bluuebunny/crossref_metadata_2025_split huggingface dataset:
FACTORS AFFECTING POTASSIUM UPTAKE AND LOSS BY BEECH MYCORRHIZA
Authors: EDMONDS A. S. , WILSON J. M. , HARLEY J. L. 
Published: May 2006

SUMMARYMaximum potassium uptake is achieved by beech mycorrhizas from concentrations of chloride of about 0.2 mM. Addition of NaCl up to 0.5 mM does not significantly reduce K+ uptake from 0.1 mM chloride solutions, although the KCl significantly reduces Na+ uptake. Potassium is rapidly lost from mycorrhizal tissues at temperatures above 20° C, but only after some delay from tissues at lower temperatures. Addition of calcium ions (up to 1.0 mM CaCl2) does not significantly affect potassium uptake or loss. CaCl2 added to RbCl solutions slightly reduces Rb+ uptake. Losses of K+ from mycorrhizal tissues at temperatures above 20°C may be prevented by the application of glucose or fructose. Neither the process of carbohydrate uptake nor the increased internal concentration of carbohydrate itself is responsible for the reduction in potassium loss. It seems probably that factors bringing about the retention of potassium are generated in carbohydrate metabolism. The potassium loss engendered by high osmotic pressure of the external solution seems to be a separate phenomenon from that which occurs at high temperatures.
MITOCHONDRIA OF MYCORRHIZAL ROOTS OF FAGUS SYLVATICA
Authors: COLEMAN J. O. D. , HARLEY J. L. 
Published: May 2006

SUMMARYMitochondria were isolated from beech mycorrhizas, by disruption of the tissue in a medium containing PVP and reducing agents, to counteract the enzyme denaturing actions of endogenous phenols, tannins and the products of phenoloxidase activity.Electron microscopic examination of the isolated mitochondria showed that they were structurally intact, and spectral analysis revealed that their cytochrome composition was marked by a particularly high content of cytochrome b557.The mitochondria actively respired with the Krebs cycle intermediates α‐ketoglutarate, malate + pyruvate and succinate, and with exogenous NADH. In each case the oxidation was tightly coupled to phosphorylation, and ADP:O ratios were obtained which indicated that three sites of oxidative phosphorylation were associated with the respiration of the NAD‐linked substrates α‐ketoglutarate and malate + pyruvate, and two sites with the respiration of succinate and exogenous NADH.The inhibitors rotenone, antimycin A and cyanide blocked electron flow at the known sites of action in the electron transport chain. Rotenone completely inhibited the oxidation of both α‐ketoglutarate and malate + pyruvate, but had no effect on the oxidation of succinate or NADH. Oxidation of the four substrates was found to be partially sensitive to antimycin and to cyanide which caused a maximal inhibition of 50–60% in the rate of respiration. The antimycin‐ and cyanide‐insensitive respiration was abolished by mCLAM.It was concluded that there was at least one fraction of the mitochondrial population which had a cyanide‐insensitive pathway of respiration, and that the respiratory system of the mitochondria in this fraction could best be explained by a model in which the respiratory chain is branched from substrate to oxygen, one branch via cyanide‐sensitive cytochrome oxidase and the other via a cyanide‐insensitive alternate oxidase. No oxidative phosphorylation was found to be associated with the alternate pathway of oxidation with succinate as substrate. Evidence is presented to show that the cyanide‐sensitive pathway was the favoured route of oxidation under phosphorylating conditions, whereas the alternate pathway only operated when electron flow along the cyanide sensitive pathway was restricted either by inhibitors or by the imposition of respiratory control. Some implications of these findings in relation to the physiology of the mycorrhizal system are discussed.
ORGANIZATION AND ACTIVITY OF THE ROOT CAP MERISTEM OF AVENASATIV A L.
Authors: HARKES P. A. A. 
Published: May 2006

SUMMARYStudies were made on the organization and mitotic activity of the cap meristem of the primary root of Avena sativa, 40–96 h after germination. The meristem comprises two sub‐populations differing in mitotic index, in planes of division and in cell size. In the initial cells, both longitudinal and transverse divisions occur, whereas in the peripheral part of the meristem only transverse divisions were observed. Isotope labelling experiments indicated an average cycle time of the cap initials of 11 h. Calculations of radial and longitudinal transit times based on the average cycle time and the ratio between longitudinal and transverse divisions showed that, on an average, it takes c. 365 h in the radial direction and c. 134.4 h in the longitudinal direction before descendants of the most centrally situated initial cell are sloughed off. The displacement of cells in the root cap was followed by labelling with tritiated thymidine; the results agreed with the positions predicted from the calculated transit times. Assuming growth to be symplastic, a number of predictions were made about the behaviour of a putative quiescent centre in the meristem of the root proper.
THE EFFECT OF CLIMATE ON GRAIN DEVELOPMENT IN BARLEY AT AN UPLAND SITE
Authors: PRINCE S. D. 
Published: May 2006

SUMMARYBarley grown at an upland site in the Pennines (Malham) produced grains that were smaller than those of plants grown at the same latitude, but 300 m lower altitude (Lancaster) and at a site in the region of commercial barley production (Cambridge). Grain development occurred 1 month later in the upland climatic conditions. The physiology of grain‐development was investigated and a climatic effect on the capacity of the grains to accept assimilates is suggested as the cause of lower grain‐weight at the upland site.
THE ASSAY OF ATP:UREA AMIDOLYASE IN WHOLE CELLS OF CHLORELLA
Authors: THOMAS E. M. , SYRETT P. J. 
Published: May 2006

SUMMARYIn some strains of Chlorella (Ie, 8k, 9a, 21), urea amidolyase activity can be assayed by incubating frozen/thawed cells with 14C‐urea and ATP. In other strains (8b, 8c, 8p, nm, nn), ATP is ineffective in the assay with frozen/thawed cells but phosphoenolpyruvate is effective. Avidin, which inhibits urea amidolyase activity by complexing with biotin, inhibits the activity in cells of the first group of strains but not in cells of the second group. These differences in behaviour are attributed to differences in the permeability of cell walls; they correlate with other differences described earlier.
NITROGEN ASSIMILATION AND TRANSPORT IN VASCULAR LAND PLANTS IN RELATION TO INTRACELLULAR pH REGULATION
Authors: RAVEN J. A. , SMITH F. A. 
Published: May 2006

SUMMARYThe assimilationof ammonium ion in plant cell cytoplasm produces at least one H+ per NH+4; N2 fixation generates 0.1‐0.2 H+ per N assimilated; NO‐3 assimilation produces almost one OH‐ per NO‐3. H+ or OH‐ produced in excess of that required to maintain cytoplasmic pH for H+ or OH‐, the major process involved is H+ efflux (frequently by active transport) from the cell. IN higher land plants, much of assimilated N occurs as hoot protein; the shoot cells have no direct acess to the H+ and OH‐ sink of the soil solution.When ammonium ion is the N source it is assimilated into organic‐N in the roots. The shoot is supplied with a mixture of amino‐acids, amides and organic acids which an be incorporated (with neutral photosynthate) into cell material without damaging pH changes. Similar considerations apply to symbiotic N2 assimilation in root nodules. IN both cases the excess H+ generated in the root cell cytoplasm is exerted is excreted to the soil solution; there is no mechanism whereby photolithotrophic plant can, in the long term, counter intracellular acidity without resort to active H+ efflux to an extracellular sink.When nitrate is reduced in roots, the organic compounds involved in N transportged to the shoot are similar to those used when ammonium or N2 is the N source with similar implications for the regulation of shoot pH. The excess OH‐ generated in the roots is partly excreted to the soil solution, and partly neutralized by the ‘biochemical pH stat’ which produces strong organic acids from essentially neutral precursors.When nitrate is assimilated solely in shoots, the excess OH‐ is initially neutralized by the operation of the biochemical pH state. Storage of the inorganic cation‐organate in shoot cell vacuoles could lead to turgor and volume regulation problems in these cells. These are avoided when an insoluble salt (calcium oxalate) is the product of the pH stat, or when the cation organate is translocated to the roots where organate breakdown regenerates OH‐, whcih is lost to the soil solution.This mixture of biochemical, and long and short distance transport processes, enables cells remote from a large sink for H+ or OH‐ to produce protein without unfavourable pH changes. These processes related to pH regulation during N assimilation have important consequences for the carbon and energy economy of the plant.
NATURALLY OCCURRING CYTOKININS IN AONLA (EMBLICA OFFICINALIS GAERTN.) FRUIT
Authors: RAM SANT , RAO T. RAJA 
Published: May 2006

SUMMARYThe fruit of Emblica officinalis remains dormant for a period of 31/2 months after setting. Studies on endogenous cytokinin activity of the fruit including exogenous applications of cytokinin suggest that dormancy may not be due to cytokinin deficiency. Fruit making rapid growth following dormancy was found to contain six cytokinin‐like substances, active in the soybean cotyledon callus test. Three of these were tentatively identified as zeatin, zeatin riboside and zeatin nucleotide.The authors are grateful to Dr K. Koshimitzu, Kyoto University, Japan, for the gift of an authentic sample of dihydrozeatin and to the Council of Scientific and Industrial Research, New Delhi, for the award of Senior Research Fellowship to one of them (S.R.).
REVERSAL OF ABSCISIC ACID INDUCED STOMATAL CLOSURE BY BENZYL ADENINE
Authors: DAS V. S. R. , RAO I. M. , RAGHAVENDRA A. S. 
Published: May 2006

SUMMARYBenzyl adenine enhanced stomatal opening in isolated epidermal strips of Commelina benghalensis and Tridax procumbens. The stimulation was maximum at a concentration of 5 × 10‐5 M BA. But kinetin had no remarkable effect on stomatal opening. The activity of benzyl adenine was observed over a narrow range of concentrations, from 10‐5 M to 10‐4 M. The increase in stomatal aperture was more pronounced in Commelina than in Tridax. Presence of benzyl adenine in the medium prevented the stomatal closure expected from abscisic acid and could reverse considerably the stomatal closure induced earlier by abscisic acid. It is felt that the balance between abscisic acid and cytokinins can possibly control the stomatal aperture effectively.
EFFECTS OF VERBASCUM THAPSUS LEAF HAIRS ON HEAT AND MASS TRANSFER: A REASSESSMENT
Authors: PARKHURST DAVID F. 
Published: May 2006

SUMMARYQuantitative results of an earlier paper by Wuenscher (1970) are corrected, and the implications for the adaptive significance of mullein leaf hairs discussed. Wuenscher's paper seemed to show that the leaf hairs thickened the leaf boundary layer by a distance equal to the thickness of the hair layer, causing boundary layer resistance to increase by a factor of 90. The corrections indicate that the hairs increase boundary layer resistance by a factor of about 2.The results imply that measured differences in total transpiration resistance were due to higher stomatal (or cuticular) resistance of normal hairy leaves compared with shaved leaves. Such higher epidermal resistances would tend to reduce photosynthesis. The hypothesis is made that plant species having dense leaf hairs and growing in full sunlight are likely to have high temperature optima for photosynthesis. A related hypothesis is that such species are likely to use the C4 pathway for carbon assimilation, as mullein apparently does. Finally, it is pointed out that dense leaf hairs increase boundary layer resistance to a value equivalent to that of larger glabrous leaves. Thus, the hypotheses suggested should also apply to plants having large leaves and growing in full sunlight.
THE KREBS CYCLE AND CONTROL OF DORMANCY IN THE AGARICUS BISPORUS SPORE
Authors: RAST DORA , STAUBLE E. J. , ZOBRIST P. 
Published: May 2006

SUMMARYAlthough defective in the catabolic part of the Krebs cycle, dormant spores of Agaricus bispours display the full complement of the enzymes of this pathway, with the possible exception of the α‐ketoglutarate dehydrogenase complex. This could, however, be functionally replaced by the enzymes of the γ‐aminobutyrate shunt (i.e. glutamate dehydrogenase, glutamate decarboxylase, γ‐aminobutyrate aminotransferase and succinate‐semialdehyde dehydrogenase) that have been shown to occur in these spores. The possible identity of the metabolite causing the observed inhibition of succinate dehydrogenase is discussed. The results are compared with those obtained from other fungi.
LICHEN PHYSIOLOGY XV. THE EFFECT OF DIGITONIN AND OTHER TREATMENTS ON BIOTROPHIC TRANSPORT OF GLUCOSE FROM ALGA TO FUNGUS IN PELTIGERA POLYDACTYLA
Authors: CHAMBERS SUSAN , MORRIS M. , SMITH D. C. 
Published: May 2006

SUMMARYDigitonin abolishes the ability of the fungal component of Peltigera polydactyla to absorb glucose and increases the permeability of the fungal cell membrane so that substantial amounts of mannitol are released. Digitonin has no detectable effect on the algal component (Nostoc) so that it can be used as a selective inhibitor against the fungus in the intact lichen. During photosynthetic 14C fixation by the intact lichen in the presence of digitonin, there is a large release of 14C‐glucose to the medium. This shows that in symbiosis, transport of glucose out of the alga is not primarily caused by or dependent upon fungal uptake acting as a sink.Pretreatment of the lichen with glucose results in uptake of the sugar into both the algal and the fungal cells, increasing the pool size of algal glucose and stimulating efflux of previously absorbed glucose, and also depressing the rate of subsequent glucose uptake by the fungus. Pretreatment also causes a marked release of 14C‐glucose to the medium during 14C‐fixation, but the amount of 14C‐glucose released when fungal uptake is completely prevented, as in an‘inhibition’experiment, is severely reduced.Pretreatment of the lichen with 2‐deoxy‐glucose disrupts the fungal metabolism of glucose but has little effect on the algal cells, causing a large release of 14C‐glucose whether or not 2‐deoxy‐glucose is present during the subsequent 14C‐fixation.Pretreatment with sorbose causes a marked reduction of 14C‐glucose release from the alga in the lichen, as if absorbed sorbose successfully competes with glucose for the efflux mechanism. The affinity of the efflux mechanism for sorbose, together with its previously reported insensitivity to a wide range of inhibitors, suggests by analogy to studies in other organisms that it is a facilitated diffusion system.Digitonin, 2‐deoxy‐glucose and sorbose represent a group of inhibitors of glucose movement between the symbionts which act at different sites in the process. Although external 12C‐glucose can be used to interfere with 14C‐glucose movement between the symbionts in ‘inhibition techniques’, it affects glucose transport mechanisms in both fungus and alga, so making interpretation difficult of quantitative data produced by the technique on rates and amounts of transport. The qualitative value of the‘inhibition technique’in identifying mobile compounds remains undoubted.Prolonged illumination of the lichens (which increases the size of the glucose pool within the alga) or feeding with mannitol (the fungal product formed from glucose) has little effect on transport between the symbionts.
SOME LIMITATIONS ON PLANT GROWTH AND DEVELOPMENT IN TUNDRA REGIONS‐AN INVESTIGATION USING PHYTOMETERS
Authors: WALTON D. W. H. , SMITH R. I. L. 
Published: May 2006

SUMMARYThe use of oats as phytometers for seasonal studies of microclimatic favourability and nutrient limitations is reported. The effect of age and development on growth parameters in long‐term experiments is illustrated by comparison with data from related short‐term experiments. Regression analyses were carried out on seasonal growth data to discover patterns of growth and development. Intersite differences were more clearly demonstrated by plants grown in nutrient‐rich media than by those grown in soil and were most marked under poor weather conditions. Highly significant differences in growth existed between seasons for the nutrient‐treated vermiculite experiments and between treatments for the soil and vermiculite experiments. The use of regression analyses to explain dry matter accumulation is discussed, and the usefulness of phytometers in growth assessment is considered.
REDUCED POLLEN VIABILITY IN THE ONION (ALLIUM CEPA)
Authors: OCKENDON D. J. , GATES P. J. 
Published: May 2006

SUMMARYThe fluorescein test was found to be a rapid and reliable method of assessing pollen viability in onions. This test revealed the presence of many pollen grains which contained cytoplasm but which were inviable as judged by germination on artificial media. There was very great variation in pollen viability between flowers on a plant, between anthers on a flower and between different parts of a single anther. Both viable and inviable grains occurred in large clumps consisting chiefly of one type of grain. Plants flowering in August which were nominally male fertile and had pollen grains with cytoplasmic contents, nevertheless, showed very high levels of pollen inviability. Possible reasons for this are considered.
CELL PERMEABILITY AND REGULATION OF INTRACELLULAR SODIUM CONCENTRATION IN A HALOPHYTIC AND A GLYCOPHYTIC MOSS
Authors: BATES J. W. 
Published: May 2006

SUMMARYTreatment with sodium chloride solutions led to loss of intracellular potassium and uptake of sodium in both the halophytic moss Grimmia maritima and the glycophyte G. pulvinata. In the presence of calcium, potassium loss and sodium uptake were considerably reduced in G. maritima, but in G. pulvinata, while potassium loss was reduced, net uptake of sodium was stimulated at high external sodium concentrations. In G. pulvinata sodium uptake from artificial seawater solutions was considerably reduced and potassium loss stimulated by increasing the external magnesium concentration. Magnesium had little effect on the retention or uptake of cations by G. maritima. Prewetting had no effect on G. maritima but it reduced subsequent seawater‐induced sodium uptake and potassium loss in G. pulvinata and stimulated sodium uptake from calcium‐free sodium chloride solutions.Experiments with the metabolic inhibitors, 2:4 dinitrophenol, malonate and arsenate demonstrated that sodium uptake by G. pulvinata and potassium retention by both species may be under metabolic control. An experiment in which the intracellular sodium contents of G. maritima and G. pulvinata were artificially increased and then sodium loss measured indicated that sodium efflux is inhibitor‐sensitive in G. maritima but not in G. pulvinata. The results suggest that G. maritima maintains normal cation levels under saline conditions by a combination of a low permeability to cations and the possession of a sodium efflux pump.
STUDIES ON THE ORIGIN OF SOME HYDROLYTIC ENZYMES ASSOCIATED WITH THE LEAVES AND TENTACLES OF DROSERA SPECIES AND THEIR ROLE IN HETEROTROPHIC NUTRITION
Authors: CHANDLER G. E. , ANDERSON J. W. 
Published: May 2006

SUMMARYExtracts from the leaves and tentacles of field‐grown plants of Drosera whittakeri, D. binata and D. auriculata had acid protease activity. Several pH optima were associated with some extracts, implying the presence of several proteolytic enzymes but other extracts showed proteinase activity at all acid pH values with no well‐defined pH optima. Only one distinct pH optimum of proteinase activity (pH 2.6) was associated with the leaves and tentacles of axenic cultures of D. binata. Chitinase activity was present in field‐grown plants of D. whittakeri and D. binata. It was not detected in axenic cultures of D. binata nor was it induced when chitin was applied to the tentacles of plants raised in axenic culture. Several of the many bacteria associated with field‐grown plants of D. whittakeri were isolated and found to secrete active extracellular proteinases with acid pH optima. These organisms could account for much of the proteolytic activity associated with extracts of field‐grown plants. Application of a fungicide/antibiotic mixture to the tentacles of non‐sterile plants of D. whittakeri inhibited insect‐enhanced growth. It is concluded that microbial hydrolytic enzymes play an essential role in this process.
THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE
Authors: STRIBLEY D. P. , READ D. J. 
Published: May 2006

SUMMARYMycorrhizal and non‐mycorrhizal plants of Vaccinium macrocarpon were grown in a controlled environment for 12 weeks on sand supplied with five different concentrations of ammonium nitrogen in a logarithmically increasing series ranging from 1.0 to 56.0 parts/106. All plants received a full complement of other mineral elements essential to growth. Interactions between the effects of mycorrhizal infection and nitrogen concentration were studied through the calculation of various growth‐functions.With increasing concentrations of ammonium nitrogen, uninfected plants showed significant increases in whole‐plant dry weight, percentage nitrogen content and specific absorption rate for N accompanied by decreases in root/shoot ratio and the value of the allometric constant k (the ratio of the logarithmic growth‐rates of root and shoot). Mycorrhizal infection induced similar changes at intermediate levels of nitrogen supply but did not affect seedlings grown under the highest and lowest concentrations of nitrogen used. Differences due to infection were generally smaller than those between uninfected plants from successive nitrogen treatments.The implications of these results are discussed in relation to the significance of mycorrhiza in the nitrogen nutrition of ericaceous plants in their natural habitats.
ECOLOGICAL PHYSIOLOGY OF THE LICHEN HYPOGYMNIA PHYSODES
Authors: FARRAR J. F. 
Published: May 2006

SUMMARYThe effects of ‘severe’ and ‘mild’ cycles of wetting and drying on Hypogymnia physodes were investigated. Each 24‐h cycle of the ‘severe’regime consisted of 3 h soaking in buffer followed by 21 h in air (becoming air‐dry in 1‐2 h), all at 20°C in light or dark. After seven ‘severe’cycles in the light, polyol levels remained high; mannitol, arabitol and ribitol were continually turned over, since there was a heavy loss of previously fixed 14C from each. In the dark, there was some decline in polyol levels after 7 days, presumably because the polyol pool could not be replenished by photosynthesis. During ‘severe’regimes, the carbon loss from the polyol pool was much greater than could be explained by respiration. Nevertheless, if maintenance of high rates of photosynthesis and large pools of polyols are taken as criteria of healthy thalli, then ‘severe’ cycles of wetting and drying are less deleterious than constant saturation.‘Mild’cycles were carried out at 5°C, with a 12 h light/12 h dark photoperiod, and involved much more gradual drying and wetting than the ‘severe’ regime. Thalli showed a rise in ability to photosynthesize during the first 16 days of this treatment. It is concluded that in general, a fluctuating water content is more beneficial to lichens than constant saturation.The results described in this and other papers are used to formulate the concept of‘physiological buffering’. This postulates that the response of lichens to severe environmental stress is characterized by depletion and marked turnover of the polyol pool, so buffering insoluble material such as proteins against such stress. A substantial proportion of photosynthesis in lichens is devoted to maintaining the polyol pool at a high level, leaving only a small amount available for growth processes.