PLANT PHYSIOLOGY , Vol 115, Issue 2 609-616, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Sucrose Accumulation in the Sugarcane Stem Is Regulated by the Difference between the Activities of Soluble Acid Invertase and Sucrose Phosphate Synthase
Y. J. Zhu, E. Komor and P. H. Moore
Hawaii Agriculture Research Center (Y.J.Z.), United States Department of Agriculture, Agricultural Research Service (P.H.M.), 99-193 Aiea Heights Drive, Suite 300, Aiea, Hawaii 96701
To assess the relative importance of morphological and biochemical factors
in the regulation of sucrose (Suc) accumulation in the sugarcane (Saccharum
spp. hybrids) stem, we investigated morphological and biochemical
correlates of Suc accumulation among parents and progeny of a family
segregating for differences. In contrast to the parents, no relationship
was observed between morphology and the level of Suc accumulation among the
progeny. The level and timing of Suc accumulation in the whole stalk and
within individual internodes was correlated with the down-regulation of
soluble acid invertase (SAI) activity. High SAI activity prevented most,
but not all, Suc accumulation. There was a critical threshold of SAI
activity above which high concentrations of Suc did not accumulate. This
low level of SAI activity was always exceeded in the internodes of the
lower-Suc-storing genotypes. However, low activity of SAI was not
sufficient by itself to account for the Suc accumulation in the
higher-Suc-storing genotypes. Major differences in Suc accumulation among
the population were attributed to the difference between activities of SAI
and Suc phosphate synthase, provided SAI is below the critical threshold
concentration. This result is not unexpected, since the pathway of Suc
transport for storage involves Suc hydrolysis and resynthesis.