摘要:

AbstractPredicted values of photoequilibrium ratios and rates of photoconversion and cycling, calculated from known optical parameters of purified phytochrome and the spectral photon flux distribution of the light sources used, arc often applied in the evaluation of the relationships between the state of phytochrome and the expression of phytochrome‐mediated responses. This is commonly done when the state of phytochromein vivocannot be determined experimentally. The ‘predicted’ states of phytochrome may be quite different from the actual onesin vivofor several reasons: the particular set of optical parameters of purified phytochrome used in the calculations and the difficulties encountered in correcting the predicted values for the contribution of the non‐photochemical reactions (dark reversion, destruction, synthesis), the effects of the optical properties of the tissue (light attenuation, scattering, trapping) on the rate of phytochrome photo‐conversion, and the geometrical relationships between irradiated sample and the light source. At present, in many studies, it is not possible to avoid using predicted values of the state of phytochrome. The limitations imposed by the use of ‘predicted’ values in the interpretation of results obtained in plant photomorphogenesis research should be always c

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01780.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA compilation of existing data on higher plant responses to heat‐shock temperatures has been utilized to produce a biochemically based model of integrated cellular responses to elevated temperatures. This model describes a potential mechanism for the triggering of several biochemical responses to a thermally induced leakage of extracellular or vacuolar ions into the cytoplasm. It seems possible that many of the observed heat‐shock responses are involved in the protection of (a) enzymes from inactivation and (b) nucleic acids from cleavage induced by the presence of elevated levels of specific met

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01781.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA reappraisal is offered of old and new observations of substantial day‐night changes of citric‐acid levels in crassulacean acid metabolism (CAM). In contrast to malic acid, the biochemical consequences and the ecophysiological significance of nocturnal accumulation of citric acid in CAM have not received due attention. Considerations show that citric‐acid accumulation does not provide a means for nocturnal storage of CO2. It may, however, serve carbon retention by internal recycling and sustain the water budget affording a vacuolar osmoticum. Since citric‐acid accumulation energetically is considerably more favourable than malic‐acid accumulation, this may have important ecophysiological implications. The questions raised by these reflections can and need to be tackled exper

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01782.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effects of sodium chloride on water‐use efficiency of a number of varieties of rice have been investigated. Sensitivity to salinity in rice arises in large part from excessive rates of sodium ion transport to the shoot consequent upon high rates of transpirational water loss. Varietal differences in water‐use efficiency were found: these were greater when measured for whole shoots over a period of one week, than when made as instantaneous measurements on individual leaves. Salinity had rather little effect on water use efficiency but overall resistance of seedlings to salt was, in general, greater the greater the water‐use efficiency. The reasons for the differences between varieties are discussed in terms of differences in growth pattern: among the seven varieties investigated, water‐use efficiency and salt‐resistance were lower in dwarfed as opposed to non‐dwarfe

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01783.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe comparative Na+tolerance ofChora buckelliicultured in freshwater (FW) or artificial Waldsea water (AWW, which contains about 110 mol m−3each Na+, Mg2+, Cl−and SO2‐4was tested with respect to the external Na+to Ca2+ratio (Na: Ca). Fifty per cent of FW cells subjected to 70 mol m−3NaCl, which raised Na:Ca from 10: 1 to 700: 1 and the external osmotic pressure from 0.024 to 0.402 MPa, died within 6 d. Death was associated with the loss of Na/K selectivity, H+‐pump activity and turgor. Restoration of Na:Ca to 10:1 in high Na+medium with CaCl2ensured 100% survival and maintained H+‐pump activity and Na/K selectivity of FW cells. Turgor was regulated within 3 d with net uptake of Na+, K+and Cl−in the vacuolc. Mg2+was not as effective as Ca2+in enhancing survival or maintaining H+‐pump activity and Na/K selectivity of FW cells in the presence of elevated Na+. However, turgor was regulated within 3 d by accumulation of Cl−and an unknown cation in the vacuole. All AWW cells subjected to an increase of 70 mol m−3NaCl, which raised Na: Ca from 16:1 to 25: 1 and the external osmotic pressure from 0.915 to 1.22 MPa, survived and maintained H+‐pump activity. Turgor was regulated within 6d by accumulating Na+, K+and Cl−in the vacuole. All AWW cells subjected to 70molm−3NaCl in a medium in which Na:Ca was equal to 700:1 survived and maintained H+‐pump activity, but showed loss of Na/K selectivity. Turgor was regulated with an unkn

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01784.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe freshwater CharophyteChora corallinadies when subjected to 70 molm−3NaCl if the Ca2+concentration is 0.1 mol m−3. This stress is accompanied by a depolarization of the cell to a membrane potential more positive than EK, a net influx of Na+into the vacuole, and a net loss of K+from the vacuole. Raising the Ca2+concentration to 7 mol m−3in the presence of elevated Na+restores the Na+to Ca2+ratio to 10: 1 as in the control solution, and results in enhanced survival even though turgor is not regulated. Mg2+is not a good substitute for Ca2+. It is suggested that the main reason thatC. corallinafails to occupy saline habitats is its failure to regulate turgor, not sensitivity to Na+, since the latter is similar to that seen inC. buckellii, which is found in saline hab

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01785.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractPreviously, accumulation of a 31‐kDa polypeptide had been observed in the light‐harvesting apparatus of thylakoids of maize leaves exposed to 5°C and high light (Haydenet al., 1986). The accumulation and disappearance of this 31‐kDa polypeptide in thylakoids of maize leaves are examined as a function of photon flux density and temperature. The accumulation of large amounts of the polypeptide at 5°C was light‐dependent during a 6‐h chill period, with 50% of maximal accumulation occurring at a photon flux density of 60 μmol m−2s−1.Some polypeptide accumulation did occur in leaves kept in the dark at 5°C for 6 h, i.e. ca. 18% of that accumulating at a photon flux density of 1500 μmol m−2s−1. The temperature optimum for polypeptide accumulation was ca. 9°C with greater than 50% of maximal accumulation being achieved between 5 and 11°C. The breakdown of maximally accumulated polypeptide on returning leaves to 25°C was complete after 1 h, had a half‐time of ca. 20 min and was independent of light. Breakdown of the polypeptide was also observed when thylakoids isolated from chilled leaves were incubated at 25°C. Reductions of thylakoid incubation temperature between 13 and 5°C markedly reduced the rate of polypeptide disappearance. The accumulation of the polypeptide is discussed in relation to temperature and light effects on the rate of the polypeptide synthesis and of peptidase activities. The results are also discussed in the context of accumulation of the polypeptide in maize leaves in the field and consideration is given to the possib

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01786.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo monoclonal antibodies (AFRC MAC 184 and 185) have been raised in rats against a synthetic octadecapeptide corresponding to the N‐terminus ofAvenaphytochrome. The peptide was conjugated to tuberculin purified protein derivative (PPD) for immunization and the cell lines screened by ELISA using the free peptide. Both antibodies bind to intact 124‐kDa phytochrome on Western blots and in a double antibody sandwich ELISA. In the ELISA, they have an approximately four‐fold higher affinity for Pr than Pfr. Conformational changes during photoconversion, therefore, involve the extreme N‐terminus of the phytochrome m

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01787.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractPotassium (86Rb) influx from 200 mmol m−3KCl into dark grown, decapitated maize seedlings 6 d old) was stimulated by nitrate pretreatment. The stimulus was clearly evident by 6h exposure to nitrate and required 12–24 h for maximal expression. Decay of the nitrate‐stimulated potassium influx was more than 50% complete within 3 h after transfer to nitrogen‐free solutions. The stimulation of potassium influx was entirely accounted for by an increase in the influx component that was resistant to inhibition by presence of 200 mmol m−3ambient ammonium. In contrast, the component of potassium influx that was sensitive to inhibition by ambient ammonium was unaffected by nitrate pretreatment. Exposure to the glutamine synthetase inhibitor L‐methionine‐dl‐sulphoximine (MSX) during nitrate pretreatment stimulated the resistant component but the sensitive component was nearly eliminated. Pretreatment with ammonium increased the resistant component of potassium influx within 3 h, i.e. before it was increased by nitrate pretreatment, but the sensitive component was concomitantly restricted. The latter recovered partially during extended pretreatment with ammonium. The data indicate that the resistant component responded positively to increases in tissue ammonium concentrations whereas the sensitive component was unaffected by tissue ammonium except at concentrations in excess of 10μmol g−1. Ammonium influx was also stimulated by nitrate pretreatment and to a greater extent than potassium influx. Presence of MSX with nitrate during pretreatment resulted in a further stimulation in ammonium influx. The parallel increases in root ammonium concentrations with the two pretreatments imply that part of the increase in ammonium influx was a consequnce of increased counter‐transport with

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01788.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractProtein synthesis during seed germination, a stage vulnerable to salinity stress, was investigated. The responses of barley genotypes, CM72 (California Mariout 72) and Prato, toward salinity were different during seed germination. Germination of CM72 was unaffected up to 0.34 kmol m−3(2%) NaCl, but that of Prato was reduced 30% by 0.17 kmol m3NaCl and 75% by 0.34 kmol m−3NaCl. Therefore, the former genotype is relatively more salt‐tolerant than the latter. Protein synthesis in roots, shoots, and embryos was investigated in these two genotypes before and after salinity stress. The uptake of S‐methionine and its incorporation into protein were significantly reduced by salinity in both genotypes. The inhibition of global protein synthesis was significant in roots and shoots. Proteins from different tissues were resolved by single and two dimensional gels. The steady‐state protein levels were maintained remarkably well during salinity stress in roots and shoots. Likewise, proteins in germinating embryos were stable except for a 42‐kilodalton protein unique to the salt tolerant genotype which was apparently degraded during salinity stress. Salinity, around 0.34 kmol m−3NaCl, induced both quantitative and qualitative changes in the expression of some proteins labelledin vivo.The quantitative changes included repression or enhancement of synthesis of selected groups of proteins. Around 8% of the nearly 400 resolved proteins in a tissue was affected this way. Some of the proteins in this category were specific to each genotype. About 1 % of the total showed qualitative changes; these proteins were expressed only during salinity stress. In roots, two proteins (28, 41.7 kilodaltons) were detected in CM72 and five (28, 45, 60.5, 76.5, 82.5 kilodaltons) in Prato; only the 28‐kilodalton protein was common to both genotypes. In shoots, four proteins (45, 60.5, 76.5, 82.5 kilodaltons) were found only in Prato and these were similar to those induced in roots. The four new proteins (32, 37.5, 89, 92 kilodaltons) in germinating embryos were apparently induced only in CM72; these were distinctly different from those detected in developed roots and shoots. The unique protein changes induced by salinity stress during germination (this study) and seedling growth studies reported earlier (Ramagopal, 1987b) are apparently different. The findings demonstrate that ontogeny plays an important role in the expression of tissue‐specific proteins during salinity stress in the salt tolerant and sensitive

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01789.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY