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951.
K. S. Kumarasinghe F. Zapata G. Kovacs D. L. Eskew S. K. A. Danso 《Plant and Soil》1986,90(1-3):293-299
Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha–1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two15N methods. In the first,Azolla caroliniana (Willd.) was labelled with15N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha–1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of15N-urea was applied separately or in combination with either 250 or 330 kg N ha–1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha–1 to 430 kg N ha–1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using15N-labelledAzolla, this method is preferable to the15N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at –20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla. 相似文献
952.
Nitrate and ammonium absorption by plants growing at a sufficient or insufficient level of phosphorus in nutrient solutions 总被引:1,自引:0,他引:1
J. K. Schjørring 《Plant and Soil》1986,91(3):313-318
Summary Absorption of nitrate and ammonium was studied in water culture experiments with 4 to 6 weeks old plants of barley (Hordeum vulgare L.), buckwheat (Fagopyrum esculentum L. Moench) and rape (Brassica napus L.). The plants were grown in a complete nutrient solution with nitrate (5.7±0.2 mM) or nitrate (5.6±0.2 mM) + ammonium (0.04±0.02 mM). The pH of the nutrient solution was kept at 5.0 using a pH-stat. It was found that phosphorus deficiency reduced the rate of nitrate uptake by 58±3% when nitrate was the sole N source and by 83±1% when both nitrate and ammonium were present. The reduction occurred even before growth was significantly impeded by P deficiency. The inhibition of the uptake of ammonium was less,i.e. ammonium constituted 10±1% of the total N uptake in the P sufficient plants and 30±5% in the P deficient plants. The reduction of nitrate absorption greatly decreased the difference between the uptake of anions and cations. It is suggested that P deficiency reduced the assimilation of NO
3
–
into the proteins, which might cause a negative feedback on NO
3
–
influx and/or stimulate NO
3
–
efflux. 相似文献
953.
Summary The leaf and root nitrate reductase activities were measured in 7 day-old barley seedlings by anoxic nitrite accumulation in darkness, during 48h after the transfer from a N-starved medium to a 1.5 mM K15NO3 medium. Thisin situ nitrate reduction was compared with the15N incorporation in the reduced N fraction of the whole seedlings.The nitrate reduction integrated fromin situ measurements was lower than the reduced15N accumulation. The rootin situ nitrate reductase activity seemed to account for only the third of the real root nitrate reduction, which may have been responsible for the overall underestimation. This discrepancy was partly explained by the ability of the root to reduce nitrite in an anoxic environment.These results suggest that, after correction of thein situ estimation of the nitrate reduction. the roots contribute to about 50% of the total assimilation. 相似文献
954.
Summary Removal of all but one leaf from pepper plants prevented the senescence of the remaining leaf and caused increases of approximately 140, 200, and 200%, respectively in leaf area, weight, and nitrate reductase activity. Development of the fruit (fresh and dry weight increases) was only approximately 65% of that of fruit on control plants. 相似文献
955.
Summary Cadmium and zinc uptake parameters were determined for intact corn (Zea mays L.) seedlings grown for 15 and 22 in nutrient solutions containing levels of Cd and Zn that were similar to those found in
soil solutions. Uptake of both elements was assumed to follow Michaelis-Menten kinetics. Calculations were based on the concentrations
of free ionic Cd (Cd2+) and Zn (Zn2+) rather than the total solution concentration. Rates of Zn uptake were measured by determining depletion of Zn for periods
of up to 30 h from solutions containing initial concentrations of 1.5 and 10μmol Zn 1−1. Depletion curves suggested that Zn uptake characteristics were similar at both levels of Zn in solution. The Imax for Zn
uptake decreased from 550 to 400 pmol m−2 root surface s−1 between 16 and 22 d of growth while Km decreased from 2.2 to 1.5 μmol Zn2+ 1−1. Cadmium uptake parameters were measured by controlling Cd2+ activities in nutrient solution betwen 6.3 to 164 nmol l−1 by continuous circulation of nutrient solution through a mixed-resin system. Imax for Cd uptake was 400 pmol m−2 root surface s−1 at 15 and 22 d of growth. The magnitude of Km increased from 30 to 100 nmol Cd2+ 1−1 during this time period. The Km value suggests that corn is efficient for Cd uptake. The results of these uptake studies
are consistent with the observed uptake of Zn and Cd by corn seedlings in soils. 相似文献
956.
Relationship between growth,nitrogen fixation and assimilation in a legume (Medicago sativa L.) 总被引:1,自引:0,他引:1
Summary Symbiotic N2 fixation, NO
3
−
assimilation and protein accumulation in the shoots were measured simultaneously in alfalfa (Medicago sativa L.) grown in the field or in pots, in order to study how the balance between the two modes of nitrogen nutrition could be
influenced by agronomic factors, such as harvest, mineral nitrogen supply and drought stress.
During periods of rapid growth, fixation and assimilation may function simultaneously; they are antagonistic at the beginning
and at the end of the growth cycle, when the nitrogen requirement of the plant is lower. When nitrogen nutrition does not
limit growth, mineral nitrogen supply favours assimilation at the expense of fixation, but does not modify the amount of nitrogen
accumulated, which is adjusted to the growth capacity of the plant.
After cutting, nitrate assimilation compensated for the decrease in fixation and supplied the plant with the nitrogen required
by the regrowth, the proliferation of which determined the fixation recovery.
Drought stress decreased N2 fixation much more than NO
3
−
assimilation. The latter made growth recovery possible when water supply conditions became normal again.
These results suggested the existence of an optimum level of nitrate assimilation, which differed depending on the age of
the plants and allowed both maximum growth and fixing activity. 相似文献
957.
Abstract: Rats were given 75 mg/kg of 5,5-diphenylhydantoin (phenytoin) or vehicle 30 min prior to 75 mg/kg of 1, 1, 1-trichloro-bis( p -chlorophenyl)ethane ( p, p' -DDT) (p.o.) or chlordecone (i.p.) and tremor was measured 12 h later. Rats were then killed, and regional brain levels of biogenie amines and their acid metabolites and amino acids were determined. Pretreatment with phenytoin significantly attenuated the tremor produced by p, p' -DDT but enhanced that produced by chlordecone. p, p' -DDT had significant effects on the levels of asparate, glutamate, 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), whereas chlordecone increased glycine, 5-HIAA, and MHPG levels. Pretreatment with phenytoin blocked p.p' -DDT-induced increases of aspartate in the brainstem and spinal cord, 5-HIAA in the hippocampus, and MHPG in the brainstem and hypothalamus. Phenytoin significantly enhanced chlordecone-induced increases of MHPG in the brainstem. These data indicate that organo-chlorine-induced increases in noradrenergic activity in the brainstem and spinal cord may be directly related to the tremorigenic effects of these chemicals. 相似文献
958.
Extracellular Fluid Proteins of Goldfish Brain: Evidence for the Presence of Proteases and Esterases 总被引:1,自引:1,他引:0
Preparations of enriched fractions of extracellular fluid (ECF) proteins from goldfish brain were found to contain protease(s) and esterase(s). The N-substituted furanacryloyl (FA) peptides FA-Phe-Gly-Gly and FA-Phe-OMe were used as model substrates for determining protease and esterase activity, respectively, in a spectrophotometric assay. Studies of the profile of substrate specificity and identification of the types of compounds that were effective as inhibitors showed that these ECF enzymes have some distinctive properties. GSH, but not GSSG, and EDTA inhibited the protease(s) without influencing the esterase(s), whereas L-1-tosylamide-2-phenylethylchloromethyl ketone blocked both protease and esterase activities of ECF. Most of the protease and esterase properties of ECF could be bound to concanavalin A-Sepharose affinity chromatographic columns in association with ependymin--a brain extracellular protein. These observations indicate that ECF may contain a metalloprotease(s) and raise the possibility that the ependymins might be a substrate for these ECF enzymes. 相似文献
959.
GABAB Receptor-Mediated Enhancement of Vasoactive Intestinal Peptide-Stimulated Cyclic AMP Production in Slices of Rat Cerebral Cortex 总被引:7,自引:4,他引:3
Basal and vasoactive intestinal peptide (VIP)-stimulated accumulations of cyclic AMP were measured in slices of rat cerebral cortex. Neither gamma-aminobutyric acid (GABA) nor the selective GABAB receptor agonist (-)-baclofen stimulated basal cyclic AMP accumulation, whereas VIP caused a large dose-dependent increase in cyclic AMP levels. However, in the presence of 100 microM (-)-baclofen, the effects of VIP on cyclic AMP accumulation were significantly enhanced, with the responses to 1 microM and 10 microM VIP being approximately doubled. The enhancing effects of (-)-baclofen was dose related (1-1,000 microM), but an enhancing effect was not observed with 100 microM (+)-baclofen. In the presence of the GABA uptake inhibitor nipecotic acid (1 mM), GABA caused a similar dose-related enhancement of the VIP response. The ability of either GABA or (-)-baclofen to augment VIP-stimulated production of cyclic AMP was not mimicked by the GABAA, agonists isoguvacine and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and was not antagonized by the GABAA antagonist bicuculline. The putative GABAB antagonist 5-aminovaleric acid (1 mM) significantly reduced the effect of (-)-baclofen. The ability of (-)-baclofen to enhance VIP-stimulated accumulation of cyclic AMP was observed in slices of rat cerebral cortex, hippocampus, and hypothalamus. These results indicate that GABA and (-)-baclofen can enhance VIP-stimulated accumulation of cyclic AMP in rat brain slices via an interaction with specific GABAB receptors. 相似文献
960.
Binding of the Novel Serotonin Agonist 8-Hydroxy-2-(Di-n-Propylamino) Tetralin in Normal and Alzheimer Brain 总被引:5,自引:2,他引:3
Binding of [3H]8-hydroxy-2-(di-n-propylamino) tetralin, a putative ligand for the 5-hydroxytryptamine (5-HT, serotonin) 1A recognition site, was measured in neocortex from postmortem human brain. The substance was found to bind to a saturable site with a KD value and pharmacological profile similar to that of rat. Binding to membranes from normal human temporal cortex was found to significantly correlate (inversely) with age. A significant reduction in binding, reflecting decreased density of recognition sites, was observed in the frontal cortex of patients with Alzheimer's disease (48% loss). This region in the dement brains showed unaltered presynaptic 5-HT function (5-HT and 5-hydroxyindoleacetic acid content) whereas 5-HT concentration was reduced in the temporal cortex. 相似文献