Phloem loading

Van Bel AJE, Gamelai YV, Ammerlan A, Bik LPM. Dissimilar phloem loading in leaves with symplasmic and apoplasmic minor-vein configurations. Planta 1992 186 518-525. 

This rate Is much slower than normal phloem loading, for example In healthy soybeans ( ). 

Riesmeier, J.W., Willmitzer, L., and Frommer, W.B., Evidence for an essential role of the sucrose transporter in phloem loading and assimilate partitioning, EMBO J., 13, 1-7, 1994. 

Phloem Loading. How does sucrose which is produced in the mesophyll cells of source leaves enter the translocation stream and how does this sucrose exit from the translocation stream in the sink regions More importantly, can this tell us anything about agrichemical transport Figure 1A shows an autoradiograph of a source leaf following the accumulation of C-sucrose ( C-label is in white). The label is accumulated markedly into the vein network com-... 

The characteristics of the phloem loading system can be summarized as follows. Sucrose loading is (1) dependent on metabolism (2) carrier-mediated (3) selective for sucrose (4) maintains a high concentration inside the phloem which is the basis for the osmotically-driven mass flow of solutions and (5) dependent on the factors which control assimilate supply to the loading sites (e.g., photosynthesis, sucrose synthesis, and sucrose movement between leaf cells, and within subcellular compartments such as the cytoplasm and vacuole) ((>, 7 ). 

Vascular Anatomy. One aspect of the translocation system that is often overlooked is the influence of the structural features of the plant s vascular system on solute transport. For example, although much of what is known about phloem loading has been derived from a few dicotyledon leaves, all dicotyledon leaves are not similar. A notable example is the soybean leaf. Soybean leaves are specialized in that they have a unique cell type called the paraveinal mesophyll... 

Figure 2. Model for phloem loading of sucrose. See text for details. Reproduced with permission from Ref. 8. Copyright 1980. Academic Press.

Van Bel, A.J.E. 1993. Strategies of phloem loading. Annu. Rev. Plant Physiol. Plant Mol. Biol. 

Phloem loading of sucrose is decisive for the speed of mass flow, because sucrose is the dominant solute in the sieve tube sap of nearly all plant species. The interaction of sucrose metabolism, starch storage and phloem export in source leaves and the effects on sugar status in phloem was presented. The sucrose concentrations was revealed by a NMR imaging method. 

Reduced carbon transport from leaves dne to inhibition of phloem loading... 

Braun DM, Wang L, Ruan YL. Understanding and manipulating sucrose phloem loading, unloading, metabolism, and signalling to enhance crop yield and food security. J Exp Bot. 65(7) (2014) 1713-1735. 

F. Malek and D. A. Baker, Proton Co-transport of Sugars in Phloem Loading, Planta 135, 297-299 (1977). 

Hao, J. H., et al. (2014). Low night temperatures inhibit galactinol synthase gene expression phloem loading in melon leaves during fruit development. Russian Journal of Plant... 

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