In:
Functional Plant Biology, CSIRO Publishing, Vol. 27, No. 9 ( 2000), p. 815-
Abstract:
This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
Carbohydrates are synthesised in photosynthetically active source tissues and exported, in most species in the form of sucrose, to photosynthetically less
active or inactive sink tissues. Sucrose hydrolysis at the site of utilisation contributes to phloem unloading. This phenomenon links sink metabolism with
phloem transport to, and partitioning between, sinks. Invertases catalyse the irreversible hydrolysis of sucrose and thus are expected to contribute to
carbohydrate partitioning. Different invertase isoenzymes may be distinguished based on their intracellular location, their isoelectric points and pH optima.
Extracellular, cell-wall-bound invertase is uniquely positioned to supply carbohydrates to sink tissues via an apoplasmic pathway, and links the
transport sugar sucrose to hexose transporters. A number of studies demonstrate an essential function of this invertase isoenzyme for phloem
unloading, carbohydrate partitioning and growth of sink tissues. Extracellular invertases were shown to be specifically expressed under conditions that
require a high carbohydrate supply to sink tissues. Further, their expression is upregulated by a number of stimuli that affect source–sink relations.
Substrate and reaction products of invertases are not only nutri-ents, but also signal molecules. Like hormones and in combination with hormones and
other stimuli, they can regu-late many aspects of plant development from gene expression to long-distance nutrient allocation. Based on studies in
Chenopodium rubrum, tomato (Lycopersicon esculentum) and tobacco
(Nicotiana tabacum), the regulation of extracellular invertase and its function in assimilate partitioning, defence reactions and
sugar signal transduction pathways are discussed.
Type of Medium:
Online Resource
ISSN:
1445-4408
Language:
English
Publisher:
CSIRO Publishing
Publication Date:
2000
SSG:
12
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