摘要:

ABSTRACTThe infected cells of soybean (Glycine max) root nodules require ATP production for ammonia assimilation and purine synthesis under microaerobic conditions. It is likely that the bulk of this demand is supplied through mitochondrial oxidative phosphorylation. Mitochondria purified from root nodules respired and synthesized ATP in sub‐micromolar oxygen concentrations as measured by leghaemoglobin spectroscopy and luciferase luminescence. Both oxygen uptake and the apparent ATP/O ratio declined significantly as the oxygen concentration fell below 100 μmol m−3. Cytochrome‐pathway respiration by root nodule mitochondria had a higher apparent affinity for oxygen (Km 50 μmol m−3) than did mitochondria isolated from roots (Km 125 μmol m−3). Electron micrographs showed that mitochondria predominated at the periphery of infected cells adjacent to gas‐filled intercellular spaces, where the oxygen concentration is predicted to be highest. Calculations of oxygen concentration and nitrogen fixation rates on an infected cell basis suggest that the measured rates of ATP production by isolated mitochondria are sufficient for the quantifiable in vivo requirements of ammonia assimilation and purine synthesis. The possible roles of mitochondrial respiration in the control of infected cell metabolism are

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe inhibitory effects of PEG on whole‐plant growth can exceed the effects of other osmolytes such as NaCI, and this has been ascribed to toxic contaminants, or to reduced oxygen availability in PEG solutions. We investigated another possibility, namely that PEG has an additional inhibitory effect on root water transport which in turn affects leaf development. The effects on first‐leaf growth of applications of PEG 6000 or isoosmotic NaCI to the roots were determined using hydroponically grown maize (Zea maysL.) seedlings. Leaf growth rates were inhibited within minutes of PEG application to the roots and remained inhibited for days. The inhibitory effects on growth of NaCI, and also of KCl and mannitol, were much smaller. The comparative effects of NaCI and PEG on root water transport were determined by assaying pressurized flow through excised roots. PEG induced a 7‐fold greater inhibition of flow through live roots than NaCI. Killing of the roots by heat treatment, to reduce cell membrane resistances to solute penetration, nearly doubled the flow rate for roots in NaCI, but not for roots in PEG. We suggest that the greater viscosity of PEG solutions, as compared with NaCI, may be a primary factor contributing to the additional inhibition of water flow through live and killed roots. PEG did not have additional effects on leaf turgor but had a 3 times greater inhibitory effect than NaCI on the irreversible extensibility of the leaves and induced 16 times more leaf accumulation of the growth inhibitory stress hormone abscisic acid (ABA). We conclude that greater inhibition of root water transport by PEG 6000, as compared with NaCI, leads to additional reductions in extensibility, additional ABA accumulation, and a greater inhibition of leaf g

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWinter wheat (Triticum aestivumL., ev. Mercia) was grown in a controlled‐environment facility at two CO2concentrations (targets 350 and 700 μmol mol−1), and two temperature regimes (tracking ambient and ambient + 4°C). Observations of phenology, canopy growth, dry matter production and grain yield were used to test the ARCWHEAT1 simulation model. Dry‐matter production and grain yield were increased at elevated CO2concentration (27 and 39%, respectively) and reduced at increased temperature (−16 and −35%, respectively). ARCWHEAT1 substantially underestimated canopy growth for all treatments. However, differences in the facility environment from field conditions over the winter, indicated by the unusually rapid canopy growth observed in this period, meant that empirical model relationships were being used outside the conditions for which they were developed. The ARCWHEAT productivity submodel, given observed green area indices as inputs, overestimated the effect of CO2on productivity. An alternative, more mechanistic submodel of productivity, based on the SUCROS87 and Farquhar&von Caemmerer models, simulated observed crop biomass very closely. When these productivity simulations were inputed into the ARCWHEAT1 partitioning and grain‐fill submodels, grain yield was predicted poorly, mainly as a result of the assumption that the number of grains is proportional to total growth during a short pre‐anthesis phase. While yield was not correlated with growth in this phase, it was correlated with growth in longer pre‐anthesis phases, indicating that ARCWHEAT1 could be improved by taking into account the contribution of earlier growth in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTChanges in the properties of soil solution in the rhizosphere of developing radish plants were investigated. Variations in these properties were expected to affect the distribution and speciation of metals in the soil and soil solution. Applications of essential nutrients were linked to plant transpiration rates and prevented excess addition of nutrient ions, so that subtle changes in soil solution composition would not be obscured. Soil solution pH, the concentration of dissolved organic carbon (DOC) and the concentrations of major and trace elements in solution were found to vary over time. Strict control of fertilizer additions led to the maintenance of a relatively low ionic strength in the soil solution, and under such conditions trace metal solubility appeared to be highy influenced by the concentration of DOC. A chemical speciation analysis was performed which showed that, while dissolved Cd and Zn were largely uncomplexed in unplanted soil, Cd and Zn in the rhizosphere existed mainly as complexed forms. It is hypothesized that this is partly a result of Ca‐metal‐ligand equilibrium in solution, with higher Ca concentrations in unplanted soil leading to more of the Cd and Zn in solution existing in the uncomplexed state. Changes in the concentrations of uncomplexed Cd and Zn with time gave the best correlations with changes in plant uptake of these metals over time, supporting the hypothesis that plants mainly absorb the free metal ion from soil solut

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe water relations of shoots of young jack pine (Pinus banksiana Lamb.) seedlings were examined 6 and 15 weeks after the initiation of four different dynamic nitrogen (N) treatments using a pressure‐volume analysis. The N treatments produced a wide range of needle N concentrations from 12 to 32 mg g−1dry mass and a 10‐fold difference in total dry mass at 15 weeks. Osmotic potential at full turgor did not change over the range of needle N concentrations observed. Osmotic potential at turgor‐loss point, however, declined as N concentrations decreased, indicating an increased ability of N‐deficient jack pine plants to maintain turgor. The increase could be attributed largely to an increase in cell wall elasticity, suggesting that elasticity changes may be a common, significant adaptation of plants to environmental stresses. Dry mass per unit saturated water almost doubled as needle N level dropped from 32 to 12 mg g−1and was inversely correlated to the bulk modulus of elasticity. This suggests that cell wall elasticity is determined more by the nature of its cross‐linking matrix than by the total amount of cell wall material present. Developmental change was evident in the response of some water relation variables to

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA nitrogen‐based model of maintenance respiration (Rm) would link Rmwith nitrogen‐based photosynthesis models and enable simpler estimation of dark respiration flux from forest canopies. To test whether an N‐based model of Rmwould apply generally to foliage of boreal and subalpine woody plants, I measured Rm(CO2efflux at night from fully expanded foliage) for foliage of seven species of trees and shrubs in the northern boreal forest (near Thompson, Manitoba, Canada) and seven species in the subalpine montane forest (near Fraser, Colorado, USA). At 10°C, average Rmfor boreal foliage ranged from 0.94 to 6.8μmol kg−1s−1(0.18–0.58 μmol m−2s−1) and for subalpine foliage it ranged from 0.99 to 7.6 μmol kg−1s−1(0.28–0.64μmol m−2s−1). CO2efflux at 10°C for the samples was only weakly correlated with sample weight (r = 0.11) and leaf area (r = 0.58). However, CO2efflux per unit foliage weight was highly correlated with foliage N concentration [r = 0.83, CO2flux at 10°C (mol kg−1s−1) = 2.62 × foliage N (mol kg−1)J, and slopes were statistically similar for the boreal and subalpine sites (P=0.28). CO2efflux per unit of foliar N was 1.8 times that reported for a variety of crop and wild

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTExpression of the genesle20, ni3212, le25andlcyp2was quantified in relation to soil and plant water status for pot‐grown tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) in a replicated trial in a partially environmentally controlled glasshouse. Leaf water potential, relative water content, stomatal conductance and gravimetric soil water content were measured at 0800,1200 and 1600 h on three days during the imposition of three different watering regimes. Paired leaf samples were analysed for mRNA. Plant‐to‐plant variability was quantified and partitioned.le20mRNA was found in all leaves and responded both to short‐term diurnal fluctuations in water status and to more severe stress, though with reduced sensitivity to the greatest stresses. An overnight decline inle20mRNA was independent of soil or plant water status. The pattern of expression forni3212was similar thoughni3212mRNA was much more abundant and the overnight drop in expression was not significant.le25mRNA was only detected where leaf water potential was below −0.9 MPa and increased linearly with further decline in leaf water potential.lcyp2was constitutively expressed with a diurnal pattern characterized by a sharp depression at 1600 h but with expression being enhanced by increasing water deficit at all times. The control and significance of the four genes are discussed in relation to the proposed function of their respective gene

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00580.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTMature pea (Pisum sativum L., cv. Meteor) leaves were exposed to two levels of UV‐B radiation, with and without supplementary UV‐C radiation, during 15 h photoperiods. Simultaneous measurements of CO2assimilation and modulated chlorophyll fluorescence parameters demonstrated that irradiation with UV‐B resulted in decreases in CO2assimilation that are not accompanied by decreases in the maximum quantum efficiency of photosystem II (PSII) primary photochemistry. Increased exposure to UV‐B resulted in a further loss of CO2assimilation and decreases in the maximum quantum efficiency of PSII primary photochemistry, which were accompanied by a loss of the capacity of thylakoids isolated from the leaves to bind atrazine, thus demonstrating that photodamage to PSII reaction centres had occurred. Addition of UV‐C to the UV‐B treatments increased markedly the rate of inhibition of photosynthesis, but the relationships between CO2assimilation and PSII characteristics remained the same, indicating that UV‐B and UV‐C inhibit leaf photosynthesis by a similar mechanism. It is concluded that PSII is not the primary target site involved in the onset of the inhibition of photosynthesis in pea leaves induced by irradi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00581.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe roles of phytochrome A (phyA), phytochrome B (phyB) and a putative blue‐light (BL) photoreceptor (HY4) in the control of hypocotyl growth by natural radiation were investigated usingphyA, phyBandhy4mutants ofArabidopsis thaliana. Full sunlight inhibited hypocotyl growth to a larger extent in wild‐type (WT) than inphyA, phyBand, particularly,hy4seedlings. In WT seedlings, hypocotyl growth was promoted by selectively lowering BL irradiance, lowering red‐light (R) plus far‐red‐light (FR) irradiance or lowering the R/FR ratio (which was achieved either by increasing FR or by reducing R). The effects of lowering BL were reduced inhy4and exaggerated inphyAseedlings. The effects of lowering R+FR were reduced inphyAand exaggerated inhy4seedlings. NeitherphyBnorhy4mutants responded to low R/FR ratios. Neighbouring plants reflecting FR without shading caused subtle reductions of the R/FR ratio. This signal promoted hypocotyl growth in WT but not inphyA, phyBorhy4seedlings. Intermediate canopy shade produced similar effects in all genotypes. Under deep shade, de‐etiolation was severely impaired in phyA seedlings, which died prematurely. Thus, the FR ‘high‐irradiance reaction’ mediated byphyAcould be important for seedling survival und

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00582.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTPressure within guard cells in strips of intact epidermis of Tradescantia virginiana was controlled with a pressure probe apparatus after the guard cells had been filled with silicone oil. Pressure was increased and decreased incrementally between 0.0 and 4.1 MPa to cause inflation and deflation of the guard cells. At steady‐state guard cell pressures, the width of the stomatal pore was recorded and plotted against pressure. The pressure required for near‐maximum aperture was 4.1 MPa. Aperture as a function of pressure was sigmoi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00583.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY