摘要:

The liquid in the free space of leaf cell walls, the apoplast, is in direct contact with the plasma membrane and its nutrient uptake systems. Therefore, the pH of the apoplast is of utmost interest. We have elaborated a non‐destructive method by which excised sunflower leaves (Helianthus annuuscv. Erika) were perfused with fluorescein isothiocyanate‐dextran (FITC‐dextran) (4 000 Da) via the transpiration stream. We showed that leaf apoplast pH can be measured by using the fluorescence ratio technique together in conjunction with this dye. Evidence is provided that FITC‐dextran does not penetrate the plasma membrane over a period of ca 17 h from the beginning of dye perfusion. Dye enrichment in the leaf apoplast did not cause an ‘inner filter effect’ and thus the fluorescence ratio was only dependent on pH. In vivo calibration yielded a pKa of 5.92, which was virtually identical to the pKa of 5.93 calculated for dye solutions. Hence, FITC‐dextran can be detected in complex environments and covers a pH range prevailing in the leaf apoplast.Based on this method we developed a microscope image technique visualizing pH gradients between various cell types. The pH in the lumen of the xylem vessel was ca 0.3–0.5 units lower than that of the apoplast of surrounding cells. Nitrate present in the leaf apoplast caused an increase in pH, especially in the dark. Under these conditions, in the intercostal area, the apoplast pH around the stomata was ca 0.5–1.0 units higher than that of the surroundin

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Etioplast development and protochlorophyllide (Pchlide) accumulation was studied in wheat seedlings (Triticum aestivumL. cv. Walde, Weibull) grown in darkness on gibberellic acid (GA3), gabaculine (3‐amino‐2,3‐dihydrobenzoic acid), or on a combination of the two. The results were compared with the features of seedlings grown on water only. GA3enhanced shoot growth and promoted etioplast development. A correlation was observed between the appearance of prolamellar bodies (PLBs) and of phototransformable Pchlide. Gabaculine, a known tetrapyrrole biosynthesis inhibitor, delayed growth, slowed down the rate of PLB formation and caused structural alterations of the etioplasts up to 48 h of germination. Gabaculine also delayed the formation of phototransformable Pchlide as well as overall Pchlide biosynthesis, as determined by low‐temperature fluorescence emission in vivo. The spectral blue‐shift of newly formed chlorophyllide (Chlide) was delayed in irradiated dark‐grown gabaculine‐grown seedlings, indicating an inhibited dissociation of Chlide and NADPH‐Pchlide oxidoreductase (Pchlide reductase: EC 1.3.1.33). Thus there is a close correlation between accumulation of Pchlide and etioplast development, also under conditions when development is enha

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A fast‐growing normal and a slow‐growing gibberellin‐deficient mutant ofLycopersicon esculentum(L.) Mill. cv. Moneymaker were used to test the hypothesis that slow‐growing plants reduce NO3−in the root to a greater extent than do fast‐growing plants. Plants that reduce NO3−in the root may grow more slowly due to the higher energetic and carbon costs associated with root‐based NO3−reduction compared to photosynthetically driven shoot NO3−reduction. The plants were grown hydroponically with a complete nutrient solution containing 10 mMNO3−and the biomass production, gas exchange characteristics, root respiratory O2consumption, nitrate reductase activity and translocation of N in the xylem were measured. The gibberellin‐deficient mutants accumulated more total N unit−1dry weight than did the faster‐growing normal plants. There were no significant differences between the genotypes in the rates of photosynthesis expressed on a leaf dry weight basis. The plants differed in the proportion of photosynthetic carbon available to growth due to a greater proportion of daily photo‐synthate production being consumed by respiration in the slow‐growing genotype. This difference in allocation of carbon was associated with differences in the specific leaf area and specific root length. In addition, a greater leaf weight ratio in the fast‐growing than in the slow‐growing plants indicates a greater investment of carbon into biomass supporting photosynthetic production in the former. We did not find differences in the activity or distribution of nitrate reductase or in the N composition of the xylem sap between the genotypes. We thus conclude that the growth rate was determined by the efficiency of carbon partitioning and that the site of NO3−reduction and assimilation was not relat

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Although leaf photosynthesis and plant growth are initially stimulated by elevated CO2concentrations, increasing insensitivity to CO2(acclimation) is a frequent occurrence. In order to examine the acclimation process, we studied photosynthesis and whole plant development in swiss chard (Beta vulgarisL. Koch ssp.ciela) and sugarbeet (Beta vulgarisL. ssp.vulgaris) grown at either ambient or twice ambient concentrations of CO2. In an initial controlled environment study, photosynthetic acclimation to elevated CO2levels was observed in both subspecies 24 days after sowing (DAS) but was not observed at 42 and 49 DAS for sugarbeet or at 49 DAS for swiss chard. Although sugarbeet and swiss chard differed in root size and morphology, this was not a factor in the onset of photosynthetic acclimation. The reversal of photosynthetic acclimation that was observed in older plants grown at elevated CO2, concentrations was associated with a rapid increase in root development (i.e. increased root: shoot [R/S] ratio), increased sucrose levels in sinks (roots) and no differences in total soluble leaf protein of either subspecies relative to the ambient CO2condition. In a second set of experiments, swiss chard and sugarbeet were grown in outdoor Plexiglass chambers at different times of the year (i.e. summer and early fall). Average 24‐h temperature was 30.7 and 19.4°C for the summer and fall plantings, respectively. In agreement with the controlled environment study, lack of photosynthetic acclimation, determined from the response of photosynthesic rate to internal CO2concentration, was correlated with increased root biomass and sucrose concentration relative to the ambient condition. However, photo‐synthetic acclimation was observed depending on the season, i.e. summer (swiss chard) or fall (sugarbeet), suggesting that acclimation was affected by environmental factors, such as temperature. Data from both experiments suggest that continued long‐term photosynthetic stimulation may be dependent upon the ability of increased CO2to stimulate new sink development which would allow full utilization of the additional carbon made available in a high CO2envir

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00849.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Within the genusPolygonuma large variation was found between species with regard to stomatal number, gas phase resistance, intracellular resistance and dark respiration. Interspecific variation in CO2compensation concentration and intercellular CO2concentration at constant external concentration were comparatively small. Correlations were found between stomatal number and gas phase resistance, stomatal number and Γ, and Γ and the product of dark respiration rate and intracellular resistance. The influence of dark respiration and stomatal number on photosynthetic gas exchange is discussed. It was concluded that dark respiration in light was enhanced by 22% as a mean value in 9Polygonumspecies and by 62% inPolygonum lapathifoliu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00850.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abscisic acid‐insensitive mutants ofArabidopsis thalianaL. var. Landsbergerectawere selected for their decreased sensitivity to ABA during germination. Two of these mutants,abi‐1andabi‐2, display a wilty phenotype as adult plants, indicating disturbed water relations. Experiments were undertaken to find out if this results from insensitivity of mutant stomates to ABA.Growth conditions and methods to isolate epidermal strips were optimized to study stomatal movement. Wild type stomates required external ionic conditions comparable to those found for other species such asCommelina communis. The largest light‐induced opening ofA. thalianastomates was found at an external KCl concentration of 50 mM. Stomatal apertures were increased by lowering external Ca2+to 0.05 mM. The apertures of stomates incubated with 10 μMABA were not altered by changes in Ca2+from 0.05 to 1.0 mM.Stomates of allabimutants showed a light‐stimulated stomatal opening. The opening of wild type andabi‐3stomates was inhibited by ABA, while stomates ofabi‐1andabi‐2did not respond to ABA. The insensitivity ofabi‐1andabi‐2stomates to ABA may thus explain the observed distu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00851.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

35S‐L‐cysteine was fed to a mature leaf of 3‐year‐old beech trees via a flap. After 1 to 4 h the distribution of35S‐radioactivity was analysed in the leaves as well as the bark and wood of the trunk and the main root. Transport of35S out of the fed leaf amounted to 0.3–1.2% of the total35S taken up. The branches of the trees did not act as sink organs for the exported radioactivity. The main portion of the35S‐radioactivity transported out of the fed leaf was found in basipetal parts of the trunk. Only a small portion of35S‐radioactivity was transported in acropetal direction. The distribution of the35S‐radioactivity within the trunk showed a higher portion of35S in the bark than in the wood. In both tissues, bark (70 to 80%) and wood (60 to 70%), the35S was predominantly found in the HCl soluble fraction. However,35S‐cysteine, the compound fed to the leaves was not exported out of the fed leaf. Along the trunk35S‐cysteine was neither determined in bark nor in wood sections. The only low molecular mass S‐compounds found was35S‐glutathione (GSH). The35S‐sulphate detected in bark and wood origined from cysteine oxidation in the leaf tissue and from contamination of the35S‐cysteine feeding solution. The ratio of GSH to sulphate decreased with increasing distance from the fed leaf. Apparently,35S‐radioactivity was transported as sulphate and GSH in the phloem in basipetal direction, but GSH was removed preferentially out of the phloem along the transport path.35S‐radioactivity exported out of the phloem and transported into the wood of the trunk was not retranslocated in the xylem. It may therefore be assumed that part of the35S translocated was stored in ray cells, medullary sheath cells and/or pith parenchyma cells. Girdling experiments in which the bark of the trunk was peeled off basipetal to the branch containing the f

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00852.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

InBidens pilosaL. (var.radiatus), wounding of both cotyledons induces the inhibition of hypocotyl growth. This morphogenic response occurs only if plantlets have been tranferred 24 h before from a non‐permissive (ion‐rich) to a permissive (deionized water) incubation medium. We have defined three kinds of experimental conditions where the wound‐response depends on the ionic content of the incubation medium: (1) permissive, allowing inhibition of hypocotyl growth; (2) non‐permissive, leading to storage of the wound signal; and (3) conditions required to recall the stored wound signal. Under these three experimental conditions, the accumulation of two stress‐related genes,tch1(calmodulin) andhsp70, was investigated using northern blots of poly(A)+and polysomal RNA. Under permissive conditions the wound response was characterized by a marked increase intch1andhsp70‐like poly(A)+RNA and by a slight association of these mRNAs with polysomes, 30 to 60 min after mechanical perturbation. In contrast, under non‐permissive conditions, we only observed a decrease in the accumulation of the two transcripts incorporated into polysomes. Under conditions that allow expression of the previously‐stored wound signal, we showed an increase in transcript accumulation (hsp70‐like gene) or an increase in the level of mRNA associated with polysomes (tch1‐like gene). These results suggest that transcriptional and post‐transcriptional regulation may occur at least at the level of transcript incorporation into the polysomes. This mechanism would be involved both after the immediate wound response and during the storage of

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00853.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The possible participation of several major components of the signal transduction pathway in photoperiodic flower induction was examined inPharbitiscotyledons. Exogenous applications of GTP‐γ‐S (1–10 μM) or of the phorbol ester, phorbol 12‐myristate‐13‐acetate (PMA, 0.1–5.0 μM) toPharbitisplants held under a marginal inductive period (11.5 h dark) significantly increased their flowering response. Membrane lipid fluidity, GTP‐binding and protein kinase activity were increased following a single flowering‐inducing dark period of 16 h; however, a light‐break of 10 min that abolished flower induction failed to reverse the dark‐induced increase in these processes. Photo‐inductive dark conditions significantly increased the content of diacylglycerol (DAG) and phosphoinositides in the cotyledon membranes, together with the activities of their kinases, and a light break decreased them to control levels and below. In addition, a single spraying with GTP‐γ‐S or PMA at 1 μMsignificantly increased both the lipid content and the kinase activities. These compounds also enhanced the kinase activities in vitro. It is concluded that DAG and phosphoinositide metabolism play a role in the linking of the photoperiodic induction of the phytochrome with the fl

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Purified plasma membrane fractions were obtained from leaves ofPicea abiesL.,Pinus sylvestrisL.,Fagus sylvaticaL. andQuercus roburL., whereas plasma membranes fromPinus halepensisMill, proved to be more difficult to obtain, perhaps due to the higher content of volatile substances in this plant species. Plasma membranes were purified by both phase partitioning and free‐flow electrophoresis from microsomal fractions and identified on the basis of biochemical and in some cases morphological and cytochemical markers. Electron micrographs revealed that membrane vesicles fromPinus sylvestrisexhibited a very clear dark‐light‐dark pattern and measurements of membrane thickness showed that it ranged from 6 to 10 nm. Most membranes were 8 nm thick and stained with phosphotungstic acid at low pH, both typical characteristics of the plasma membrane. Enzymatic identification of plasma membranes consisted in the determination of the vanadate‐sensitive ATPase (EC 3.6.1.3) activity. The specific activity in the upper phase (U2) fraction was 10–25 times higher than those in the lower phase and microsomal fractions, depending on plant species. 1,3‐β‐glucan synthase II (EC 2.4.1.3), another putative plasma membrane marker, was not detected in the plasma membrane‐enriched fractions of conifer needles and showed a very low specific activity in membranes of deciduous trees. Contamination by membranes of other origin was determined by analysis of membrane markers: cytochromecoxidase (EC 1.9.3.1) for mitochondria, inosine diphosphatase (EC 3.6.1.6) for Golgi apparatus, cytochromecreductase (EC 1.6.2.4) for endoplasmic reticulum, and pyrophosphatase (EC 3.6.1.1) for tonoplasts. The main, but relatively low contamination, was due to tonoplasts, as determined by the activity of pyrophosphatase. Plasma membrane characteristics were quite different depending on the season during which needles were taken. Membrane preparations of better quality were more easily obtained from samples tak

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00855.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY