Yl. Ruan et al., THE DIFFERENTIAL EXPRESSION OF SUCROSE SYNTHASE IN RELATION TO DIVERSE PATTERNS OF CARBON PARTITIONING IN DEVELOPING COTTON SEED, Plant physiology, 115(2), 1997, pp. 375-385
Developing cotton (Gossypium hirsutum L.) seed exhibits complex patter
ns of carbon allocation in which incoming sucrose (Suc) is partitioned
to three major sinks: the fibers, seed coat, and cotyledons, which sy
nthesize cellulose, starch, and storage proteins or oils, respectively
. In this study we investigated the role of Suc synthase (SuSy) in the
mobilization of Suc into such sinks. Assessments of SuSy gene express
ion at various levels led to the surprising conclusion that, in contra
st to that found for other plants, SuSy does not appear to play a role
in starch synthesis in the cotton seed. However, our demonstration of
functional symplastic connections between the phloem-unloading area a
nd the fiber cells, as well as the SuSy expression pattern in fibers,
indicates a major role of SuSy in partitioning carbon to fiber cellulo
se synthesis. SuSy expression is also high in transfer cells of the se
ed coat facing the cotyledons. Such high levels of SuSy could contribu
te to the synthesis of the thickened cell walls and to the energy gene
ration for Suc efflux to the seed apoplast. The expression of SuSy in
cotyledons also suggests a role in protein and lipid synthesis. In sum
mary, the developing cotton seed provides an excellent example of the
diverse roles played by SuSy in carbon metabolism.