摘要:

Abstract.The effect of short‐term changes in the water potential (from 0 to – 2.5 MPa) by addition of PEG 4000 to the nutrient solution was investigated with respect to nitrate uptake and reduction in 3‐week‐old wheat plants (Triticum aestivum, cv Fidel). Plants were harvested at the end of 12‐h treatments in the dark. The water potential of the mature leaves was similar to that of the medium down to – 0.8 MPa and was maintained at this level even though the external water potential was much lower. The medium water potential of 0.8 was a threshold level below which elongation of the youngest leaf was inhibited. Increase of the PEG concentration in the medium brought about a decrease of evapotranspiration and enhancement of nitrate uptake. No difference in the rate of nitrate reduction was observed, although thein vitronitrate reductase activity was lowered. Nitrate accumulation in the shoot was ascribed both to the stimulation of net uptake from the medium, and to the mobilization and translocation of nitrate from the root. It is suggested that increase in the storage pool of nitrate in shoots was related to the role of NO3−as

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01131.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.To study whether an electrical potential difference exists across the nuclear envelope or inner nuclear membrane of plant cells, the authors have used an optical probe of membrane potential, the cationic fluorescent dye, DiOC6(3) (MW = 572.5). This dye was microinjected into the nucleoplasm of isolatedAcetabularianuclei (which are still surrounded by a thin layer of cytoplasm) and its subnuclear localization visualized by fluorescence microscopy. Striking differences, which seemed to be correlated with the developmental stage of the isolated nucleus, were observed. In nuclei isolated from cells at the stage of early cap stage formation, the dye was restricted to the nuclear envelope. In nuclei isolated from cells with intermediate or fully developed caps, there was increased nucleoplasmic staining, and the staining of the envelope was frequently diminished or abolished. In all nuclei, the dye remained within the nucleus after injection. Cytoplasmic staining was only observed when nuclei isolated from cells at the stage of early cap formation were incubated in a hyper‐ or hypo‐tonic medium. Various ionophores, injected before the dye into the nucleoplasm, had no effect on the subsequent nuclear localization of DiOC6(3), although they did rapidly induce nucleolar condensation in nuclei isolated from cells at the stage of early cap formation. The results suggested that the electrical properties ofAcetabularianuclear envelopes or inner nuclear membranes change during cell maturation. Furthermore, the retention of the dye in the nucleoplasm under isotonic conditions indicated that the nuclear pores were not open channels for molecules of this s

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01132.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The specific effects of hypoxia and various inhibitors on stomatal opening in the light and closing in the dark were characterized in isolated epidermis fromCommelina communisL. Reducing the guard cell metabolism with hypoxia and the uncoupler carbonyl cyanide‐m‐chloro‐phenyl‐hydrazone, CCCP, respectively, inhibited both stomatal opening and closing. Stomatal closing was very efficiently blocked by CCCP and this effect could be readily reversed by washing out the inhibitor. The authors were unable to inhibit stomatal opening with ATPase‐inhibitors, without also affecting closing. Orthovanadate, up to 2 mol m−3, affected neither opening nor closing. Dicyclohexylcarbodiimide, DCCD, and diethylstilbestrol, DES, inhibited opening as well as closing to about 50%. The K+‐channel blocker tetraethylammonium chloride, TEA‐Cl, inhibited both stomatal opening and closing, as did phenyl acetic acid, PAA, a compound considered to interfere with blue light induced stomatal opening. The results are discussed in the view that the uncontrolled K+leakage from the guard cells is low, that K+efflux during stomatal closing, as well as K+influx during opening, occurs through specific K+‐channels and that ATP and/or a membrane potential seems to be needed to keep th

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01133.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The CAM vineHoya australisand three C3vines,Smilax australis, Ipomoea pes‐capraeandKennedta rubicunda, were studied at a site on the coast of northeastern New South Wales, Australia. The level of CAM activity (nocturnal acid accumulation) was comparable inH. australisgrowing in full sunlight and in deep shade. Acclimation to shade byH. australiswas indicated by thinner leaves, increased chlorophyll content, decreased chlorophylla/bratios, lower dark respiration rates, and lower light compensation points. When growing in full sunlightH. australisexhibited reductions in photochemical efficiency, as indicated by reduced quantum yields and Fv/Fmfluorescence from PS II as well as low rates of photosynthesis at high light. Sun leaves ofH. australisexperienced a massive quenching of fluorescence from PS II during normal exposure to midday irradiance which was rapidly reversible under low irradiance conditions in the late afternoon. This quenching indicated a reduction in photochemical efficiency, part of which could be accounted for by an increase in non‐radiative energy dissipation, while part of it was due to one or more processes not yet identified. Changes in PS II fluorescence from shadeH. australisexposed to full sunlight suggest a decrease in the rate constant for photochemistry indicative of damage to the reaction centre, as well as an increase in non‐radiative energy dissipation. The C3vineS. australiswas also shade tolerant, but exhibited little evidence of photoinhibition when growing in full sunlight.Ipomoea pescapraeandK. rubicunda, both of which were apparently shade intolerant (being found only in full sunlight), possessed high quantum yields and much higher photosynthetic capacities than eitherH. australisorS. australis.From this study, and several others, it appears that plants possessing CAM experience photoinhibition to a greater degree than do C3species in full sunlight under natural conditions, which is probably exacerbated by some degree of CAM

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01134.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The fitting of the generalized Richards function to germination data by using two nested iterative and least squares regression procedures to estimate the four parameters (all of which can be associated with features of biological growth) is demonstrated. The program also involves a procedure of parallel curve analysis which makes comparisons between two curves by examining the whole process represented by the curve and not just a point or portion thereof. Excellent agreement between observed and expected values was obtained by analyzing data which defined patterns of germination exhibiting a range of rates and final percentages. The program also calculates a number of derived quantities including maximum daily rate of germination and time to 50% of final germination.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01135.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Ethylene was found to promote two distinct processes during germination of redroot pigweed (Amarantus retroflexusL.) seeds: embryo expansion that splits the seed coat (incomplete germination), and radicle penetration through the more elastic endosperm (complete germination). The two events can be separated in time by subjecting seeds to low water potential or low CO2levels, which arrest germination of some seeds at the incomplete stage. Ethylene applications to incompletely germinated seeds promote complete germination, with a response threshold near 0.02 cm3m−3and saturation near 0.5 cm3m−3. Higher ethylene concentrations (0.5 to 50 cm3m−3) given during the first day of seed imbibition also increase the percentage of seeds which initiate embryo expansion and split the seed coat. Light and elevated CO2also promote radicle penetration of the endosperm in seeds incubated under water stress. The results support the view that the germination pause at the incomplete stage is an adaptation to environmental stresses that can be overcome with exogenous ethylene or certain other st

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01136.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The construction and evaluation of a temperature‐correctedin situthermocouple psychrometer for measurement of leaf water potential (Ψ) is described. The instrument utilized two chromel‐constantan thermocouples which allowed for detection of both the psychrometric zero offset and the temperature differential between the sample and the Peltier measuring junction. The psychrometer was subjected to stable temperature gradients while in contact with reference solutions of sodium chloride, and the effects of thermal gradients were quantified. Regression analysis indicated that temperature differentials were responsible for errors in water potential determinations of approximately –7.73 MPa°C−1. When installed on leaves of field‐grown cotton (Gossypium hirsutumL.), corn (Zea maysL.) and soybean (Glycine maxL. Merr) the instrument detected temperature differentials up to 0.1°C (–6.0 μV) which were associated with relatively small shifts in psychrometric zero offsets (–0.05––0.75 μV). Results indicated that substantial errors in apparent Ψ were caused by non‐isothermal conditions between the leaf and the psychrometer measuring junction. The relative magnitude of these errors could be quantified and the corrected results showed good agreement with conventional psychrometric determination of Ψ on excised samp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01137.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Gas exchange measurements were made on single leaves of three C3and one C4species at air speeds of 0.4 and 4.0 m s−1to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m−2s−1at the lower air speed, and 1.2 to 1.5 mol m−2s−1at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C3species, and about 3 Pa lower in the C4species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C3species. The commonly reported values of substomatal carbon dioxide pressure for C3and C4species were found to occur only when measurements were made at the higher

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01138.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Books reviewed in this article:CYTOKININS: PLANT HORMONES IN SEARCH OF A ROLE.Edited by R. Horganand B. JeffcoatROOT DEVELOPMENT AND FUNCTION.Edited by P. J. Gregory, J. V. Lakh&D. A. Rose

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01139.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY