Protein Phosphorylation in the Sieve Tubes of Rice Plants

Proteins and their phosphorylation were examined in rice phloemsap that had been collected by the insect laser technique. Analysisby SDS-PAGE indicated that rice phloem sap contained over 150proteins. The total protein concentration was 150–200ng µl^-1. Analysis of proteins extracted from leaves, rootsand seeds revealed that several major low-molecular-weight proteinswere confined to the rice phloem sap. Maintenance of rice plantsunder stable environmental conditions was associated with aconstant complement of proteins in the phloem sap. Phosphorylation and dephosphorylation of proteins were detectedin the sieve tubes and occurred in a light dependent mannerwhen [