摘要:

Abstract.The carbon, water and nutrient relations of the xylem parasitesLoranthus europaeusandViscum laxumand their respective hosts.Quercus roburandPinus sylvestris, were followed throughout clear days in July in order to study water and nutrient interactions in a simple system in which the plant growth depends on the host for its water and nutrients. At similar quantum flux densities, temperatures and vapour pressure deficits, the mistletoes had higher rates of transpiration and lower leaf water potentials than their hosts, but similar rates of CO2assimilation. Based on measurements of the nutrient content of the xylem and on seasonal measurements of the biomass and the tissue nutrient content, the present study suggests that the high rates of transpiration may be necessary for the parasites to take up sufficient nitrogen from the xylem of the host for production of biomass (leaves, fruits and stems).

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589756

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Seasonal patterns in photosynthetic temperature acclimation and growth were investigated in the sedge,Carex eleocharisBailey, a species which has demonstrated a marked capacity for shifts in the photosynthetic temperature optimum in previous growth chamber studies. The seasonal production of new leaves was 90% complete by the earliest study date, June 3. Shifts in the photosynthetic temperature optimum of 10°C (from 15 to 25°C) were observed during the months of June and July. These results indicate thatin situacclimatory adjustments inC. eleocharisoccur in existing leaf tissue, rather than new leaves which are produced as the season progresses. Despite the 10°C increase in the temperature optimum, mean mid‐day leaf temperatures were higher than the optimum throughout the summer. A broad temperature response appeared to be more important than the acclimation adjustments in maintaining near‐maximum photosynthesis rates during the mid‐day period. Seasonal shifts in the photosynthetic temperature optimum were not as great as those previously observed in growth chamber studies. This discrepancy arises because of the capacity for growth chamber grown plants to produce new leaves with temperature response characteristics closely tuned to the growth temperature regime. In field‐grown plants the production of 90% of the leaves during the cool portion of the season places limitations on the potential for acclimation to the warmer midsummer te

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589761

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The effectiveness of a red‐light pulse acting through phytochrome in inducing primary leaf expansion in 9‐d‐old etiolated bean (Phaseolus vulgarisL. ev. Limburg) seedlings is strongly increased by a continuous far‐red light (CFR) pretreatment. This increase in effectiveness of a red pulse is positively correlated with the time and the fluence rate of the CFR pretreatment. Escape from photoreversibility of this red pulse after the CFR pretreatment is extremely slow (more than 3 d). When a dark period is interposed between the end of the CFR pretreatment and the inductive red pulse the photoreversible part of the response to this pulse is highly dependent upon the photostationary state of phytochrome at the onset of the dark period.The results give strong evidence for the synergistic activity of two components of phytochrome action during leaf growth induction, one of them acting via a very stable Pfr f

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589766

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Nitrate uptake intoChara corallinacells at different external pH (pHo) after different NO3−pretreatment conditions has been investigated. Following NO3−pretreatment (0.2 mol m−3NO3−) there was little effect of pHoon subsequent net NO3−uptake intoCharacells. After N deprivation (2 mmol m−3NO3−) there was a pronounced effect of pHoon nitrate uptake, the maximum rate occurring at pHo4.7. There was no consistent relationship between OH−efflux and NO3−uptake in short term experiments (<1 h). NO3−efflux was also sensitive to pHo, the maximum rate occurring at ∼ pHo5.0. An inhibitor of the proton pump, DES, immediately stimulated NO3−uptake into cells pretreated with NO3−and prevented the time‐dependent decrease in NO3−, uptake intoCharacells that had been previously treated with low N (2 mmol m−3NO3−). NO3−efflux was found to be very sensitive to DES withKi= 0.7 mmol m−3. At the optimum pHofor NO3−uptake the effect of DES on membrane potential (ψm) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO3−uptake and H+pump activity. A new model for NO3−uptake is proposed whic

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589779

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.When an organ is subject to unilateral illumination, light entering the organ is attenuated very efficiently and the irradiance at the ‘shaded’ surface is only a small percentage of that at the illuminated surface. The light gradient across the organ is approximately exponential, being steepest across the first few cell layers. The penetration of light into an organ was found to be similar with red or blue light and was largely independent of the pigmentation of the organ. Studies of light transmission in organs infiltrated with liquids of different refractive index showed that refraction and reflection were the main factors in establishing the light gradient in organs.The implications of the measured light gradients are discussed briefly in relation to models of phototrop

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589785

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Exposure of young bean foliage to acid rain induces free‐radical‐mediated lipid peroxidation and causes the same disruptive changes in the molecular organization of membrane lipid‐bilayers that are observed during natural leaf senescence. Young plants were misted daily for 7d with simulated acid rain for a 2h period. Wide angle X‐ray diffraction revealed the presence of gel‐phase lipid in a fraction containing predominantly chloroplast membranes isolated from treated leaves, and the lipid‐phase transition temperature of these membranes rose from below −30°C to ∼ 36°C over the treatment period. The formation of gel‐phase lipid is known to be associated with lipid peroxidation, and it is therefore significant that production of ethane and levels of malondialdehyde in the leaves, which are both products of lipid peroxidation, rose throughout the treatment period. There was also increased production of ethylene and superoxide radical, which are typical responses of plant

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589789

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Diurnal courses of leaf conductance, water potential and environmental parameters were measured through the year. The seasonal decreases in plant water potentials were greatest in evergreenH. arbutifolia, intermediate in winter deciduousC. occidentalisand least in drought deciduousA. californica.The seasonal patterns of water use were very similar. Estimates of soil root‐stem conductances to liquid water flux indicate that during the spring, conductances are high, that during the early summer there is a daily shift from high morning conductances to lower afternoon conductances, and that late summer conductances are lo

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589798

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Tissue and cell water relations parameters were followed forHeteromeles arbutifolia, Cercis occidentalisandAesculus californica, in an environment exhibiting seasonally increasing drought. The extensive seasonal osmotic adjustment of evergreenH. arbutifoliaand the moderate adjustment inC. occidentalisclosely matched their respective seasonal decreases in minimum daily water potential. Summer deciduousA. californicaexhibited only small drops in osmotic potential and water potential. Experiments with irrigated plants indicated that drought was not required for the osmotic adjustment ofH. arbutifoliaandC. occidentalis.However, inH. arbutifoliadrought treatment enhanced osmotic adjustment. In irrigatedH. arbutifolia, osmotic adjustment was mainly the result of an accumulation of osmotica. In drought‐stressed plants, the same change in osmotic potential resulted from a combination of accumulation of osmotica and a decrease in symplast volum

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589802

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The germination responses of a nondormant seed population ofAmaranthus patulusBertol, at constant sub‐optimal temperatures in the range of 10–34°C were analysed through a detailed time‐course study. Although a final germination percentage of nearly 100% was attained at temperatures above 18°C, it fell abruptly to zero with decreasing temperature from 17 to 10°C. The final germination percentage,v.temperature plotted on a normal probability scale yielded a straight line, indicating normality of the lower limit temperature within seed population with an estimated mean of 13.75°C and a standard deviation of 1.50°C. Simple linear relationships were obtained between the temperature and the germination rates, i.e., the reciprocals of the time taken to germinate by the subpopulations with 20–80% germination. The linear relationships were characterized by similar base temperatures or theoretical limit temperatures of about 11°C but there was a variation in the required ‘thermal times’ (θ), the distribution of which could be approximated for the seed population by the following distribution function:wheremis the median of the distribution andAis a parameter characterizing the pattern of the distribution. When the germination rates were calculated after subtracting 10–14 h from the time actually consumed in germination, linear Arrhenius relationships were obtained. The apparent activation energy estimated from the linear regression of Arrhenius plot was approximately 100 kJ mol−1with all

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589809

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.A mathematical model which describes the germination percentage dependency on time and temperature of a seed population was derived from the experimental results with a seed population ofAmaranthus patulusBertol. under sub‐optimal temperature conditions (Washitani&Takenaka, 1984). The equation of the model which is a modified thermal time model iswhereGis germination percentage at a certain time after the start of imbibition (t) at a certain temperature (T), μT1and σT1are the mean and standard deviation of lower limit temperature among the seeds belonging to the seed population, andTb, m, andAare the parameters characterizing the linear relationship between the rate and temperature, namely,Tbis the base temperature,m, the median of the required thermal time andA, a parameter determining the pattern of the variation of the required thermal time within seed population, respectively. The equation yields time courses for germination which are very similar to those observed by experim

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11589812

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY