bluuebunny/crossref_metadata_2025 huggingface dataset:
MITOCHONDRIA OF MYCORRHIZAL ROOTS OF FAGUS SYLVATICA
Authors: COLEMAN J. O. D. , HARLEY J. L.
Published: May 2006

Mitochondria 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

Studies 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

Barley 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

In 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

The 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

The 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

Benzyl 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

Quantitative 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

Although 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

Digitonin 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

The 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

The 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.
A NOTE ON THE THEORY OF DICHOTOMOUS KEYS
Authors: SANDVIK LEIV
Published: May 2006

The problem of constructing dichotomous keys with maximum probability of right determination is discussed. Under some assumptions it is shown that keys in which all taxa are gathered on the last two levels have this property. The discussions also indicate that keys generally should be made as ‘short’as possible.
CELL PERMEABILITY AND REGULATION OF INTRACELLULAR SODIUM CONCENTRATION IN A HALOPHYTIC AND A GLYCOPHYTIC MOSS
Authors: BATES J. W.
Published: May 2006

Treatment 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

Extracts 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

Mycorrhizal 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

The 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.
THE UPTAKE AND METABOLISM OF PHOSPHATE BY THE LICHEN HYPOGYMNIA PHYSODES
Authors: FARRAR J. F.
Published: May 2006

Hypogymnia physodes showed active uptake of inorganic phosphate (Pi) from, very dilute solutions (less than IO5 nmol Pi dm‐3). Approximate values of Vmax and Km compare with published data for phloem and maize roots. Pi absorbed from these dilute solutions was not exchangeable, but that absorbed from solutions of IO5–IO6 nmol Pi dm‐3 was exchangeable. There was some evidence, but not conclusive, that two types of uptake mechanism existed. The metabolism of absorbed Pi was similar to that described in other lichens and included appreciable incorporation into a fraction which may be largely polyphosphate. The ecological significance of this is discussed.

Calculations based upon the reported concentration of Pi in rainwater, rates of uptake of Pi by H. physodes from solutions of equivalent concentration, and growth rate (as an indicator of Pi needs) show that the lichen would only need one hour of rain per week to maintain its phosphorus status. It is therefore unlikely that phosphorus limits the growth of the lichen in nature.
THE VIABLE SEED CONTENTS OF ANT‐HILL AND PASTURE SOIL *
Authors: KING T. J.
Published: May 2006

The viable seed contents of ant‐hill and pasture soils were estimated in samples from acidic grassland on Rhossili Down, Gower peninsula, South Wales. The pasture soils contained 9150 seeds per m2 and the same mass of ant‐hill soil produced 6121 seedlings per m2, including 4030 of Aira praecox L. Twelve species had at least four times as many seeds in pasture soil than in ant‐hill soil. Most of these species are more abundant in the pasture than on the ant‐hills, perhaps partly through inefficient seed dispersal.
GENETIC VARIATION OF EUCALYPTUS OBLIQUA IN FIELD TRIALS
Authors: BROWN A. G. , ELDRIDGE K. G. , GREEN J. W. , MATHESON A. C.
Published: May 2006

The growth and survival of Eucalyptus obliqua seedlings from twenty‐two provenances throughout the range of the species in south‐eastern Australia were studied in three field trials in Tasmania and Victoria. Early results indicated significant variation among provenances for several growth parameters and for survival. Ranking for height was consistent on the two low‐altitude planting sites and similar to that in previously reported glasshouse studies. Within provenances there were also significant differences between families for growth and survival.

These results suggest that genetic improvement of the species is possible, not only by selection of the most suitable provenances for particular sites, but also by the selection of superior individual trees within a provenance.
THE LOW TEMPERATURE LIMIT FOR SEED GERMINATION
Authors: SIMON E. W. , MINCHIN ANN , MCMENAMIN MARY M. , SMITH J. M.
Published: May 2006

At 2O°C, cucumber and mung bean seeds germinate rapidly. As the temperature is lowered to 14°C, the time required for 50% germination increases with a Ql0 of about 2. However, between 14 and 11°C, Q10 rises to 60–1600 (cucumber) and 87 (mung bean); below 11°C only a small percentage of seeds will germinate. At 10°C, the roots never extend to more than 1.5 mm, while a length of 2.5 mm is necessary for germination. Exogenous supply of various amino acids and hormones fails to alleviate the block to germination in the cold. The mitotic index of root cells in cucumber seedlings is low at 5°C. However, at 22°C the seeds can germinate even under conditions that inhibit mitosis (0.02% colchicine or following γ‐irradiation). There is little indication of leakage from cucumber seeds in the cold. Arrhenius plots of the respiration of imbibed seeds, of the growth of 1‐cm long roots and the respiration of root tips are a1! linear. It is concluded from the high Q10 figures for germination in the cold that the failure of germination may result from a denaturation of proteins.
LOCALIZATION OF CHLORIDE IN LEAF CELLS OF THE HALOPHYTE SUAEDA MARITIMA BY SILVER PRECIPITATION
Authors: HARVEY DIANA M. R. , FLOWERS T. J. , HALL J. L.
Published: May 2006

Chloride has been localized in leaf cells of Suaeda maritima by the silver precipitation technique. The major site of precipitation was the cell vacuole although deposits were found at other sites, particularly in the chloroplasts of plants grown without salt. Considerable loss of chloride from the tissue occurred during the preparative procedure and the validity of the technique is discussed.
TRANSLOCATION AND TRANSFER OF NUTRIENTS IN VESICULAR–ARBUSCULAR MYCORRHIZAS
Authors: COX GUY , TINKER P. B.
Published: May 2006

Tracings of electron micrographs of mycorrhizal roots of onion were measured using an image‐analysing computer and the results were used to derive estimates of the volume occupied by the fungal arbuscules, the increase in volume of host cytoplasm after infection and the area of interface between fungus and host. The average lifespan of an arbuscule was deduced from the proportions of living and senescent arbuscules measured in light microscope preparations. These measurements were used to evaluate two hypothetical mechanisms for transfer of phosphorus from fungus to host. It was concluded that digestion of the fungus by the host was not likely to be a significant factor in phosphorus transfer. Transfer of phosphorus across the membranes of living fungus and host appeared to be a more probable mechanism.
THE VEGETATIONAL HISTORY OF PARTS OF SOUTH AND EAST DURHAM
Authors: BARTLEY DAVID D. , CHAMBERS CARL , HART‐JONES BARBARA
Published: May 2006

Late‐Devensian and Flandrian deposits are described from six sites in lowland Durham, ranging from Neasham, near Darlington, in the south, to Thorpe Bulmer, near Hartlepool in the north‐east. Pollen diagrams from each site are presented and show the changes in vegetation of the different areas. At Thorpe Bulmer the tundra vegetation of the Older Dryas period gave way to rather open birchwoods in the Allerod and there was then a return to sedge tundra in the Younger Dryas. This sequence is compared with others in Durham, Yorkshire and Northumberland. The Flandrian sequence opens with the development of birchwoods followed by the appearance of the more thermophilous forest trees. There are in the late Boreal and early Atlantic periods local differences in the forest, as for instance in the early establishment of alder at Mordon Carr (7760 B.P.) and the prevalence of pine around Bishop Middleham, the latter being related to the close proximity of Magnesian Limestone. The ‘elm decline’is dated at 5500–5200 B.P. and there are after that a number of clearance phases beginning with small scale clearance by Neolithic people from about 5200 B.P. From the Bronze Age on there are local differences, again presumed to be related to the proximity of Magnesian Limestone and to soil differences. At Bishop Middleham there is a massive clearance of forest and spread of pasturing from 3660 B.P., reaching a maximum at 3360 B.P. (Middle Bronze Age) when cereal cultivation was introduced. Except for Hutton Henry where there was considerable clearance the rest of the area saw only moderate and temporary clearance at this time. At Thorpe Bulmer there is evidence for intensive cultivation of hemp and some cereals from 2064 B.P. (Late Pre‐Roman Iron Age) rising to a maximum in the Roman period (1730 B.P.) and continuing at a low level until the Norman Conquest (852 B.P.). At nearby Hutton Henry there is evidence for extensive agriculture around 1842 B.P. but in the southern part of the region such clearance was not reached until much later (1213 B.P. at Neasham). In all these deposits there are interesting differences in rate of peat growth from one period to another and at Thorpe Bulmer there is a very long break in the sequence.
A LATE PLEISTOCENE AND HOLOCENE POLLEN DIAGRAM FROM LYNCH'S CRATER, NORTHEASTERN QUEENSLAND, AUSTRALIA
Authors: KERSHAW A. P.
Published: May 2006

The pollen diagram from Lynch's Crater extends the climatic and vegetation record for the Atherton Tableland back to about 60,000 years B.P. Subtropical rain forest, with abundant Araucaria, was present around the site from before 60,000 B.P. to about 38,000 B.P. and existed under about half the present‐day annual rainfall. This was replaced by sclerophyll vegetation between 38,000 and 27,000 B.P. as a result of a decrease in precipitation, a decrease in temperature or the activities of aboriginal man. In any case the agent of rain forest destruction was probably fire. The record for the last 10,000 years or so is probably incomplete and radiocarbon dates unreliable, but changes during this period are in broad agreement with those evidenced from previously described sites within the area. The sequence from Lynch's Crater provides a basis for the interpretation of many problematical features of present‐day vegetation distributions.
SOME PROPERTIES OF THE SOLUBLE ACID PHOSPHATASES OF ROOTS OF ZINC‐TOLERANT AND NON‐TOLERANT CLONES OF ANTHOXANTHUM ODORATUM
Authors: COX R. M. , THURMAN D. A. , BRETT M.
Published: May 2006

Summary

An electrophoretic survey of soluble acid phosphatases present in roots of individual plants of Anthoxanthum odoratum from a zinc‐tolerant and a non‐tolerant population showed that eight acid phosphatases differed in their frequency of occurrence between the two populations. No correlation was detected between the presence of any one set of soluble acid phosphatases and the index of zinc tolerance which suggests that there is no one zinc‐tolerant genotype. Mine plants possessed higher soluble acid phosphatase activities than pasture plants; this could account for the higher Km values detected in mine individuals. The sensitivity of soluble acid phosphatase activity to inhibition by zinc was the same both for the four tolerant and nontolerant individuals examined though small intrapopulation differences in the degree of inhibition/ stimulation were observed. It was concluded that soluble acid phosphatases of these roots do not show adaptations to zinc, or, if they do, they are not revealed by the types of measurement made here.
TEMPERATURE ON PHOTOSYNTHESIS AND TRANSPIRATION IN POPULATIONS OF SESLERIA CAERULEA (L) ARD.
Authors: LLOYD N. D. H. , WOOLHOUSE H. W.
Published: May 2006

Summary

Samples of populations of Sesleria caerulea (L) Ard. were grown under controlled conditions. Rates of photosynthesis and transpiration were measured in an open gas system over the leaf temperature range, 7.5°–30°C. Populations differed significantly in light‐saturated photosynthetic rates and these differences resided in the stomatal resistance to CO2 assimilation.
ENDOGENOUS GROWTH REGULATORS IN RELATION TO SIDE SHOOT DEVELOPMENT IN THE TOMATO
Authors: TUCKER D. J.
Published: May 2006

Summary

A study has been made of the endogenous factors controlling lateral bud initiation and development in the variety Craigella, and two isogenic lines of this variety, Craigella Blind (blbl) and Craigella Lateral Suppressor (isls), in both of which side shoot growth is suppressed to varying degrees. Winter‐ and summer‐sown plants are compared.

Lateral Suppressor plants contained higher endogenous levels of auxin in their apices, mature leaves and stems than did normal plants, but lower level of cytokinins in all parts except the stem, where the levels were similar in both types. The levels of abscisic acid‐like substances were consistently higher in the stems of Lateral Suppressor plants than in the corresponding tissue of normal plants, but other plant parts showed a more variable pattern. Lateral Suppressor plants contained higher levels of gibberellin than did normal plants.

Blind plants contained higher levels of auxin in the apices and stem than did normal plants, but the levels in mature leaves showed no consistent pattern. Higher levels of abscisic acid‐like substances were present in the stem and axillary buds of blind plants than in normal plants, with again a more variable pattern in other plant parts. The levels of cytokinins and gibberellins varied considerably between the two sowing dates.

A possible hormonal mechanism of control of axillary bud development is discussed.
THREONINE/SERINE DEHYDRATASE ACTIVITY IN ANGIOSPERMOUS PARASITES
Authors: NANDAKUMAR S. , KACHRU D. N. , KRISHNAN P. S.
Published: May 2006

Summary

Both species of broomrape tested were devoid of L‐threonine dehydratase and L‐serine dehydratase activity. When the seeds of three species of dodder were examined, threonine dehydratase activity was present in two but absent in the third. The enzyme could also not be demonstrated in the seed of a green mistletoe. Absence of threonine/serine dehydratase may be a factor necessitating or associated with the parasitic existence of broomrape. The significance of the presence of threonine dehydratase in some seeds and absence in some others is briefly discussed.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS
Authors: READ D. J. , KOUCHEKI H. K. , HODGSON J.
Published: May 2006

Summary

The intensity of vesicular‐arbuscular mycorrhizal infection was assessed in the major vegetation types of east‐central England. All of the most important species of grassland, scrub and woodland were mycorrhizal and each individual of any species normally carried a heavy VA infection. Members of the Gramineae were particularly heavily infected. In limestone grassland, infection extended to members of the Cyperaceae and Juncaceae. Infection levels were high throughout the year, the highest levels occurring in the most nutrient‐stressed situations.

Mycorrhiza develops soon after germination, often while seedlings are still in the cotyledon stage. Since numbers of viable Glomus type spores are low, infection is thought to arise from root to root contact rather than from spores. The Ecological implications of the widespread infection are discussed.
ENVIRONMENTAL‐PHYSIOLOGICAL INTERACTIONS IN LICHENS
Authors: MacFARLANE J. D. , MAIKAWA E. , KERSHAW K. A. , OAKS A.
Published: May 2006

Summary

The nitrogenase activity in Peltigera polydactyla was examined during varying periods of darkness and after re‐illumination. There was an immediate decrease in activity of about 50% when the lichen was darkened, followed by a progressive further decrease of activity with time. Recovery to the original level of activity on re‐illumination showed an increasing lag as the dark period was extended. The effect of an external carbon source on nitrogenase activity was also examined and very large increases in activity were induced in the light, by both 2% glucose and mannitol. The decrease during a dark period was, however, still very marked.
ELECTRON‐MICROSCOPICAL STUDIES ON THE PHYCOBIONT COCCOMYXA SCHMIDLE
Authors: PEVELING ELISABETH , GALUN MARGALITH
Published: May 2006

Summary

The ultrastructure of the phycobiont, Coccomyxa, was compared in some asco‐ and basidiolichens. All phycobionts investigated contained a single cup‐shaped chloroplast, multivesicular bodies and large storage bodies. In the chloroplast of the phycobionts in ascolichens, many plastoglobuli occurred regularly whereas, in those of the basidiolichens, no plastoglobuli were present. The multivesicular bodies were associated with varying numbers of vesicles and storage bodies. The storage bodies increased when the lichens were kept dry for several months. By cytochemical tests, the lipid nature of these bodies was suggested. The possible function of the different structures is discussed in comparison with the ultrastructure of other lichens.
DISPERSAL AND CHANGES IN THE LOCAL DISTRIBUTIONS OF EVERNIA PRUNASTRI AND RAMALINA EARINACEA
Authors: TAPPER RICHARD
Published: May 2006

Summary

Changes in the distributions of Evernia prunastri and Ramalina farinacea along an elm avenue have been recorded for 52 months. During this time colonization by Evernia prunastri and Ramalina farinacea has occurred over a distance of 30 m. A mathematical method is described to relate the distribution of thalli to the distance of ropagule dispersal. This method may be applicable to other situations where colonization is occurring and the source of plant propagules is known.
THE BREAKDOWN OF PARAQUAT AND DIQUAT BY SOIL FUNGI
Authors: SMITH S. N. , LYON A. J. E. , SAHID ISMAIL BIN
Published: May 2006

Summary

Mucor hiemalis, Zygorhynchus heterogamous, Aspergillus niger and Penicillium frequentans were incubated in media containing either [methyl‐14C] paraquat or [ethylene‐14C] diquat. Aspergillus niger liberated 14CO2 from both herbicides and Penicillium frequentans only from paraquat. Mucor hiemalis and Zygorhynchus heterogamous were unable to release 14CO2 from either. Those species able to degrade paraquat or diquat have correspondingly low intracellular levels of the herbicides and are able to tolerate high concentrations in the medium. By contrast, species unable to break them down are characterized by high intracellular levels and by their inability to grow at low concentrations. Tolerance to these herbicides appears to be the result of an ability to degrade them.
A SCANNING ELECTRON MICROSCOPIC STUDY ON THE DEVELOPMENT OF TENDRILS OF PARTHENOCISSUS TRICUSPIDATA SIEB. & ZUCC.
Authors: JUNKER STEFFEN
Published: May 2006

Summary

This report describes a scanning electron microscopic study on the surface of developing tendrils of Parthenocissus tricuspidata Sieb. & Zucc. Epidermal cells of mature branchlets are densely covered with minute corrugations which we shall call microplicae, while the epidermis of immature branchlets is smooth. Epidermal cell surfaces of pads first appear very folded, but develop into a densely packed pattern of hemispheres. When stimulated, heavy exudation of a sticky fluid enables the pad to adhere to a support. Subsequently, epidermal cells nearest the point of contact elongate extensively and divide periclinically, whereas the remaining epidermal cells swell and undergo anticlinal divisions. The adhesive fluid passes through the wall o epidermal cells, accumulates under the cuticle causing the latter to bleb, and is finally exuded from a hole in the cuticular blebs.
STUDIES ON THE INTERACTIONS BETWEEN THE EMBRYONIC AXIS AND THE COTYLEDONS DURING GERMINATION IN PISUM SATIVUM L.: THE INFLUENCE OF INCUBATION CONDITIONS
Authors: BRYANT J. A. , HACZYCKI S. J.
Published: May 2006

Summary

The effects of removal of the embryonic axis on the development of enzyme activities in the cotyledons of peas have been studied. Excised cotyledons incubated aseptically in large culture vessels show greater increases in acid ribonuclease and acid phosphatase activities than do cotyledons of intact seeds. In excised cotyledons incubated aseptically in Petri dishes, neither enzyme exhibits the normal increase in activity observed to intact seedlings. The significance of these results is discussed.
A BIOSYSTEMATIC STUDY OF THE CREEPING SPEARWORTS AT LOCH LEVEN, KINROSS
Authors: GIBBS P. E. , GORNALL R. J.
Published: May 2006

Summary

Synthetic interspecific hybrids and backcross progeny of Ranunculus flammula L. and R. reptans L. have been compared for their morphology, phenotypic response to submersion, fertility, and breeding system, with transplant specimens of R. reptans‐like plants from Loch Leven. The two species were found to be fully inter‐fertile. The Loch Leven transplants were found to show a striking similarity to backcross progeny of F1 interspecific hybrids ×R. reptans, thus providing experimental evidence for the introgressive hybrid status of these plants as proposed by previous authors.
EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON THE GROWTH AND CYTOKININ CONTENT OF TWO POPULATIONS OF DACTYLIS GLOMERATA (COCKSFOOT)
Authors: MENHENETT ROGER , WAREING P. F.
Published: May 2006

The effects of photoperiod (8 or 16 hr, SD or LD) and temperature (low or high, 8° or 20°C) on the growth and cytokinin content of Norwegian and Portuguese populations of Dactylis glomerata (Cocksfoot) were investigated.

In general, conditions which promote active leaf growth (LD or high temperature) of plants of the Norwegian population tend to result in lower levels of cytokinin bases and/or nucleosides and in higher levels of ‘nucleotide’ cytokinins than conditions which lead to reduced growth rate (SD or low temperature). In some ‘transfer’ experiments the changes in hormone levels preceded detectable changes in growth rate. Cytokinins which behaved similarly to zeatin and zeatin riboside on Sephadex LH 20 columns were detected.

The lack of response to application of exogenous zeatin or 6‐benzylaminopurine, together with the data on endogenous cytokinins, suggests that the level of cytokinin bases and nucleosides was not limiting the growth rate of the Norwegian population in SD at 8°C. However, if ‘nucleotide’ cytokinins are significant for growth rate under unfavourable conditions then this class of hormone may be involved in the responses to day length and temperature.
CYTOKININS IN XANTHIUM STRUMARIUM L.: THE METABOLISM OF CYTOKININS IN DETACHED LEAVES AND BUDS IN RELATION TO PHOTOPERIOD
Authors: HENSON I. E. , WAREING P. F.
Published: May 2006

Endogenous cytokinin activity in leaves and buds of Xanthium strumarium L. (as estimated by the soybean callus bioassay) declined by about 80% during the 24 h following detachment from the plant. The decline in activity was little influenced by the photoperiod to which the detached organs were exposed.

When zeatin was supplied to detached leaves it underwent rapid metabolism. The main cytokinin‐active metabolite, which was readily detectable an hour after the start of zeatin uptake, eluted from a Sephadex LH20 column with the same elution volume as zeatin riboside. Substantial differences due to photoperiod, in either the rate or the pattern of zeatin metabolism, were not detected.
PROMOTION OF ROOT INITIATION BY GIBBERELLIC ACID IN LEAF DISCS OF TOMATO (LYCOPERSICON ESCULENTUM) CULTURED IN VITRO
Authors: COLEMAN WARREN K. , GREYSON RICHARD I.
Published: May 2006

Gibberellic acid (GA3) stimulated the rooting of tomato leaf discs cultured on a defined nutrient medium in continuous darkness. In the presence of 2 × 10−4 M tryptamine, GA3 significantly enhanced root initiation over the concentration range of 1 × 10−8 M to 1 × 10−4 M. GA3 could be replaced by GA4/7 but not by kinetin. Indole‐3‐lactic acid was a highly active indole derivative in the induction of rooting in the tomato leaf discs. This effect was significantly enhanced by GA3. Possible reasons for this observation are discussed.
MAXIMUM PHOTOSYNTHETIC RATE‐A CASE STUDY IN APPLE
Authors: AVERY D. J.
Published: May 2006

Widely different rates of carbon dioxide assimilation by apple leaves have been reported. Data from forty‐nine papers are examined and likely reasons for their variation are deduced. Many studies were made on glasshouse‐grown plants, the leaves of which can have a very different structure and photosynthetic capacity from those grown outdoors. Other biological aspects including the influence of fruits are discussed. Leaf temperatures have rarely been measured but there is evidence that excessive temperatures occurred in some studies and many other assimilation rates were probably decreased by less obviously extreme conditions. The rates of air flow employed have often been inadequate for true assimilation rates to be obtained. However, many rates higher than those normally quoted have been obtained by several workers including the author and it is concluded that the maximum photosynthetic rate of apple leaves in normal air is at least 35 mg CO2 dm−2 h−1.