32P Uptake Research Articles

Phosphorus and Potassium Ion Dynamics in a Vertisol Soil and in Cotton Plants (Gossypium hirsutum L) During a Waterlogging Event

ABSTRACT The aim is to examine the nutrient ion dynamics in a Vertisol soil undergoing waterlogging to ascertain whether soil solution concentration and/or nutrient uptake dynamics are the cause of boll shedding in cotton. Cotton was grown in pots, and the soil waterlogged after 76 days at which time injections of 33P and 86Rb were made to trace phosphorus (P) and potassium (K) dynamics. After seven days, waterlogging in the pots were drained and an injection of 32P was made to trace P dynamics during the recovery period. Redox fell rapidly during waterlogging, and soil solution concentrations of P, K, sodium (Na), and manganese (Mn) increased. Biomass accumulation was less in the waterlogged treatment than in the non-waterlogged control. In the 7-day recovery period, shoot biomass increased in the waterlogged treatment and root biomass weight continued to decline. Recovery of 33P was 10 times higher in the control than in the waterlogged treatment during the 7-day waterlogging period treatment. Uptake of 86Rb in the control treatment was more than twice that of the waterlogged treatment during this period. Uptake of both33P and 86Rb increased during recovery but remained higher in the control treatment. Uptake of 32P occurred during post-waterlogging but remained higher in the control treatment. Reduced uptake of P and K during waterlogging is most likely due to damage to the uptake mechanisms of the roots rather than a reduction in the concentration of nutrients in the soil solution under waterlogged conditions.

Phosphorus acquisition by wheat from organic and inorganic sources labelled with 32P and 33P radioisotopes

ABSTRACT: Investment in soil phosphorus (P) capital in the tropics is often constrained by poor availability of mineral fertiliser to small-scale farmers. Consequently, new sustainable agricultural cropping strategies are required to maintain fertility and maximise crop yields. The co-application of Tithonia diversifolia (Tithonia) green manure and mineral fertiliser (KH2PO4) together (integrated nutrient management) in comparison to the addition of one or the other alone has been hypothesized to promote crop P uptake. The aim of this study was to critically evaluate the benefits of integrated nutrient management practices in laboratory experiments. Wheat was grown as a test crop in microcosms to which either 32P-labelled mineral fertiliser or 33P-labelled Tithonia was added either singly or in combination. Exclusion meshes were used to determine the role of arbuscular mycorrhizal (AM) fungi in P uptake from the different P sources. The rate of uptake of both 32P and 33P by mycorrhizas was similar, and the rate of mycorrhizal P capture was comparable to that of roots. Generally, there was little difference in wheat P acquisition under integrated nutrient management treatments in comparison to P acquisition from 32P-mineral fertiliser or the addition of 33P-Tithonia alone. Overall, Tithonia residues were not very effective in supplying P to wheat over a short time evaluation period, suggesting that mineral fertilisers will still be required to satisfy crop demand.

Relative comparison of tissue specific bioaccumulation and radiation dose estimation in marine and freshwater bivalve molluscs following exposure to phosphorus-32

With respect to environmental protection, understanding radionuclide bioconcentration is necessary to relate exposure to radiation dose and hence to biological responses. Few studies are available on tissue specific accumulation of short-lived radionuclides in aquatic invertebrates. Short-lived radionuclides such as 32Phosphorus (32P), although occurring in small quantities in the environment, are capable of concentrating in the biota, especially if they are chronically exposed. In this study, we firstly compared tissue specific bioaccumulation and release (depuration) of 32P in adult marine (Mytilus galloprovincialis, MG) and freshwater bivalve molluscs (Dreissena polymorpha, DP). Secondly, using the Environmental Risk from Ionising Contaminants Assessment and Management (ERICA) tool, we calculated tissue specific doses following determination of radionuclide concentration. Marine and freshwater bivalves were exposed for 10 days to varying 32P concentrations to acquire desired whole body average dose rates of 0.10, 1.0 and 10 mGy d−1. Dose rates encompass a screening dose rate value of 10 μGy h−1 (0.24 mGy d−1), in accordance with the ERICA tool. This study is the first to relate tissue specific uptake and release (via excretion) of 32P from two anatomically similar bivalve species. Results showed highly tissue specific accumulation of this radionuclide and similarity of accumulation pattern between the two species. Our data, which highlights preferential 32P accumulation in specific tissues such as digestive gland, demonstrates that in some cases, tissue-specific dose rates may be required to fully evaluate the potential effects of radiation exposure on non-human biota. Differential sensitivity between biological tissues could result in detrimental biological responses at levels presumed to be acceptable when adopting a ‘whole-body’ approach.

Effects of a bacterivorous nematode on rice 32P uptake and root architecture in a high P-sorbing ferrallitic soil

Soil bacterivorous nematodes are key plant mutualists that increase nutrient availability for plants either by enhancing the mineralization of organic compounds (the “mineralization pathway”) or by increasing plant lateral root branching following shifts in internal plant metabolism, and subsequently leading to a higher volume of soil prospected by the roots (the “hormonal pathway”). The effects of these organisms on the nutrition of plants growing in strongly nutrient-deficient ferrallitic soils, especially in soils with limited available inorganic phosphorus (P), are poorly known, as are the pathways involved. In our study, using Oryza sativa (Poaceae) and Acrobeloides sp. (Cephalobidae), we tested the “mineralization” and “hormonal” hypotheses in an acidic P-depleted Ferralsol from the Madagascar highlands. We assessed the effect of nematode inoculation on (i) inorganic P flow from soil to plant using the 32P labelling technique and (ii) plant root architecture using a rhizobox device. We showed that the ability of Acrobeloides sp. to enhance P uptake in plants is strongly limited in Ferralsols. However, when the soil pH was corrected with dolomite, Acrobeloides sp. increased plant P uptake probably through the “mineralization” pathway (higher microbial turnover). Indeed, the L-value increased by 49% in the presence of nematodes and dolomite, suggesting the production of unlabelled plant-available P, probably through a higher net P mineralization when the nematodes were inoculated. Using the rhizobox technique, we also observed increased root length in the presence of nematodes but the specific root length, the tip number and the root branching density did not increase in the presence of nematodes, suggesting that nematodes did not increase plant P uptake and growth in this soil as proposed by the “hormonal” hypothesis. From an ecological intensification perspective, to promote agro-ecological development in tropical regions, our results suggest that amending ferrallitic soils with P-rich organic matter and correcting soil pH with an appropriate amount of dolomite may constitute suitable agronomic actionable triggers to drive the mutualistic activity of bacterivorous nematodes.

The role of organic acids on the uptake and relationship of phosphorus and zinc in corn (Zea mays L.) by application of 32P and 65Zn radioisotopes

ABSTRACTTo investigate the effect of oxalic and citric acids on the uptake and relationship of phosphorus and zinc in corn (Zea mays L.), some greenhouse experiments were performed by individual and combined application of monopotassium phosphate [KH232PO4] and zinc sulfate [65ZnSO4.7H2O] fertilizers in microcosm. For this purpose after planting corn seeds, solutions of phosphorus (32P) and zinc (65Zn) (14 and 2 M) and organic acids treatments (1 and 10 mM) were injected in microcosms at suitable times. Then, plants were harvested, digested, extracted, and activity of 32P and 65Zn was measured in samples. Results revealed that the highest uptake of 32P in shoots was 18.8% and observed at 10 mM concentration of oxalic acid. But no effect on 65Zn uptake was seen and the highest uptake was observed in control (1.27%). The highest uptake of 32P and 65Zn in plant shoots and roots was observed at 10 mM concentration of oxalic and citric acids, respectively.

Rhizosphere yeasts improve P uptake of a maize arbuscular mycorrhizal association

Plant roots associate with microorganisms to acquire phosphorus (P) from the soil including arbuscular mycorrhizal (AM) fungi and phosphate solubilizers such as yeasts. However, information on interactions between AM fungi and yeasts is limited. The objective of the present study was to examine possible cooperation between the AM fungus Rhizophagus irregularis and the rhizosphere yeasts Cryptococcus flavus and Candida railenensis in terms of maize plant growth and P uptake employing P isotope tracer monitoring. Compartmented growth units with root-hyphal (RHC) and hyphal (HC) mesh bags allowed studying interactions between R. irregularis and yeasts with and without roots. The P isotope dilution method was used to measure possible phosphate solubilization in soil by the rhizosphere yeasts with subsequent P uptake by the AM association. Plants were grown for 8 weeks in low P soil under controlled growth chamber conditions. Main results showed strong plant growth promotion after inoculation with R. irregularis and both yeast species altered the specific root length of maize. The yeasts also improved maize shoot P content, but only in mycorrhizal plants. More specifically yeasts improved AM hyphal 32P uptake, but not that of root 33P uptake. On the other hand, yeasts had no effect on extraradical growth of R. irregularis. Inoculation with yeasts did not result in P isotope dilution measured as specific P isotope activity, indicating that the reported improved P uptake from AM associations in combination with yeasts was most likely not related to P solubilization, whereas alteration in root growth and specific root length seems more likely mechanisms of interactions. We conclude that rhizosphere yeasts promote P nutrition of arbuscular mycorrhizal maize linked to improved specific root length and AM hyphal P uptake.

Identification of the First Sodium Binding Site of the Phosphate Cotransporter NaPi-IIa (SLC34A1)

Transporters of the SLC34 family (NaPi-IIa,b,c) catalyze uptake of inorganic phosphate (Pi) in renal and intestinal epithelia. The transport cycle requires three Na+ ions and one divalent Pi to bind before a conformational change enables translocation, intracellular release of the substrates, and reorientation of the empty carrier. The electrogenic interaction of the first Na+ ion with NaPi-IIa/b at a postulated Na1 site is accompanied by charge displacement, and Na1 occupancy subsequently facilitates binding of a second Na+ ion at Na2. The voltage dependence of cotransport and presteady-state charge displacements (in the absence of a complete transport cycle) are directly related to the molecular architecture of the Na1 site. The fact that Li+ ions substitute for Na+ at Na1, but not at the other sites (Na2 and Na3), provides an additional tool for investigating Na1 site-specific events. We recently proposed a three-dimensional model of human SLC34a1 (NaPi-IIa) including the binding sites Na2, Na3, and Pi based on the crystal structure of the dicarboxylate transporter VcINDY. Here, we propose nine residues in transmembrane helices (TM2, TM3, and TM5) that potentially contribute to Na1. To verify their roles experimentally, we made single alanine substitutions in the human NaPi-IIa isoform and investigated the kinetic properties of the mutants by voltage clamp and 32P uptake. Substitutions at five positions in TM2 and one in TM5 resulted in relatively small changes in the substrate apparent affinities, yet at several of these positions, we observed significant hyperpolarizing shifts in the voltage dependence. Importantly, the ability of Li+ ions to substitute for Na+ ions was increased compared with the wild-type. Based on these findings, we adjusted the regions containing Na1 and Na3, resulting in a refined NaPi-IIa model in which five positions (T200, Q206, D209, N227, and S447) contribute directly to cation coordination at Na1.

The uptake of 32P by spruce seedlings (Picea abies (L.) Karst.) growing in competition with grass

The uptake of 32P by spruce seedlings (Picea abies (L.) Karst.) growing in competition with grass

Functional Identification of the Na1 Site of the Phosphate Cotransporter NaPi-IIa

Gene products of the SLC34 family (NaPi-IIa,b,c) catalyse uphill transport of inorganic Pi in renal and intestinal epithelial tissue and require 3 Na+ ions and one divalent Pi to bind with the protein before translocation. The first Na+ interaction is a critical event in the transport cycle. For electrogenic isoforms (NaPi-IIa,b), the voltage dependence of cotransport is determined by (i) displacement charges intrinsic to the protein that alter the sidedness of cation accessibility and (ii) movement of cations to the so-called Na1 site, within the transmembrane field. Li+ ions can substitute for Na+ at Na1 but not at the other sites (Na2,3). Refinements of a homology model of NaPi-IIa in the outward facing conformation, based on the crystal structure of the dicarboxylate transporter VcINDY, have allowed prediction of residues that contribute to cation coordination at Na1. To establish their involvement, we made single alanine substitutions at putative positions in each repeat unit (RU1,2) of the human NaPi-IIa isoform and investigated the kinetic properties of the mutants by voltage clamp and 32P uptake. Comparison of the steady-state and presteady-state kinetics with the WT profile allowed further refinement of the putative Na1 region. Substitutions at 3 positions in RU2 resulted in non-functional mutants that nevertheless showed cation interactions, as evidenced by resolvable presteady-state relaxations. In contrast, 5 functional mutants in RU1 resulted in marginal changes in substrate apparent affinities, yet at three positions, we observed significant hyperpolarizing shifts of voltage dependence. Importantly, the ability of Li+ ions to substitute for Na+ ions was increased compared with the WT. Our data suggest that these positions in RU1 are critical for cation coordination at Na1 and place Na1 cytosolic to the Na2-Pi-Na3 binding region, which is common to all NaPi-II isoforms.

微細気泡水の電気化学的特性の定量的評価及び応用実験との相関について

For introducing the use of fine bubbles (FB) in industrial applications, it is important to understand their properties and the mechanisms of the effect in order to utilize them effectively. However, it is difficult to observe FB directly because of their small size. We measured the electrochemical properties of water containing FB in order to examine the effect of FB on ions macroscopically. The conductivity of the FB water generated from purified water was lower than that of the purified water. In particular, the decrease in the conductivity of the FB water supports the hypothesis that ions are closely involved in the generation mechanism of FB. We also analyzed the effect of FB water on the nutrient uptake of soybean seedlings. For the uptake experiment, we used radio isotope elements (137Cs, 22Na, 32P) at different pH conditions. As a result, we have found the increased uptake of 137Cs and 22Na and the decreased uptake of 32P compared with distilled water. There was no correlation between pH value and the effect of FB water. Transpiration rate was not significantly different between FB water and distilled water. Although questions still remain in the elements efficiency in ions (anion or cation), these results suggest a possible influence of fine bubbles on the plant activity to uptake nutrient ions.

Proposed biokinetic model for phosphorus

This paper reviews data related to the biokinetics of phosphorus in the human body and proposes a biokinetic model for systemic phosphorus for use in updated International Commission on Radiological Protection (ICRP) guidance on occupational intake of radionuclides. Compared with the ICRP’s current occupational model for systemic phosphorus (Publication 68, ), the proposed model provides a more realistic description of the paths of movement of phosphorus in the body and greater consistency with experimental, medical, and environmental data regarding its time-dependent distribution. For acute uptake of 32P to blood, the proposed model yields roughly a 50% decrease in dose estimates for bone surface and red marrow and a six-fold increase in estimates for liver and kidney compared with the model of Publication 68. For acute uptake of 33P to blood, the proposed model yields roughly a 50% increase in dose estimates for bone surface and red marrow and a seven-fold increase in estimates for liver and kidney compared with the model of Publication 68.

Impact of Mycorrhizae Formation on the Phosphorus and Heavy-Metal Uptake of Alfalfa

Three pot experiments were set up to determine how efficiently mycorrhizal fungi affect the uptake, translocation, and distribution of labeled phosphorus (32P), phosphorus (P), and heavy metals in alfalfa (Medicago sativa L.). In experiments 1 and 2, the efficiencies of different arbuscular mycorrhizal fungi (AMF) species including Glomus mosseae, G. etunicatum, G. intraradices and a mixed strain (G. mosseae, Gigaspora hartiga, and G. fasciculatum) on uptake, translocation, and distribution of 32P and P in alfalfa were investigated, respectively. In a third experiment, the efficiency of G. mosseae on uptake and distribution of heavy metals [cadmium (Cd), cobalt (Co), lead (Pb), and combinations] was tested. Results of experiments 1 and 2 suggest that G. mosseae was the most effective at increasing the uptake of 32P and P. Experiment 3 result showed that in the triple-metal-contaminated soil, inoculated plants had greater Co (32.56 mg kg−1) and Pb (289.50 mg kg−1) concentration and G. mosseae enhanced the translocation of heavy metals to shoot. Hence, mycorrhizal alfalfa in symbiosis with G. mosseae can be used for remediation of heavy metals polluted soils with high efficiency.

A study of 32P-phosphate uptake in a plant by a real-time RI imaging system

Abstract It is very important to visualize the process of nutrient absorption and distribution to study the physiological activity of the plant. We developed a real-time radioisotope (RI) imaging system, where RI tracers were applied to the plant sample. This system allowed the quantitative measurement concerning the uptake of nutrients labeled with radioisotopes, such as 45Ca, 35S, 32P and 14C as long as several days. The β-rays emitted from the sample were converted to light by a CsI(Tl) scintillator and were guided to a highly sensitive CCD camera. The scintillator surface was covered with an Al plate to avoid LED light penetration but allow selected β-ray penetration. We employed Lotus japonicus for the plant sample and observed the 32P-phosphate absorption in roots and the accumulation to the aboveground part of the plant. The environment condition of daytime and night was simulated by the ON/OFF of LED timer and the accumulation manner of the 32P-phosphate in roots and leaves during daytime and night was analyzed. The accumulation of 32P-phosphate in leaves was highly dependant on light irradiation and higher when the LEDs was turned on, whereas the absorption of 32P-phosphate in root was higher when the LEDs was turned off. The transfer function concerning the transportation of phosphate within the plant during the developmental stage was obtained from the analysis of 32P uptake images. We are now trying to get specific moving images of each radioisotope when two kinds of isotopes, such as 32P and 35S, were applied at the same time to the plant, through an image analysis.

A review and model assessment of 32P and 33P uptake to biota in freshwater systems

Bioaccumulation of key short-lived radionuclides such as 131I and 32,33P may be over-estimated since concentration ratios ( CRs) are often based on values for the corresponding stable isotope which do not account for radioactive decay during uptake via the food chain. This study presents estimates for bioaccumulation of radioactive phosphorus which account for both radioactive decay and varying ambient levels of stable P in the environment. Recommended interim CR values for radioactive forms of P as a function of bioavailable stable phosphorus in the water body are presented. Values of CR are presented for three different trophic levels of the aquatic food chain; foodstuffs from all three trophic levels may potentially be consumed by humans. It is concluded that current recommended values of the CR are likely to be significantly over-estimated for radioactive phosphorus in many freshwater systems, particularly lowland rivers. Further research is recommended to field-validate these models and assess their uncertainty. The relative importance of food-chain uptake and direct uptake from water are also assessed from a review of the literature. It can be concluded that food-chain uptake is the dominant accumulation pathway in fish and hence accumulation factors for radioactive phosphorus in farmed fish are likely to be significantly lower than those for wild fish.

Protein kinase C isotypes in signal transduction for the 1,25D 3-MARRS receptor (ERp57/PDIA3) in steroid hormone-stimulated phosphate uptake

We undertook studies to determine which isotype(s) of protein kinase C (PKC) is/are activated by ligand binding to the 1,25D 3-MARRS receptor (ERp57/PDIA3) and subsequent stimulation of phosphate uptake. Isolated intestinal epithelial cells from vitamin D-replete chicks were exposed to 1,25(OH) 2D 3 for 1, 3, or 5 min, thoroughly chilled, homogenized, and P 2 fractions (20,000 × g post-nuclear pellet) prepared. Western analyses with anti-pan PKC revealed steroid-stimulated redistribution to P 2 membranes 1 min after hormone. Using this time point, cells were treated with vehicle, 130-, 300- or 650-pM hormone. Western blots with anti-PKCα exhibited redistribution to membranes in a biphasic dose–response curve: slightly stimulated at the lowest dose, maximal at 300 pM 1,25(OH) 2D 3, and equivalent to control levels at the highest dose, paralleling hormone-mediated phosphate uptake. Westerns with anti PKCβ also revealed hormone-mediated differences, while those with anti PKCγ did not. RNAi studies were then performed with siRNA against PKCα or PKCβ. Untransfected cells treated with hormone for 7 min exhibited enhanced 32P uptake relative to vehicle controls. Cells transfected with either active siRNA revealed decreased 32P uptake in both controls (relative to untransfected controls), and hormone treated cells. However, control and transfected cells treated with hormone had equivalent levels of uptake. Western blot analyses confirmed decreased immunoreactivity in transfected cells. Chemical PKCα (safingol) and PKCβ ([3-(1-(3-Imidazol-1-ylpropyl)-1H-indol-3-yl)-4-anilino-1H-pyrrole-2,5-dione] blockers also confirmed the results from siRNA and demonstrated decreased 32P uptake in cells treated with 1,25(OH) 2D 3 plus blockers in comparison with cells treated with 1,25(OH) 2D 3 alone. Thus, PKCα and PKCβ are both involved in steroid-stimulated phosphate uptake.

Real-time imaging of ion uptake from root to above-ground part of the plant using conventional beta-ray emitters

We present real-time imaging of 32P-phosphate within a living plant as well as that in culture solution toward roots. The above-ground part of the plant was irradiated with light from LED and roots were kept in dark. The plant was Lotus japonicus, cv. Miyakojima MG20 and real-time 32P-phosphate uptake manners in young, flowering and adult phase were visualized. In the case of young plant, there was a preferential translocation of 32P in younger leaves. When the sample was treated with phosphate deficient condition, 32P uptake amount was much higher. In an adult phase, 32P uptake was high at pods.

Evaluation of Mychorrhizae Symbiosis Efficiency with Barley (Hordeum vulgare L.) through 32P Uptake under Soils Contaminated with Heavy Metals

Evaluation of Mychorrhizae Symbiosis Efficiency with Barley (Hordeum vulgare L.) through 32P Uptake under Soils Contaminated with Heavy Metals

The Journal of Biological Chemistry, Volume 203, 1953: Enzyme secretion and the incorporation of P32 into phospholipides of pancreas slices.

1. When enzyme secretion was stimulated by carbamylcholine or acetylcholine (with eserine) in slices of pigeon pancreas, the incorporation of P32 into the phospholipide fraction of the stimulated slices was, after 2 hours, 4.8 to 8.7 (average, 7.0) times greater than the incorporation of P32 into the phospholipides of control slices. Neither respiration nor the incorporation of P32 into acid-soluble phosphate esters was increased. 2. Pilocarpine, which on a weight for weight basis was much less effective than carbamylcholine or acetylcholine in stimulating enzyme secretion in pancreas slices, was also much less effective in stimulating the uptake of P32 into phospholipides. 3. The stimulatory effects of carbamylcholine on both enzyme secretion and the incorporation of P32 into phospholipides were abolished by atropine. 4. The specific activity of the phospholipides from slices incubated anaerobically was less than 5 per cent of that observed aerobically. Anaerobically, carbamylcholine did not stimulate the incorporation of P32 into phospholipides to any significant extent. The specific activity of the acid-soluble phosphate esters after anaerobic incubation was 34 per cent of that found aerobically. 5. Cholinergic drugs had little or no effect on the incorporation of P32 into the phospholipides of the following tissue slices: pigeon and guinea pig liver, guinea pig heart ventricle, pigeon gizzard (smooth muscle), and guinea pig kidney cortex. A relatively slight stimulation of P32 uptake into phospholipides was observed in slices of pigeon brain (65 per cent) and guinea pig brain cortex (40 per cent). 6. Stimulation of amylase synthesis in slices of pigeon pancreas by the addition of a mixture of amino acids had no effect on the incorporation of P32 into phospholipides.

Contributions of pro‐oxidant and anti‐oxidant conditions to the actions of 24,25‐dihydroxyvitamin D3 and 1,25‐dihydroxyvitamin D3 on phosphate uptake in intestinal cells

The steroid hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] rapidly stimulates the uptake of phosphate in isolated chick intestinal cells, while the steroid 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] inhibits the rapid stimulation by 1,25(OH)2D3. Earlier work in this laboratory has indicated that a cellular binding protein for 24,25(OH)2D3 is the enzyme catalase. Since binding resulted in decreased catalase activity and increased H2O2 production, studies were undertaken to determine if pro-oxidant conditions mimicked the inhibitory actions of 24,25(OH)2D3, and anti-oxidant conditions prevented the inhibitory actions of 24,25(OH)2D3. An antibody against the 24,25(OH)2D3 binding protein was found to neutralize the inhibitory effect of the steroid on 1,25(OH)2D3-mediated 32P uptake. Incubation of cells in the presence of 50 nM catalase was also found to alleviate inhibition. In another series of experiments, isolated intestinal epithelial cells were incubated as controls or with 1,25(OH)2D3, each in the presence of the catalase inhibitor 3-amino-1,2,4-triazole, or with 1,25(OH)2D3 alone. Cells exposed to hormone alone again showed an increased accumulation of 32P, while cells treated with catalase inhibitor and hormone had uptake levels that were indistinguishable from controls. We tested whether inactivation of protein kinase C (PKC), the signaling pathway for 32P uptake, occurred. Incubation of cells with phorbol-13-myristate (PMA) increased 32P uptake, while cells pretreated with 50 microM H2O2 prior to PMA did not exhibit increased uptake. Likewise, PMA significantly increased PKC activity while cells exposed to H2O2 prior to PMA did not. It is concluded that catalase has a central role in mediating rapid responses to steroid hormones.

Soil physical properties and root activity in a soybean second crop/maize rotation under direct sowing and conventional tillage

Soil degradation is the result of interactions involving the soil itself, human activity, climate, relief, and vegetation. These can lead to changes in —or even the loss of— certain characteristics of the soil, reducing its present and future productive capacity. The aim of this study was to determine the behaviour of a number of soil physical variables and total organic carbon content, as well as the root activity and yield of crops grown in rotation (soybean in 1998/1999 and maize in 1999/2000) under direct sowing (DS) and conventional tillage (CT) conditions. Root activity was assessed using an isotopic methodology involving the uptake of 32P. The root activity of the soybean crop, which grew under normal rainfall conditions, was greater under CT conditions. That of the maize crop, which grew when rainfall was well below normal, was greater under DS conditions. Bulk density was higher and total porosity lower in the upper 0.10 m of the soil in the DS plots. Conventional tillage led to lower penetration resistance values in the upper layers of the soil profile. No differences in soil total organic carbon were found between the two tillage systems. The soil water content of the upper soil layers was higher under DS. The yield of the soybean crop under CT was 57% higher than under DS. The yield of maize was affected by water deficiency; higher yields were obtained with DS than with CT.