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901.
The carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) grown hydroponically at a constant pH on either 4 mM or 12 mM NO3
- or NH4
+ nutrition were investigated using either 14C or 15N techniques. Greater allocation of 14C to amino-N fractions occurred at the expense of allocation of 14C to carbohydrate fractions in NH4
+-compared to NO3
--fed plants. The [14C]carbohydrate:[14C]amino-N ratios were 1.5-fold and 2.0-fold greater in shoots and roots respectively of 12 mM NO3
--compared to 12 mM NH4
+-fed wheat. In both 4 mM and 12 mM N-fed maize the [14C]carbohydrate:[14C]amino-N ratios were approximately 1.7-fold and 2.0-fold greater in shoots and roots respectively of NO3
--compared to NH4
+-fed plants. Similar results were observed in roots of wheat and maize grown in split-root culture with one root-half in NO3
--and the other in NH4
+-containing nutrient media. Thus the allocation of carbon to the amino-N fractions occurred at the expense of carbohydrate fractions, particularly within the root. Allocation of 14N and 15N within separate sets of plants confirmed that NH4
--fed plants accumulated more amino-N compounds than NO3
--fed plants. Wheat roots supplied with 15NH4
+ for 8 h were found to accumulate 15NH4
+ (8.5 g 15N g-1 h-1) whereas in maize roots very little 15NH4
+ accumulated (1.5 g 15N g-1 h-1)It is proposed that the observed accumulation of 15NH4
+ in wheat roots in these experiments is the result of limited availability of carbon within the roots of the wheat plants for the detoxification of NH4
+, in contrast to the situation in maize. Higher photosynthetic capacity and lower shoot: root ratios of the C4 maize plants ensure greater carbon availability to the root than in the C3 wheat plants. These differences in carbon and nitrogen partitioning between NO3
--and NH4
+-fed wheat and maize could be responsible for different responses of wheat and maize root growth to NO3
- and NH4
+ nutrition. 相似文献
902.
903.
What is in the intercellular spaces of roots? Evidence from the cryo-analytical-scanning electron microscope 总被引:7,自引:0,他引:7
The schizogenous intercellular spaces (i. e. those small spaces formed by cell walls coming apart) in the cortex of the roots of field-grown maize ( Zea mays L.) were studied in planed transverse faces of frozen tissue, very lightly etched and coated with Al. The spaces were mostly filled with either fluid or, in the drier roots, with a flaky deposit. This deposit may have been left behind when water was withdrawn, or may have been debris dislodged by the planing. Even in roots with mostly dry spaces, some wet, fluid-filled spaces remained. X-ray microanalysis of the wet spaces revealed that the fluid contained K (average concentration 230 m M , range 50–750 m M ) and Ca (average concentration 100 m M , range 15 to 550 m M ), and occasionally small amounts of S, P or Cl. No other balancing inorganic anions were detected. Concentrations in the wet intercellular spaces showed considerable variation between one space and the next, and were often quite different from those in the vacuoles of adjacent cells. However, overall the vacuoles of the cells surrounding the spaces showed mean concentrations, and distributions of concentrations, indistinguishable from those of the wet spaces. Analyses of the deposits in the dry spaces were less reliable because of their uneven surface, but the same ions in about the same amounts were found there. The contents of the spaces showed no correlation with either the time of collection of the roots, or with distance from the root tip. Nor was there any change in concentration of these ions in the spaces when the roots were grown for 19 h in distilled water mist. Experiments and evidence are presented suggesting that the observed distribution of ions is probably not an artefact. Pilot experiments showed similar distributions of extracellular ions in roots of barley, Sudan grass and soybean 相似文献
904.
In order to investigate the physiological basis of the differential Cd distribution and the degree of variation of this Cd
distribution among maize inbred lines, six inbreds designated earlier as ‘shoot Cd excluders’ (B73, H99, and H96) and ‘non-shoot
Cd excluders’ (B37, H98, and N28) were grown in nutrient solution culture at different external Cd levels or at different
pH. The characterization of the inbreds according to their shoot/root partitioning of Cd was consistent, independent of pH
or level of Cd supply. The Cd concentrations in the plants were highest at the highest pH of the solution cultures. Generally,
there was a positive correlation between the Cd concentrations in shoots and xylem exudates. It was shown that the Cd concentration
in the roots is particularly important in the Cd distribution process. Above a ‘critical’ internal Cd concentration in the
roots, specific for each inbred, the ability to retain Cd is strongly diminished. It is concluded that structural and/or physiological
characteristics of the roots are involved in Cd partitioning. 相似文献
905.
玉米精细胞及体细胞原生质体表膜蛋白的比较 总被引:1,自引:1,他引:0
以低渗冲击法(改良两步法)及Percoll密度梯度离心,成功分离纯化生活玉米(Zeam ays)精细胞;以混合酶解法制备玉米叶原生质体和愈伤组织原生质体;以NHS-生物素标记完整精细胞及原生质体表膜蛋白,进行SDS-PAGE和Western blot,并以辣根过氧化物酶标亲和素检测被标记的表膜蛋白。结果表明,在精细胞中标记蛋白有4 种,分子量分别为48、59、67、79 kD;叶片原生质体中有5 种,分子量分别为54、58、66、71、78 kD;愈伤组织原生质体中仅有2 种,分子量67 和80 kD。其中48 kD蛋白为精细胞所特有,54 kD 和71 kD蛋白为叶片细胞所特有 相似文献
906.
Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-m nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shootroot ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots. 相似文献
907.
T. M. Schindler R. Bergfeld P. Van Cutsem D. v. Sengbusch P. Schopfer 《Protoplasma》1995,188(3-4):213-224
Summary Aiming to elucidate the possible involvement of pectins in auxin-mediated elongation growth the distribution of pectins in cell walls of maize coleoptiles was investigated. Antibodies against defined epitopes of pectin were used: JIM 5 recognizing pectin with a low degree of esterification, JIM 7 recognizing highly esterified pectin and 2F4 recognizing a pectin epitope induced by Ca2+. JIM 5 weakly labeled the outer third of the outer epidermal wall and the center of filled cell corners in the parenchyma. A similar labeling pattern was obtained with 2F4. In contrast, JIM 7 densely labeled the whole outer epidermal wall except the innermost layer, the middle lamellae, and the inner edges of open cell corners in the parenchyma. Enzymatic de-esterification with pectin methylesterase increased the labeling by JIM 5 and 2F4 substantially. A further increase of the labeling density by JIM 5 and 2F4 and an extension of the labeling over the whole outer epidermal wall could be observed after chemical de-esterification with alkali. This indicates that both methyl- and other esters exist in maize outer epidermal walls. Thus, in the growth-controlling outer epidermal wall a clear zonation of pectin fractions was observed: the outermost layer (about one third to one half of wall thickness) contains unesterified pectin epitopes, presumably cross-linked by Ca2+ extract. Tracer experiments with3H-myo-inositol showed rapid accumulation of tracer in all extractable pectin fractions and in a fraction tightly bound to the cell wall. A stimulatory effect of IAA on tracer incorporation could not be detected in any fraction. Summarizing the data a model of the pectin distribution in the cell walls of maize coleoptiles was developed and its implications for the mechanism of auxin-induced wall loosening are discussed.Abbreviations CDTA
trans-1,2-diaminocyclohexane-N,N,N,N-tetraacetic acid
- CWP
cell-wall pellet
- IAA
indole-3-acetic acid
- LSE
low-salt extract
- TCA
trichloroacetic acid; Tris tris-(hydroxy-methyl)aminoethane 相似文献
908.
Thiols of Cu-treated maize plants inoculated with the arbuscular-mycorrhizal fungus Glomus intraradices 总被引:2,自引:0,他引:2
Mycorrhizal colonization of roots, fresh weight, content of cysteine, γ-glutamylcysteine (γEC). glutathione (GSH), thiol groups in Cu-binding peptides (CuBP), and the uptake of Cu were measured in roots and shoots of maize ( Zea mays L., cv. Honeycomb F-1) grown in quartz sand, with Cu at 0, 4.5, 9, 15 and 30 μg g−1 added with or without inoculum of the arbuscular-mycorrhizal fungus (AMF) Glomus intraradices . In control plants (no Cu added) AMF significantly reduced shoot growth, but did not affect root growth. At an external Cu supply of 9 μg (g quartz sand)−1 or higher, both mycorrhizal colonization and growth of roots and shoots of mycorrhizal and non-mycorrhizal plants were significantly reduced.
With up to 9 μg Cu g−1 , mycorrhizal colonization increased the content of cysteine, γEC and GSH in the roots. However, the amount of thiols in CuBPs was not increased by mycorrhizal colonization in Cu-treated plants and no differences in Cu uptake were detected between non-mycorrhizal and mycorrhizal plants. A CuBP-complex with a relative molecular mass of 7300 and a SH:Cu ratio of 1.77:1 was separated on a Sephadex G-50 column from both non-inoculated and inoculated roots of Cu-treated plants. HPLC chromatography of the CuBPs of both non-inoculated and inoculated roots resulted in a similar peak pattern, indicating that no additional CuBPs were formed by the fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu-toxicity. 相似文献
With up to 9 μg Cu g
909.
Carotenoid composition in Zea mays developed at sub-optimal temperature and different light intensities 总被引:2,自引:0,他引:2
The content and composition of pigments were examined in the third leaf of Zea mays L. plants grown under controlled environment at near-optimal temperature (24°C) or sub-optimal temperature (14°C) at a light intensity of either 200 or 600 μmol m?2 s?1. Compared to leaves grown at 24°C, leaves grown at 14°C showed a large reduction in the chlorophyll (Chl) content, a marked decrease in the Chl a/b ratio, and a large increase in the ratio of total carotenoids/Chl a+b. Leaves grown at 14°C showed a much lower content of β-carotene than leaves grown at 24°C, while the content of the carotenoids of the xanthophyll cycle (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was markedly higher in the former leaves as compared to the latter leaves; neoxanthin and lutein were affected by the growth temperature to a much lesser extent. The xanthophylls/β-carotene ratio was about three times higher in leaves grown at 14°C as compared to leaves grown at 24°C. On a chlorophyll basis, the two types of leaves hardly differed in their level of β-carotene, while the levels of the xanthophylls (including lutein and neoxanthin) were higher in 14°C-grown leaves as compared to 24°C-grown leaves. In leaves grown at 14°C, 40 and 56% of the V+A+Z pool was in the form of zeaxanthin at low light intensity and high light intensity, respectively. Only trace amounts of zeaxanthin, if any, were present in leaves grown at 24°C. The changes in the pigment composition induced by growth at sub-optimal temperature were more pronounced at a light intensity of 600 as compared to 200 μmol m?2 s?1. In the given range, the light intensity slightly affected the composition of pigments in leaves grown at 24°C. The physiological significance of the modifications to the pigment composition induced by growth at sub-optimal temperature is discussed. 相似文献
910.
Summary We investigated changes of thiols (GSH, GSSG, and cysteine) induced by transplasma membrane electron transport after addition of artificial electron acceptors and the influence of the thiol level on redox activity. GSH, GSSG, and cysteine content of maize (Zea mays L. cv. Golden Bantam) roots and coleoptile segments was determined by high performance liquid chromatography with a fluorescence detector. GSSG increased after treatment with 0.8 mM diamide, an SH-group oxidizer. GSH level of roots increased after treatment with diamide, while GSH levels of coleoptiles decreased. Incubation of roots with the GSH biosynthesis inhibitor buthionine-D,L-sulfoximine for 6 days lowered the glutathione level up to 80%. However, the GSH/GSSG ratio of maize roots remained constant after treatment with both effectors. The GSH/GSSG ratio and the glutathione level were changed by addition of artificial electron acceptors like hexacyanoferrate (III) or hexabromoiridate (IV), which do not permeate the plasma membrane. Hexacyanoferrate (III) reduction was inhibited up to 25% after the cellular glutathione level was lowered by treatment with diamide or buthionine-D,L-sulfoximine. Proton secretion induced by reduction of the electron acceptors was not affected by both modulators. The change in glutathione level is different for roots and coleoptiles. Our data are discussed with regard to the role of GSH in electron donation for a plasma membrane bound electron transport system.Abbreviations Buthionine-D,L-sulfoximine
s-n-butyl-homocysteine sulfoximine
- cys
cysteine
- diamide 1,1-azobis
(N,N-dimethyl-formamide)
- DTE
dithioerythritol
- EDTA
ethylenediaminetetraacetic acid
- GSH
reduced glutathione
- GSSG
oxidizied glutathione, glutathione disulfide
- HBI IV
hexabromoiridate (IV) (K2[IrBr6])
- HCF III
hexacyanoferrate (III) (K3[Fe(CN)6]
- NEM
N-ethylmaleimide
- PM
plasma membrane
- Tris
Tris(hydroxymethyl)aminomethane 相似文献