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51.
Harald Kosegarten Franz Grolig Andreas Esch Karl-Heinz Glüsenkamp Konrad Mengel 《Planta》1999,209(4):444-452
A fluorimetric ratio technique was elaborated to measure apoplastic pH in the outer root cortex of maize (Zea mays L.) grown hydroponically. A newly synthesized fluorescent probe, fluorescein boronic acid (pKa = 5.48), which covalently binds to the cell wall of the outer cell layers, was used. Under conditions of saturating ion concentrations
the apoplastic pH was determined along the root axis ranging from 1 to 30 mm behind the root tip. Apoplastic pH was recorded
for root segment areas (1 mm2), and pH values of high statistical significance were obtained. With an external solution of pH 5, the apoplastic pH was
about pH 5.1 in the division zone, between pH 4.8 and 4.9 in the elongation region and about pH 4.9 in the root hair zone.
At an external pH of 8.6, the difference between the external pH and the apoplastic pH was considerably more, with a pH of
5.2–5.3 in all root zones. Addition of 1 mM NH4
+ caused a small apoplastic pH decrease (0.05 of a pH unit) in all root zones. Apoplastic alkalization upon application of
6 mM NO3
− was highest (0.3 of a pH unit) in the zone where root hairs emerge; in the division and early elongation zones, apoplastic
pH increased only transiently. In the presence of 10 mM HCO3
−, NO3
− elicited a higher and persistent alkalization (0.06–0.25 of a pH unit) in all root zones. Application of fusicoccin reduced
apoplastic pH from 4.85 to 4.75 in the elongation zone, while inhibition of the H+-ATPase with vanadate alkalized the apoplast in the root hair zone from pH 5.4 to 5.6. The observed pH differences along the
root axis upon differential N supply and application of HCO3
− provide evidence that this new pH technique is a useful tool with which to measure apoplastic pH, and in future may permit
measurements at microsites at the cell level by use of microscope imaging.
Received: 26 August 1998 / Accepted: 4 May 1999 相似文献
52.
The hydraulic conductivities of excised whole root systems of wheat (Triticum aestivum L. cv. Atou) and of single excised roots of wheat and maize (Zea mays L. cv. Passat) were measured using an osmotically induced back-flow technique. Ninety minutes after excision the values for single excised roots ranged from 1.6·10-8 to 5.5·10-8 m·s-1·MPa-1 in wheat and from 0.9·10-8 to 4.8·10-8 m·s-1·MPa-1 in maize. The main source of variation was a decrease in the value as root length increased. The hydraulic conductivities of whole root systems, but not of single excised roots, were smaller 15 h after excision. This was not caused by occlusion of the xylem at the cut end of the coleoptile. The hydraulic conductivities of epidermal, cortical and endodermal cells were measured using a pressure probe. Epidermal and cortical cells of both wheat and maize roots gave mean values of 1.2·10-7 m·s-1·MPa-1 but in endodermal cells (measured only in wheat) the mean value was 0.5·10-7 m·s-1·MPa-1. The cellular hydraulic conductivities were used to calculate the root hydraulic conductivities expected if water flow across the root was via transcellular (vacuole-to-vacuole), apoplasmic or symplasmic pathways. The results indicate that, in freshly excised roots, the bulk of water flow is unlikely to be via the transcellular pathway. This is in contrast to our previous conclusion (H. Jones, A.D. Tomos, R.A. Leigh and R.G. Wyn Jones 1983, Planta 158, 230–236) which was based on results obtained with whole root systems of wheat measured 14–15 h after excision and which probably gave artefactually low values for root hydraulic conductivity. It is now concluded that, near the root tip, water flow could be through a symplasmic pathway in which the only substantial resistances to water flow are provided by the outer epidermal and the inner endodermal plasma membranes. Further from the tip, the measured hydraulic conductivities of the roots are consistent with flow either through the symplasmic or apoplasmic pathways.Symbols
L
p, cell
cell hydraulic conductivity
-
L
p, root
root hydraulic conductivity
-
L
p, root
calculated root hydraulic conductivity
-
root reflection coefficient 相似文献
53.
The K+-sensitive fluorescent dye benzofuran isophthalate (PBFI) and the pH-sensitive fluorescein isothiocyanate dextran (FITC-Dextran)
were used to investigate the influence of light/dark transitions on apoplastic pH and K+ concentration in intact leaves of Vicia faba L. with fluorescence ratio imaging microscopy. Illumination by red light led to an acidification in the leaf apoplast due
to light-induced H+ extrusion. Similar apoplastic pH responses were found on adaxial and abaxial sides of leaves after light/dark transition.
Stomatal opening resulted only in a slight pH decrease (0.2 units) in the leaf apoplast. Gradients of apoplastic pH exist
in the leaf apoplast, being about 0.5–1.0 units lower in the center of the xylem veins as compared with surrounding cells.
The apoplastic K+ concentration in intact leaves declined during the light period. A steeper light-induced decrease in apoplastic K+, possibly caused by higher apoplastic K+, was found on the abaxial side of leaves concentration. Simultaneous measurements of apoplastic pH and K+ demonstrated that a light-induced decline in apoplastic K+ concentration indicative of net K+ uptake into leaf cells occurs independent of apoplastic pH changes. It is suggested that the driving force that is generated
by H+ extrusion into the leaf apoplast due to H+-ATPase activity is sufficient for passive K+ influx into the leaf cells.
Received: 7 March 2000 / Accepted: 12 May 2000 相似文献
54.
In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca2+ ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca2+ concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca2+ binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance. 相似文献
55.
Rates of diffusion into roots of maize 总被引:1,自引:1,他引:0
56.
Tamotsu Hoshino Masato Odaira Midori Yoshida Sakae Tsuda 《Journal of plant research》1999,112(2):255-261
Received 8 January 1999/ Accepted in revised form 6 April 1999 相似文献
57.
Several nitrogen compounds were identified and quantified in the apoplastic and symplastic sap of sugarcane stems. The sap of stems was composed mainly of soluble sugars, which constituted 95% of the total organic compounds detected. Sap also contained nitrogen compounds, with amino acids (50-70% of N) and proteins (20-30% of N), being the main nitrogenous substances, as well as inorganic forms as ammonium, nitrite and nitrate, in low concentrations (<20% of N). Serine, proline, alanine and aspartic acid together represented around 60% of the amino acids of the sap of both field grown and high nitrogen fertilized plants, and non-nitrogen fertilized plants inoculated with Gluconacetobacter diazotrophicus. The total amino acid content of apoplastic sap was six to nine times lower in non-nitrogen fertilized plants than in fertilized ones. The possible roles of these substances to regulate endophytic associations with sugarcane are also discussed. 相似文献
58.
Francesca Sicilia Benedetta Mattei Felice Cervone Daniela Bellincampi Giulia De Lorenzo 《Biochimica et Biophysica Acta - Proteins and Proteomics》2005,1748(1):9-19
An extracytoplasmic 86.7 kDa protein was isolated from intercellular washing fluids (IWF) of Phaseolus vulgaris etiolated hypocotyls. Micro sequencing of tryptic peptides of the 86.7 kDa protein revealed 100% identity with a bean lipoxygenase (LOX) protein fragment. Purified P87-LOX exhibited LOX activity characterized by an optimal pH of 6.0 and linolenic acid as an optimal substrate, and was classified as a 13-LOX with respect to its positional specificity of linoleic acid oxygenation. A protein identical to P87-LOX, as determined by MALDI-TOF analysis and biochemical characterization, was purified from hypocotyl microsomes. Immunoblot analysis showed that P87-LOX is present in plasma membrane-enriched fractions, from which it was solubilized using high ionic strength buffers. These observations suggest that P87-LOX is a peripheral protein associated to the apoplastic face of the plasma membrane. 相似文献
59.
Changes in ascorbic acid levels in apoplastic fluid during growth of pine hypocotyls. Effect on peroxidase activities associated with cell walls 总被引:3,自引:0,他引:3
The apoplastic fluid of pine ( Pinus pinaster Aiton) hypocotyls contains ascorbic acid (AA) and dehydroascorbic acid (DHA). The amounts of ascorbic and dehydroascorbic acids were in the nmol (g fresh weight)−1 range and decreased with the hypocotyl age as well as along the hypocotyl axis. The ratio AA/(AA+DHA) also decreased with the hypocotyl age and along the hypocotyl. Both ascorbic oxidase and peroxidase activity against ascorbic acid showed very low activity not only in the apoplastic fluid but also in the fractions ionically and covalently bound to the cell walls. However, the peroxidase activity in the three abovementioned fractions was strongly increased in the presence of ferulic acid. That stimulation effect increased with the hypocotyl age and from the apical towards the basal region of the hypocotyls of 10-day-old seedlings. Furthermore, the oxidation of ferulic acid by apoplastic and ionically- and covalently-bound peroxidases was inhibited by ascorbic acid as long as ascorbate was available. A regulatory role of apoplastic ascorbic acid levels in the formation of dehydrodiferulic bridges between wall polysaccharides catalysed by cell wall peroxidases and thus in the cell wall stiffening during plant growth is proposed. 相似文献
60.
Rup Kumar Kar 《Plant signaling & behavior》2011,6(11):1741-1745
Terrestrial plants most often encounter drought stress because of erratic rainfall which has become compounded due to present climatic changes.Responses of plants to water stress may be assigned as either injurious change or tolerance index. One of the primary and cardinal changes in response to drought stress is the generation of reactive oxygen species (ROS), which is being considered as the cause of cellular damage. However, recently a signaling role of such ROS in triggering the ROS scavenging system that may confer protection or tolerance against stress is emerging. Such scavenging system consists of antioxidant enzymes like SOD, catalase and peroxidases, and antioxidant compounds like ascorbate, reduced glutathione; a balance between ROS generation and scavenging ultimately determines the oxidative load. As revealed in case of defence against pathogen, signaling via ROS is initiated by NADPH oxidase-catalyzed superoxide generation in the apoplastic space (cell wall) followed by conversion to hydrogen peroxide by the activity of cell wall-localized SOD. Wall peroxidase may also play role in ROS generation for signaling. Hydrogen peroxide may use Ca2+ and MAPK pathway as downstream signaling cascade. Plant hormones associated with stress responses like ABA and ethylene play their role possibly via a cross talk with ROS towards stress tolerance, thus projecting a dual role of ROS under drought stress. 相似文献