Bidirectional Translocation of Sugars in Sieve Tubes of Squash Plants

Trip, P.; Gorham, Paul R.

doi:10.1104/pp.43.6.877

Cited by 44 publications

(8 citation statements)

References 11 publications

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“…1). This period of bidirectional transport through a petiole is well established in the literature (1,19) and consistently occurs in leaves and petioles which were approximately half-grown (34 shows the decrease in area importing from source regions. Data points for the latter omitted for clarity.…”

mentioning

confidence: 55%

Structural and Physiological Changes in Sugar Beet Leaves during Sink to Source Conversion

Fellows

Geiger²

1974

Plant Physiol.

136

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The onset of export during leaf development was correlated with changes in metabolism and ultrastructure and with patterns of solute distribution in the developing seventh leaf of sugar beet (Beta vulgaris L.) in order to study the cause of initiation of translocation. Infrared gas analysis of carbon dioxide uptake showed a broad peak for net photosynthesis dm(2 at 35 to 40% final laminar length. Pulse labeling with 14CO2 demonstrated that maximum import of translocate occurred at 25% final laminar length; export was first observed at 35% final laminar length. Between 40 and 50% final laminar length a rapid increase in amount of export occurred, primarily as a result of the increase in the area of leaf which was exporting. Whole leaf autoradiography revealed that onset of phloem loading spread basipetally from the leaf tip; loading was initiated at about 22% final laminar length and was essentially complete by 50% final laminar length. Those areas which clearly exhibited loading no longer imported from other parts of the plant while the area in transition still appeared to import label from source regions.There was little difference between source and sink leaf tissue in the kinetic parameters Kj and Jmas (30) for uptake of exogenous sucrose supplied via free space. The concentration of solutes in sieve elements and companion cells of the sink leaf was highest in the mature tip area and gradually decreased in the direction of the immature base. There appeared to be no dramatic structural transformation within the phloem of the minor veins that was closely correlated with the time when phloem loading or export began. Rather, there appeared to be a gradual differentiation of phloem which resulted in a sizable proportion of the population of minor vein sieve elements and companion cells attaining maturity in the older sink regions prior to initiation of phloem loading. The area of the leaf undergoing development appeared to exhibit the beginnings of phloem loading 30 to 45 hours prior to onset of export. Import continued into the area in transition until the full level of vein loading was attained. Structural maturation of the phloem and onset of phloem loading are felt to be more preparatory in nature rather than immediately causal events which triggered export.The initiation of export out of a developing leaf, we believe, is the result of the increasing solute content within the sieve element and companion cells of the minor veins, in particular.The higher osmotic pressure in the sieve tubes causes a reversal of the previously inward directed gradient and produces a mass

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mentioning

confidence: 55%

Structural and Physiological Changes in Sugar Beet Leaves during Sink to Source Conversion

Fellows

Geiger²

1974

Plant Physiol.

136

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“…Such a significant loss, in this case probably representing a continuous exchange with indigenous water, may explain why labeled water movement in the phloem presents some patterns different from that of sucrose and other tracers (Biddulph and Cory, 1957;Gage and Aronoff, 1960;Choi and Aronoff, 1966;and Trip and Gorham, 1968). Actually the plasmalemma of sievetube members should be permeable to water even though they are quite impermeable to sucrose.…”

Section: Radial Loss From the Phloemmentioning

confidence: 91%

“…This, of course, is the only sense in which bidirectional movement has significance-and it is still doubtful that it has ever been successfully demonstrated with materials normally found in plants. The experiment that appears most convincing is that of Trip and Gorham -(1968) wherein tritiated sugar (glucose-6-T) was induced to move into a young leaf that had just begun to export l~-labeled sugar (from 1~02). The questionable aspect of this work is with the state of maturity of the leaf in whose petiole the bidirectional movement was supposed to occur.…”

Section: E Bidirectional Movementmentioning

confidence: 99%

Mechanisms of Translocation of Plant Metabolites

Biddulph

2015

Physiological Aspects of Crop Yield

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“…But this is not bidirectional transport in the controversial sense. Some pretty hard evidence for bidirectional transport through a single sieve tube has been produced by Trip and Gorham (47), although even their data are not unequivocal. The validity of experimental evidence is rarely absolute; it always depends on more or less subjective interpretation.…”

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confidence: 99%

Long Distance Transport

Zimmermann

1974

Plant Physiol.

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A few years ago, I attended a 1-day symposium on long distance transport at a national meeting in a country abroad. Towards the end of the day, as the participants became tired and no general agreement was in sight, one observer from an allied discipline remarked, "Why can't you translocation workers make any progress, you still discuss the same miserable old models that were proposed 40 The 19th century produced innumerable theories of sap ascent. The "climbing theory," which originated with Malpighi and was advocated as late as 1910 by LeClerc, visualized the water as moving up the xylem in steps and being held in place by the ridges of the vessels in a valvelike manner. Another obscure concept is that of the "Jamin's chains," chains of bubbles in vessels that were said to somehow propel the water up the stem into the leaves while in fact they were a mere artifact of preparation. There were many others. The main problem was the difficulty of seeing water in the conducting elements. Water in vessels is usually under tension, and when a preparation is made for observation, air is drawn into the vessels. This gave rise to the notion that vessels are not normally water filled, an opinion held by the well known plant physiologist, Sachs, and maintained by some workers until quite recently on the basis of sophisticated reasoning. Sachs also maintained that diffusion is the mechanism by which photosynthetic products are distributed throughout the plant. Because of his great influence, Sachs' effect upon translocation research was rather negative, although he was undoubtedly an outstanding scientist in other respects.The turn of the century brought significant progress. It was recognized that the ascent of sap in the xylem is a physical phenomenon and does not depend on living cells (42), although this concept was challenged repeatedly until relatively recent times. A significant discovery was the observation that twigs (4) and models involving evaporation of water from clay cups (1,14) could raise water above barometric height. These experiments gradually gave rise to Dixon's cohesion theory (11). Dixon was a sort of radical among many respected scholars who still maintained a variety of "vital" theories, including the idea that root pressure provides the necessary force to push water into the top of trees. However, evidence in support of the cohesion theory accumulated gradually. Friedrich (18), who in 1897 invented the dendrograph to record tree growth, found diurnal shrinkage of trees which obviously was not a result of growth but of a fluctuating water content of the stem. This was later followed up in more detail by MacDougal et al. (30).Renner was able to demonstrate tensile water in fern sporangia (37) and Dixon made the first attempt to measure tensions in plants directly (1 1).During the first quarter of the 20th century little progress was made in phloem-transport research. It is very likely that interest which had been so keen during the second part of the preceding century turned to other problems. Plant...

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Bidirectional Translocation of Sugars in Sieve Tubes of Squash Plants

Cited by 44 publications

References 11 publications

Structural and Physiological Changes in Sugar Beet Leaves during Sink to Source Conversion

Structural and Physiological Changes in Sugar Beet Leaves during Sink to Source Conversion

Mechanisms of Translocation of Plant Metabolites

Long Distance Transport

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