Journal of Experimental Botany

FENSOM, D., S.;WANLESS, I., R.

doi: 10.1093/jxb/18.4.563pmid: N/A

Abstract By measuring the number of water molecules per ion which were moved electro-osmotically through cells of Nitella translucens and N. flexilis it has been shown that a significant difference existed between samples of these species in 1965. In each species the electro-osmotic efficiency was greater with Na+ than with K++. Also 10-4 to 10-5 M IAA tended to decrease electro-osmotic efficiencies while IAA, after 30 min. treatment, produced a significant increase in water flow into the treated end of a living cell. Calculations based on this work suggest that about 108–109 pore sites per cm2 exist on the surface membranes for Na+ or K+ ion transport. This content is only available as a PDF. © Oxford University Press

VAUGHAN,, D.;MACDONALD, I., R.

doi: 10.1093/jxb/18.4.578pmid: N/A

Abstract The development of invertase activity in storage tissue disks of Beta vulgaris during ageing under aseptic conditions has been studied. The invertase is formed initially in the cell wall and subsequently appears in the cytoplasm. In disks up to 1.0 mm thick, invertase is formed throughout the tissue, but in thicker disks only limited activity appears in the interior. In disks up to 1.0 mm thick, treatment with ethyl acetate prior to enzyme assay increases the measured activity by rendering ‘inaccessible’ soluble invertase available to sucrose in the assay medium. In thicker disks, pretreatment with ethyl acetate also increases the measured invertase activity by facilitating sucrose penetration to the centre of the tissue. Osmotic shock affects invertase activity in the same manner as ethyl acetate treatment. The significance of these results is discussed in relation to the induction and development of invertase activity in the disk and in the cell. This content is only available as a PDF. © Oxford University Press

VAUGHAN,, D.;MACDONALD, I., R.

doi: 10.1093/jxb/18.4.587pmid: N/A

Abstract The effect of several inhibitors on the development of invertase activity and the increase in RNA content of red beet disks aged under aseptic conditions has been studied. Purine and pyrimidine bases (I.o mM) do not affect, but the corresponding analogues may inhibit or stimulate, the development of the enzyme. The increase in activity is not inhibited by I.o mM proline and phenylalanine, but is strongly inhibited by similar concentrations of hydroxyproline and p-fluorophenylalanine. Development is also inhibited by high concentrations of actinomycin D. Substances which inhibit development also inhibit increase in the RNA content. These results are discussed and a possible mechanism is suggested. This content is only available as a PDF. © Oxford University Press

SINCLAIR,, JOHN

doi: 10.1093/jxb/18.4.594pmid: N/A

Abstract A study has been made of the ion distributions in the leaf cells of the moss, Hookeria lucens. The cells were subjected to chemical analysis and electrical potential measurements. The observed internal concentrations were 210 mM/1 for potassium, 3.9 mM/1 for sodium, 22 mM/1 for calcium, and 27 mM/1 for chloride. A wide range of electrical potential values were obtained. While a majority of these values were grouped around —145 mV, a significant number were found at —200 mV. Nernst potentials for the various ions were calculated and compared with the observed electrical potentials. This content is only available as a PDF. Author notes 1 Present address: Biochemistry Dept., Allan Hancock Foundation, University of Southern California, Los Angeles, California 90007. © Oxford University Press

PEEL, A., J.

doi: 10.1093/jxb/18.4.600pmid: N/A

Abstract When 14CO2 was applied to the leafy shoot of a stem segment, the xylem of which was perfused with distilled water, a proportion of the activity was detected in the xylem exudate, mainly in the form of sucrose. Experiments in which 36Rb, 22Na, or 32P-phosphate were applied to the cambial surface of a raised portion of bark revealed that these solutes could also pass into the xylem exudate. With the ions, the amount which moved into the xylem vessels was dependent upon the time of year at which the experiments were performed. This content is only available as a PDF. © Oxford University Press

FORD,, J.;PEEL, A., J.

doi: 10.1093/jxb/18.4.607pmid: N/A

Abstract 14C-labelled sugars (sucrose, glucose, and fructose) were supplied to the cambial surface of bark strips of willow, and in conjunction with the aphid stylet technique (Weatherley, Peel, and Hill, 1959), the movement into and distribution of activity in the sieve tube sap was examined. As well as sucrose, free hexoses and sugar phosphates were found to contain the 14C-label, and rapid interconversions occurred between these compounds somewhere along the entry route. Sucrose entry into the sieve elements was accompanied by at least a partial breakdown into its component hexoses, and the involvement of a sugar phosphate pool was also demonstrated. Possible transformation sites on the entry route between the solution bathing the cambial surface and the sieve element vacuole are discussed. This content is only available as a PDF. © Oxford University Press

GOULDING, K., H.;MERRETT, M., J.

doi: 10.1093/jxb/18.4.620pmid: N/A

Abstract The kinetics of 3H-acetate assimilation by Chlorella pyrenoidosa in the light were examined. The primary products of assimilation were glycollate and succinate. After 10 sec glycollate contained 45 per cent and succinate 25 per cent of the tritium incorporated by the cells. The percentage of the total tritium in glycollate and succinate fell with time while that in citrate increased. Initially the specific activities (μc of 3H per μmole of acid) of succinate and glycollate were greater than citrate. When 3H-14C-2-acetate was added to the cells, total dpm for 3H and 14C in glycollate rapidly reached a steady state and gave a 3H/14C ratio of 10, compared with a 3H/14C ratio of 4 in the acetate. This 3H/14C ratio in glycollate is found because 3H is derived from 3H-14C-2-acetate and because the 14C is diluted with cold carbon from elsewhere. The addition of 14CO2 at the same time as 3H-14C acetate decreased the 3H/14C ratio in glycollate but incorporation of 14C from 14CO2 into glycollate was slower than incorporation from 14C-2-acetate. Although 14C from acetate rapidly appeared in glycollate, 14C-labelled glyoxylate was not detected. The 3H/14C ratio observed in glycollate rules out formation of glycollate from acetate via glycoaldehyde. The available evidence did not support glycollate formation via the Calvin cycle. 14C from 14C-Z-acetate appeared in glycollate before it did in phosphoglyceric acid. Total dpm for 3H, 14C, and 3H/l4C ratio in Calvin cycle intermediates were not in equilibrium with glycollic acid. This content is only available as a PDF. © Oxford University Press

BARBER, D., A.;SHONE, M. G., T.

doi: 10.1093/jxb/18.4.631pmid: N/A

Abstract Experiments have been carried out to determine the extent to which rubidium and strontium, recently absorbed by excised barley roots, can be divided into discrete fractions, namely, ions which are extractable with water, those which are exchangeable, and those remaining in the tissue at the end of the experiment. The object of this study was to determine whether the behaviour of cations could be validly interpreted in terms of the electrical double-layer theory as had been previously demonstrated for anions. To facilitate the interpretation of the results obtained, comparable experiments were carried out on a cation-exchange resin and on gelatin. The behaviour of strontium accorded qualitatively with the theory providing allowance was made for effects due to the hydrolysis of negative sites and for the presence of positive charges in the roots. For rubidium, on the other hand, the situation was much more complex. Not only was there evidence even at 0.2°C for sites which retained a high specificity for this ion, but also movement of the ion due to physical diffusion was masked by concurrent metabolic activity. It was concluded that a meaningful separation of the over-all uptake of rubidium into successive steps of exchange absorption and metabolic accumulation cannot be made. This content is only available as a PDF. © Oxford University Press

BUTTERY, B., R.;BOATMAN, S., G.

doi: 10.1093/jxb/18.4.644pmid: N/A

Abstract Various forms of wounding result in increases in hydrostatic pressure in the laticiferous phloem tissue of Hevea brasiliensis; regular tapping, a form of controlled wounding, probably causes a similar response. When a tree is ring-barked, there is a transient fall in turgor immediately above and below the ring, presumably owing to loss of latex during cutting. This is followed by a pressure increase which is particularly marked above the ring, suggesting the accumulation of metabolites. Isolation of an ‘island’ of tissue, by cuts down to the wood, results in a steep fall in turgor within it, although a relatively slow recovery may follow. Partially isolated panels show smaller falls and a more rapid rise. It appears that a functional phloem connexion permits a more rapid recovery of osmotic and turgor pressures following latex losses, both in the isolation experiments and in normal tapping. Growth regulators such as 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) increase latex yields by prolonging latex flow after tapping. In untapped trees treatment with 2,4,5-T results in a slow and fairly small increase in turgor pressure, but this effect may not be apparent if trees are regularly tapped. When the tapping cut is opened, there is a rapid fall in pressure immediately under the cut. This loss in turgor spreads through the latex-vessel system as latex flows towards the cut, but recovery is apparent near the cut even before flow ceases. Pressure gradients indicate a rapid formation of a localized resistance to flow at or near the cut surface. This process appears to play a major part in restricting flow. The increased yields which result both from regular tapping and after 2,4,5-T treatment appear to result from a delay in this sealing process. The mechanisms by which the barrier to flow is built up and delayed by 2,4,5-T treatment are not clearly understood. This content is only available as a PDF. Author notes 1 Present address: Research Station, Canada Department of Agriculture, Harrow, Ontario, Canada. 2 Present address: Jealott's Hill Research Station, nr. Bracknell, Berks., England. © Oxford University Press

DALE, J., E.

doi: 10.1093/jxb/18.4.660pmid: N/A

Abstract Disks cut from leaves of different ages were cultured on media with and without added carbohydrate. Relative growth-rates for changes in area of disks were found to be similar to those for intact leaves, and to decline as the age of the parent material increased. Cellular changes occurring concurrently with this decline were followed. Protein per cell was found to increase in disks cultured in the light on sucrose but not in the absence of supplied carbohydrate. This requirement for carbohydrate could not be satisfied by materials produced endogenously in the light, even though under these conditons starch was formed and there were large increases in cell-wall material. Changes in disks and in intact leaves of the same age were broadly similar. The large effects of light and carbohydrate supply are discussed in relation to disk expansion and leaf growth in general. This content is only available as a PDF. © Oxford University Press