Studies on Morphogenesis in Rice Plant : IX. On the structure of vascular bundles and phloem transport in the spikelet

A technique has been developed to biosynthesize a water-soluble extract of 11C-labelled photosynthate high in [11C]sucrose. The extract can be produced in less than 1 half-life (20 min) and is of high activity. When 11C-labelled extract was fed to the individual vascular bundles of other living plants, 11C was taken up and translocated, and on the basis of direct and indirect evidence it was largely in the form of [11C]sucrose.11C-labelled extract, if fed to a flap or gentle scraping on the surface of a sunflower stem (or corn, cow-parsnip, pine, or elm) was translocated both apically and basally from the feed point. Incisions into xylem vessels produced very rapid tracer movements which seemed to be associated with xylem vessel liquid cavitation and also transpiration pull. Shallower cuts produced translocation patterns similar to 11CO2 leaf feedings and are thought to be largely in the phloem. Phloem transport was blocked by ice chilling; xylem transport was only slightly affected by ice, if at all. Phloem translocation profiles often displayed steps at the front of mass flow, and later appeared to have peaks of activity moving along them. The movements were sometimes rapid (>6 cm min−1) and appeared to be complex, as if different channels were conducting at different speeds in parallel.

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Aspects arising from the use of inhibitors in phloem transport studies

Canadian Journal of Botany ◽

10.1139/b80-104 ◽

1980 ◽

Vol 58 (7) ◽

pp. 816-820 ◽

Cited By ~ 4

Author(s):

Johannes Willenbrink

Keyword(s):

Carbon Metabolism ◽

Cell Membranes ◽

Cytochalasin B ◽

Potassium Cyanide ◽

Phloem Transport ◽

Vascular Bundles ◽

Pelargonium Zonale ◽

Transport Studies ◽

Central Bundle ◽

Sugar Phosphates

Experiments on the movement of 14C-assimilates through dissected vascular bundles of Pelargonium zonale are reviewed. Potassium cyanide (KCN) applied to the central bundle causes localized, reversible blockage of transport. Both antimycin and atractylate, but not ouabain inhibit the movement of metabolites through the phloem. The proton ionophore, CCCP completely suppresses translocation at 10−7 M, however, cell membranes are damaged. Valinomycin applied to cut bundles causes serious disturbances in carbon metabolism as shown by the increased label in sugar phosphates. Cytochalasin B does not affect translocation. Limitations on conclusions drawn from inhibitor studies are discussed.

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Symplasmic phloem unloading and post-phloem transport during bamboo internode elongation

Tree Physiology ◽

10.1093/treephys/tpz140 ◽

2020 ◽

Vol 40 (3) ◽

pp. 391-412 ◽

Cited By ~ 2

Author(s):

Lin Deng ◽

Pengcheng Li ◽

Caihua Chu ◽

Yulong Ding ◽

Shuguang Wang

Keyword(s):

Parenchyma Cell ◽

Phloem Transport ◽

Assimilate Transport ◽

Vascular Bundles ◽

Radial Transport ◽

Phloem Unloading ◽

Transport Pathways ◽

Bamboo Shoots ◽

Parenchyma Cells ◽

Symplastic Pathway

Abstract In traditional opinions, no radial transportation was considered to occur in the bamboo internodes but was usually considered to occur in the nodes. Few studies have involved the phloem unloading and post-phloem transport pathways in the rapid elongating bamboo shoots. Our observations indicated a symplastic pathway in phloem unloading and post-unloading pathways in the culms of Fargesiayunnanensis Hsueh et Yi, based on a 5,6-carboxyfluorescein diacetate tracing experiment. Significant lignification and suberinization in fiber and parenchyma cell walls in maturing internodes blocked the apoplastic transport. Assimilates were transported out of the vascular bundles in four directions in the inner zones but in two directions in the outer zones via the continuum of parenchyma cells. In transverse sections, assimilates were outward transported from the inner zones to the outer zones. Assimilates transport velocities varied with time, with the highest values at 0):00 h, which were affected by water transport. The assimilate transport from the adult culms to the young shoots also varied with the developmental degree of bamboo shoots, with the highest transport velocities in the rapidly elongating internodes. The localization of sucrose, glucose, starch grains and the related enzymes reconfirmed that the parenchyma cells in and around the vascular bundles constituted a symplastic pathway for the radial transport of sugars and were the main sites for sugar metabolism. The parenchyma cells functioned as the ‘rays’ for the radial transport in and between vascular bundles in bamboo internodes. These results systematically revealed the transport mechanism of assimilate and water in the elongating bamboo shoots.

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