PHOTOASSIMILATE TRANSLOCATION IN THE PETIOLE OF CYCLAMEN AND PRIMULA IS INDEPENDENT OF LATERAL RETRIEVAL

Phloem translocation of photoassimilates between source and sink is co nsidered to be linked with active retrieval of sugars leaked to the va scular apoplast. This hypothesis was evaluated by studying photoassimi late movement in petioles of intact plants of Cyclamen persicum and Pr imula obconica in the presence of inhibitors affecting sucrose retriev al (PCMBS, CCCP). Inhibitor solutions were applied by rinsing locally isolated petiole bundles or by injection into the petiole parenchyma. PCMBS and CCCP reduced [C-14]sucrose retrieval from the petiole apopla st by the vascular cells and altered the distribution pattern of C-14- photoassimilates within the petiole tissues. However, these treatments did not affect translocation through the petiole phloem. Evidence is provided that the reagents were present in the vascular apoplast surro unding the translocating phloem. It was concluded that assimilate move ment in the petiole of Cyclamen and Primula was independent of apoplas tic retrieval.