saxony.     

Optimum utilization of sewage sludge of low and high metal content for grain production on arid lands

Summary Two municipal sludges, one from a highly industrialized city, Chicago, Il, and another from a little industrialized, highly agricultural area, Tucson, AZ are compared for winter barley production on Pima c 1 (Typic torrifluvent). Both sludges were responsible for highly significant additions of Zn, Cu, Ni, Cd and P to the soil each year when applied at the rates of 100 mt/ha singly and 20 mt/ha each year for 4 years. Nitrogen responses for barley straw and grain were observed from both sludges. Tucson sludge appears to be attractive as a potential fertilizer, not only as an NPK source, but also for its organic matter and minimal amounts of heavy metals. The Chicago sludge with relatively high levels of heavy metals, particularly Cd, appears poorly suited as a fertilizer, if used for an extended period of time, because of the plant's tendency to take up elevated levels of certain heavy metals. Some parts of barley plants proved to be a better indicator of heavy metal uptake and concentration than others. The diagnostic-tissue test promises to be a useful tool to warn against undesirable accumulation of heavy metals. Fortunately, when compared with other plant parts, the heavy metal in grain was the least altered as a result of continued sewage sludge use on arid land. The soil's neutral to slightly alkaline pH and the presence of lime throughout the soil profile appeared to be critical factors in keeping plant uptake of heavy metals relatively low as compared with soils of other climates.     

Response of potatoes to N fertilizer: Quantitative relations for components of growth

Summary Quantitative relationships for key processes influencing N response were derived from measurements of inorganic N in soil, the weights and N contents of foliage and tubers made at intervals during growth of maincrop potatoes in 11 N fertilizer experiments.Apparent mineralization rates (calculated from measurements of N uptake and inorganic N in the top metre and averaged over the growth period) were remarkably similar from site to site despite wide differences in the textures, water contents and organic matter contents of the soils. They were mostly about 0.78 kg N ha^–1 m^–1 d^–1.Inorganic N in the top 50 cm of soil was rapidly removed by the crop until it fell on all sites to a low value (about 4 g N cm^–3) which was maintained for the remainder of the growth period. When N fertilizer was applied, growth rate until at least the end of July was always well defined by a single coefficient in a previously derived equation. Average values of this coefficient for each of the soil types and for each of the years in which the experiments were carried out were within 20% of each other.The minimum %N in the dry matter needed to permit maximum growth rate declined with increase in plant weight in a similar manner to that previously found for other crops.Equations were found for the partition of assimilate and of nitrogen between the foliage and tubers. The coefficients in them were little affected by whether or not N fertilizer was applied.According to these relationships the maximum potential dry weight yield of tubers is 20 t ha^–1 and requires the crop to contain at least 290 kg N ha^–1.     

Availability of water controls Crassulacean acid metabolism in succulents of the Richtersveld (Namib desert,South Africa)

Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO₂-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life.Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO₂ uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO₂ fixation is only performed when the water status of the plant can be improved simultaneously.Abbreviations CAM Crassulacean acid metabolism - VPD water vapour pressure deficit Dedicated to Professor H. Ziegler on the occasion of his 60th birthday     

Modulation of carrier-mediated uptake of abscisic acid by methyl jasmonate in Phaseolus coccineus L

The effects of methyl jasmonate and jasmonic acid on uptake of abscisic acid (ABA) by suspension-cultured runner-bean cells and subapical runner-bean root segments have been investigated. Increasing concentrations of methyl jasmonate inhibit ABA uptake by the cultured cells with a K _i of 22±3 M. This is not due to cytoplasmic acidification or to effects on metabolism of ABA, and is not additive with inhibition of radioactive ABA uptake by nonradioactive ABA. Uptake of indol-3-yl acetic acid (IAA) is unaffected by methyl jasmonate. The maximum effect of nonradioactive ABA in inhibiting uptake of radioactive ABA, previously shown to reflect saturation of an ABA carrier, is generally greater than the effect of maximally inhibitory concentrations of methyl jasmonate. Similar results were obtained with root segments, but longer incubation times were necessary to observe inhibitory effects of methyl jasmonate. Demethylation of methyl jasmonate to jasmonic acid does not appear to be required since similar concentrations of jasmonic acid had no observable direct effect on ABA uptake other than that attributable to cytoplasmic acidification. Histidine reagents, a proton ionophore and acidic external pH all affect in parallel the inhibition by methyl jasmonate and nonradioactive ABA of uptake of radioactive ABA by the cultured cells. There is no effect of ABA or nonradioactive methyl jasmonate on uptake of radioactive methyl jasmonate by the cultured cells. It is proposed that methyl jasmonate interacts with the ABA carrier. Various models for this interaction are discussed.Abbreviations ABA abscisic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - IAA indol-3-yl acetic acid