XVI International Botanical Congess

Rice phloem sap collected by the insect laser method contains a number of proteins and RNAs. Some of the macromolecules were identified by peptide sequence analysis and RT-PCR amplification. Thioredoxin (TRX) h is the most characterized protein. TRX h protein and mRNA is present in the phloem sap and transgenic tobacco plants expressing TRX h has a increased size exclusion limit of plasmodesmata in mesophyll cells. Transgenic plants expressing GUS under control of the TRX h promoter were generated. Analysis of phloem sap revealed presence of GUS mRNA but not GUS activity, suggesting macromolecular import into the sieve element is selective process to proteins and less selective to RNA molecules.