The storage of fructans in the internode of cereals is an important phenomenon because it serves as a supplement to contributions from the remaining green tissue to the filling of grains in the head and thus to yield. Fructan storage and remobilization is also an interesting biological phenomena ideal for studying phloem transport. Sucrose, the substrate for fructan synthesis in the internode regions, is transported via the phloem, so storage of fructans contribute to sink strength of the internode region. In remobilization from the internode to the developing grain, fructans serve as the principal carbohydrate utilized thus the internode becomes a source tissue. Control of fructan synthesis and degradation in the internode then is one of the chief components that allows a sink tissue to change into a source tissue. How do tissues unload assimilates for storage in the internode as "sink tissues", later become "source tissues" for delivery of carbohydrates to the developing caryopsis in the head? Regulation of this transition from sink to source tissues in mature cells remains one of the fundamental questions of carbon partitioning in plants. Partitioning into and out of the fructan pool in cereal internodes is one of the unique systems where this regulation can be studied. This Chapter reviews recent information about fructan storage and repartitioning in relation to source and sink transitions.


Stem remobilization was last reviewed by Schnyder at the Second International Fructan Symposium in 1992 (1). The Review by Schnyder (1) contains numerous references the earliest being from the year 1869 (2) to the latest in 1992 (3, 4). At the Third International Symposium in 1996 remobilization was not addressed consequently this Chapter presents a review of the literature of fructan increase and decrease in the internode of cereals principally barley (Hordeum vulgare L.) and wheat (Triticum aestivum L) published after 1992. From the literature prior to 1993 Schnyder (1) concluded fructans could account for up to 45% of the dry weight of the stem. The amount however was variable due to cultivar differences and in the ability of these cultivars to mobilize stem reserves. Schnyder further reports that the amount of the reserves accumulated or mobilized is dependent on the environment during accumulation or during grain filling (1). The variation in genetic response to the environment has resulted in a large range, 11 to 44%, for the contribution of stored stem reserves to dry matter accumulated in the caryopsis (1).


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