摘要:

ABSTRACTStranglers must undergo a transformation in growth form from epiphyte to tree to become reproductive mature and thus require developmental and/or physiological plasticity to cope with radical changes in their rooting environment. Differences in leaf structure and water relations between epiphytic‐phase and free‐standing individuals were marked in the five Ficus species examined. EpiphyticFicushad several‐fold higher specific leaf area (cm2g−1) and 2‐ to 4‐fold lower stomatal densities than conspecific trees. Osmotic potentials at full saturation were, on average, 0‐6 MPa higher (less negative) and the bulk modulus of elasticity approximately 50% lower in epiphytic plants than in conspecific trees. This resulted in leaves of epiphytic and tree individuals losing turgor at approximately the same relative water content, hut at a substantially higher leaf water potential in the epiphytic plants. In contrast, differences in leaf structure and water relations between epiphytes and trees ofClusia minorandCoussapoa villosawere small. In greenhouse experiments, alteration of the water and nutrient supply to epiphytic F. tuerckheimmii plants did not lead to significant changes in l

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTNaturally grown trees of Mediterranean evergreen oak (Quercus ilexL.), representing the climax species of the region, were enclosed in six large open‐top chambers and exposed to ambient and elevated CO2concentrations during a 3 year period. Maximum daily net photosynthetic rates measured at the two different CO2concentrations were from 30 to 100% higher in elevated than in ambient [CO2] throughout the experimental period. The increase in maximum daily photosynthesis was also accompanied by a 93% rise in the apparent quantum yield of CO2assimilation, measured during periods of optimum soil moisture conditions. Hence, no clear evidence of down‐regulation of net photosynthetic activity was found. Interactions between atmospheric CO2concentration and plant water stress were studied by following the natural evolution of drought in different seasons and years. At each level of water stress, the maximum rate of carbon assimilation was higher in elevated than in ambient [CO2] by up to 100%.Analysis ofin vivochlorophyll fluorescence parameters in normal (21%) and low (2%) oxygen concentrations provided useful insights into the functioning and stability of the photosynthetic processes. The photochemical efficiency of PSII (Fv/Fm) progressively decreased as drought conditions became more evident; this trend was accentuated under elevated [CO2]. Thermal de‐excitation processes were possibly more significant under elevated than under ambient [CO2], in a combination of environmental stresses.This research suggests two possible conclusions: (i) a ‘positive’ interaction between elevated [CO2] and carbon metabolism can be obtained through relief of water stress limitation in the summer months, and (ii) elevated [CO2], under drought conditions, may also enhance the significance of slow‐relaxin

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe interrelationships between the induction of CAM and the turnover of malate and citrate in the dicotyledenous treeClusia minorwere compared with seasonal changes in rainfall, leaf water status, PFD and photoinhibitory responses during the transition from wet to dry season in Trinidad. Over a period of 8 weeks, as rainfall declined from a maximum observed around week 3, leaf xylem tensions measured at dusk and dawn reflected the concurrent reduction in day‐time carbon gain and an increase in the diel turnover of malate (exposed leaves) and citrate (shaded leaves). Clear seasonal trends were observed in the turnover of malate and citrate during the transition from wet to dry season. In contrast to the declining back‐ground concentrations of citrate during the wet‐dry season transition, malate accumulation was markedly enhanced and the ratio of malalc:citrate accumulated overnight increased as the dry season advanced. Photo‐inhibitory responses, assessed by chlorophyll fluorescence, indicated that photochemistry was largely determined by the diurnal course of PFD incident on leaves, regardless of the magnitude of internal CO2release from malate and citrate decarboxylation. In the long term, photochemical efficiency in both shaded and exposed leaves appeared to decline as the dry season progressed. Although there was a clear linear relationship between integrated PFD and overnight accumulation of malate, no such correlation was found for citrate. However, citrate breakdown during the day showed a much closer correlation with PFD as compared to malate, with levels of citrate measured at dusk declining in response to higher daily light intensities. Moreover, enhanced citrate decarboxylation during the day was strongly correlated with increased CAM and overnight accumulation of both malate and

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe studied the effects of variations of water flux through the plant, of diurnal variation of water flux, and of variation of vapour pressure deficit at the leaf on compensation pressure in the Passioura‐type pressure chamber, the composition of the xylem sap and leaf conductance inRicinus communis. The diurnal pattern of compensation pressure showed stress relaxation during the night hours, while stress increased during the day, when water limitation increased. Thus compensation pressure was a good measure of the momentary water status of the root throughout the day and during drought. The bulk soil water content at which predawn compensation pressure and abscisic acid concentration in the xylem sap increased and leaf conductance decreased, was high when the water usage of the plant was high. For all xylem sap constituents analysed, variations in concentrations during the day were larger than changes in mean concentrations with drought. Mean concentrations of phosphate and the pH of the xylem sap declined with drought, while nitrate concentration remained constant. When the measurement leaf was exposed to a different VPD from the rest of the plant, leaf conductance declined by 400mmol m−2s−1when compensation pressure increased by 1 MPa in all treatments. The compensation pressure needed to keep the shoot turgid, leaf conductance and the abscisic acid concentration in the xylem were linearly related. This was also the case when the highly dynamic development of stress was taken into ac

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIn barley leaves, there is a dramatic alteration of gene expression upon treatment with jasmonates leading to the accumulation of newly formed proteins, designated as jasmonate‐inducible proteins (JIPs). In the present study, a new jasmonate‐inducible cDNA, designated pHvJS37, has been isolated by differential screening of a γgt10 cDNA library constructed from mRNA of jasmonate‐treated barley leaf segments. The open reading frame (ORF) encodes a 39‐9 kDa polypeptide which cross‐reacts with antibodies raised against thein vivoJIP‐37. The hydropathic plot suggests that the protein is mainly hydrophilic, containing two hydrophilic domains near the C‐terminus. Database searches did not show any sequence homology of pHv.JS37 to known sequences. Southern analysis revealed at least two genes coding for JIP‐37 which map to the distal portion of the long arm of chromosome 3 and are closely related to genes coding for JIP‐23. The expression pattern of the JIP‐37 genes over time shows differential responses to jasmonate, abscisic acid (ABA), osmotic stress (such as sorbitol treatment) and desiccation stress. No expression was found under salt stress. From experiments using an inhibitor and intermediates of jasmonate synthesis such as α‐linolenic acid and 12‐oxophytodienoic acid, we hypothesize that there is a stress‐induced lipid‐based signalling pathway in which an endogenous rise of jasmonate switches on JIP‐37 gene expression. Using immunocytochemical techniques, JIP‐37 was found to be simultaneously located in the nucleu

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00402.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe have studied some characteristics of marcescent leaves (withered retained leaves) and senescent leaves inQuercus subpyrenaica, a tree species that plays a major role in the climatic transition forests between temperate and mediterranean environments in north‐eastern Spain. Leaves were taken from the upper and lower halves of the tree crown, both in the south‐ and north‐exposed parts of the tree. Leaves receiving low photosynthetic photon flux density (PPFD) undergo autumnal senescence, which is associated with decreases in photosynthetic pigments and decreases in the chlorophyllato chlorophyllbratio. Leaves receiving higher PPFD underwent senescence at a later date. Leaves situated in the upper, south‐exposed part of the tree, which receive the highest PPFD, showed no signs of senescence and remained photosynthetically active for a longer period of time, marcescence occurring suddenly at the end of the season. Marcescence is unlikely to cause an improvement in nutrient recycling, since the removal of nutrients proceeded similarly in marcescent and senescent leaves. Marcescence may increase the time‐span of the assimilation capacity for a significant period of time during September and October, when high light intensities and mild temperatures occur. The phenomena triggering marcescence may be related to low tem

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe Arctic is often assumed to be an NH4+‐dominated ecosystem. This review assesses the validity of this assumption. It also addresses the question of whether Arctic plant growth is limited by the ability to use the forms of nitrogen that are available. The review demonstrates that several sources of soil nitrogen are available to Arctic plants, including soluble organic nitrogen (e.g. glycine, aspartic acid and glutamic acid), NH4+and NO−3. In mesic Arctic soils, soluble organic nitrogen is potentially more important than either NH+4or NO−3. Many Arctic species are capable of taking up soluble organic nitrogen (either directly and/or in association with ectomycorrhizae), with the greatest potential for soluble organic nitrogen uptake being exhibited by deciduous species. The ability to take up soluble organic nitrogen may enable some Arctic plants to avoid nitrogen limitations imposed by the slow rate of organic matter decomposition. NO−3is also present in many Arctic soils, especially calcareous soils and soils near flowing water, animal burrows and bird cliffs. Arctic species characteristic of mesic and xeric habitats are capable of taking up and assimilating NO−3. Even when present in lower concentrations in soils than NH+4, NO−3is still an important source of nitrogen for some Arctic plants. Arctic‐plants therefore have a variety of nitrogen sources available to them, and are capable of using those nitrogen sources. Taken together, these findings demonstrate that the Arctic is not an NH+4dominated ecosystem. Symbiotic fixation of atmospheric N2does not appear to be an important source of nitrogen for Arctic plants. The reliance of Arctic plants on internal recycling of nitrogen substantially reduces their dependence on soil nitrogen uptake (this is particularly the case for slow‐growing evergreens). Despite the high level of internal nitrogen recycling, Arctic plant growth remains limited by the low levels of available soil nitrogen. However, Arctic plant growth is not limited by an inability to utilize any of the available forms of nitrogen. The potential effects of climatic warming on nitrogen availability and use are discussed. The question of whether the Arctic ecosystem is uniquely different from temperate nitrogen‐deficient ecosystems

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe variation in stomatal characters in leaves from oneAlnus glutinosa(L.) Gaertn. tree is analysed. Measurements were taken from over 70 sites on the abaxial surfaces of representative ‘sun’ and ‘shade’ leaves having the same insertion point. The mean values of stomatal density and index in the shade leaf were significantly lower (71 and 93%, respectively) than those for the sun leaf. Within leaves, up to 2.5‐fold differences in stomatal density values were observed. Contour maps derived from the data reveal non‐random trends over the leaf surface. Correlations between stomatal density, epidermal cell density and stomatal index indicate that the variation in stomatal density within leaves arose primarily from local differences in stomatal differentiation, rather than from local differences in leaf expansion. This research demonstrates that a high level of variation in stomatal characters occurs both within and between leaves. We conclude that a well‐defined sampling strategy should be used when estimating stomatal characters for (tree) leaves. Furthermore, the leaf's insertion point and situation within the tree crown should be taken into account. We discuss the implications of these findings for palaeoclimatic interpretations and emphasize the need for great caution when drawing conclusions based solely on stomat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTMolecular investigation of the process of cold acclimation in woody plants has been limited by the superimposition of dormancy‐related events on the process of cold tolerance development. To address this limitation, we have used the grapeVitis labruscanaL. ev. Concord to develop a system in which the developmental programme of dormancy can be induced seperately from cold acclimation. Using this system we have characterized differential accumulation of several proteins in grape buds during the normally superimposed endodormancy and cold acclimation programmes, and in buds which have entered only the endodormancy programme. A set of 47 kD proteins accumulated during endodormancy without cold acclimation to a level similar to that found in endodormant and cold‐acclimated buds, but without any associated increase in bud cold‐acclimation level. However, a 27 kD LEA‐like protein accumulated only in cold acclimated buds. We conclude that expression of the 47 kD glycoprotein is endodormancy‐related, but is not strictly related to the development of cold acclimation, while the 27 kD protein appears to be more specific to cold acclimation. In addition to strengthening the association of LEA‐like proteins with cold acclimation, this system allows more specific assessment of cold acclimation‐associated phenomena in overw

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe effects of Ca2+and cell turgor on Na+influx were examined in two charophytes,lamprothamnium papulo‐SUM(salt‐tolerant) andChara corallina(salt‐sensitive), to try to identify causes of salinity toxicity. Mortality was associated with Na+ influx, with the two species showing similar sensitivities to high Na+influx. InLamprothamnium, toxic influxes of Na+occurred at much higher external Na+concentrations than inChara. The differences in Na+influx at the same Na+concentration were not due to different responses to external Ca2+.Lamprothamniumadjusts its turgor in response to increasing NaCl whereasCharacannot. In solutions of KC1 up to at least 200 mol m‐3, however,Chararegulated turgor, and when KC1 was subsequently replaced with NaCl, Na+influx was low and similar to that in Lamprothamnium at the same Na* concentration.Characells which were not turgor‐adjusted in KCI had Na+influxes 2‐5‐fold higher than the turgid cells. Thus, it appears that turgor is a major determinant of Na+influx, and therefore of cell survival. We found no evidence that the mechanism of Na+influx inCharais different from that inLamprothamnium. Higher susceptibility ofCharato NaCl seems to result from inability to regulate turgor, in turn leading to to

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY