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991.
Michael A. Grusak 《Planta》1995,197(1):111-117
To understand the whole-plant processes which influence the Fe nutrition of developing seeds, we have characterized root Fe(III)-reductase activity and quantified whole-plant Fe balance throughout the complete 10-week (10-wk) life cycle of pea (Pisum sativum L., cv. Sparkle). Plants were grown hydroponically in complete nutrient solution with a continuous supply of chelated Fe; all side shoots were removed at first appearance to yield plants with one main shoot. Root Fe(III)-reductase activity was assayed with Fe(III)-EDTA. Flowering of the experimental plants began on wk 4 and continued until wk 6; seed growth and active seed import occurred during wks 5–10. Vegetative growth terminated at wk 6. Iron(III) reduction in whole-root systems was found to be dynamically modulated throughout the plant's life cycle, even though the plants were maintained on an Fe source. Iron(III)-reductase activity ranged from 1–3 mol Fe reduced · g –1 DW · h–1 at early and late stages of the life cycle to 9.5 mol Fe reduced · g–1 DW · h–1 at wk 6. Visual assays demonstrated that Fe(III)-reductase activity was localized to extensive regions of secondary and tertiary lateral roots during this peak activity. At midstages of growth (wks 6–7), root Fe(III)-reductase activity could be altered by changes in internal shoot Fe demand or external root Fe supply: removal of all pods or interruption of phloem transport from the reproductive portion of the shoot (to the roots) resulted in lowered root Fe(III)-reductase activity, while removal of Fe from the nutrient solution resulted in a stimulation of this activity. Total shoot Fe content increased throughout the 10-wk growth period, with Fe content in the non-seed tissues of the shoot declining by 50% of their maximal level and accounting for 35% of final seed Fe content. At maturity, total seed Fe represented 74% of total shoot Fe; total Fe in the roots (apoplasmic and symplasmic Fe combined) was minimal. These studies demonstrate that the root Fe(III)-reductase system responds to Fe status and/or Fe requirements of the shoot, apparently through shoot-to-root communication involving a phloem-mobile signal. During active seed-fill, enhanced root Fe(III)-reductase activity is necessary to generate sufficient Fe2+ for continued root Fe acquisition. This continuing Fe supply to the shoot is essential for the developing seeds to attain their Fe-content potential. Increased rates of root Fe(III) reduction would be necessary for seed Fe content to be enhanced in Pisum sativum.Abbreviations BPDS
bathophenanthrolinedisulfonic acid
- DAF
days after flowering
- DW
dry weight
- EDDHA
N,N-ethylenebis[2-(2-hydroxyphenyl)-glycine]
- wk
week
This project has been funded in part with federal funds from the U.S. Department of Agriculture, Agricultural Research Service under Cooperative Agreement number 58-6250-1-003. The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. The author wishes to acknowledge S. Pezeshgi and K. Koch for their excellent technical assistance, L. Loddeke for editorial comments, and A. Gillum for assistance with the figures. 相似文献
992.
J. K. Schjoerring J. G. H. Bock L. Gammelvind C. R. Jensen V. O. Mogensen 《Plant and Soil》1995,177(2):255-264
The seasonal course of nitrogen uptake, incorporation and remobilization in different shoot components of winter oilseed rape (Brassica napus L.) was studied under field conditions including three rates of 15N labelled nitrogen application (0, 100 or 200 kg N ha-1) and two irrigation treatments (rainfed or watered at a deficit of 20 mm). The total amount of irrigation water applied was 260 mm, split over 13 occasions in a 7-week-period ranging from 1 week before onset of flowering until 4 weeks after flowering.Nitrogen application and irrigation increased plant growth and nitrogen accumulation. Irrespective of N and irrigation treatment more than 50% of total shoot N was present in the stem when flowering started. At the end of flowering, pod walls were the main N store containing about 30–40% of shoot N. The quantities of N remobilized from stems and pod walls amounted in all treatments to about 70% of the N present in these organs at mid-flowering. At harvest, stem and pod walls each contained about 10% of total shoot N, the remaining 80% being incorporated into seeds. The main component contributing to the response of seed N accumulation to nitrogen application and irrigation was pods in axillary racemes. Up to 20 kg N ha-1, corresponding to about 10% of final shoot N content, was lost from the plants by leaf drop.Irrigation increased the recovery at harvest of applied N from 30% to about 50%, while the level of N application did not affect the N recovery. 15N labelled (fertilizer derived) nitrogen constituted a greater proportion of the N content in old leaves than in young leaves and increased with age in the former, but not in the latter. Relative to soil N, fertilizer derived N also contributed more to the N content of vegetative than to that of reproductive shoot components. Small net changes in shoot N content after flowering reflected a balance between N import and export, leading to continuous dilution of 15N labelled N with unlabelled N. 相似文献
993.
In tobacco plants the net uptake of sulphate and its transport to the shoot were determined after cultivation with low, normal,
and high sulphate supply. The relative amount of the sulphate taken up that was transported to the shoot was used as a measure
of xylem loading. Net uptake of sulphate and its transport to the shoot were low in tobacco plants grown with low sulphate,
and high in plants cultivated with high sulphate. Xylem loading, however, was relatively low in tobacco plants grown with
high sulphate and relatively high in tobacco plants grown with low sulphate supply. Pre-culture in low sulphate containing
nutrient solution also resulted in a high proportion of the absorbed sulphate being transported into the xylem if normal sulphateconcentration
was supplied afterwards. Fumigation with H2S or SO2 reduced net uptake of sulphate in tobacco plants grown with normal, but not with high sulphate supply. Sulphate transport
to the shoots was diminished by H2S or SO2 fumigation in tobacco plants grown with normal and high sulphate supply. Also the relative amount of the sulphate taken up
that was transported to the shoot was lowered by fumigation with H2S or SO2 in tobacco plants grown with normal sulphate supply. Apparently, the diminished sulphate transport to the shoot upon H2S or SO2 fumigation can only partially be explained by a smaller sulphate uptake. Sulphur nutrition of tobacco plants also seems to
be controlled by xylem loading of sulphate. The possible role of glutathione as a signal regulating sulphur nutrition of tobacco
plants upon fumigation with H2S and SO2 is discussed. 相似文献
994.
The effect of nitrogen fertilisation on growth, foliar nutrients and water relations of four families of radiata pine (Pinus radiata, D. Don) currently in the Australian breeding program was examined from age six to 11 years. At this stage, the stand was ready for commercial thinning. The annual rainfall at the site varied from 563 to 733 mm.Application of nitrogen fertiliser resulted in stem wood volume at age nine years of 178 m3 ha-1 in the controls, compared with 228 m3 ha-1 in plots treated with 600 kg N ha-1. Pre-dawn needle water potential () measured in three consecutive summers (when rainfall ranged from 53 to 106 mm) were consistently higher (less water stress) in nitrogen fertilised than in control trees. Similarly, the water stress integral (S) decreased consistently with increasing levels of nitrogen, although total water use in fertilised trees would have been substantially higher because fertiliser application increased the leaf area index. The relationship between S and basal area was strong and paralleled that of foliar nitrogen concentration and basal area growth. Therefore, nitrogen application increased growth rates of trees by improving the nutrient status of trees and lowering the water stress on trees in summer.Families showed markedly different responses of basal area growth to nitrogen, ranging from an increase of 9.4% over three years for the least responsive family to 99.0% for the most responsive. There was no nitrogen × family interaction on or S suggesting that the large genetic variation in the growth response to nitrogen is mediated by factors other than water relations. These results have implications for managing highly productive plantations grown in an environment where rainfall is low compared to potential evapotranspiration. 相似文献
995.
Seven banana cultivars (Musa acuminata, AAA group) were inoculated with two species of vesicular arbuscular mycorrhizal (VAM) fungi (Glomus mosseae and Glomus macrocarpum) in a greenhouse experiment. Inoculated plants had generally greater shoot dry weight and shoot phosphorus concentrations compared to the noninoculated plants. A great variation in dependency on mycorrhizal colonization was observed among the banana cultivars. Cv. Williams showed the highest relative mycorrhizal dependency (RMD) and cv. Poyo the lowest. For all the cultivars studied, inoculation with G. macrocarpum resulted in the highest RMD values. Both root dry weight and root hair length or density of the noninoculated plants were inverserly correlated with the RMD values of cultivars. 相似文献
996.
J. O. Siqueira Orivaldo J. Saggin-Júnior Waldo W. Flores-Aylas Paulo T. G. Guimarães 《Mycorrhiza》1998,7(6):293-300
This paper reports a 6-year field study of the effects of mycorrhizal pre-colonization of coffee seedlings on initial crop
development and coffee bean yield in a low-fertility Oxisol amended with superphosphate (P) at planting. The experiment included
five P rates (0, 20, 40, 80 and 160 g plant–1 P2O5) combined with seven fungal treatments [non-mycorrhizal control, pre-colonization with a mix of Glomus clarum and Gigaspora margarita (CM) and with five isolates of Glomus etunicatum]. Inoculated and non-inoculated outplants were raised under glasshouse conditions, transplanted into the field in January
1989 and monitored until July 1995. Plant height and stem diameter were greatly enhanced by P application and were higher
in mycorrhizal seedlings than in controls up to 19 months after transplanting (MAT) but were not different at 26 MAT. Inoculation
effects on tree canopy diameter were significant up to 26 MAT, at which time mycorrhizal colonization was high (43–55%), but
did not differ amongst plants, regardless of whether or not the plants had been pre-colonized at the nursery stage. Root colonization
and spore number in the soil were reduced by high P rates at 26 MAT. The first bean yield (1991) was highly enhanced by P
and all pre-colonization treatments (38% increment over control) and these factors showed a significant interaction. Three
isolates of G. etunicatum showed yield enhancements above 50%. The P rate for maximal yield was 207 g plant–1 P2O5 for non-pre-colonized and approximately 100 g plant–1 for pre-colonized plants. For this harvest, the mycorrhizal biofertilizer effect was equal to 254 kg ha–1 P2O5. In subsequent years, pre-colonization effects were reduced and inconsistent. In 1992, 1993 and 1995, yield was affected
by P but not by mycorrhizal inoculation. In 1994 there was a P versus mycorrhiza interaction and CM and G. etunicatum-Var gave higher yields than non-precolonized plants. Considering accumulated yield for this 5-year period, P application
resulted in high yield increment in all treatments, whereas pre-colonization effects were extremely diminished. However, despite
inconsistency amongst mycorrhizal treatments, pre-colonization effects were detected at the fifth harvest in some fungal treatments.
Based on the total yield of five harvests, maximal productivity was achieved with CM at 20 g plant–1 P2O5 and with CM and G. etunicatum-Var at the highest P rate. Diminishing mycorrhizal effects over time are related to colonization of non-precolonized seedlings
by the indigenous fungi and to the reduced external P requirement of the mature crop. If adequate phosphorus is applied at
planting, pre-colonization of outplants with selected arbuscular mycorrhizal fungi enhances early crop development and productivity
of coffee in low-fertility soils of Brazil.
Accepted: 3 October 1997 相似文献
997.
Mechanisms of potassium absorption by higher plant roots 总被引:18,自引:0,他引:18
Potassium, as a plant macronutrient, is accumulated in plant cells from relatively dilute soil solutions and is indispensable for many vital processes. Studies characterising potassium uptake by roots stretch back over many decades. However, it is only with the introduction of modern electrophysiological and molecular techniques that investigations have been possible at a molecular level. Such approaches have confirmed the existence of discrete high and low affinity uptake systems at the root plasma membrane and have greatly enhanced our understanding of the underlying molecular nature of these uptake systems.
High affinity K+ uptake from micromolar external K+ levels is coupled to H+ transport as demonstrated independently by patch clamping of single root protoplasts and by studying the transport system after expression in Xenopus oocytes . The measured coupling ratio between the two ions is 1:1 and is sufficient to account for an accumulation ratio in excess of 106 , a value which encompasses experimental observations on K+ accumulation.
Low affinity K+ uptake activates at relatively high external K+ levels in the millimolar range and is 'passive' i.e. down the electrochemical gradient for potassium. In two higher plant species single cell inward potassium currents have been identified which are associated with low affinity potassium uptake. Furthermore, specific ion channels which underlie these potassium influxes and form a major constituent of the low affinity potassium uptake pathway have been identified and characterised. 相似文献
High affinity K
Low affinity K
998.
Bioavailability index for quantitative evaluation of plant availability of extractable soil trace elements 总被引:2,自引:0,他引:2
A new index, Bioavailability Index (BI) and the corresponding experimental method were developed for quantitative evaluation
of bioavailability of the extractable soil trace elements. Soils were first treated with various extractants (DTPA, HCl, NH2OH·HCl+HCl) separately to remove the extractable elements. The soils after extraction were washed with deionised water to
eliminate the extractant and its pH was adjusted with Ca0 and finally restored to its original pH level. Wheat (Triticum aestivum L.) and rape (Brassica chinensis) were planted in the untreated and treated soils for 8 weeks. The concentrations of the trace elements in plants were determined
after harvest. Nutrient accumulation by plants is significantly reduced due to removal of extractable trace elements from
the soil. BI of the extractable fraction was proportional to the ratio of plant accumulation reduction to trace element extractability.
In the present study, BI value of the total content of soil trace elements was designated as 1. Though only a minor fraction
of the total soil nutrient, generally less than 5%, was removed by DTPA, the nutrient accumulation by plants, especially for
wheat, was reduced greatly, leading to relatively large BI values. For wheat, the average BI values of the eight nutrients
Cu, Mn, Zn, Ni, Co, Pb, Cr, and V were found to be 22.7, 17.6 and 17.4 for the three testing soils, and for rape, the corresponding
values of 8.9, 10.0 and 11.0 were obtained, indicating that the DTPA-extractable elements represent the highly available fraction
of the total content. The BI values for HCl-extractable elements were much lower compared with those for DTPA. For wheat,
the average BI values for the three soils are 2.0, 1.9 and 2.4, and for rape, the corresponding values are 4.8, 4.1 and 3.7.
The high availability of DTPA-extractable trace elements and relatively low availability of HCl-extractable trace elements
highlight the significant role that chelation action might play in plant nutrient acquisition.
The different responses of wheat and rape to the soils previously subjected to the same extraction procedure could be explained
by their genotypical differences in sensitivity to nutrient deficiencies. The quantitative nature of BI makes it valuable
in the study of nutrient bioavailability and plant accumulation mechanisms. 相似文献
999.
The aim of this study was to determine the effects of nitrogen (N) fertilization methods on root distribution and mineral element concentrations of White Marsh grapefruit (Citrus paradisi MacFadyen) trees on sour orange (C. aurantium Lush) rootstock on a poorly drained soil. At 0–15 cm depth of soil, root density was significantly greater for trees receiving 112 kg N ha-1 yr-1 as dry granular broadcast than those receiving the same amount of N as fertigation. Of the total roots in the top 60 cm soil, >75% was at 0–15 cm and <10% was at 30–60 cm. Root density was greatest near the emitter. Nitrogen concentration of roots was greater for the trees which received fertigation as compared to the trees which received dry fertilizer broadcast or no N. 相似文献
1000.
Stuart R. Gelder 《Hydrobiologia》1984,115(1):71-81
Lumbricillus lineatus selectively ingests masses of organic and inorganic interstitial particles from a sand-clay substratum in the upper littoral zone. Particle-masses are ingested, passed along the esophagus and into the anterior intestine where the pH becomes acid. A- and C-esterases, acid -galactosidase, acid phosphatase and -N-acetylglucosaminidase are present in the epithelium, while the rotating food masses are surrounded by a membrane of sulphated, acid glycoprotein. These enzymes, with the exception of acid phosphatase and the addition of aminopeptidase M, are also present in the epithelia of the mid and posterior intestinal regions where the pH is alkaline. The cells in the ventral wall of the mid intestinal region contain high concentrations of alkaline phosphatase, acid -galactosidase and -N-acetylglucosaminidase. The food consists of absorbed organics and bacteria with absorption and intracellular digestion occurring along the intestine, particularly in the mid ventral region. 相似文献