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° vs 25°, 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° to 30° 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°.