摘要:

Abstract.The present investigations were designed to identify proton pumps in seed coats ofPhaseolus vulgarisL. Vacated seed‐coat halves were exposed to bathing solutions with indicators for proton pump action and the pH changes in the media were measured. Fusicoccin increased the rate of proton extrusion from the seed coats. Orthovanadate and abscisic acid retarded the proton extrusion evoked by fusicoccin. Abolition of the proton extrusion by parachloromercuriphenylsulphonic acid was partially reversed by diethioerythritol. The extrusion was stimulated by high osmolarities (100 mol m−3sorbitol), potassium ions (100 mol m−3KCI) and light. Old seed coatsreactedmore rapidly to fusicoccin treatments than young ones. Proton pumping in seed coats and cotyledons showed differential responses to fusicoccin, K+and sucrose. In contrast to seed coats, medium acidification by cotyledons was prohibited by addition of sucrose. The significance of proton pumps for photosynthate transferin vivois disc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01203.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.This is a physical analysis of water movement in wheat (Triticum) and tall fescue (Festuca arundinacea) leaves placed in the Scholander pressure chamber. It takes into account the efflux resistances of water movement through the xylem and water flow across the cell membranes. Xylem resistance was estimated using Poiseuille's law.Leaves which had been pressurized in the chamber were embedded, sectioned, examined under a light microscope and photographed. Cells were intact but distorted and xylem vessels were intact. Cells in portions of the blade squeezed by the chamber sealing grommet were crushed, but xylem vessels remained intact.By applying pressure several tenths of a megapascal in excess of the balance pressure, water was forced from each leaf through the severed end which protruded from the chamber. Efflux curves were drawn by plotting the total water expressed as a function of time after the pressure increase. Water efflux from the shortest wheat leaf lasted only 10 min while efflux from the longest continued for up to 40 min. The efflux from a tall fescue leaf which was rehydrated and cut to a shorter length was much more rapid than efflux from the original leaf.Experiments combined with mathematical analysis suggested that the effect of leaf length on efflux is related to a high resistance to water flow through vascular bundles. Xylem resistance would be sufficient to produce this effect if it were 10 times greater than that predicted by Poiseuille's law. Both the observations of water flow from the cut end of the leaf and the mathematical model suggested very little water flows from bundles with vessels of diameter less than 12 μm. The apparent explanation is high resistance to water flow through these small diameter vessels

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Hypericin, a photodynamic pigment, occurring in members of the Hypericaceae, can induce photosensitivity in grazing animals. The pigment has been isolated from the glandular trichomes located on the calyx ofHypericum hirsulum.Hypericin is shown to be capable of sensitizing the photo‐oxidation of methyl linolenate. This activity is reduced in the presence of crocin, a carotenoid. Evidence for the generation of singlet molecular oxygen by hypericin is provided by the monitoring of oxygen consumption during the photosensitized oxidation of imidazole. Rates of oxygen consumption were modified by deuterium oxide and sodium azide. The photodynamic action of hypericin on pea leaf discs results in the promotion of photo‐oxidative damage, measured by pigment loss and ethane production. These results are discussed in relation to the possible function of hypericin within the plant and the role of photo‐dynamic reactions in n

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01204.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.This paper describes the effect of prolonged treatments with red or blue light on the capacity of the milo (Sorghum vulgarePers.) shoot to respond to Pfr in subsequent darkness. Two groups of enzymes were studied. In group I (NADP‐dependent glyceraldehyde‐3‐phosphate dehydrogenase, NADP‐GPD. EC 1.2.1.13 and ribulose‐bisphosphate carboxylase, carboxylase, EC 4.1.1.39) enzyme formation is strongly enhanced by red light pulses (operating through phytochrome) whereas in group II (NAD‐dependent glyceraldehyde‐3‐phosphate dehydrogenase, NAD‐GPD, EC 1.2.1.12 and NAD‐dependent malate dehydrogenase, MDH. EC 1.1.1.37) enzyme formation hardly responds to red light pulses.In group 1 a 24‐h treatment with blue light (but not with red light) leads to a strong increase in responsivity to Pfr whereas in group II a 24‐h treatment with blue or red light does not increase responsivity to Pfr in subsequent darkness.The specific effect of blue light cannot be explained by an effect of light on gross protein synthesis. Rather, the data indicate that amplification of responsivity to Pfr by blue light is a specific process directly related to the mechanism of modulation of gene ex

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01205.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.The effect of chlorophyll fluoresence on the spectral light gradients within a model green leaf was examined under different light qualities (day‐light, sunset, canopy) and different quantum efficiencies. Light fluxes within the leaf tissue are nearly doubled in the emission domain of fluorescence but the effect on the phytochrome photoequilibrium is very smal

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01206.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Chlorophyll fluorescence emission spectra and the kinetics of 685 mm fluorescence emission from wheat leaf tissue and thylakoids isolated from such tissue were examined as a function of excitation wavelength. A considerable enhancement of fluorescence emission above 700 nm relative to that at 685 nm was observed from leaf tissue when it was excited with 550 nm rather than 450 nm radiation. Such excitation wavelength dependent changes in the emission spectrum occurred over an excitation spectral range of 440–660 nm and appeared to be directly related to the total quantity of radiation absorbed at a given excitation wavelength. Experiments with isolated thylakoid preparations demonstrated that changes in the fluorescence emission spectrum of the leaf were attributable to the optical properties of the leaf and were not due to the intrinsic characteristies of the thylakoid photochemical apparatus. This was not the case for the observed excitation wavelength dependent changes in the 685 nm fluorescence induction curve obtained from leaf tissue infiltrated with DCMU. Excitation wavelength dependent changes in the ratio of the variable to maximal fluorescence emission and the shape of the variable fluorescence induction were observed for leaf tissue. Isolated thylakoid studies showed that such changes in the leaf fluorescence kinetics were representative of the way in which the photochemical apparatusin vivowas processing the absorbed radiation at the different excitation wavelengths. The results are considered in the context of the use of fluorescence emission characteristics of leaves as non‐destructive probes of the photochemical apparatusin v

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01207.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Pressure—volume (P—V) curves were generated on roots and shoots of coastal Douglas fir [Pseudotsuga menziesii(Mirb.) Franco] seedlings using two procedures. In the first (Method A), samples were dehydrated inside a pressure chamber. Exuded stem sap was collected and weighed at successive pressure increases to derive the P—V curve. In the second method (Method B). excised samples were allowed to dry outside the pressure chamber by evapotranspiration. They were weighed periodically to determine sap loss and their corresponding balance pressures were determined in a pressure chamber in order to derive the P—V curve.Estimates of volume averaged osmotic potential at full turgor and water potential at zero turgor which were derived graphically from the P—V curves, were different for each method. In general, estimates were more negative in Method A, by as much as 1.5 MPa in one case. Also, Method B did not record an osmotic adjustment in seedlings which were subjected to severe water stress while Met

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01208.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Leaf conductance responses to leaf to air water vapour partial pressure difference (VPD) have been measured at air speeds of 0.5 and 3.0 ms−1in single attached leaves of three species in order to test the hypothesis that leaf conductance response to VPD is controlled by evaporation from the outer surface of the epidermis, rather than by evaporation through stomata. Total conductance decreased linearly with increassing VPD at both air speeds, but was decreased 1.6 3.0 times as much as by a given incrase in VPD at high than at low air speed. depending on species. In all species the relationship between leaf conductance and the gradient for evaporation from the epidermis was the same at both values of boundary layer conductance, supporting the hypothesis that direct epidermal evaporation controls stomatal guard cell behaviour in responses of stomata to VPD in these specie

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01209.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Apical 3‐cm root segments excised from 2‐d‐old squash seedlings (Cucurbita pepoL. cv. Early Prolific Straightneck) that were germinated and grown between sheets of paper towelling moistened with H2O2incorporated 144±10 nmol (± SE.n= 15) NaH14CO3into uridine nucleotides (∑UMP) per gram intact roots during the 3‐h incubation period (Lovatt, Albert&Tremblay, 1979). Continued culture of squash seedlings in this manner for an additional 24 or 48 h had no effect or slightly increased (30%) the activity of the orotic acid pathway. However, transfer of 2‐d‐old seedlings to Shive's nutrient solution reduced the activity of the orotic acid pathway within 15 h to 2.3 nmol NaH14CO3incorporated into ∑UMP per gram apical 3‐cm root segments during the 3‐h incubation period. The observed decrease in capacity to synthesize pyrimidine nuclotidesde novoparalleled the reduction in glucose content of the roots and was reversed by supplying glucose during hydroponic culture in Shive's nutrient solution. Root elongation was not affected by the reduced activity of the orotic acid pathway nor by the decreased level

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01210.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Mitochondrial ultrastructure in the cells of coleoptiles of 4 d seedlings was investigated under conditions of a 1.5, 3, and 36 h anoxia and with subsequent transfer of the seedlings, after a 1.5 h anoxia, from the anaerobic into an aerobic medium. Even with short‐term anoxia (1.5 h) destructive changes take place in the ultrastructure of mitochondria, which are reversible not only following the transfer of these seedlings from the anaerobic into aerobic conditions, but also with their continued maintenance under strict anoxia. Irreversible changes in the ultrastructure of mitochondria were seen only with a more prologed (36 h and longer) anoxia. The observed phenomena are discussed from the viewpoint of energy provision of the seedling cells in anoxia and post‐ano

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1985.tb01211.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY