摘要:

ABSTRACTSeeds ofSisymbrium officinale(L.) Scop, that are buried under natural conditions in soil pass annually through a seasonal pattern of changes in dormancy. Dormancy is broken in autumn‐winter and re‐induced in summer. To elucidate dormancy regulation in this species under natural conditions, a detailed analysis of the changes in sensitivity to some relevant germination factors was carried out Germination data fitted as logistic dose response curves showed that sensitivity to light and nitrate, both indispensable stimuli for germination of this species, varied with the seasons. Patterns of shifts in requirement for light and nitrate were remarkably similar. Sensitivity increased when both primary and secondary dormancy were alleviated, and it was reversed during induction of secondary dormancy. During alleviation of primary dormancy in spring 1991, the fluence response curves exhibited a biphasic character with responses occurring both in the very‐low‐fluence‐range and in the low‐fluence‐range. The nitrate dose response data could all be fitted as monophasic curves, although responses might have occurred in two distinct ranges as well. From interpretation of curve parameters, it is postulated that dormancy is regulated by changes in the number of phytochrome and nitrate receptors, in shifts in the binding characteristics of the receptors and/or in shifts in the response chain initiated by the ligand‐receptor interaction. Somewhere in this response chain, biosynthesis of gibberellins (GAs) is stimulated. By use of the GA biosynthesis inhibitor tetcyclasis, it was indirectly proven that the capacity to synthesize GAs indeed varied with the seasons. Sensitivity to GAs gradually increased from burial onwards and was not particularly related to changes in dormancy. Thus, except for the first few months of burial, GA sensitivity may not be regarded as a limiting factor in controlling dormancy

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00894.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTChanges of ABA levels in chilled rice (Oryza sativaL.) seedlings of two varieties were determined. On exposure to chilling, ABA concentration rapidly increased in the chilling‐tolerant cultivar (cv. Tainung 67, TNG.67) but not in the chilling‐sensitive cultivar (cv. Taichung Native 1, TN.1). Both detached shoots and roots of TNG.67 seedlings showed a significant ABA increase after exposure to chilling. TN.1 seedlings could not accumulate ABA under low temperature but well‐watered status. Exogenous application of the ABA biosynthetic inhibitor, fluridone, reduced ABA accumulation, as well as survival ratio of chilled TNG.67 seedlings. Electrolyte leakage and leaf conductance were also increased by the inhibitor and the effects could be reversed by exogenously applied ABA. ABA concentrations in xylem sap of TNG.67 seedlings increased within 4 h after chilling, and this was temporally coincident with the reduction of leaf conductance. The roles of endogenous ABA in the tolerance of rice seedlings to chilling on a whole plant basis are discussed and sugg

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00895.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTLevels of carbonic anhydrase activity were determined on a total (60 EUmg−1protein), external (7.36 EU), internal (50.14 EU) and protoplast (15.63 EU) basis forRanunculus penicillatus(Dumort.) Bab ssp.pseudofluitans(Syme) S. Webster, a freshwater aquatic macrophyte, by conventional electrometric methods. The site of activity of ‘external’ carbonic anhydrase (CA) has been visualized using 5‐Dimethylaminonapthalene‐1‐ sulphonamide (DNSA)‐CA fluorescent complex formation, and is postulated to be closely associated with the epidermal cell wall. The photosynthetic rate ofR. penicillatusssp.pseudofluitansat pH 9.0 is in excess of the uncatalysed rate of production of CO2from HCO−3, and this plant is therefore using HCO−3for photosynthesis. The possible contribution of CA activity to inorganic carbon assimilation, and specifically to transport of HCO−3, in submerged aquatic

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00896.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe electrical potential difference (p.d.) between two points on the surface of a plant root is shown to be a measure of the difference between the transmembrane potentials at those two points. More precisely, it is shown that axial differences in electrical potential on the surface of the root, or within several tenths of millimeters of it in the rhizosphere, are primarily a result of axial differences in p.d. across the plasmalemma of cells in the cortex, with an additional small effect from axial differences in p.d. across the plasmalemma of cells in the stele. This conclusion results from a model of the root as a three‐conductor electrical transmission line. The model requires the solution of a set of differential equations, but simple algebraic approximations are found to apply over a range of model parameters derived from published data. Given the predictions of the model, it follows that, for many research purposes, microelectrode measurements could be replaced with measurements of p.d. on the surface of the root. Such measurements offer substantial advantages over microelectrode measurements: they are non‐invasive; they do not include the potential difference across the tonoplast; they measure a spatial average of many cells, not just a single cell; and the measurement is physically robust. Surface potential measurements do not, however, measure trans‐membrane potential at one point, but measure differences in trans‐membrane po

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00897.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTQuercus ilexL. growing in the southern Mediterranean Basin region is exposed to xylem embolism induced by both winter freezing and summer drought. The distribution of the species in Sicily could be explained in terms of the different vulnerability to embolism of its xylem conduits. Naturally occurring climatic conditions were simulated by: (1) maintaining plants for 3h at ambient temperatures of 0, ‐1.5, ‐2.5, ‐5.0 and ‐11°C; and (2) allowing plants to dry out to ratios of their minimum diurnal leaf water potentials (Ψ1) to that at the turgor loss point (Ψtlp) of 0.6, 0.9, 1.05, 1.20 and 1.33. The loss of hydraulic conductivity of one‐year‐old twigs reached 40% at ‐1.5°C and at Ψ1/ΨtlP= 1.05. Recovery from these strains was almost complete 24 h after the release of thermal stress or after one irrigation, respectively. More severe stresses reduced recovery consistently. The percentages of xylem conduits embolized following application of the two stresses, were positively related to xylem conduit diameter. The capability of the xylem conduits to recover from stress was positively related to the conduit diameter in plants subjected to summer drought, but not in the plants subjected to winter freezing stress. The ecological significance of the different vulnerabilities to embolism of xylem conduits under naturally occurring climatic cond

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00898.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTWinter wheat (Triticum aestivumL., cv. Mercia) was grown in chambers under light and temperature conditions similar to the UK field environment for the 1990/1991 growing season at two levels each of atmospheric CO2concentration (seasonal means: 361 and 692 μmol mol−1), temperature (tracking ambient and ambient +4°C) and nitrogen application (equivalent to 87 and 489 kg ha−1total N applied). Total dry matter productivity through the season, the maximum number of shoots and final ear number were stimulated by CO2enrichment at both levels of the temperature and N treatments. At high N, there was a CO2‐induced stimulation of grain yield (+15%) similar to that for total crop dry mass (+12%), and there was no significant interaction with temperature. This contrasts with other studies, where positive interactions between the effects of increases in temperature and CO2have been found. Temperature had a direct, negative effect on yield at both levels of the N and CO2treatments. This could be explained by the temperature‐dependent shortening of the phenological stages, and therefore, the time available for accumulating resources for grain formation. At high N, there was also a reduction in grain set at ambient +4°C temperature, but the overall negative effect of warmer temperature was greater on the number of grains (‐37%) than on yield (‐18%), due to a compensating increase in average grain mass. At low N, despite increasing total crop dry mass and the number of ears, elevated CO2did not increase grain yield and caused a significantdecreaseunder ambient temperature conditions. This can be explained in terms of a stimulation of early vegetative growth by CO2enrichment leading to a reduction in the amount of N available later for the formation and fi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00899.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTMesembryanthemum crystallinumplants were irrigated with 400 mol m−3NaCl to induce CAM and levels of leaf starch, and activities of starch‐degrading enzymes were measured. During Crassulacean acid metabolism (CAM) induction, daily starch turnover gradually became more pronounced and was three‐ to four‐fold greater than in leaves of C3plants after 3 weeks. Activities of α‐ and β‐amylase, D‐enzyme and starch phosphorylase all increased 10‐ to 20‐fold within 3 weeks of the start of salt treatment. Activities of α‐ and β‐amylase increased more than fourfold within the first 24 h of salt treatment, which is the fastest increase in enzyme activities so far measured during the induction of CAM with salt solution in intact plants of this species. Most enzyme activities were partially chloroplastic; however, the principal starch‐degrading activity was constituted by an extra‐chloroplastic β‐amylase. CAM starch‐phosphorylase activity, which was mainly chloroplastic, exhibited a two‐ to three‐fold diurnal change in parallel with starch content. CAM induction inM. crystallinumis clearly associated with greater starch turnover and enhanced starch‐degrading enzyme activities, which as catalysts of the initial reaction to release carbon for synthesis of phosphoenolpyruvate (PEP) appear highly significant for the functioning of the CAM pathway. The diurnal rhythm of phosphorylase ac

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00900.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTElevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured inGossypium hirsutumL. grown in 35 and 65 Pa CO2for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2stimulated biomass production (107%) and net photo‐synthetic rates (35–50%). Total day‐time respiration (Rd) was not significantly affected by growth CO2partial pressure. However, night respiration (Rn) of leaves grown in 65 Pa CO2was significantly greater than that of plants grown in 35 Pa CO2. Correlation of Rdand Rnwith leaf expansion rates indicated that plants in both CO2treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2appeared to be related to increased starch accumulation rather than to changes in leaf nit

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00901.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTMeasurements were made of the influx of45Ca into internodal cells ofChara corallinain solutions containing high concentrations of NaCl. Increasing salinity in the range 4–100mol m−3NaCl resulted in a doubling of Ca2+influx at the plasmalemma. A time‐course of Ca2+influx in 50 mol m−3NaCl, 0.5mol m−3CaCl2showed that while influx at the plasmalemma increased only 1.5‐fold, influx to the vacuole increased by up to 15‐fold. This was interpreted as being due to inhibition of active Ca2+efflux from the cell. The stimulation of Ca2+influx by increasing salinity appeared to be principally a response to reduced turgor since similar stimulations were obtained when turgor was reduced by NaCl, Na2SO4or mannitol. When cells were plasmolysed Ca2+influx increased by 10–20‐fold. The increased permeability was relatively specific for Ca2+and was inhibitable by La3+. Survival of cells in high salt conditions was increased by 30 mmol m−3La3+, which inhibited Ca2+influx. Paradoxically, survival can also be extended by increasing external Ca2+which leads to a higher influx. Therefore, it seems unlikely that the ameliorative effect of Ca2+on the sensitivity of plants to high NaCl is mediated by Ca2+entry across the plasmalemma. It seems more likely that the principal role of Ca2+under these conditions is exerted externally through the control of membrane volta

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00902.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTSupplemental far‐red (FR) illumination of light‐grown grass seedlings inhibits tiller production while enhancing leaf elongation. Although much is known about FR enhancement of internode elongation in dicots, relatively little research has been conducted to determine the effects of FR on monocot development. In growth chamber experiments, fibre optics were used to direct supplemental FR to elongating leaf blades, main stem bases and mature leaf blades of light‐grown barley (Hordeum vulgareL.) seedlings. Our objective was to identify specific sites of perception for FR enhancement of leaf elongation and inhibition of tiller production, and to assess potential FR effects on tiller senescence. Far‐red illumination of elongating leaves or of the main stem base reduced the total number of tillers per plant, primarily by reducing secondary and tertiary tiller production, and enhanced leaf elongation. However, leaf elongation was less sensitive to stem base treatments than to illumination of the elongating blade. Increased leaf length resulted from increased leaf elongation rate, while the duration of leaf elongation was unaffected. Exposure of mature leaf blades to FR had no effect on tillering or leaf elongation. None of the FR treatments led to tiller senescence. Localization of FR perception in vertically oriented tissues such as elongating blades and stem bases permits early detection of reflected light from neighbouring plants, allowing rapid response to impending comp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00903.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY