Source-to-Sink Translocation of Sucrose in Arabidopsis rsx1 Mutants

Abstract

In developing source leaves, secondary plasmodesmata (2^o-PD) develop in the cell wall between companion cells (CCs) and sieve elements (SEs). 2^o-PD are thought to promote sucrose export from CCs to SEs. In our previous studies, we showed that restricted sucrose export 1 (rsx1) mutants developed incomplete 2^o-PD between CCs and SEs, leading to restricted translocation of ¹⁴CO₂-assimilates to shoots. To further understand the function of RSX1 in sugar translocation, we examined translocation of ¹⁴CO₂ assimilates in transgenic Arabidopsis expressing RSX1 under the control of CaMV35S promoter. In wild-type rossete plants (WT), ¹⁴CO₂-assimilates in source leaves were largely translocated to a sink leaf just above the source leaf. In rsx1-2 mutants, sugar translocation was significantly inhibited (5% compared to WT), Which were fully recovered in rsx1-2 transRSX1:sGFP plants. These results indicated that RSX1 promotes source-to-sink translocation of sucrose. Moreover, in Pro35S-RSX1/- plants, the translocation from a source leaf to roots was significantly increased.