In the U.S., sugarbeet usually is planted in the spring and harvested as late as possible in the fall to allow maximum growth and yield potential. Processing companies use polarimetry as a rapid means of analysis of sucrose at the time of delivery of each harvested truckload of sugarbeets, and grower payments are based on their sugarbeets' sucrose content as well as tonnage. In some years, processing laboratory sucrose data appear to show an unexpected, rather sudden late-season increase in sucrose percentage in the roots. Much confusion has existed about this apparent late-season accumulation of sucrose, particularly with regard to the effects of temperature and precipitation. A phytochemical and physiological analysis of the potential for accumulation of sucrose and several related oligosaccharides shows that the accumulation of raffinose (galactosyl sucrose) and higher galactosyl homologs can contribute significantly to the optical rotation of sugarbeet extracts in late season. Raffinose synthesis involves the action of a cold-induced enzyme, galactinol synthetase, providing a rational basis for the widely-held (though incorrect) belief that "a light frost causes sugaring-up," or a rapid and significant accumulation of sucrose in the root. Thus, a plausible phytochemical explanation of "apparent" late-season sucrose accumulation now is possible.

Key words: Beta vulgaris, galactinol synthetase, polarimetry, raffinose, sucrose