摘要:

AbstractThis review deals with recent advances in the structural characterization of pectins and the gels which they form, in relation to auxin‐induced extension growth, the ripening of fruit, and cellular recognition. Pectins are block polysaccharides. Heavily branched, largely methyl‐esterified blocks alternate with unbranched blocks of varying degrees of esterification. The unbranched, non‐esterified blocks can aggregate through calcium binding to form the junction zones that hold a gel together. The aggregates are of two, or possibly four, chains at low calcium levels, and larger with excess calcium. The fall in wall pH during auxin‐induced growth activates glycanase enzymes. These may attack some components of the pectic fraction, as well as xyloglucans. Pectin‐bound calcium ions may be displaced but this probably has little effect on gel strength. Pectins may be cross‐linked by diferulate esters when growth stops. The softening of ripe fruit is due to loss of cohesion in the pectin gel. In apples this results from replacement of the pectins by more esterified forms. In many other fruits it results from depolymerization by polygalacturonases, assisted by pectinesterases, so that the remaining segments are too short for effective calcium binding. Pectins have a further role in the recognition reactions between plant cells and some of their bacterial and funga

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614586

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe terminology currently employed in studies concerned with the osmotic responses of plant cells is reviewed with specific reference to (1) the suitability of expressions in general use and (2) the application of such terms to experimental studies. The widely used termosmoregulationis shown to be an inappropriate and misleading expression when used to describe the adjustments in cellular solute concentration which frequently accompany changes in external salt concentration. Such usage ofosmoregulationshould be discouraged; more suitable expressions (e.g.osmoacclimation, osmotic adjustment, turgor/volume regulationorturgor maintenance, osmoadaptation)should be employed, depending upon the context.

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614591

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIt is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 μV and possessing risetimes (10–90%) of approximately 200 ms, are known to be elicited in etiolated stems ofPisum sativumL. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ionopho

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614606

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractPith water storage capacity and its role in plant‐water relations were studied in seven giant rosette species of the genusEspeletiafrom the Venezuelan Andes. Readily available water from the pith was calculated to be capable of sustaining mean transpiration for up to 2.5 h. The relative importance of water stored in the pith, however, differed among species. The species that grow in the higher and colder environments tended to have a greater capacitance than the species that grow in the lower and less extreme environments. The pith volume per unit leaf area (PV/LA) was found to be a good indicator of the relative water storage capacity of the adult individuals of each species. Diurnal fluctuations in leaf water potential were not as pronounced in the species with higher PV/LA values. The species‐specific PV/LA was highly correlated with the leaf turgor loss point and with the total resistance to water flow from soil to leaves. These results suggested that species‐specific capacitance in the genusEspeletiais a response to temperature‐limited soil water availability and that cold tropical environments with frequent subfreezing temperatures tend to select for high water storage capacity in giant rosette

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614612

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractField flooding of established alfalfa(Medicago sativaL.) and birdsfoot trefoil(Lotus corniculatusL.) for up to 12 d resulted in a significant increase in alcohol dehydrogenase activity (ADH) and an increase in theKmof ADH in both species. Root concentration of ethanol increased throughout the flooding regime in alfalfa roots. No ethanol was detected in any trefoil root samples. Alfalfa plants which had shoots removed 5 d prior to flooding accumulated significantly higher levels of root ethanol and showed flooding injury sooner, indicating a significant effect of shoots on development of flooding injury.Alfalfa and trefoil plants grown in the greenhouse were flooded and ethanol in the transpiration effluent was trapped and measured. Alfalfa transpired measurable quantities of ethanol which peaked just prior to development of shoot injury symptoms. No ethanol was detected in the transpiration effluent from trefoil shoots. Flooded roots of both alfalfa and trefoil excreted ethanol but alfalfa roots synthesized more total ethanol and retained a larger proportion in the roots than did trefoil.While the ethanol accumulation response in alfalfa and trefoil are consistent with the ethanol ‘self‐poisoning’ hypothesis of flooding injury, the very small quantities of ethanol found in these roots still raises questions as to its absolute effect in the

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614629

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe present work deals with the characterization of an ATP‐dependent proton translocation monitored by the ΔpH probe acridine orange.The ATP‐dependent proton translocation has an optimum activity at pH 6.5 and is substrate specific for ATP. It is stimulated by Cl−, HCO3−and Br−, but is insensitive to several monovalent cations. Divalent cations (Mg2+or Mn2+) are required for proton translocation, while in the presence of Ca2+no uptake is observed. NO3−, NO2−and citrate strongly inhibit proton uptake. On the contrary, F−, SO42−, malate, pyruvate, succinate, oxalate and acetate have no inhibitory effect. Proton uptake is stimulated by valinomycin and unaffected by molybdate. Two thiols, dithioerythritol and dithiothreitol, are able partially to prevent the FCCP‐abolished proton uptake or partially restore the ATP‐dependent proton translocation in FCCP‐collapsed vesicles.It is suggested that pea stem microsomes possess an electrogenic ATPase, acting as a proton pump, which, on the basis of its characteristics, can be tentatively associated with membr

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614633

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractLeaf growth is one of the most sensitive of plant processes to water deficits and is frequently inhibited in field crops. Plants were acclimated for 2 weeks under a moderate soil water deficit to determine whether the sensitivity of leaf growth could be altered by sustained exposure to low water potentials. Leaf growth under these conditions was less than in the controls because expansion occurred more slowly and for less of the day than in control leaves. However, acclimated leaves were able to grow at leaf water potentials (Ψ1) low enough to inhibit growth completely in control plants. This ability was associated with osmotic adjustment and maintenance of turgor in the acclimated leaves. Upon rewatering, the growth of acclimated leaves increased but was less than the growth of controls, despite higher concentrations of cell solute and greater turgor in the acclimated leaves than in controls. Therefore, factors other than turgor and osmotic adjustment limited the growth of acclimated leaves at high ψ1Four potentially controlling factors were investigated and the results showed that acclimated leaves were less extensible and required more turgor to initiate growth than control leaves. The slow growth of acclimated leaves was not due to a decrease in the water potential gradient for water uptake, although changes in the apparent hydraulic conductivity for water transport could have occurred. It was concluded that leaf growth acclimated to low ψ1, by adjusting osmotically, and the concomitant maintenance of turgor permitted growth where none otherwise would occur. However, changes in the extensibility of the tissue and the turgor necessary to initiate growth caused generally slow growth in the acclimated leav

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614641

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractWith a view to defining factors regulating the growth responses of sunflower to salinity, plants were grown in solution culture (0, 50 or 100 mol m−3NaCl) and under natural light, and the areas of every leaf measured once or twice daily from 22 until 38 d after germination. During this period, carbon availability for growth was manipulated by changing light levels and by the use of a photosynthesis inhibitor, DCMU.Salinity reduced relative leaf expansion rates per plant (RLER) by an average of 0.04 (50 mol m−3) and 0.08 (100 mol m−3) m2m−2d−1compared with control plants of equivalent leaf area: the effects were found in expanding leaves regardless of age or size.Control plants expanded faster during the day than the night, but plants grown in salt had an almost constant RLER throughout the 24 h, indicating that salt influences the rate of utilization of assimilates independently of their production. DCMU reduced RLER considerably in both control and salt‐treated plants and reduced the advantage of control plants during the day. Conditions of low light also reduced the differences in RLER between control and salt‐treated plants.When salt was removed from the root medium of non‐DCMU plants, the expansion rates equalled that of the controls within 24 h and remained at the same levels for the following 3 d measurement period: this recovery applied to leaves of all ages. Salt‐grown plants with no photosynthesis (DCMU treatments) also increased their expansion rates upon removal of salt from the root medium, thus providing further evidence that growth was not limited by carbohydrate status, i.e. that salt influences growth primarily via its effects on the rate of utilization of s

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614653

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractCalmodulin (Cam), the heat‐stable, ubiquitous, Ca2+‐dependent regulator protein, has been purified to apparent homogeneity from germinating radish seeds (Raphanus sativus). The characteristics of radish Cam‐molecular weight, absorption spectrum, Ca2+‐dependent activation of brain phosphodiesterase (PDE)‐are very similar to those described for Cam from other plant materials. Radish Cam, like other plant Cam, shows some differences to Cam of calf brain.The total amount of Cam in radish embryos at 24 h of germination isca.37 μg g−1fresh weight. Approximately 95% of the total amount of Cam is present in the soluble fraction (supernatant at 100,000g).The level in the embryo axis strongly increases in the first 24 h of germination (+540%); this increase is strongly reduced when the germination is inhibited by abscisic acid (ABA). In the presence of Ca2+, no ‘free’ Cam (i.e. not bound to other structures) is present in the soluble fraction, suggesting that, during early germination, Cam level is a limiting factor for the activities of Ca2+‐Cam‐dependent systems. These studies suggest that Cam plays an important role in the early phases of seed germination.An inhibitor of the Ca2+‐Cam‐dependent phosphodiesterase is present in the soluble fraction from radish embryos; this substance decreases during germination. A possible role of this inhibitor during the early germinatio

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614660

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIn a study of the lipid composition of the uplandEmpetrum nigrumsubspp.hermaphroditumandEmpetrum nigrumsubspp.nigrumwith a lowland distribution, no evidence was found to support the suggestion that lipids (triacylglycerols) play a major energy storage role in the leaves of alpine species. On a quantitative basis the triacylglycerols constituted less than 5% of the total lipid in both species and the lowland species possessed the higher levels of total lipid, neutral lipid and triacylglycerols. It is suggested that the presence of a well‐developed waxy cuticle might account for the high total lipid levels encountered in dwarf evergreen shrub

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11614677

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY