PARTITIONING OF CARBON IN SPLIT ROOT SYSTEMS OF BARLEY - EFFECT OF TEMPERATURE OF THE ROOT

The time-course of partitioning of recently fixed photosynthate to a barley root was followed during a step change in the temperature of the root. The induced change in partitioning had a response time of about 1 h, whilst the change in respiratory loss from the root of labelled and unlabelled CO2 was much faster. These observations suggest that while a sudden temperature change has an immediate effect upon the metabolic rate of the roots it is not the metabolic rate as such which influences import (sink strength). The reported temperature responses are consistent with the supposition that the size of the cytosolic pool of sugar in the root, which is supplied directly by phloem import and used as a substrate for root metabolism, appears to control import into the root.