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

Abstract

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[degree] vs 25[degree], approximately). The half-time of inhibi-tion, defined as the time required for 50% inhibition of the control or pre-cooling rate, varied from 4 to 15 min., and the half-time of re-covery from 30 to 100 min. 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 per-mit essentially full recovery, subsequent re-warming of the petiole zone to 25[degree] to 30[degree] 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 trans-location process, after a suitable thermal adaptation period. Thermally adapted petiole systems de-adapted after periods as short as 1 hr. at 25[degree].