Recovery of Cold-Inhibited Phloem Translocation in Sugar Beet

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Abstract
Translocation studies were undertaken on a simplified single source leaf-single sink leaf sugar be system to test various predictions of the Ferrier and Christy (1975) mathematical recovery model translocation inhibited by cold. Experiments were performed by using a steady state MC-labellii system for the source leaf and translocation into the sink leaf was monitored with a Geiger-Muell system. A specially designed Peltier apparatus enabled cooling of the source petiole to 1 °C at vario positions on the petiole, as well as over different lengths. Results of experiments testing changes in (1) cold block length, (2) cold block position, and (3) sink unloading rate, showed little difference in ti time course of recovery. These results are at variance with the predictions of the mathematical recove model. Additional experiments were performed to assess the potential involvement of phloe anastomoses in the recovery response. Selective petiolar incision/excision experiments showed: (1) that the monitored sink obtained 14C-labelled material via only a few of the vascular bundles within the source petiole, and (2) that anastomoses were capable of re-establishing translocation. This information was used to develop a revised model of translocation recovery following cold-induced inhibition, ai this model is based on the utilization of adjoining, interconnected sieve-tubes which become integrat into the pathway that supplies this sink.