摘要:

AbstractA new experimental method is used to determine simultaneously the quantity and composition of the sap exuded by a detopped root system at the same time that a pressure deficit of desired magnitude can be applied to the stem stump.The technique was used in a study of the transport of radioactive sulfate through the roots of young sunflower plants placed on complete nutrient solutions labelled with35S.The complications by the time factor on the composition and rate of the sap stream in experiments of this type were observed and discussed. The time of detopping the roots was very critical as the conditions of sulfate transport were greatly changed some time after the excision.A rectilinear connection existed between the rate of sulfate transport in the sap and the water flow at sap flow velocities comparable with transpiration rates. When the transport of water was very slow, the rate of sulfate transport became constant and independent of the water stream. It was suggested that diffusion or water flow could act as motive force for the ion transport in some non‐metabolic phase of transfer in the roots. The addition of 2,4‐DNP to the test solution severely interfered with the water and sulfate transport conditions in the ro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07044.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe sudden changes in the rates of transpiration and water uptake which occurred when the osmotic potential of the nutrient solution surrounding the roots of young wheat plants was rapidly changed were studied. The transpiration was measured by the aid of the microwave hygrometer and the water uptake by a recording poto‐meter specially built for this investigation.When the osmotic potential of the nutrient solution was rapidly increased by adding mannitol, there was a temporary transpiration increase. The maximum increase was greater but the total time of the temporary increase shorter when a higher mannitol concentration was used. The quantity of water transpired by the shoots due to the temporary transpiration increase seemed to be fairly constant irrespectively of the mannitol concentration. The water transport to the shoots was immediately reduced when the osmotic potential was rapidly increased. The immediate reduction was greater when a higher mannitol concentration was used. After the immediate reduction the rate of water transport increased without delay.When the osmotic potential of the nutrient solution was rapidly decreased by withdrawing mannitol there was a temporary transpiration decrease, and the water transport to the shoots was immediately increased. After this increase the rate of water transport started to decrease at once. When, however, the mannitol concentration had been 0.30Mor higher, the transpiration rate increased progressively, and the change of the rate of water transport was small.The results indicate that the primary effect of the rapidly changed osmotic potential is localized to the root surface. The rapidly reduced water transport to the shoots after adding mannitol brings about the temporary transpiration increase. The course of events after withdrawing mannitol is just the reverse to that when adding mannito

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07045.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe influence of oxygen concentration in the range 0–21% on photosynthesis in intact leaves of a number of higher plants has been investigated.Photosynthetic Co2fixation of higher plants is markedly inhibited by oxygen in concentrations down to less than 2%. The inhibition increases with oxygen concentration and is about 30% in an atmosphere of 21% O2and 0.03% Co.2. Undoubtedly, therefore, oxygen in normal air exerts a strong inhibitory effect on photosynthetic Co2fixation of land plants under natural conditions.The inhibitory effect of oxygen is rapidly produced and fully reversible.The degree of inhibition is independent of light intensity.The quantum yield for Co2fixation,i.e. the slope of the linear part of the curve for Co2uptakeversusabsorbed quanta, is inhibited to the same degree as the light saturated rate at all oxygen concentrations studied.Diverse species of higher plants, varying greatly in photosynthetic response to light intensity and Co2concentration, and with light saturated roles of Co2fixation differing by a factor of more than 10 times, show a remarkable similarity in their response to oxygen concentration. By contrast, when studied under the same conditions as the higher plants, the green algaeChlorellaandUlvadid not show‐any measurable inhibition of photosynthetic Co2fixation. Similarity, the increase in fluorescence intensity with increasing oxygen concentrations found in higher plants also was not seen inChlorella. The present results, together with previous data on the photosynthetic response of algae to oxygen concentration, indicate that the photosynthetic apparatus of higher plants differs considerably from that of algae in its sensitivity to oxygen.The inhibitory effect of oxygen on photosynthetic Co2fixation in higher plants is somewhat higher at wavelengths which excite preferentially photosystem I. Also, the Emerson enhancement of Co2fixation measured when a far red beam of low intensity is imposed on a background of red light is greater under low oxygen concontrution than under air. Measurements of reversible light‐induced absorbance changes reveal that the change at 591 nm, probably caused by pla.stocyanin, is affected by oxygen concentration only if photosystem II is excited. the reducing effect on plastocyanin, caused by excitation of this system, decreases with increasing oxygen concentration. From these results it is suggested that a possible site of the inhibition by oxygen is in the electron carrier chain between the two photosystems. Oxygen might act as an electron acceptor at this site, causing reducing power to react back with molecular oxygen. However, this hypothesis does not account for equal inhibitions of the quantum yield and the light saturated rate of photosynthetic CO2uptake.Through the photosynthetic process plants take up carbon dioxide and evolve oxygen. The present high concentration of molecular oxygen in the atmosphere is generally considered to have arisen from the activity of photo‐synthetic organisms. The effect of oxygen concentration would seem, therefore, to he a problem of great interest, not only in the field of the biophysics and biochemistry of photosynthesis, but in ecology and other branches of biology as well.It was discovered by Warburg (1920) that high concentrations of oxygen inhibit the rate of photosynthetic oxygen evolution in the unicellular algaChlorella. Since then, it has been confirmed by various authors that oxygen cconcentrations in the range 21–100 per cent have a marked inhibitory effect on photosynthesis, particularly at saturating light intensities. There is some evidence that under conditions when carbon dioxide concentration limits photosynthesis, the inhibition may become obvious even in 21 per cent oxygen. The inhibition has not been considered to operate at low light intensities. A review on the subject has been given by Turner and Brittain (1962).Various hypotheses have been put forward to explain the inhibitory effect of oxygen, commonly referred to as the Warhurg effect. Some authors favor the idea of enzyme inhibition; Turneret al. (1958) that one or more enzymes of the carbon reduction cycle are inactivated by oxygen: lirianlals (1962) that enzymes of the oxygen‐evolving complex are inhihited. Other hypotheses concern back‐reactions in which molecular oxygen is taken up, thus reversing the photosynthetic process. These reactions include photo‐oxidation, photorespiration, and the Mehler reaction (Tamiyaet al., 1957). At present, there is no generally accepted hypothesis explaining the effect.The often conflicting results on which these hypotheses were based have been obtained mostly on algae. The first observation of an inhibitory effect on photosynthesis in a higher plant was made hy McAlister and Myers (1940) in wheat leaves. They found that the photosyntlietic CO2uptake was markedly lower in air than in an atmosphere of about 0.5 per cent oxygen. At the CO2concentration used (0.03%) the inhibition was present both at high and moderate light intensities. No data were obtained at low light intensities.Although the study of the effect of oxygen concentration on photosynthesis in higher plants would seem to be of great interest, particularily since the natural environment of most land plants is an atmosphere with an oxygen content of 21 per cent, it has attracted very little attention. To the author's knowledge no thorough investigation on the subject has been published.The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO2fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO2fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07046.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe effect of 2,4‐dinitrophenol (DNP) on sucrose‐14C transport in Soya seedlings has been analysed. The aim was to distinguish between an effect of the inhibitor on sugar movement within the phloem sieve tubes themselves, and on the prior steps of uptake and secretion of sugar into the conducting cells.DNP drastically inhibited sucrose‐14C transport if it was applied to the14C‐treated leaf immediately before, or during,14C supply. Transport was also strongly inhibited if DNP was applied along the translocation path while the14C‐treated leaflet was still in position on the plant. When, bowever, DNP was applied through the cut petioles of the primary leaves after removal of the14C‐treated terminal leaflet of the first trifoliate leaf, no inbibition was observed. On the contrary, transport appeared to have been promoted: significantly more14C disappeared from the upper regions of DNP‐treated plants as compared with controls, while in the lower plant parts more14C accumulated. Different rates of synthesis of sucrose‐14C into non‐alcohol‐soluble compounds could not account for this result. A similar stimulatory effect was observed when DNP was applied to the cut petiole of a primary leaf opposite that treated with14C.Several indications were obtained that14C which has reached the lower parts of the plant may circulate upwards again through the phloem within about 15 minutes. When sucrose‐14C was introduced into the roots via the xylem, both DNP treatment and prior steam girdling resulted in the apparent accumulation of14C in the lower plant parts. the results would be compatible with DNP inhibition of upwards movement in the phloem. DNP might also have affected sugar uptake processes in cells neighbouring the translocation path.It is concluded that the inhibitory effect of DNP on downwards phloem transport reported by earlier workers was probably due to an effect on uptake and/or secretion into the sieve tubes, not to an effect on the conducting cells themselves. Modern theories for phloem transport are discussed in the li

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07047.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe cells used in the present investigation had a phosphate content of about 20 per cent as compared with the status in normal cultures. The uptake of phosphate during a period of 4 hours was determined at a pH of 6,5, kept constant with the aid of a citrate buffer.In the absence of CO2, light increased the uptake of phosphate with saturation around 14,000 erg/cm2s. With 5 per cent CO2in the air the relationship was more complicated, and the uptake of phosphate must he related to more than one process during active photosynthesis.The inhibiting effect of CO2in air was noticeable already at low concentrations both in light and in darkness. With the system used, this supports earlier indications for internal recycling of orthophosphate, CO2was inhibiting also in nitrogen in the light.Selenate in a concentration of 2 mM gave a slight and rather irregular inhibition.—Anaerobiosis had no effect in the light but gave a large decrease in the dark.—DNP (0.1 mM) was somewhat more active in the dark than in the light. The lower concentrations tested had no effect in either case.—Menadione (0.1 mM) inhibited strongly, and more in illuminated than in non‐illuminate

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07048.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe effect of light on peach leaf and flower bud break was examined. It was found that leafless dormant shoots were light‐perceptive organs. Darkness, after light preconditioning during dormancy, reduced leaf bud opening; however, light was obligatory when the shoots were preconditioned in the dark. Relatively short exposures to light were sufficient to stimulate leaf bud break. Terminal buds were less inhibited by darkness than were laterals. Flower bud break was inhibited in light after dark preconditioning. The red region of the spectrum was found to be active; the phytochorome system seems to be involved in the light reactions, as the red light effect was reversible with subsequent far‐red illumination. Supplementary light, producing long‐day conditions, could partly compensate for insufficient chilling. A possible sequence of reactions in the plant is sugg

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07049.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractHydroxyhenzoic acids were tested for their effects on oxidation of the reduced nicotinamide adenine dinucleotide (NADH) in the absence of added H2O2and Mn2* by an enzyme preparation from tobacco leaves(Nicotiana tabacum,var. White Gold). For comparison, a commercial horseradish peroxidase was also used. The rate of NADH oxidation was followed spectruphotometrically at 340 nm.Mono‐ and dihydroxybenzoic acids exerted significant effect on the rate of NADU oxidation, yet their effectiveness was determined by the number and position of the hydroxyl group on the ring. 4‐Hydroxybenzoic acid was very effective in stimulating the reaction. Shifting the hydroxyl from the 4‐ to the 3‐position and from the 3‐ to the 2‐position decreased activity. 2,4‐ And 2,5‐dihydroxybenzoic aeids were more active than the other dihydroxy‐iscuners in stinulating oxidation of NADH. the dihydroxybenzoic acids with the hydroxyls in adjacent positions were less effective, and their activity was affected by other phenolic activators. In the presence of 4‐hydroxybenzoic acid which enhanced oxidation of NADH, 2,4‐ and 2,5‐dihydroxybenzoic acids further stimulated the reaction, but 3,4‐, 2,3‐ and 2,6‐dibydoxybenzoic acids were inhibitory. The inhibition by 3,4‐ and 2,3‐dihydroxybenzoic aciils was non‐competitive.The enzymes extracted by a L‐cysteine‐containing buffer showed lower NADH‐oxidase activity.The enzyme preparation possessed peroxidase activity. The activity of NADH‐oxidase inereased when H2O2and Mi2* were present in addition to 4‐hydroxy‐benzoic acid. The effect of the position and number of hydroxyl substitution on the rate of NADH oxidation by borseradish peroxidase was also significant. This suggests the involvement of peroxidase in the NADH‐oxidase system of tobacco leaves. However, a combination of the inactivated enzyme solution and active horseradish peroxidase with peroxidase activity equivalent to that of the enzyme preparation from tobacco leaves did not reconstitute the NADH‐oxidase activity of tobacco leaves. This and other evidence suggests that the soluble NADH‐oxidizing zyme system

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07050.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractA promotion of expansion of etiolated bean leaf disks by ultraviolet (UV) radiation was confirmed. The optimum conditions for the effeet were found to be 5 seconds UV exposure followed by 24 hours of incubation at 25°C and pH 6.2. Macerations and sections of the treated and control disks indicated that the basis of the response was an increase in the number of cells in the UV treated disks. Experiments with indolebutyric acid (IBA) andp‐chlorophenoxyisobutyric acid (PCIB) indicated that the UV apparently acted to reduce a superoptimal endogenous auxin level to an optimum level which resulted in promotion of the expansi

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07051.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractA soluble ATP‐ase from bean roots was discovered. The enzyme was assayed by measuring the release of inorganic P from32P‐labelled ATP. The enzyme is strongly stimulated by hoth sodium and potassium ions, in the alkaline pH range. Its characteristics are compared to that of the animal membrnnal ATP‐ase which is presumably involved in the transport of ions in animal ti

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07052.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

AbstractThe reaction of indoles with the Salkowski reagent has been examined. It was found that the concentration of acid as well as the concentration and anionic component of the iron salt employed are critical factors in the choice of a reagent that will fail to react—or will react maximally with a given indole. Tryptamine can be reproducibly assayed with a reagent containing 0.01MFe(NO3)3in 7.0MHCIO4. Two ml of this reagent are added to two ml of the sample. The absorbancy is read at 450 nm after 90 minutes under uniform light conditions. Versions of this reagent can also be used for the quantitative colorimetric determination of tryptophan or indoleacetic aci

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1966.tb07053.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY