TRANSPORT OF PHOTOASSIMILATES IN YOUNG TREES OF FRAXINUS AND SORBUS : MEASUREMENT OF TRANSLOCATION IN VIVO

: Translocation of photoassimilates was studied on 2-year-old trees of Fraxinus excelsior and Sorbus aucuparia using the short-lived isotope 11C. Leaflets of different leaves on the same plants were radiolabeled showing that both carbon distribution and speeds of transport may vary with leaf position. Within 2 h after pulse feeding with 11CO2, mainly the lower leaves distributed radiolabel to the roots in Fraxinus, whereas in Sorbus, the upper leaves were also involved. By repeated pulse applications to selected leaves, temporal profiles of 11C transport were followed on individual plants from April to October. Early in the season, within 2 h after pulse labelling, 30–40% of the fixed radiolabel was exported from leaves in Fraxinus and about 20% in Sorbus. Thereafter export started to decline, particularly in Fraxinus, and the distribution of radiolabel between stem and roots could alter depending on the position of the feed leaf. Speeds of translocation obtained along the rachis and stem showed high variability, but they did not necessarily slow down before the end of the season. The speeds monitored at the rachis of Fraxinus leaves (30–75 cm h−1) were generally lower than those found on Sorbus (50–130 cm h−1). As reported in the literature, the two tree species translocate different carbohydrates and show remarkable differences in the ultrastructure of their vascular systems. In that context it is interesting that the temporal profiles of 11C radioactivity obtained from F. excelsior and S. aucuparia could clearly be distinguished by their characteristic shapes. The results are discussed in terms of anatomical characteristics of the conducting tissues and possible differences in phloem loading.

[1]  J. Beltrán,et al.  Distribution of photoassimilates in the pea plant: chronology of events in non-fertilized ovaries and effects of gibberellic acid , 1989, Planta.

[2]  M. Madore,et al.  Stachyose and mannitol transport in olive (Olea europaea L.) , 1993, Planta.

[3]  Ute Harms,et al.  Localization of a storage protein in the wood ray parenchyma cells of Taxodium distichum (L.) L. C. Rich. by immunogold labeling , 1992, Trees.

[4]  Y. Gamalei.  Structure and function of leaf minor veins in trees and herbs , 1989, Trees.

[5]  Y. Gamalei.  Structure and function of leaf minor veins in trees and herbs , 1989, Trees.

[6]  P. Saranpää,et al.  Lipids and sterols of Pinus sylvestris L. sapwood and heartwood , 1987, Trees.

[7]  R. Dickson,et al.  Translocation pathways in the petioles and stem between source and sink leaves of Populus deltoides Bartr. ex Marsh. , 1982, Planta.

[8]  M. Zimmermann.  Translocation velocity and specific mass transfer in the sieve tubes of Fraxinus americana L. , 1969, Planta.

[9]  P. Larson.  Phyllotactic transitions in the vascular system of Populus deltoides bartr. as determined by 14C labeling , 2004, Planta.

[10]  J. W. Palmer,et al.  Carbon partitioning between apple fruits: short- and long-term response to availability of photosynthate , 1997 .

[11]  S. Jahnke,et al.  Photoassimilate translocation in the petiole of Cyclamen and Primula is independent of lateral retrieval , 1997 .

[12]  M. R. Thorpe,et al.  A method for monitoring γ-radiation from an extended source with uniform sensitivity , 1996 .

[13]  J. Volenec,et al.  Seasonal variations in soluble sugars and starch within woody stems of Cornus sericea L. , 1993, Tree physiology.

[14]  A. Bel,et al.  Strategies of Phloem Loading , 1993 .

[15]  A. Moing,et al.  Carbon fluxes in mature peach leaves. , 1992, Plant physiology.

[16]  R. Turgeon,et al.  The evidence for symplastic Phloem loading. , 1991, Plant physiology.

[17]  T. Koike.  Photosynthesis and expansion in leaves of early, mid, and late successional tree species, birch, ash, and maple , 1987 .

[18]  J. D. Goeschl,et al.  Experimental tests of the Münch-Horwitz theory of phloem transport: effects of loading rates , 1986 .

[19]  R. E. Dickson,et al.  14C Translocation pathways in honeylocust and green ash: Woody plants with complex leaf forms , 1986 .

[20]  M. R. Thorpe,et al.  Further Evidence of Apoplastic Unloading into the Stem of Bean: Identification of the Phloem Buffering Pool , 1984 .

[21]  N. Nelson,et al.  Distribution of [14C]‐labeled photosynthates within intensively cultured Populus clones during the establishment year , 1983 .

[22]  R. Drouin,et al.  Translocation of 11C from leaves of Helianthus, Heracleum, Nymphoides, Ipomoea, Tropaeolum, Zea, Fraxinus, Ulmus, Picea, and Pinus: comparative shapes and some fine structure profiles , 1979 .

[23]  J. Troughton,et al.  Relations between Light Level, Sucrose Concentration, and Translocation of Carbon 11 in Zea mays Leaves. , 1977, Plant physiology.

[24]  M. A. Saunders,et al.  Translocation and accumulation of translocate in the sugar beet petiole. , 1969, Plant physiology.

[25]  R. Bieleski.  Accumulation and Translocation of Sorbitol in Apple Phloem , 1969 .

[26]  K. L. Webb,et al.  Sorbitol Translocation in Apple , 1962, Science.

[27]  M. Zimmermann.  Translocation of Organic Substances in Trees. I. The Nature of the Sugars in the Sieve Tube Exudate of Trees. , 1957, Plant physiology.