摘要:

A procedure has been developed for the isolation of gas bubbles from the cavities of leaves ofAzolla rubra. Mature leaves of exponentially growingAzollaplants were carefully cut under water with a razor blade. The gas bubbles in the cavities were driven out by a stream of water running from a glass capillary and collected in another capillary that was filled with distilled water. This allowed the collection of a sufficient number of gas bubbles for analysis. The concentration of oxygen in the gas obtained was slightly lower than that in the external air. The diffusion of external15N2into the gas bubbles was low. The concentration of15N2in gas bubbles was only 2% of that of the external air even after incubation ofAzollaplants in15N2in light or in darkness for 20 h.The method described here for isolation and analysis of gas bubbles should permit further studies of the properties of the gas bubbles in the cavities ofAzollaleaves.

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930101.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

Almost homogeneous populations representing different developmental stages of somatic embryos (globular, torpedo‐shaped, plantlets) and vacuolated cells were obtained from a cell suspension culture of carrot. The concentrations of S‐adenosylmethionine (SAM), S‐adenosylhomocysteine (SAH) and methylated DNA were determined in embryos at different developmental stages and were found to increase during somatic embryogenesis. The highest increase during embryogenesis was a 5‐fold increase in the level of SAM. A considerable increase in the methylation index (SAM/SAH ratio) was also found. We propose that the levels of SAM and SAH may be involved in the control of somatic embryogenesis by affecting the level of DNA methylation, which in turn might cause differential changes in gene activation. An increase in the level of SAM may be a prerequisite for progression of embryogenesis and the development of complete

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930102.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

With the ultimate purpose of clarifying the mechanism for aluminium (Al) toxicity and for Al tolerance, we tried to isolate cDNAs whose expression is induced by Al treatment and phosphate (Pi) starvation. We performed Pistarvation and Al treatment (two‐step treatment) on suspension‐cultured cells ofNicotiana tabacumL. cv. Samsun and then constructed a cDNA library using poly(A)+‐RNA derived from the treated cells. Four independent cDNA clones (pAL 111, 139, 141 and 142) were isolated from the library by differential screening. Northern blot hybridization analysis indicated that the expression of these clones was induced by Pistarvation. Furthermore, we found that pAL 111 and pAL 142 are also induced by Al treatment. The complete cDNA sequencing of these 4 clones was determined. The results indicated that pAL111 is identical to theparAgene ofN. tabacum, which is described as an auxin‐regulated gene and that pAL142 is highly homologous to theparBgene ofN. tabacumwhose product has glutathione S‐transferase (GST, EC 2.5.1.18) activity. Furthermore, we found a cysteine‐rich domain in the amino acid sequence of pAL139. No DNA and deduced amino acid sequences homologous to the pAL141

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930103.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

We report an effective system for introducing exogenous DNA into cells of embryonic calli ofOryza sativaL. cv. Japonica. Plant cells were pretreated in hypertonic buffer to draw some of the water from the cells and were then put into medium of less negative osmotic potential containing exogenous DNA and treated immediately with a laser microbeam (λ=355 nm) to puncture holes in the cell wall and membrane. The pretreatment of the cells generated a gradient of osmotic pressure between the inside and outside of the cells, which facilitated the uptake of material into cells through the laser perforations. Bright yellow‐green fluorescence could be detected inside cells that had been bathed in a solution containing the fluorescent molecule calcein. β‐Glucuronidase (GUS) genes were successfully introduced into rice cells as indicated by gene expression both in post‐treated cells and in plantlets derived from kanamycin‐resistant calli that had been treated by th

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930104.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

Sunflower seedlings (Helianthus annuuscv. Licia Stella) reached a mild, moderate and severe level of water deficit stress after 5, 8 and 11 days of soil water depletion, respectively. At a moderate level of water deficit stress, an elastic adjustment occurred. At the same time, in response to a minor osmotic potential (Ψπ) and an intermediate rate of water potential (Ψw) decrease, glutathione level increased and enzyme activities related to the ascorbate/glutathione cycle were induced. At severe water deficit stress, the efficiency of this defence mechanism fell, oxidative processes intensified and soluble protein content decreased further. The results of the present experiments suggest that during water deficit stress the water status of the plants plays a key role in the activation of defence mechanis

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930105.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

Plant cells react to different environmental stimuli in different ways. The plant growth regulator abscisic acid (ABA) has been reported to be produced and involved in stress responses. To understand the role of ABA in relation to stress responses, we chose the ABA‐induced RAB (responsive to ABA) gene as a marker to study both dehydration and osmotic‐induced stress responses in rice cell suspensions. The kinetics of RAB gene expression under ABA, dehydration and mannitol treatments were studied. Dehydration‐induced RAB expression was slower as compared to both ABA‐ and mannitol‐induced RAB gene expression. Under dehydration conditions, the expression of RAB gene was correlated with an increase in endogenous ABA levels. Inhibition of protein or ABA synthesis prevented RAB expression under dehydration treatment. Under mannitol treatment, the RAB mRNA accumulated as fast as with ABA treatment, though there was no endogenous ABA accumulation. Inhibition of protein synthesis had no effect on mannitol‐induced RAB gene expression. Proton pump inhibitor, calcium channel and outward rectifying potassium channel blockers reduced both dehydration‐ and mannitol‐induced RAB gene expression. The potassium channel blocker BaCl2reduced mannitol‐induced RAB gene expression while it had no effect on dehydration‐induced RAB gene expression. The possible differences in signal transduction between dehydration and osmotic s

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930106.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

The conventional view of root‐cap mucilage as an expanded blob of mucilage is characteristic only of root tips in contact with free water. In soil, the mucilage is almost always a dry coating over the tip to which soil particles adhere. The kinetics of expansion of root‐cap mucilage ofZea maysroots grown in field soil, in soil in pots, and axenically on agar, were determined when the mucilage was exposed to water. On the soil‐grown roots the increase in mucilage volume was linear with time, sometimes reaching a constant volume during the 6 h of measurement, but sometimes not. This linear expansion is interpreted as limited by the rate at which the condensed mucilage in the periplasmic and intercellular spaces of the root cap passes to the exterior of the cap, expanding as fast as it arrives outside in the water. The height of the plateau is interpreted as a measure of the amount of mucilage initially present in the interior spaces. Because of the greater availability of water in the axenic roots grown on 1% agar, the mucilage was already outside the root cap, and it expanded more rapidly. It reached a final volume about 10‐fold greater than that on the soil‐grown roots. The volume increase was curvilinear with time. An analysis of these curves suggested that this swelling on axenic roots was a diffusion of mucilage outwards from the flanks of the root cap, and the diffusivity of the mucilage was estimated as 4 × 10−8cm2s−1. The molecular radius derived from this diffusivity was 34 nm, and the estimated molecular weight w

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930107.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

Atmospheric CO2enrichment is increasingly being reported to inhibit leaf and whole‐plant respiration. It is not known, however, whether this response is unique to foliage or whether woody‐tissue respiration might be affected as well. This was examined for mid‐canopy stem segments of white oak (Quercus albaL.) trees that had been grown in open‐top field chambers and exposed to either ambient or ambient + 300 µmol mol−1CO2over a 4‐year period. Stem respiration measurements were made throughout 1992 by using an infrared gas analyzer and a specially designed in situ cuvette. Rates of woody‐tissue respiration were similar between CO2treatments prior to leaf initiation and after leaf senescence, but were several fold greater for saplings grown at elevated concentrations of CO2during much of the growing season. These effects were most evident on 7 July when stem respiration rates for trees exposed to elevated CO2concentrations were 7.25 compared to 3.44 µmol CO2m−2s−1for ambient‐grown saplings. While other explanations must be explored, greater rates of stem respiration for saplings grown at elevated CO2concentrations were consistent with greater rates of stem growth and more stem‐wood volume present at the time of measurement. When rates of stem growth were at their maximum (7 July to 3 August), growth respiration accounted for about 80 to 85% of the total respiratory costs of stems at both CO2treatments, while 15 to 20% supported the costs of stem‐wood maintenance. Integrating growth and maintenance respiration throughout the season, taking into account treatment differences in stem growth and volume, indicated that there were no significant effects of elevated CO2concentration on either respiratory process. Quantitative estimates that could be used in modeling the costs of woody‐tissue growth and maintenan

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930108.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

The acquired freezing tolerance of jack pine seedlings (Pinus banksianaLamb.) conditioned at low nonfreezing temperatures and short photoperiods was determined by comparison of seedling survival to that of nonconditioned (control) seedlings following exposure to −5 and −10°C. Compared to that of controls, survival of conditioned seedlings was markedly increased following exposure to freezing temperatures. A 1‐week conditioning treatment significantly increased the survival of the seedlings after exposure to −5°C, but was less effective on seedlings exposed to −10°C. Conditioning periods of 2 and 4 weeks resulted in higher survival of seedlings exposed to both −5 and −10°C. The changes of two root‐plasma‐membrane‐associated enzyme activities, H+‐ATPase and NADH‐dependent ferricyanide reductase, were studied in enriched plasma membrane fractions during conditioning and after freezing. Post‐freezing activities of both enzymes were enhanced by conditioning at low temperatures and short photoperiods. These changes may be related to the increased frost hardiness

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930109.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY

摘要:

Fungal laccase oxidized derivatives of hydroxycinnamic acid. The rates decreased in the order sinapic acid>ferulic acid ≥p‐coumaric acid. The laccase oxidized sinapyl alcohol faster than coniferyl alcohol. The rates of oxidation of the hydroxycinnamic acid derivatives by an isoenzyme of peroxidase from horseradish decreased in the orderp‐coumaric acid>ferulic acid ≥ sinapic acid. The peroxidase oxidized coniferyl alcohol much faster than sinapyl alcohol. The laccase and the peroxidase predominantly oxidized (a) ferulic acid in a reaction mixture that containedp‐coumaric acid and ferulic acid, (b) sinapic acid in a mixture ofp‐coumaric acid plus sinapic acid, and (c) sinapic acid in a mixture of ferulic acid plus sinapic acid. In a reaction mixture that contained both coniferyl and sinapyl alcohols, both fungal laccase and horseradish peroxidase predominantly oxidized sinapyl alcohol. From these results, it is concluded (1) that thep‐hydroxyphenyl radical can oxidize guaiacyl and syringyl groups and produce their radicals and (2) that the guaiacyl radical can oxidize the syringyl group under formation of its radical; and that (3) in both cases the reverse reactions

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1995.930110.x

出版商:Munksgaard International Publishers    

年代:1995

数据来源: WILEY