Abstract
Uniformly labelled [14C]glucose was introduced into the xylem of segments of willow stem. Forty-eight hours later sieve-tube sucrose was collected via servered aphid stylets, and the distribution of radioactivity in the hexose moieties of this was compared with the distribution in those of sucrose extracted from the segment. Very little correlation was found between the two sets of values, indicating possible inversion during loading. This lack of correlation could not be attributed to contributions to the sieve-tube sucrose from pools of labelled hexoses in the segment. Further experiments, however, showed quite high degrees of correlation between sieve-tube sucrose and sucrose extracted from the wood, indicating that the latter tissue was a major source of sieve-tube sucrose. This conclusion was substantiated in experiments in which sieve-tube exudate, obtained from stem segments, was compared with exudate obtained from the isolated bark of the segment. In other experiments, stylets were established on stem segments, then on isolated pieces of bark obtained from these segments. Sucrose and potassium exudation rates fell by as much as 50% on removing the bark from the segment. It was not possible to formulate a precise figure for the contribution of the wood to stylet exudation owing to injury effects and the complexity of the experimental system. No firm evidence could be found in support of the view that sucrose is inverted during loading of sieve elements from the storage cells of the stem.
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References
Brovchenko, M.I. (1967) Some proofs of the splitting of sucrose during its movement from mesophyll into the fine bundles of sugar beet leaves. Sov. Plant Physiol. 14, 352–359
Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A., Smith, F. (1956) A colorimetric method for determination of sugars and related substances. Anal. Chem. 28, 350–356
Ford, J., Peel, A.J. (1967) The movement of sugars into the sieve elements of bark strips of willow. I. Metabolism during transport. J. Exp. Bot. 18, 607–619
Gardner, D.C.J., Peel, A.J. (1971) Transport of sugars into the sieve elements of willow. Phytochemistry 10, 2621–2625
Geiger, D.R. (1975) Phloem loading. In: Encyclopedia of plant physiology, N.S., vol. 1: Transport in plants I. Phloem transport, pp. 395–431, Zimmermann, M.H., Millburn, J.A., eds. Springer. Berlin Heidelberg New York
Giaquinta, R. (1976) Evidence for phloem loading from the apoplast. Plant Physiol. 57, 872–875
Giaquinta, R. (1977) Sucrose hydrolysis in relation to phloem loading in Beta vulgaris. Plant Physiol. 60, 339–343
Giaquinta, R. (1980) Mechanism and control of phloem loading of sucrose. Ber. Dtsch. Bot. Ges. 93, 187–201
Hatch, M.D., Glasziou, K.T. (1964) Direct evidence for translocation of sucrose in sugar cane leaves and stems. Plant Physiol. 39, 180–184
Heyser, W. (1980) Phloem loading in the maize leaf. Ber. Dtsch. Bot. Ges. 93, 221–228
Jones, M.G.K., Outlaw, W.H., Lowry, O.H. (1977) Enzyme assay of 10-7 to 10-4 moles of sucrose in plant tissues. Plant Physiol. 60, 379–383
Komor, E., Rotter, M., Waldhauser, J., Martin, E., Cho, B.H. (1980) Sucrose proton symport for phloem loading in the Ricinus seedling. Ber. Dtsch. Bot. Ges. 93, 211–219
Kozlowski, T.T., Keller, T. (1966) Food relations of woody plants. Bot. Rev. 32, 293–382
Kramer, P.J., Kozlowski, T.T. (1979) Physiology of woody plants. Academic Press, New York San Francisco London
Kriedemann, P., Beevers, H. (1967) Sugar uptake and translocation in the castor bean seedling. II. Sugar transformations during uptake. Plant Physiol. 42, 174–180
Kursanov, A.L., Brovchenko, M.I., Butenko, E.P. (1967) Transformation of sugars absorbed by the leaf tissues of sugar beets. Sov. Plant Physiol. 14, 684–691
Malek, F., Baker, D.A. (1977) Proton co-transport of sugars in phloem loading. Planta 135, 297–299
Peel, A.J. (1975) Investigations with aphid stylets into the physiology of the sieve tube. In: Encyclopedia of plant physiology, N.S., vol. 1: Transport in plants I. Phloem transport, pp. 171–195, Zimmermann, M.H., Milburn, J.A., eds. Springer, Berlin Heidelberg New York
Sacher, J.A., Hatch, M.D., Glasziou, K.T. (1963) Sugar accumulation cycle in sugar cane. III. Physical and metabolic aspects of cycle in immature storage tissues. Plant Physiol. 38, 348–354
Wenger, K.R. (1953) The sprouting of sweetgum in relation to season of cutting and carbohydrate content. Plant Physiol. 28, 35–49
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Peel, A.J. Loading and source of sugars for the sieve elements in stems of willow. Planta 158, 512–516 (1983). https://doi.org/10.1007/BF00397242
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DOI: https://doi.org/10.1007/BF00397242