Phloem unloading in tobacco sink leaves: insensitivity to anoxia indicates a symplastic pathway

Planta ◽  
1987 ◽  
Vol 171 (1) ◽  
pp. 73-81 ◽  
Author(s):  
R. Turgeon
Keyword(s):  
Phloem Unloading ◽  
Symplastic Pathway

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

2020 ◽  
Vol 40 (3) ◽  
pp. 391-412 ◽  
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.

Histochemical Examination of Invertase Activities in the Growing Tip of the Plant Root

2017 ◽  
Vol 10 (1) ◽  
pp. 35-45
Author(s):  
N.F. Lunkova ◽  
N.A. Burmistrova ◽  
M.S. Krasavina
Keyword(s):  
Plant Root ◽  
Invertase Activity ◽  
Root Tip ◽  
Elongation Zone ◽  
Root Tips ◽  
Phloem Unloading ◽  
Meristem Cell ◽  
Transition To Elongation ◽  
Different Tissues

Background:A growing part of the root is one of the most active sinks for sucrose coming from source leaves through the phloem. In the root, sucrose is unloaded from conducting bundles and is distributed among the surrounding cells. To be involved in the metabolism, sucrose should disintegrate into hexoses by means of degrading enzymes.Aims:The aim of this research was to explore the possibility of the involvement of one such enzymes, invertase, in phloem unloading as well as distribution of its activity in the functionally different tissues of the plant root tips.Method:To estimate the enzyme activities in root tissues, we applied two techniques: the histochemical method using nitro blue tetrazolium. The localization of phloem unloading was studied with carboxyfluorescein, a fluorescent marker for symplastic transport.Results:Invertase activity was not detected in the apical part of the meristem. It appeared only between the basal part of this zone and the beginning of the elongation zone. There is the root phloem unloading in that area. Invertase activity increased with increasing the distance from the root tip and reached the highest values in the region of cell transition to elongation and in the elongation zone. The activities of the enzyme varied in different tissues of the same zone and sometimes in the neighboring cells of the same tissue. Biochemical determination of invertase activity was made in the maize root segments coincident to the zones of meristem, cell elongation and differentiation. The results of both methods of determination of invertase activity were in agreement.Conclusion:It was concluded that phloem unloading correlated with invertase activity, possibly because of the activation of invertase by unloaded sucrose. Invertase is one of the factors involved in the processes preparing the cells for their transition to elongation because the concentration of osmotically active hexoses increases after cleavage of sucrose, that stimulates water entry into the cells, which is necessary for elongation growth.

scholarly journals Phloem unloading follows an extensive apoplasmic pathway in cucumber (Cucumis sativus L.) fruit from anthesis to marketable maturing stage

2011 ◽  
Vol 34 (11) ◽  
pp. 1835-1848 ◽  
Author(s):  
LIPING HU ◽  
HUIHUI SUN ◽  
RUIFU LI ◽  
LINGYUN ZHANG ◽  
SHAOHUI WANG ◽  
...  
Keyword(s):  
Cucumis Sativus ◽  
Phloem Unloading ◽  
Cucumis Sativus L

scholarly journals Induction of Phloem Unloading in Arabidopsis thaliana Roots by the Parasitic Nematode Heterodera schachtii

1996 ◽  
Vol 112 (4) ◽  
pp. 1421-1427 ◽  
Author(s):  
A. Bockenhoff ◽  
DAM. Prior ◽  
FMW. Grundler ◽  
K. J. Oparka
Keyword(s):  
Arabidopsis Thaliana ◽  
Parasitic Nematode ◽  
Heterodera Schachtii ◽  
Phloem Unloading

scholarly journals Phloem Unloading in Developing Leaves of Sugar Beet

1987 ◽  
Vol 83 (1) ◽  
pp. 49-52 ◽  
Author(s):  
J. Gougler Schmalstig ◽  
Donald R. Geiger
Keyword(s):  
Sugar Beet ◽  
Phloem Unloading

A morphometric analysis of the phloem-unloading pathway in developing tobacco leaves

Planta ◽  
1988 ◽  
Vol 176 (3) ◽  
pp. 307-318 ◽  
Author(s):  
Biao Ding ◽  
M. V. Parthasarathy ◽  
Karl Niklas ◽  
Robert Turgeon
Keyword(s):  
Morphometric Analysis ◽  
Phloem Unloading ◽  
Tobacco Leaves

scholarly journals Transcripts repressed at the stop of phloem unloading highlight the energy efficiency of sugar import in the ripening V. vinifera fruit.

2021 ◽  
Author(s):  
Stefania Savoi ◽  
Laurent Torregrosa ◽  
Charles Romieu
Keyword(s):  
Cell Wall ◽  
Regulatory Elements ◽  
Solute Concentration ◽  
Growth Patterns ◽  
Individual Growth ◽  
Sugar Accumulation ◽  
Minor Role ◽  
Phloem Unloading ◽  
Sugar Transporters ◽  
A Minor

AbstractTranscriptomic changes at the cessation of sugar accumulation in the pericarp of Vitis vinifera were addressed on single berries re-synchronized according to their individual growth patterns. The net rates of water, sugars and K+ accumulation inferred from individual growth and solute concentration confirmed that these inflows stopped simultaneously in the ripe berry, while the small amount of malic acid remaining at this stage was still being oxidized at a low rate. Resynchronized individual berries displayed negligible variations in gene expression among triplicates. RNA-Seq studies revealed sharp reprogramming of cell wall enzymes and structural proteins, associated with an 80% repression of specific sugar transporters and aquaporins on the plasma or tonoplast membranes, at the stop of phloem unloading in the three genotypes and two environments investigated. The prevalence of SWEET transporters suggests that electrogenic transporters would just play a minor role on the plasma membrane of SE/CC complex, and the one of the flesh, while sucrose/H+ exchangers dominate on its tonoplast. Cis-regulatory elements present in their promoters allowed to sort these transporters in different groups, also including specific TIPs and PIPs paralogs, and cohorts of cell wall related genes. These results lead us to propose which structural, developmental and energy adaptations would give this fruit such a power of attraction for water and photoassimilates.

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