摘要:

The development of somatic embryos is, in many plants, inhibited by 2,4‐dichlorophenoxyacetic acid (2,4‐D) and other auxins. The finding that difluoromethylornithine (DFMO) can counteract this inhibition has been used to test some of the hypotheses for the mechanism of inhibition.Inhibition of somatic embryogenesis in carrot (Daucus carotaL.) by exogenous ethylene (from ethephon), antioxidants (ascorbic acid and glutathione), ethanol/acetaldehyde and abscisic acid was not counteracted by DFMO, indicating that the inhibitory effect of 2,4‐D is not manifest through the formation of these compounds. Embryogenesis was abolished by micromolar concentrations of the polar auxin transport inhibitors 2, 3, 5‐triiodobenzoic acid (TIBA), N‐1‐naphthylphthalamic acid (NPA) and 9‐hydroxyfluorene‐9‐carboxylic acid (HFCA). This inhibition was counteracted to a considerable extent by DFMO. Inhibition by relatively high concentrations of the antiauxin 2‐(p‐chlorophenoxy)‐isobutyric acid (CPIB), which does not affect polar auxin transport, was in contrast not counteracted by DFMO. These findings indicate that exogenous auxins may inhibit embryogenesis by interfering with the ability of postglobular embryos to set up internal auxin gradients necessa

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05272.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Green and red tomato pericarp tissues were subjected to stress‐relaxation analyses to evaluate their physical properties. Significant decreases in the initial stress, minimum stress‐relaxation and maximum stress‐relaxation times in the red tissues predict the losses of both viscosity and elasticity in the tissue. Cell walls of red fruit yielded more water‐soluble polysaccharides and less pectin, hemicelluloses and cellulose. Average molecular mass of pectin determined by gel filtration chromatography was similar in the green and red, but molecular mass of hemicellulose of red fruit walls was reduced to 50% of that of the green fruit. The decreases in the amount of hemicellulose B and in the average molecular mass were associated primarily with the degradation of xylo‐glucans. These data demonstrate that pectin solubilization, depolymerization of xyloglucans and over‐all changes in the quantity of cell wall polysaccharide fractions contribute to tomato frui

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05273.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In 3‐day‐old wheat (Triticum aestivumL. cv. Marinat) seedlings, 100 μMABA blocked the growth and altered the level of K+in both the shoot and root. The presence of ABA increased the putrescine titer during a 24‐h treatment. Increasing the endogenous level of K+by the addition of 10 mMKCl to the ABA‐treated seedlings, inhibited the effect of ABA on growth and putrescine level. In both tissues, ABA increased putrescine content at low concentrations (1 μM), reaching the maximal effect at 100 μM. Putrescine increase induced by ABA was inhibited by both α‐difluoromethylarginine (DFMA) and α‐difluoromethylornithine (DFMO) in shoots while only the inhibitor of arginine decarboxylase was effective in the root. The presence of ABA modulated, in opposite ways, ornithine and arginine decarboxylase activities. These results are discussed in relation to ion bala

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05274.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Elongation growth of hypocotyl sections ofVigna unguiculataunder xylem perfusion was significantly enhanced when acid was applied by acid‐aerosol to an abraded hypocotyl surface in the air. The in vivo wall extensibility (φ) and the effective turgor (Pi– Y), both of which were determined by the pressure‐jump method, increased during acid‐induced growth as observed in IAA‐induced growth. The intracellular pressure (Pi), however, decreased significantly at the beginning of acid‐induced growth whereas Piscarcely changed in IAA‐induced growth. This result indicates that protons increase the effective turgor by decreasing the yield threshold as IAA does. There seems to be no essential difference between proton and auxin in the effects on the in vivo mechanical properties of the sur

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05275.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The optimal assay conditions and the trend with time in culture (28 days) of arginine decarboxylase (ADE; EC 4.1.1.19), omithine decarboxylase (ODC; EC 4.1.1.17) and diamine oxidase (DAO; EC 1.4.3.6) activities in habituated (H) and normal (N) auxin‐ and cytokinin‐requiring sugar beet callus were compared. Although the response to variations in buffer pH and EDTA and pyridoxal phosphate (PLP) concentrations varied for ADC and ODC activities between the two callus types, pH 8.3, 50 μMPLP and 5 mMEDTA were generally optimal or near‐optimal for both H and N callus. In most cases the addition of ornithine or arginine in the ADC and ODC assays, respectively, given to block the interconversion between the two substrates, resulted in lower14CO2recovery. DAO activity was very differently affected in H and N callus by the presence of polyvinylpyrrolidone in the extration buffer. However, in both cases, this activity increased with time in culure. ADC activity was always predominant in both cell lines and always higher in N callus. In the latter, ADC activity rose sharply between days 14 and 21 and then leveled off while in H callus it incresed steadily from day 14 onwards. ODC activity was also higher in N callus and peaked sharply on day 21 while in H callus it was not detectable in the second half of the culture period. In both cell lines this activity was low or nil on day 28. 3,4‐[14C]‐methionine incorporation into ethylene and polyamines was also compared in N and H callus. In the latter, ethylene synthesis was lower and [14C]‐spermidine formation higher than in N callus. This is in accord with the significantly higher spermidine titres found

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05276.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Effects of dark incubation at different temperatures were studied on dormancy and respiratory activity of seeds ofSisymbrium officinale(L.) Scop. Because germination of this species absolutely depends on the simultaneous action of light and nitrate, changes in dormancy could be studied in darkness without the interference of early germination events. Upon the start of incubation rates of O2uptake and CO2release rose. This was followed by a gradual decrease until stable levels of O2uptake and CO2release were achieved. Seeds kept for prolonged periods at 24°C, showed neither a change in germination capacity nor in rates of O2uptake and CO2release. Respiratory quotients were 0.55–0.7. The initial rise in O2uptake correlated with the rate of water uptake and with breaking of primary dormancy. However, the subsequent decline in O2uptake was not generally linked to induction of secondary dormancy. An increased O2uptake was not required during breaking of secondary dormancy. It is concluded that changes in dormancy are not generally related to changes in respiratory activity. However, germination strongly depends on respiration. The increase in O2uptake started well before radicle protrusion. A far red irradiation only reversed this increase when it was given before germination escaped from its red light antagonising action. The contribution of different respiratory pathways was followed during prolonged incubation at 24°C in darkness. KCN at 1.5 mMwas needed to inhibit the cytochrome pathway (CP) and benzohydroxamic acid (BHAM) at 30 mMto inhibit the alternative pathway (AP). These concentrations did not exert any side effects. Electron flow was predominantly via the CP, maximally 10% was via the AP. Flow through the CP declined during the first 6 days and residual respiration remained constant. Therefore, the contribution of residual respiration became relatively more important with prolonged incubation. KCN at concentrations that almost completely inhibited flow through the CP, did not dramatically reduce germination. BHAM already inhibited germination at concentrations that do not inhibit oxygen upt

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05277.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Storage protein gene expression was compared between zygotic and somatic embryos of interior spruce (Picea glauca/engelmanii complex). Somatic embryos, grown on medium containing 40 μMor 10 μMabscisic acid (ABA), and zygotic embryos accumulated IIS legumin, 7S vicilin and 2S albumin storage proteins. Zygotic embryos displayed a rapid, transient period of storage protein accumulation, while somatic embryos differentiated on 40 μMABA displayed a more prolonged, gradual accumulation, with some accumulation still evident after 9 weeks of maturation. Somatic embryos on 10 μMABA accumulated storage proteins initially, but these were rapidly degraded as the embryos germinated precociously. Legumin, albumin and vicilin transcripts were detectable in torpedo stage zygotic and somatic embryos, and increased during embryo development. Transcript levels in zygotic embryos increased during cotyledon development, but following maximum dry weight accumulation and moisture loss, transcripts declined rapidly to low levels. In contrast, somatic embryos on 40 μMABA had high transcript levels for a prolonged period. These levels were still present after 9 weeks of maturation. A decline in storage protein transcripts similar to zygotic embryos was apparent following a mild drying treatment. These results suggest that a decline in storage protein transcripts is stimulated by embryo drying during the later stages of conifer embryogenesis. Low levels of storage protein transcripts also appeared in somatic embryos on 10 μMABA, but declined during precocious germination. Osmotic stress induced storage protein and storage protein transcript accumulation. This could be partially inhibited by inclusion of the ABA biosynthetic inhibitor, fluridone. However, endogenous ABA levels did not differ significantly between embryos cultured in the presence or absence of flur

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05278.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Plasma membrane vesicles (ca 40% inside‐out, after one freeze‐thaw cycle) were extracted and purified from the shoots of oat (Avena sativa L.) and chickweed (Stellaria mediaL.) using the two‐phase aqueous polymer technique. In the presence of ATP or GTP, a rapid uptake of45Ca2+occurred (0.77 and 0.62 nmol Ca2+mg‐1protein, for ATP and GTP, respectively, in oat, and 0.53 and 0.51 nmol Ca2+mg‐1protein, for ATP and GTP, respectively, in chickweed). Nucleotide‐dependent Ca2+‐transport was sensitive to 1 μMErythrosin B (with ATP. inhibited by 52% in oat and in chickweed by 72%; with GTP, inhibition was similar in both species at ca 67%); ATP‐dependent uptake was greater in oat than in chickweed, but not stimulated by calmodulin. Addition of the calcium ionophore A‐23187 resulted in the release of label from the vesicles (41% and 63% release with ATP, and 24% and 52% release with GTP, in oat and chickweed, respectively). The results obtained suggest that Ca2+‐transport is independent of the proton pump. In oat, kinetic data indicate a discontinuity in the absorption isotherm

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05279.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In the spring of 1987, entire shoots were removed fromQuercus rubraL. saplings in two southwestern Wisconsin forest openings. Shoots possessed newly expanding leaves at the time of coppicing. All coppiced individuals sprouted from dormant stem buds near the root collar. Leaf gas exchange and water potential were monitored on these sprouts and on untreated (control)Q. rubrasaplings throughout several clear warm days during the 1987 growing season. Daily maxima and averages for sprout leaf photosynthesis and stomatal conductance generally exceeded those of controls. On average, treatment differences in daily maximum photosynthetic rate were modest (11–14%) and were attributed primarily to a 30–38% enhancement of sprout leaf stomatal conductance. Relative differences in daily average photosynthetic rate (29–39%) were substantially larger than those in daily maximum photosynthesis, owing to the fact that sprouts and controls exhibited distinct diurnal gas exchange patterns. Photosynthetic rate and stomatal conductance of control leaves typically declined during the day following a mid‐morning maximum. Sprout leaves, on the other hand, tended to maintain gas exchange rates nearer to their morning maxima throughout the day. This difference in diurnal gas exchange pattern was associated with an apparent differential leaf sensitivity to leaf‐to‐air vapor pressure gradient (VPG). The relative decline in sprout leaf gas exchange rates with increasing VPG was less than that of controls. Treatment differences in gas exchange did not appear to be related to leaf water potential or tissue water relations, but sprouts had a higher soil‐to‐leaf hydraulic conductivit

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05280.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Two experiments were conducted to examine the response ofQuercus rubraL. seedlings to coppicing. In a greenhouse experiment, growth, biomass distribution, leaf gas exchange, and water and carbohydrate relations were measured for 1‐year‐old seedlings that were either coppiced when dormant at the time of planting or left intact as controls. Coppicing induced sprouting from the base of the stem, and, in general, the physiology of sprouts and controls was similar. However, the relative growth rate (RGR) of sprouts was 9% higher than that of controls, allowing sprouts to compensate fully for the initial mass lost to coppicing. In a second experiment, in an outdoor cold frame, growth, biomass distribution, leaf gas exchange and plant water relations were measured on 1‐year‐old seedlings that were either coppiced at the time of planting (dormant‐coppiced), coppiced soon after bud break (active‐coppiced) or left intact (controls). Dormant coppicing again had little impact on seedling physiology, and dormant‐coppiced plants again compensated for initial mass loss with a higher RGR. In contrast, active‐coppiced seedlings did not compensate for initial mass loss, as their RGR did not differ from that of controls. By the tenth week of the study, leaf gas exchange rates of active‐coppiced sprouts were higher than those of dormant‐coppiced and control seedlings. Active‐coppiced sprouts also had a greater soil‐to‐leaf hydraulic conductivity (expressed on a leaf area basis) and a lower ratio of leaf area to root surface area than did controls. Across treatments, photosynthetic rate and stomatal conductance were positively correlated with soil‐to‐leaf hydraulic conductivity, and gas exchange rates and hydraulic conductivity were negatively related to leaf:root area ratio. Thus, the removal of actively growing shoots may have altered subsequent leaf gas exchange largely through coppice‐induc

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb05281.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY