VI. PRELIMINARY STUDIES OF PHOTOSYNTHESIS AND CARBOHYDRATE METABOLISM OF THE LICHEN <i>XANTHORIA AUREOLA</i>

Bednar, Thomas W.; Smith, David

doi:10.1111/j.1469-8137.1966.tb06353.x

Cited by 22 publications

(15 citation statements)

References 14 publications

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“…Marginal thallus lobes of Xanthoria aureola were collected from the roof of the University Farm, Wytham, Berks and sampled as described by Bednar and Smith (1966) and Richardson and Smith (1968). Immediately after preparation, some samples were surfacedried on filter paper and placed in a desiccator over calcium chloride for at least 20 hours at room temperature, while others were placed on very moist filter paper in Petri dishes, also at room temperature (16-21° C).…”

Section: C Smith and Susan Molesworth Materials And Methodsmentioning

confidence: 99%

Lichen Physiology Xiii. Effects of Rewetting Dry Lichens

1973

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SUMMARYTwo distinct phenomena occur when water is added to air-dry lichens: (1) an immediate nonmetabolic release of a substantial volume of gas containing 75-80% COj; and (2) a rapid rise in respiration to rates well above control values. This excess respiration ('resaturation respiration') persisted for ahout 9 hours in Peltigera polydactyla and about 2 in Xanthoria aureola and was, unlike basal respiration, azidc-and cyanide-sensitive. When the mannitol content of Peltigera discs had been doubled by feeding glucose before drying, the initial rate of subsequent resaturation respiration was correspondingly much higher. Cycles of wetting and drying caused progressive reductions both in mannitol content and resaturation respiration. In Peltigera, resaturation respiration occurred if the water content of discs had fallen below approximately 40% of maximum. Xanthoria aureola, which grows in drier habitats than Peltigera polydactyla, was much more tolerant of cycles of wetting and drying and showed much less intense resaturation respiration.

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Section: C Smith and Susan Molesworth Materials And Methodsmentioning

confidence: 99%

Lichen Physiology Xiii. Effects of Rewetting Dry Lichens

1973

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“…Mammalian hexokinase is inhibited non-competitively by glucose 6-phosphate whilst being unaffected by fructose 6-phosphate (Rose and O'Connell, 1964;Crane and Sols, 1954). It is suggested that the inhibition of glucose uptake following pretreatment in glucose is a consequence of an increased concentration of glucose 6-phosphate in the fungal cells having an inhibiting effect on the hexokinase.…”

Section: Glucose Uptake and Efflux From Lichen Algaementioning

confidence: 99%

“…This indicates that 2-deoxyglucose inhibits conversion of glucose to mannitol. Hexokinase phosphorylates 2-DG to 2-DG6-phosphate, this compound having an inhibitory effect on the next enzyme in the pathway to mannitol, phosphoglucoseisomerase (Wick et al, 1957), although it has no effect on the activity of hexokinase itself (Crane and Sols, 1954). The resulting accumulation of glucose 6-phosphate would inhibit the phosphorylation of glucose by hexokinase.…”

Section: Effects Of 2-deoxy-glucose Pretreatment On'^'-c Transport Bementioning

confidence: 99%

“…For example, in Xanthoria aureola, short-term photosynthesis experiments by Bednar and Smith (1966) showed fixed ^'C detectable in mannitol (a known fungal product) within i min and that it contained 12.7% of total fixed ''''C after 15 min. Using the 'inhibition technique' Richardson (1967) found it was necessary to incubate in '^C-ribitol (the mobile carbohydrate) for about 14 h to obtain this order of release, with only 20.4% released after 24 h. An extreme case may be Trentepohliacontaining lichens, in which only 9%-io% of total fixed ^*C was released during even 48 h 'inhibition' in the mobile carbohydrate (erythritol).…”

Section: The Value Of 'Inhibition Techniques^ In Studying Biotrophic mentioning

confidence: 99%

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LICHEN PHYSIOLOGY XV. THE EFFECT OF DIGITONIN AND OTHER TREATMENTS ON BIOTROPHIC TRANSPORT OF GLUCOSE FROM ALGA TO FUNGUS IN PELTIGERA POLYDACTYLA

1976

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SUMMARY 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.

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“…In this species, ribitol is released by the Trebouxia symbiont, and converted to mannitol and arabitol by the fungus, but it is not known if this conversion occurs immediately upon uptake, or whether a pool of ribitol can accumulate ihi the fungus. Bednar and Smith (1966) found that 24 hours after a pulse of '*C, 33.7% of the '*C in the thallus was in mannitol and 52.8% in 'pentitol' (no distinction was made between arabitol and ribitol). also studied the redistribution of a pulse of fixed ^'''C, and found approximately equal amounts in mannitol and pentitols after 24 hours; there was evidently little incorporation into arabitol, although a clear separation between arabitol and ribitol was not obtained.…”

Section: The Value Of Quantitative Data From ''Inhibition' Experimentsmentioning

confidence: 99%

Lichen Physiology Xii. The ‘Inhibition Technique’

Hill

Smith

1972

New Phytologist

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Summary During photosynthetic fixation of 14C by lichens, 14C‐carbohydrate moves from alga to fungus. If the 12C‐form of this mobile carbohydrate is added to the external medium, then the 14C‐form is released from the lichen. This observation forms the basis of the, inhibition technique', used to study movement of carbohydrates between symbionts within intact lichen thalli. The effect is specific since 14C is released from the lichen only if the 12C‐carbohydrate in the medium is identical or structurally very similar to that moving between the symbionts. This paper examines the usefulness of the technique in the study of carbohydrate movement. Lichens were exposed to a short pulse of NaH14CO3 before transfer to carbohydrate media. Relatively high concentrations of carbohydrate (20 mM–80 mM) were needed for maximum ‘inhibition’. More than half the lichens examined released over 50%, of a pulse of fixed 14C during maximum ‘inhibition’ Using 2‐desoxy‐glucose as an ‘inhibitor’ of glucose movement in Peltigera polydactyla, it was shown that the supply of glucose from the alga was more than sufficient for the metabolic requirements of the fungus. The rate release of 14C during ‘inhibition’ varied widely between different lichens, but it was not clear if this was due to differences in pool sizes of mobile caibohydrates, or to real differences in rates of carbohydrate supply. Much less carbohydrate movement between the symbionts occurred in the dark, than in the light. The effect of pH on 14C release during ‘inhibition’ contrasted sharply with effects of pH on release from freshly isolated algae. This raised further doubts whether the behavior of freshly isolated algae is similar to those in the thallus. The explanation of ‘inhibition’ on the basis of a competition between the high concentration of external carbohydrate and the much lower concentration of 14C‐carbohydrate released from the alga at fungal uptake sites may require modification in at least some lichens. Competition or exchange between 12C and 14C carbohydrates may begin at stages before the fungal uptake sites.

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VI. PRELIMINARY STUDIES OF PHOTOSYNTHESIS AND CARBOHYDRATE METABOLISM OF THE LICHEN XANTHORIA AUREOLA

Cited by 22 publications

References 14 publications

Lichen Physiology Xiii. Effects of Rewetting Dry Lichens

Lichen Physiology Xiii. Effects of Rewetting Dry Lichens

LICHEN PHYSIOLOGY XV. THE EFFECT OF DIGITONIN AND OTHER TREATMENTS ON BIOTROPHIC TRANSPORT OF GLUCOSE FROM ALGA TO FUNGUS IN PELTIGERA POLYDACTYLA

Lichen Physiology Xii. The ‘Inhibition Technique’

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