Time Course of Low Temperature Inhibition of Sucrose Translocation in Sugar Beets

Further studies are presented characterizing the time-course response of sucrose translocation in sugar beet (Beta vulgaris L. cv Klein Wanzleben) to low temperature inhibition. Only the temperature of a 2 cm zone of the source-leaf petiole was varied (1 degrees vs 25 degrees , approximately). The half-time of inhibition, defined as the time required for 50% inhibition of the control or pre-cooling rate, varied from 4 to 15 minutes, and the half-time of recovery from 30 to 100 minutes. Maximum inhibition varied from 68 to 92%. Possible uncertainties in evaluating these parameters are discussed. When the duration of the low temperature period was sufficient to permit essentially full recovery, subsequent re-warming of the petiole zone to 25 degrees to 30 degrees effected little or no increase in the translocation rate. It is evident that the interposition between source and sink of a 2 cm petiole zone maintained at a temperature generally inhibitory to physiological processes resulted in little or no impairment to the translocation process, after a suitable thermal adaptation period. Thermally adapted petiole systems de-adapted after periods as short as 1 hour at 25 degrees .