Abstract
The transport of assimilates from source to sink tissues is mediated by the phloem.
Along the vascular system the phloem changes its physiological function from loading
phloem to transport and unloading phloem. Sucrose carrier proteins have been identified
in the transport phloem, but it is unclear whether the physiological role of these
transporters is phloem unloading of sucrose or retrieval of apoplasmic sucrose back
into the sieve element/companion cell complex. Here, we describe the dynamic expression
of the Ricinus communis sucrose carrier RcSCR1 in the hypocotyl at different sink strengths. Our results
indicate that phloem unloading in castor bean is not catalysed by the phloem loader
RcSCR1. However, this sucrose carrier represents the molecular basis of the sucrose
retrieval mechanism along the transport phloem, which is dynamically adjusted to the
sink strength. As a consequence, we assume that other release carrier(s) exist in
sink tissues, such as the hypocotyl, in R. communis.
Key words
Sucrose retrieval - phloem unloading - sink strength.
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A. R. Weig
Plant Physiology
University of Bayreuth
Universitätsstraße 30
95447 Bayreuth
Germany
Email: alfons.weig@uni-bayreuth.de
Editor: G. Thiel
