摘要:

Abstract.The changes in the distribution of dissolved inorganic carbon systems resulting from biological activity are described using the dissociation equations and considering eight variables: the concentrations or activities of H+, OH−, CO2, H2CO3, HCO3−, CO32−, total carbon ∑CO2, carbonate alkalinity A−and base excess B+. Equations for the equilibrium constantsK1,K2andK3, giving their dependence on temperature, are provided. These thermodynamic constants are defined on the infinite dilution scale and their dependence on the pH‐convention adopted is stressed. From the dissociation equations and the eleclroneutrality condition a set of 15 equations were deduced, each representing the relationship between the H+‐activity and one pair of the other variables. The knowledge of two variables will, therefore, enable the calculation of all the other variables, furnishing a complete description of the C‐system. Such a description is needed to permit the calculation of the ionic strength (I) of a solution. Knowing I makes it possible to calculate the activity‐coefficients for bicarbonate and carbonate ions (Debye‐Hueckel equations), which are needed to calculate the working constants K1and K2from the thermodynamic ones. Hints for computer programs, some of them including iterative subroutines, are given. Suggestions are made for the experimental determination of K1and K2. The discussions arc restricted to dilute solutions isolated from a gaseous phase, at 1 atm, external pressure and having an ionic strength of not more than 70 mol m−3. The difficulty of providing causal explanations in studies involving the C‐syst

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01140.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.The kinetics ofin vivochlorophyll fluorescence of photosystem II (PS II) was measured at room temperature and 77 K during frost hardening of seedlings of Scots pine (Pinus sylvestrisL.), and after exposure of frost‐hardened shoots to sub‐freezing temperatures.A more pronounced decrease in variable fluorescence yield for the upper exposed than for the lower shaded surface of the needles suggested that some photoinhibition occurred during prolonged frost hardening at 50 μmol photons m−2s−1and 4°C.Reversible inhibition of photosynthesis after exposure to sub‐freezing temperatures was initially manifested as an increase of steady‐state energy‐dependent fluorescence quenching (qE) and a reduction in the rate of O2evolution. Further inhibition after treatment at still lower temperatures caused a progressive decline of steady‐state photochemical quenching (qQ) and the rate of O2evolution, whereas qEremained high. This implies an inactivation of enzymes in the photosynthetic carbon reduction cycle decreasing the consumption of ATP and NADPH, which is likely to cause an increase of membrane energization and a reduction of the primary electron acceptor (QA) of PS II. Alternatively, the changes in qQand qEmight be attributed to an inhibition of photophosphorylation. Severe, irreversible damage to photosynthesis resulted in a suppression of qEand of variable fluorescence yield, probably because the photochemical efficiency of PS II was impaired.Changes in the fast fluorescence kinetics at room temperature after severe freezing damage were interpreted as an inhibition of the electron flow from QAto the plastoquinone pool. It is suggested that irreversible freezing injury to needles of frost‐hardenedP. sylvestriscauses damage

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01141.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Plantago maritimaL. was grown at three levels of salinity, 50, 200, 350 mol m−3NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m−3NaCl was only 20% of that in plants at low salinity. Both the Na+and K+content of leaves and roots increased with external salinity. There was no change in the Na+/K+ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na+ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO2and by ribulose‐1,5‐bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO2concentration. The increased stomatal limitation of photosynthesis resulted in higher water‐use efficiency of plants grown at high

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01142.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Xylem vessels in the apical 25 cm of barley seminal axes were examined by scanning electron microscopy of fractured freeze dried or critical point dried specimens. In the apical 11 cm, there were three cross walls cm−1root in the central xylem vessel. The frequency then declined with distance but did not become less than 1.0 cm−1root until the 22–25‐cm zone.Suction was applied to the proximal end of segments of seminal axes whose surfaces had been sealed with wax to prevent radial entry of water. Perfusion of the xylem with solutions of Tinopal CBS‐X revealed the conductive xylem vessels by fluorescent staining of their walls. In the apical 20 cm of the axis, only a variable number of smaller xylem vessels conduct water. Beyond this zone, the much larger central vessel becomes functional.The flow of water (Jv) in the apical zone was very much less for a given presure (△P) than in the proximal zone>25 cm from the tip, and could be predicted by the Poiseuille equation provided the correct number of functional vessels are known. This information, together with earlier results on water uptake along the root length are used to predict the attenuation of the hydrostatic driving force for water uptake along the root length.Estimates of K+concentrations in stelar parenchyma and xylem vessels were made by electron microproble X‐ray analysis. These results show that [K+] in the xylem vessels may be two to three times greater in the zone 1–2 cm from the root tip than in the basal zone. Such a gradient of solute potential may, to some extent, offset the decreasing influence of the leaf water potential in apical zones where xylem is not f

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01143.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Measurement of light within 10–14‐d‐old green and etiolatedCucurbita pepocotyledons were made with fibre‐optic microprobes to assess the influence of chlorophyll distribution and anatomical variations in mesophyll cell type (spongy versus palisade) on internal light pattern. More than 50% of the pigment in green cotyledons occurred in the upper (adaxial) 300 μm and this gradient strongly influenced the internal propagation of 680 nm light. When the upper (adaxial) surface was irradiated with 680 nm light, almost complete absorption occurred within the first 400 μm (palisade) of approximately 1200‐μm‐thick cotyledons. In contrast, when lower (abaxial) surfaces were irradiated with 680 nm light, penetration extended throughout the spongy mesophyll to about the 700 μm depth. Measurements of collimaled and scattered light gradients at 550, 680 and 750 nm indicated that collimaled light was rapidly scattered by mesophyll cells. In cotyledons irradiated on the upper surface, spongy mesophyll cells received only scattered light. Furthermore, comparisons of scattered light gradients obtained from cotyledons irradiated on upper and lower surfaces suggested that spongy mesophyll cells scatter light more effectively than palisade cells, probably due to the greater proportion of intercellular air spaces in spongy mesophyll tissue. These data also indicate that both the spectral quality and quantity of light incident on palisade versus spongy mesophyll cells differs, perhaps contributing to developmental and physiological differences between these two mesop

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01144.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Ripening tomato fruits incubated at 35°C fail to achieve normal pigmentation, soften little and show a marked decline in ethylene evolution. Labelling studiesin vivoindicate that protein synthesis continues throughout incubation at 35°C although the spectrum of labelled proteins is different to that observed at 25°C. Translation of mRNAsin vitroshows traces of several ‘heat‐shock’ mRNAs at 35°C and the loss of several others normally found in fruit ripened at 25°C. Using ripening‐related cDNA clones as hybridization probes the expression of 12 ripening‐related genes was followed during incubation at 25°C and 35°C. In general, there was a marked decline in the amounts of these mRNAs following incubation of ripening fruit at 35°C. In particular, mRNA homologous to pTOM 6, a cDNA clone coding for polygalacturonase, a major cell wall degrading enzyme, showed a rapid decline following incubation at 35°C and after 72‐h at elevated temperature was undetectable. There was no recovery of expression during 120 h at 35°C and the application of exogenous ethylene did not overcome the inhibition of ripening or lead to the renewed accumulation of polygalacturonase mRNA. It is proposed that the failure to soften normally at elevated temperature is due, in part, to the suppression of polygalacturonase mRNA and that the inhibition of other facets of ripening at 35°C is due to the inhibition or reduced expression of other, as yet unidentified,

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01145.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Pollen development in copper‐deficient barley plants is highly irregular resulting in low and variable pollen fertility. The main cause of this sterility was found to be the abnormal development of the tapetum which becomes expansionary and invasive as the pollen develops. The ultrastructure of both tapetum and microspores is different from that of control material with irregularities of exine deposition, endopolyploidy of tapetal nuclei and an alteration of organelle composition being correlated with low fertilit

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01146.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na+and Cl−in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K+and NO3−, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m−3, respectively. There was no preferential direction of Na+or Cl−to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na+and Cl−, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m−3NaCl rapidly developed injury of oldest leaves; when this occurred, the Na+concentration in the leaflet midrib sap had increased to about 40 mol m−3and the total solute concentration to 130 osmol m−3. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building u

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01147.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract.Phloem sap was collected from petioles of growing and fully expanded leaves of lupins exposed to 0–150 mol m−3[NaCl]ext, for various periods of time. Sap bled from growing leaves only after the turgor of the shoot was raised by applying pneumatic pressure to the root. Increased pressure was also needed to obtain sap from fully expanded leaves of plants at high [NaCl]ext. Exposure to NaCl caused a rapid rise in the Na+concentration in phloem sap to high levels. The Na+concentration reached 20 mol m−3within a day of exposure and reached a plateau of about 60 mol m−3in plants at 50–150 mol m−3[NaCl]ext, after a week. There was a slower, smaller increase in the Cl−concentration. K+concentrations in phloem sap were not affected by [NaCl]ext. Cl−concentrations in phloem sap collected from growing leaves were similar to those from old leaves while Na+concentrations were somewhat increased, suggesting that there was no reduction in the salt content of the phloem sap while it flowed within the shoot to the apex. Calculations of ion fluxes in xylem and phloem sap indicated that Na+and Cl−fluxes in the phloem from leaves of plants at high NaCl could be equal to those in the xylem. This prediction was borne out by observations that Na+and Cl−concentrations in recently expanded leave

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01148.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Books reviewed in this article:THE EVOLUTION OF SEX AND ITS CONSEQUENCES.Edited by S. C. SsctearnsOXFORD SURVEYS OF PLANT MOLECULAR AND CELL BIOLOGY, VOLUME 3. Edited by B. J. Miflin

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01149.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY