AtSUC2 has a role for sucrose retrieval along the phloem pathway: Evidence from carbon-11 tracer studies

The location of the phloem within a plant, and its vulnerability to disruption, make it a difficult tissue to study and therefore non-invasive studies of phloem functionality are important. Here we compare, phloem transport, measured non-invasively, in wild type Arabidopsis thaliana, and transposon-insertion mutants for AtSUC1 or AtSUC2, giving in vivo information on the importance of these sucrose transporters for phloem transport. The suc2 mutant showed an increase in both phloem leakage and transport time, consistent with reduced sucrose uptake into both transport and collection phloem. The results are consistent with the AtSUC2 transporter being important for retrieval of leaked sucrose in the transport phloem of Arabidopsis. There was no difference in phloem transport properties between the wild type and the suc1 mutants, implying that the AtSUC1 transporter does not play a significant role within the transport phloem of Arabidopsis under the conditions of our study.

► Phloem transport of 11C-photoassimilate was compared for Arabidopsis thaliana between wild type, suc1 and suc2 knockouts.
► SUC1 is not important for phloem transport (suc1 was indistinguishable from wt).
► SUC2 assists phloem loading and retrieval (both leakage and transport time increased without suc2).
► SUC2 is not essential for phloem transport (with prolonged sugar-starvation, transport properties recovered in suc2 plants).