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61.
Internal transport of O2 from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O2 transport) in non-aerenchymatous roots.Abbreviation AEC
adenylate energy charge 相似文献
62.
The root of the water fern Azolla is a compact higher-plant organ, advantageous for studies of cell division, cell differentiation, and morphogenesis. The cell complement of A. filiculoides Lam. and A. pinnata R.Br. roots is described, and the lineages of the cell types, all derived ultimately from a tetrahedral apical cell, are characterised in terms of sites and planes of cell division within the formative zone, where the initial cells of the cell files are generated. Subsequent proliferation of the initial cells is highly specific, each cell type having its own programme of divisions prior to terminal differentiation. Both formative and proliferative divisions (but especially the former) occur in regular sequences. Two enantiomorphic forms of root develop, with the dispositions of certain types of cell correlating with the direction, dextrorse or sinistrorse, of the cell-division sequence in the apical cells. Root growth is determinate, the apical cell dividing about 55 times, and its cell-cycle duration decreasing from an initial 10 h to about 4 h during the major phase of root development. Sites of proliferation progress acropetally during aging, but do not penetrate into the zone of formative divisions. The detailed portrait of root development that was obtained is discussed with respect to genetic and epigenetic influences; quantal and non-quantal cell cycles; variation in cell-cycle durations; relationships between cell expansion and cell division: the role of the apical cell; and the limitation of the total number of mitotic cycles during root formation. 相似文献
63.
31P-Nuclear-magnetic-resonance spectra of maize (Zea mays L.) root tips, that had been induced to extrude large amounts of H+ in response to fusicoccin (FC) in the presence of potassium salts, indicate that the cytoplasmic pH does not become higher than that of controls. In fact, the cytoplasmic pH may become slightly (approx. 0.1 pH unit) lower in cells extruding H+. Estimations of the buffer capacity of the cells show that without active intracellular pH regulation, H+ extrusion caused by FC would cause the intracellular pH to rise by at least 0.6 pH unit h-1. Our results indicate that intracellular pH is tightly regulated even during extreme rates of acid extrusion, and that a rise in cytoplasmic pH is not the signal linking H+ extrusion with enhanced organic-acid synthesis or other intracellular responses to H+ pumping.Abbreviations FC
fusicoccin
- Pi
inorganic phosphate
- NMR
nuclear magnetic resonance
-
chemical shift
- MDP
methylene diphosphonic acid 相似文献
64.
Shaoliang?ChenEmail author Moitaba?Zommorodi Eberhard?Fritz Shasheng?Wang Aloys?Hüttermann 《Trees - Structure and Function》2004,18(2):175-183
The effects of hydrogel on growth and ion relationships of a salt resistant woody species, Populus euphratica , were investigated under saline conditions. The hydrogel used was Stockosorb K410, a highly cross-linked polyacrylamide with about 40% of the amide group hydrolysed to carboxylic groups. Amendment of saline soil (potassium mine refuse) with 0.6% hydrogel improved seedling growth (2.7-fold higher biomass) over a period of 2 years, even though plant growth was reduced by salinity. Hydrogel-treated plants had approximately 3.5-fold higher root length and root surface area than those grown in unamended saline soil. In addition, over 6% of total roots were aggregated in gel fragments. Tissue and cellular ion analysis showed that growth improvement appeared to be the result of increased capacity for salt exclusion and enhancement of Ca2+ uptake. X-ray microanalysis of root compartments indicated that the presence of polymer restricted apoplastic Na+ in both young and old roots, and limited apoplastic and cytoplastic Cl– in old roots while increasing Cl– compartmentation in cortical vacuoles of both young and old roots. Collectively, radical transport of salt ions (Na+ and Cl–) through the cortex into the xylem was lowered and subsequent axial transport was limited. Hydrogel treatment enhanced uptake of Ca2+ and microanalysis showed that enrichment of Ca2+ in root tissue mainly occurred in the apoplast. In conclusion, enhanced Ca2+ uptake and the increased capacity of P. euphratica to exclude salt were the result of improved Ca2+/Na+ concentration of soil solution available to the plant. Hydrogel amendment improves the quality of soil solutions by lowering salt level as a result of its salt-buffering capacity and enriching Ca2+ uptake, because of the polymers cation-exchange character. Accordingly, root aggregation allows good contact of roots with a Ca2+ source and reduces contact with Na+ and Cl–, which presumably plays a major role in enhancing salt tolerance of P. euphratica. 相似文献
65.
66.
Koji Kageyama Masako Senda Takahiro Asano Haruhisa Suga Kiyoshi Ishiguro 《Mycological Research》2007,111(4):416-423
Heterogeneity of the rDNA ITS region in Pythium helicoides and the phylogenetic relationship between P. helicoides and closely related species were investigated. In PCR-RFLP analysis of the rDNA ITS region of six P. helicoides isolates investigated, including the type culture, intraspecific variation was found at the HhaI site. The total length of fragments was longer than before cutting, indicating sequence heterogeneity within isolates. Digestion of the cloned rDNA ITS region derived from seven isolates with HhaI revealed polymorphisms among and within single zoospore isolates, and variability of the region was also present among the clones derived from the same isolate. To test whether the rDNA ITS region of closely related species and other regions in the genome of P. helicoides are also variable, the rDNA ITS region of P. ultimum and the cytochrome oxydase II (cox II) gene encoded in mitochondria were sequenced. P. ultimum had little variation in the rDNA ITS region. The cox II gene sequences of both species revealed only a low intraspecific variability and no intra-isolate variation. In the phylogenic tree based on the rDNA ITS sequences, all clones of P. helicoides formed one large clade that was distinct from the clades comprising morphologically similar species, such as P. oedochilum and P. ostracodes, and was closely related to P. chamaehyphon rather than the other species. 相似文献
67.
Wiley PR Tosi P Evrard A Lovegrove A Jones HD Shewry PR 《Plant molecular biology》2007,65(1-2):125-136
Increasing its root to shoot ratio is a plant strategy for restoring water homeostasis in response to the long-term imposition
of mild water stress. In addition to its important role in diverse fundamental processes, indole-3-acetic acid (IAA) is involved
in root growth and development. Recent extensive characterizations of the YUCCA gene family in Arabidopsis and rice have elucidated that member’s function in a tryptophan-dependent IAA biosynthetic pathway. Through forward- and
reverse-genetics screening, we have isolated Tos17 and T-DNA insertional rice mutants in a CONSTITUTIVELY WILTED1 (COW1) gene, which encodes a new member of the YUCCA protein family. Homozygous plants with either a Tos17 or T-DNA-inserted allele of OsCOW1 exhibit phenotypes of rolled leaves, reduced leaf widths, and lower root to shoot ratios. These phenotypes are evident in
seedlings as early as 7–10 d after germination, and remain until maturity. When oscow1 seedlings are grown under low-intensity light and high relative humidity, the rolled-leaf phenotype is greatly alleviated.
For comparison, in such conditions, the transpiration rate for WT leaves decreases approx. 5- to 10-fold, implying that this
mutant trait results from wilting rather than being a morphogenic defect. Furthermore, a lower turgor potential and transpiration
rate in their mature leaves indicates that oscow1 plants are water-deficient, due to insufficient water uptake that possibly stems from that diminished root to shoot ratio.
Thus, our observations suggest that OsCOW1-mediated IAA biosynthesis plays an important role in maintaining root to shoot ratios and, in turn, affects water homeostasis
in rice. 相似文献
68.
Katarína Ďurčeková Jana Huttová Igor Mistrík Marta Ollé Ladislav Tamás 《Plant and Soil》2007,290(1-2):61-68
The effect of Cd on H2O2 production, peroxidase (POD) activity and root hair formation were analyzed in barley root. Cd causes a strong H2O2 burst in the root region 0–6 mm behind the root tip. POD activity was activated in root tip and raised toward the root base
in Cd treated roots. In situ analyses showed that both elevated H2O2 production and POD activity are localized in the early metaxylem vascular bundles. Cd induces root hair formation in the
region 2 to 4 mm behind the root tip that was not detected in control roots. These results suggest that Cd-induced root growth
inhibition is at least partially the consequence of Cd-stimulated premature root development involving xylogenesis and root
hair formation, which is correlated with shortening of root elongation zone and therefore with root growth reduction. 相似文献
69.
Guillem Prats-Ejarque Jose A. Blanco Vivian A. Salazar Victòria M. Nogués Mohammed Moussaoui Ester Boix 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(1):105-117
Background
Human RNase6 is a small cationic antimicrobial protein that belongs to the vertebrate RNaseA superfamily. All members share a common catalytic mechanism, which involves a conserved catalytic triad, constituted by two histidines and a lysine (His15/His122/Lys38 in RNase6 corresponding to His12/His119/Lys41 in RNaseA). Recently, our first crystal structure of human RNase6 identified an additional His pair (His36/His39) and suggested the presence of a secondary active site.Methods
In this work we have explored RNase6 and RNaseA subsite architecture by X-ray crystallography, site-directed mutagenesis and kinetic characterization.Results
The analysis of two novel crystal structures of RNase6 in complex with phosphate anions at atomic resolution locates a total of nine binding sites and reveals the contribution of Lys87 to phosphate-binding at the secondary active center. Contribution of the second catalytic triad residues to the enzyme activity is confirmed by mutagenesis. RNase6 catalytic site architecture has been compared with an RNaseA engineered variant where a phosphate-binding subsite is converted into a secondary catalytic center (RNaseA-K7H/R10H).Conclusions
We have identified the residues that participate in RNase6 second catalytic triad (His36/His39/Lys87) and secondary phosphate-binding sites. To note, residues His39 and Lys87 are unique within higher primates. The RNaseA/RNase6 side-by-side comparison correlates the presence of a dual active site in RNase6 with a favored endonuclease-type cleavage pattern.General significance
An RNase dual catalytic and extended binding site arrangement facilitates the cleavage of polymeric substrates. This is the first report of the presence of two catalytic centers in a single monomer within the RNaseA superfamily. 相似文献70.
We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia. 相似文献