摘要:

PRODUCTION OF NATURAL COMPOUNDS BY CELL CULTURE METHODS. Edited by A. W. ALFERMANN and E.TRANSPORT PHENOMENA IN PLANTS. By D. A. BAKER (1978).

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02035.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Many authors have associated chilling injury in plants with changes in the mobility of membrane lipids but have not proposed specific mechanisms for this association.This paper explains how the mobility of membrane lipids can affect membrane thickness, membrane permeability, the electric field, cation concentration and water ordering near a membrane and hence change the conformation (and thus activity) of a membrane‐bound enzyme. The complications in such a model due to protein‐lipid interactions and lateral phase separations are also discus

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02036.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Green plants require a continuous supply of Fe as they grow, because Fe does not not move from the older to the newer leaves. Soils do not lack Feper se, but it may not be available to plants grown in alkaline soils. Plants are classed ‘Fe‐efficient’ if they respond to Fe‐deficiency stress by inducing biochemical reactions that make Fe available in a useful form, and ‘Fe‐inefficienT’ if they do not. Iron uptake induced in response to Fe stress involves release of hydrogen ions and reductants by the root. The lowered pH and presence of reductant at the root zone, along with reduction of Fe3+to Fe2+at the root surface, enables Fe2+to be taken up primarily through the young lateral roots. Ferrous iron is present throughout the protozylem and may or may not have entered the root by a carrier. The root‐absorbed Fe2+is oxidized to Fe3+at the junction of the protoxylem and the metaxylem, chelated by citrate, and then transported in the metaxylem to the plant top. In the plant, the chemical reactions injuced by Fe‐deficiency stress may affect nitrate reductase activity, use of Fe from Fe3+phosphate and chelating agents, and tolerance to heavy metals. An efficient mechanism for Fe uptake in roots appears to be important for the efficient use of

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02037.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The determination of guard cell lumen volume in relation to its geometric characteristic dimensions is presented. Stomatal movements can be divided into two stages:Spannungsphaseand motorphase, with a transition point between them. During theSpannungsphasemovement, the lumen volume increases as a result of the change in its geometric shape. At transition, the lumen volume is approximated by a portion of a circular tube with a rounded cross‐section. The volume increase during the motorphase comes from three different sources: expansion by wall stretching, increasing inner cross‐section of a guard cell by wall thinning, and polar expansion. The relationship between the aperture and the lumen volume is also established. The results set forth in this geometric model are essential to studies of the pressure interaction between a guard cell and its surrounding epidermal ce

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02038.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.A model for the distribution of radiation incident on leaves in an isolated apple tree is presented. The simulated area of shadow cast by a tree compared well with measured values. The radiation model is combined with leaf models of photosynthesis and stomatal behaviour to simulate diurnal variations in the exchanges of carbon dioxide and water by the tree. Satisfactory correspondence was obtained when observed rates of transpiration and photosynthesis were compared with simulations. Further simulations indicated the diurnal patterns of transpiration and photosynthesis to be expected for trees with various shapes and leaf areas.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02039.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The surface electric potential ofVigna sesquipedalisstem, relative to that of the root medium, was most negative in the elongating zone where the difference in pH between parenchyma (P) and xylem sap (X) was at a maximum. The surface electrical potential was found to be determined by the distribution of radial potential difference (Vsxcomprised two components; Vsx=Vpx−Vps.There were two electromotive forces, generatingVpsat the surface of the parenchyma symplast andVpxbetween P and X; both were partially dependent on respiration. The depolarization ofVpxupon removal of O2was maximal in the elongating zone, suggesting that the activity of an H+‐pump extruding protons from the parenchyma into the xylem in exchange for K+was greatest in this z

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02040.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The movement of naturally assimilated14C down the stolon of Saxifraga sarmentosa under the influence of localized cold treatments (0°‐10°C) applied over lengths up to 10 cm was followed by finding the distribution of tracer at the termination of the experiment. Inhibition is slight at 10°C and very considerable at 0°C. It is very dependent on the length treated, but is definite even when this is only 0.8 cm. Cooling the daughter plantlet to 0°C has a smaller inhibitory effect than might be expected. This is difficult to understand if ‘unloading’ is metabolic; perhaps the concentration free energy of the sucrose or other solute can be utilized in the sink terminals on the lines of the chemi‐osmotic hypothesis. If so the same source of non‐respiratory free energy might be available to energize an active sieve‐tube mechanism in mid‐path ch

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02041.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.An investigation of the uptake of Cd by intact wheat plants has been carried out. The accumulation of Cd in the roots as a function of time and external Cd concentration was determined. Since the transport of Cd to the grains and shoots was found to be small, only uptake into the root was examined further. An appreciable fraction of the Cd absorbed by the roots can be desorbed and consequently constitutes the freely diffusible and exchangeable fraction.The effect of temperature and of metabolic inhibitors on the absorption provides evidence that another Cd fraction is taken up by metabolically mediated processes. The absorption of this Cd fraction was found to be inhibited by Cu and Zn. The inhibitory effect of Cu and Zn on Cd absorption was comparable.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02042.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Uptake of [14C] glutamine into isolated pea chloroplasts has been examined by using a centrifugal filtration technique. Competition experiments showed that glutamine uptake is mediated by a dicarboxylate carrier with Km1.10 mM andVmax. 118 nmol of glutamine min−1per mg of chlorophyll. Isolated pea chloroplasts accumulated glutamine in the sucrose‐impermeable space to concentrations higher than that present in the external solution when the latter was below 0.5 mM. It is suggested that glutamine accumulation is driven by exchange (utilizing the dicarboxylate carrier) with the endogenous pool of dicarboxylates in the chloroplasts. Increasing pH stimulated glutamine uptake but inhibited that of glutamate and 2‐oxoglu‐tarate. The hypothesis is advanced that when molecules of different charge are exchanged across the chloroplast envelope via thedicarboxylatecarrier, electroneutrality is maintained by transport of protons, and that this explains the observed effects of increasing pH. The low rates of glutamine transport coupled with the strong competition of other dicarboxylates for the carrier suggest that export invivofrom the chloroplast of nitrogen in the form of glutamine is not of major imp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02043.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Uptake of [14C] adenine and [14C] cytosine into isolated pea chloroplasts has been examined by using a centrifugal‐filtration technique. These chloroplasts accumulate both compounds in the sucrose‐impermeable space to concentrations higher than that present in the external solution when the latter was below 1.0 mM. Competition experiments suggested that uptake is mediated by a carrier mechan

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1978.tb02044.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY