摘要:

ABSTRACTWhilst plant cells are apparently equipped with all the necessary molecular machinery for receptor‐mediated endocytosis, the physiological role of this process in these cells remains an enigma. In this article, we consider current opinions of endocytosis in plants and define some of the problems that have impeded progress in our under‐standing of the part played by endocytosis in the vesicle trafficking path

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00184.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTomato plants were exposed to four concentrations of CO2(350, 700, 1050 or 1400 μmol CO2mol−1) for 31 d. The light‐saturated rate of photosynthesis (A) of the unshaded fifth leaf was measured at either an ambient CO2concentration of 350 μmol CO2mol−1[A(350)] or at the level of CO2at which the plants were grown. The chloroplast protein composition and the level of transcripts of nuclear or plastid photosynthesis‐associated genes (PAGs), as well as the main carbohydrate content of the fifth leaf maintained horizontal and unshaded, were also measured during leaf development. At 60 and 95% leaf expansion, the A of high‐CO2‐grown plants measured at growth CO2was higher than theA(350) of the plants grown at ambient CO2. However, in the fully mature leaves,A(growth CO2) declined linearly as growth CO2concentration increased. TheA(350) of plants exposed to elevated CO2up to 60% leaf expanion had not acclimated to high CO2. At 95% leaf expansion,A(350) was lower in plants grown at high CO2. A versus CO2(Ci) for mature leaves showed thatAof the plants grown at high CO2was lower over the entire range than that for plants grown at present ambient CO2concentration. Lines fitted to the linear part of theA/Cicurves were concurrent at aCiof 49μmol CO2mol−1andA=−1.21μmol CO2m−2s−1. ThisCtvalue is close to Λ*(46 μmol CO2mol−1), the compensation point at 27°C calculated from the equation described in Brooks&Farquhar (1985,Planta165, 397–406). This A is an estimate of respiration in the light (R1) and was not affected by acclimation to elevated CO2. Thylakoid proteins (photo‐system I core protein, D1and D2of the photosystem II core complex, cytochromef) were all reduced by elevated CO2only in the fully mature leaves (31d exposure), whereas the large and small subunits of Rubisco and Rubisco activase proteins had already declined after 22 d exposure. Transcript levels of the plastid‐encoded PAG (rbcL, psbA, psaA‐B) were reduced in the mature leaves by elevated CO2when expressed on a total RNA basis, but they were not sensitive to elevated CO2when expressed on a chloroplast16SrRNA basis. However,rbcS, rcaandcabmRNA transcripts were lower in the plants grown at high CO2than in control plants after 22 d exposure when expressed on a nuclear rRNA basis. The loss of these nuclear PAGs was correlated with an accum

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00185.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThis study was undertaken to determine which of the two NO3−fluxes (influx or efflux) across plasma membranes of root cells is the target of those amino acids which have been shown to inhibit net NO3−uptake (Muller&Touraine 1992,Journal of Experimental Botany43, 617–623). Parallel experiments were performed to mea‐sure either the time course of15NO3−release from roots of soybean seedlings previously labelled with this isotope into non‐labelled solution, or the time course of15N accumulation from labelled15NO3−solution in non‐labelled seedlings. Focusing on the fate of15NO3−in the cytoplasmic compartment, a model is developed to describe the time courses of the accumulation and release of tracer across the plasma membranes of root cells. Both time courses can be described by the sum of an exponential plus a linear term. In our material, the linear part of the accumulation time course is obscured by the NO3−fluxes exiting the cytoplasm, and the curve thus appears to be quasilinear over several minutes. However, we show that the use of the net tracer accumulation rate during this time period as an estimate of NO3−influx does not provide accurate estimates of influx and efflux. By contrast,15NO3−efflux analysis permits calculation of the unidirectional fluxes across plasma membranes of root cells and the kinetic parameters of the cytoplasmic NO3−pool. Under our experimental conditions, efflux accounted for 30 to 50% of influx, and the cytoplasmic NO3−content was found to be in the 70–400nmol g−1fw range. Using this methodology, the effect of amino acid accumulation on unidirectional fluxes of nitrate was then examined. Pretreatments of the seedlings with an amino acid which has been shown to inhibit net NO3−uptake led to concomitant decreases in net accumulation rates of15NO3−and of reduced15N in roots and total15N in cotyledons. NO3−influx was markedly inhibited by these treatments, while NO3−efflux remained essentially unaffected, or even decreased. It is concluded that the target of the regulation of NO3−uptake by phloemtran

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00186.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSignificant differences were observed in the amount and proportion of free amino acids in different organs ofArabidopsis thaliana(L.) Heynh, ecotype Columbia. The most notable were found for proline, which formed 17–26% of the total free amino acid concentration in reproductive tissues (floret and seed), but only 1–3% of the total free amino acid concentration in vegetative tissues (rosette leaf and root). Proline accumulation was associated with tissues that had relatively low water contents. Tissues which displayed high water contents, such as rosette leaves, contained low levels of proline. A significant increase in the levels of proline accumulation occurred in plants subjected to experimentally induced low water potentials as compared to unstressed plants. For instance, an 8–10‐fold increase in proline was observed in the presence of 120 mmol kg−1NaCl or KCl, and a 20‐fold increase was stimulated by 60 mmol kg−1PEG. However, in addition to the accumulation of proline, massive accumulation of Na+, K+and Cl−ions occurred in tissues of plants stressed with salt. No significant differences were observed in mineral ions in plants stressed with PEG. Isotope tracer experiments with14C compounds established that glutamate, ornithine and arginine are precursors of the proline biosynthesis induced by PEG in response to low water potentials inArabidopsis thaliana. We conclude that the accumulation of proline in response to PEG occurs through increas

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00187.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTGas exchange data and images of leaf fluorescence were collected concurrently as stomata responded to abscisic acid (ABA) application. When 10−5kmolm−3ABA was applied to the transpiration stream in a short pulse, stomatal conductance (gs), photosynthesis (A) and intercellular CO2 concentration (Ci) decreased rapidly after a short lag period and became approximately constant after 2h. There was an apparent reduction in the A versus c1 relationship as stomata closed, but the data returned to the A versus C1 curve while stomatal conductance was constant or slowly rising during the second hour after ABA treatment. Larger amounts of ABA administered during the pulse caused larger deviations from the A versus c1 relationship. When 10−7kmolm−3ABA was applied continuously through the transpiration stream, gs, A and Cidecreased, but there was no substantial deviation from the A versus c{ curve. Fluorescence images were patchy as stomata closed for all experiments, but became slowly more uniform during the time that gas exchange was returning to the A versus Cj curve. The distribution of con‐ductance among patches was not bimodal, and larger devi‐ations from the A versus ct curve had greater ranges of pixel values and more pixel values representing low values of Cj during stomatal closure than did experiments show‐ing small or no deviation. Estimates of A and gs from fluo‐rescence images compared favourably with measured val‐ues in most cases, suggesting that the patchy distributions of fluorescence were caused by patchy distributions of stomatal conductance and that apparent reductions in the A versus ct relationship were the result of these patchy stomatai distributions and not direct effects of ABA on mesophyll functioning. The data show that stomatal patches can be temporary and that patchiness may not be reflected in gas exchange data if the range of stomatal con‐ductances is not large. These observations may explain some of the discrepancies among previous studies concerning the effect of ABA on the A ve

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00188.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influence of the 30 kDa movement protein of tobacco mosaic virus (TMV‐MP) on carbon partitioning in trans‐genie tobacco plants (Nicotiana tabacumcv. Xanthi) expressing the TMV‐MP was investigated. Using reciprocal grafting of transgenic tobacco plants expressing this movement protein and vector control plants, as well as transgenic tobacco plants expressing the TMV‐MP in phloem cells only, we showed that the interactive site involved in carbon allocation to roots is localized to the mesophyll tissue. Biomass partitioning experiments conducted on transgenic plants, in which various deletion mutant forms of the TMV‐MP (two of which included deletions in the domain responsible for increasing the size exclusion limit) were expressed, revealed that the TMV‐MP exerts its influence on carbon allocation via a mechanism that is completely independent of the TMV‐MP‐induced increase in the plasmodesmal size exclusion limit. Furthermore, small N‐ and C‐terminal deletions in the MP revealed the complexity of the interactions likely to be involved between the MP and an endogenous regulatory mechanism. We propose that the TMV‐MP interferes with an endogenous signal transduction pathway that involves macromolecular trafficking through plasmodesmata to regulate biomass partitioning between the source and

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00189.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was<0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA3) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00190.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTProton movement across plant cell membranes is part of many important physiological processes. The net proton flux to or from tissues can be determined non‐invasively by measuring the proton electrochemical potential gradient in the adjacent solution. In buffered solution, some of the protons crossing the tissue boundary diffuse as proto‐nated buffer whose flux is not included in the flux calculated from the proton (hydrogen ion) electrochemical gradient. In this theoretical paper, it is shown how experimenters can calculate the protonated buffer flux from the measured proton flux in solution. The ratio of these two components of total proton flux depends on the pH of the solution and on the concentration and pK of the buffer. For a given concentration of a buffer which has a single pK, the flux ratio rises with pH when the solution pH is lower than the buffer pK. The slope is about 2 on a log10scale. As the pH increases above the pK, the flux ratio levels off to approach its maximum. With mixed buffers, or one having two or more pK values, the flux ratios are additive: each buffer acts independently based on its concentration and its pK value. Unbuffered solutions always have the buffering effects of water itself and also of carbonates due to carbon dioxide dissolved from the atmosphere. In unbuffered solutions at pH 6, the flux carried by water and carbonate is about 1 % of the measured proton flux. This validates measurements of proton flux from tissues, made by a number of workers, in unbuffered solutions below p

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00191.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTA study was conducted to examine the hypothesis that the effects of external Al on NO3−uptake and assimilation depend upon the concentration of Al present. Young soybean seedlings [Glycine max(L.) Merrill, cv. Essex], growing under moderate acidity stress at pH 4‐2, were exposed to a range of {A13+} in solution for 3d, and to labelled 99 atom %15NO3−during the final hour of Al exposure. Uptake of15NO3−g−1root dry weight was increased by about 28% in the presence of Al at {A13+} below 10 mmolm−3, and NO3−uptake was decreased by about 12% when the {A13+} increased to 44mmoln−3. The stimulation phase closely paralleled stimulation of root elongation. At higher {A13+}, the inhibition of root elongation was much more severe than that of NO3−uptake. There was no indication of a separate effect of Al on root15NO3−reductionin situ, as the accumulation of reduced15N in the root remained a similar percentage of15NO3−uptake at all {A13+}. At higher {A13+}, the atom %15N enrichment of the insoluble reduced‐N (protein) fraction of root tips increased. This suggests that the Al inhibition of root elongation did not result from disruption of the N

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00192.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTIndirect estimates of leaf area from measurements with three commercially available instruments (DEMON, LAI‐2000 and Sunfleck Ceptometer) were compared with directly measured areas of individualRetama sphaerocarpabushes. The three indirect methods gave good estimates of the total surface area of individual bushes. For the DEMON, the method of log‐linear averaging of transmitted radiation gave estimates closer to directly measured surface area than the method of averaging transmission linearly. For the LAI‐2000, estimated surface area index multiplied by canopy projected area gave the best agreement with directly measured values. For measurements with the Sunfleck Ceptometer, values of surface area estimated from the transmission of photosynthetic quantum flux density, without correcting for diffuse radiation, gave the best agreement with directly measured values. Surface areas estimated by the three instruments were not significantly different from directly measured total (leaf + branch + stem) surface areas. Leaf surface area could be calculated from estimated total surface area minus directly measured branch surface area. Measured branch surface area was linearly related to canopy projected

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00193.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY