摘要:

ABSTRACTTo evaluate the potential responses of individual trees to climatic warming, phenological observations of clones ofLarix decidua(Mill.),Betula pubescens(Ehrh.),Tilia cor‐data(Mill.),Populus canescens(Ait.),Quercus robur(L.),Fagus sylvatica(L.) andPicea abies(L.) relocated over a large latitudinal range in Europe were analysed. The magnitude of the response of the clone was compared to that of genetically different trees of the same species in part of the latitudinal range, which were assumed to have adapted to their local climates. It was found that the responses of the date of leaf unfolding and the date of leaf fall in the clones to temperature were similar in magnitude to those in the genetically different trees. This demonstrates that trees possess considerable plasticity and are able to respond phenotypically to a major change in their local climate.For the clones ofLarix deciduaandQuercus roburthe duration of the growing season may decrease with increasing temperature, because leaf fall is advanced more than leaf unfolding. InBetula pubescensandPopulus canescens, leaf unfolding and leaf fall are advanced equally, whereas inTilia cordataandFagus sylvaticathe date of leaf fall seems to be unaltered but the date of leaf unfolding advances with increasing temperature. These differences in the duration of the growing season at increased temperature may alter the competitive balance between the species.Descriptive dynamic models showed that most of the variance in the date of leaf unfolding can be accounted for by temperature. However, a generally applicable model of leaf fall based on temperature and/or photoperiod could not improved the null model, i.e. the mean date of leaf fall, because of variability in other environmental factors.The lowest temperatures around the dates of leaf unfolding and leaf fall differed among the clones. The hypothesis that the survival of the clones is curtailed by spring frosts was supported. Thus, these lowest temper‐tures around leaf unfolding may represent thresholds below which the species cannot survive. It is argued that these thresholds may be a particularly sensitive means to evaluate the impact of climatic warming on the geographical distribution of tree spec

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00356.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTRight‐side‐out plasma membrane vesicles were isolated from wheat roots using an aqueous polymer two‐phase system. The purity and orientation of the vesicles were confirmed by marker enzyme analysis. Membrane potential (Ψ)‐dependent22Na+influx and sodium/proton (Na+/ H+) antiport‐mediated efflux across the plasma membrane were studied using these vesicles. Membrane potentials were imposed on the vesicles using either K+gradients in the presence of valinomycin or H+gradients. The ΔΨ was quantified by the uptake of the lipophilic cation tetraphenylphosphonium. Uptake of Na+into the vesicles was stimulated by a negative ΔΨ and had aKmfor extrav‐esicular Na+of 34.8 ± 5.9 mol m3. The ΔΨ‐dependent uptake of Na+was similar in vesicles from roots of hexaploid (cv. Troy) and tetraploid (cv. Langdon) wheat differing in a K+/Na+discrimination trait, and was also unaffected by growth in 50 mol m−3NaCl. Inhibition of ΔΨ‐dependent Na+uptake by Ca2+was greater in the hexaploid than in the tetraploid.Sodium/proton antiport was measured as Na+‐dependent, amiloride‐inhibited pH gradient formation in the vesicles. Acidification of the vesicle interior was measured by the uptake of14C‐methylamine. The Na+/H+antiport had a Km, for intravesicular Na+of between 13 and 19 mol m−3. In the hexaploid, Na+/H+antiport activity was greater when roots were grown in the presence of 50 mol m−3NaCl, and was also greater than the activity in salt‐grown tetraploid wheat roots. Antiport activity was not increased in a Langdon 4D chromosome substitution line which carries a trait for K+/Na+discrimination. It is concluded that neither of the transport processes measured is responsible for the Na+/K+discrimination trai

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00344.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influence of low temperature on the operation of the xanthophyll cycle and energy dissipation activity, as ascertained through measurements of chlorophyll fluorescence, was examined in two broad‐leaved evergreen species,Vinca minorL. andEuonymus kiautschovicusLoessner. In leaves examined under laboratory conditions, energy dissipation activity developed more slowly at lower leaf temperatures, but the final, steady‐state level of such activity was greater at lower temperatures where the rate of energy utilization (through photosynthetic electron transport) was much lower. The rate at which energy dissipation activity increased was similar to that of the de‐epoxidation of violaxanthin to antheraxanthin and zea‐xanthin at different temperatures. However, leaves in the field examined prior to sunrise on mornings following cold days and nights exhibited a retention of antheraxanthin and zeaxanthin that was associated with sustained decreases in photosystem II efficiency. We therefore suggest that this phenomenon of ‘photoinhibition’ in response to light and cold temperatures during the winter results from sustained photoprotective thermal energy dissipation associated with the xanthophyll cycle. Such retention of the de‐epoxidized components of the xanthophyll cycle responded to day‐to‐day changes in temperature, being greatest on the coldest mornings (when photoprotective energy dissipation might be most required) and less on warmer mornings when photosynthesis could presumably procee

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00345.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe salt‐tolerant algaChara longifolia(Robinson) is capable of regulating its turgor in response to hypotonic stress resulting from a decrease in the osmotic pressure of the medium. This regulatory process takes only 40 min in small cells (length ≤ 10 mm), but requires 3d in large cells (length ≥30mm). Turgor regulation in small cells is comprised of two phases, a fast phase reducing the increased turgor by about 25% in the First 5 min, and a second phase reducing the turgor to near the original value within 40 min. The second phase is inhibited by reducing the concentration of Ca2+in the external medium from 4.6 to 0.01 mol m−3; the first phase is less affected by the reduction of Ca2+. In the first 5 min of stress, the membrane depolarizes in a voltage‐dependent fashion, electrical conductance of the membrane increases transiently and cytoplasmic streaming is inhibited. When the external Ca2+concentration is lowered, conductance does not increase and streaming continues unaffected. In a low ionic strength medium, Ca2+is not required in the medium for turgor regulation.To test the hypothesis that there is increased Ca2+entry from the medium during turgor regulation, we measured the influx of45Ca2+into the cell. We found an increased influx of Ca2+, from 18 to 36 nmol m−2s−1during the first 30 to 90 s following osmotic stress. This increase was evident only in cells below about 7 mm in length, and was more marked in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00346.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA tobacco (Nicotiana tabacumL.) cDNA clone,Nthsp 18P, encoding a class I low‐molecular‐weight heat shock protein (LMW HSP), has been isolated from a mid‐biccllular pollen cDNA library by hcterologous hybridization with a low‐molecular‐weight heat shock cDNA clone of alfalfa. Northern analysis showed thatNthsp 18Pexpression is activated at normal temperature during the dehydration phase ofin situpollen development, just before anthesis. Induction of pollen embryogenesis by anin vitrostarvation treatment of mid‐bicellular tobacco pollen was accompanied by a dramatic increase in the levels of theNthsp 18Ptranscript, which accumulated in embryogenic pollen grains at 25°C; lower levels of this transcript were also detected in early pollen‐derived embryos. A similar pattern of expression was observed in transgcnic tobacco plants containing the promoter ofGmhsp 17.3‐B, a soybean homologue of theNthsp 18Pgene, fused to the GUS reporter gene. This is the first characterized gene shown to be transcriptionally activated during the induction of poll

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00347.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTInternal conductances to CO2transfer from the stomatal cavity to sites of carboxylation (gi) in hypostomatous sun‐and shade‐grown leaves of citrus, peach andMacadamiatrees (Lloydet al. 1992) were related to anatomical characteristics of mesophyll tissues. There was a consistent relationship between absorptance of photosynthetically active radiation and chlorophyll concentration (mmol m−2) for all leaves, including sclerophyllousMacadamia, whose transmittance was high despite its relatively thick leaves. In thin peach leaves, which had high gi, the chloro‐plast volume and mesophyll surface area exposed to intercellular air spaces (ias) per unit leaf area were similar to those in the thicker leaves of the evergreen species. Peach leaves, however, had the lowest leaf dry weight per area (D/a), the lowest tissue density (Td) and the highest chloro‐plast surface area (Sc) exposed to ias. There were negative correlations between giand leaf thickness orD/a, but positive correlations between giandScorSc/Td.We developed a one‐dimensional diffusion model which partitioned giinto a gaseous diffusion conductance through the ias (gias) plus a liquid‐phase conductance through mesophyll cell walls (gcw). The model accounted for a significant amount of variation (r2=0.80) in measured giby incorporating both components. The giascomponent was related to the one‐dimensional path‐length for diffusion across the mesophyll and so was greater in thinner peach leaves than in leaves of evergreen species. The gcwcomponent was related to tissue density and to the degree of chloroplast exposure to the ias. Thus the negative correlations between giand leaf thickness orD/arelated to giaswhereas positive correlations between giand Scor Sc/Td, related to gcw. The gcwwas consistently lower than gias, and thus represented a greater constraint on CO2diffusion in the mesophylls of these hypo

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00348.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTIncubation of radish (Raphanus sativusL.) seeds in the presence of 1 or Smol m−3Ca‐EGTA, which increased Ca2+activity in the incubation medium (c. 0.24 or 0.37 mol m−3at 24 h with respect toc. 0.13 mol m−3in the control), did not affect germination, the restoration of K+net influx, the increase in DNA and RNA levels or protein synthesis. Incubation in 1 mol m−3Na‐EGTA, which reduced Ca2+activity in the incubation medium (20 mmol m−3at 24 h), decreased the total Ca2+level in embryo axes (‐21%), but only slightly inhibited the increase in fresh weight without affecting the restoration of K+net influx, the increase in DNA and RNA levels or protein synthesis. In the presence of 5 mol m−3Na‐EGTA (Ca2+activity in the incubation medium was 0.6 mmol m−3), the decrease in the total Ca2+level was greater (c. ‐27%) and the increases in fresh weight, DNA and RNA were inhibited by about 50, 39 and 40%, respectively. These results indicate that increased Ca2+availability does not affect germination and suggest that the effect of Na‐EGTA, at least up to 5 mol m−3, is a result of an induction of Ca2+deficiency. The amount and specific activity of calmodulin (CaM) present in the soluble fraction (100 000g) of radish embryo axes greatly increased during the first 24 h of incubation (c. 5‐fold and 7‐fold, respectively). This increase was very similar in the Ca‐EGTA‐treated seeds but was inhibited (c. ‐38%) by 1 mol m−3Na‐EGTA, even if the increases in DNA and RNA levels and protein synthesis were not significantly reduced. The lower amount of CaM after 24 h of incubation in 1 mol m−3Na‐EGTA (c. ‐30%) was due to a reduction in the fraction of CaM bound to a proteinaceous CaM inhibitor present in radish seeds [M. Cocucci&N. Negrini (1988)Plant Physiology88, 910–914] and not involved in the metabolic reactivation of the seed. These results suggest that the level of CaM is controlled by Ca2+availability and that the CaM inhibitor has a role in controlling the amount of

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00349.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe effects of soil fertility (two levels of soil nitrogen and two levels of soil phosphorus) and mycorrhizal infection on pollen production and pollen grain size were studied in two cultivars of the common zucchini (Cucurbita pepo). Overall, soil fertility and mycorrhizal infection had significant effects on traits affecting the male function of plants (staminate flower production, pollen production per flower and pollen grain size). There were also differences between the cultivars for these male traits in all three experiments. In addition, pollen grain size decreased toward the end of the growing season. In the mycorrhiza experiment, both phosphate concentration per pollen grain and total phosphate content per anther were greater but not significantly greater in the mycorrhizal plants than in the non‐mycorrhizal plants. A significant negative relationship between pollen production and pollen grain size was found in the mycorrhiza and soil phosphorus experiments, indicating that there was a trade‐off between pollen production and pollen size. This study is the first to show that mycorrhizal infection has an effect on male function (pollen production and size) in addition to the well‐documented effects on female function (fruit/seed production and

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00350.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe permeability (P) of the gaseous diffusion barrier in the nodules of soybean [Glycine max(L.) Merr.] decreases when water deficits are extended over a 7 to 10 d period. The mechanism controllingPchanges is unclear, but may result from the release of water to intercellular pathways, and an associated change in the nodule water potential. The purpose of these experiments was to impose water deficit treatments rapidly in order to determine the early sequence of the responses of nodule water potential and nodule gas exchange without the complications that arise from long‐term water deficit treatments. A vertical, split‐root system was used to separate nodule drying effects from plant water deficits by replacing humidified air that was passed over upper root nodules in well‐watered plants with dry air, or by replacing the nutrient solution that surrounded lower roots with ‐1.0 MPa polyethylene glycol (PEG) solution, or by a combination of the dry air and PEG treatments. The PEG treatment caused large decreases in both the components of nodule water potential and nodule relative water content, but there was no indication that these factors had immediate, direct effects on either nitrogenase activity orP. After 7 h of the PEG treatment a significant decrease in nitrogenase activity was found but no decrease inPwas detected. These results indicate that changes in nitrogenase activity in response to water deficits precede decreases inP. Exposure of nodules to dry air in well‐watered plants had no significant effect on either nitrogenase activity orPduring the 7 h

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00351.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe mechanism of water‐stress‐induced embolism of xylem was investigated inMalosma laurinaandHeteromeles arbutifolia, two chaparral shrub species of southern California. We tested the hypothesis that the primary cause of xylem dysfunction in these species during dehydration was the pulling of air through the pores in the cell walls of vessels (pores in pit membranes) as a result of high tensions on xylem water. First, we constructed vulnerability‐to‐embolism curves for (i) excised branches that were increasingly dehydrated in the laboratory and (ii) hydrated branches exposed to increasing levels of external air pressure. Branches ofM. laurinathat were dehydrated became 50% embolized at a xylem pressure potential of ‐1.6 MPa, which is equal in magnitude but opposite in sign to the +1.6 MPa of external air pressure that caused 50% embolism in hydrated stems. Dehydrated and pressurized branches ofH. arbutifoliareached a 50% level of embolism at ‐6.0 and +6.4 MPa, respectively. Secondly, polystyrene spheres ranging in diameter from 20 to 149 nm were perfused through hydrated stem segments to estimate the pore size in the vessel cell walls (pit membranes) of the two species. A 50% or greater reduction in hydraulic conductivity occurred inM. laurinaat perfusions of 30, 42, 64 and 82 nm spheres and inH. arbutifoliaat perfusions of 20 and 30 nm spheres. Application of the capillary equation to these pore diameters predicted 50% embolism at xylem tensions of ‐2.2 MPa forM. laurinaand ‐6.7 MPa forH. arbutifolia, which are within 0.7 MPa of the actual values. Our results suggest that the size of pores in pit membranes may be a factor in determining both xylem efficiency and vulnerability to embolism in some chaparral species.H. arbutifolia, with smaller pores and narrower vessels, withstands lower water potentials but has lower transport efficiency.M. laurina, with wider pores and wider vessels, has a greater transport efficiency but requires a deeper root system to help avoid catastro‐phically low

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00352.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY