Photoassimilate translocation in the petiole of Cyclamen and Primula is independent of lateral retrieval

Abstract

Phloem translocation of photoassimilates between source and sink is considered to be linked with active retrieval of sugars leaked to the vascular apoplast. This hypothesis was evaluated by studying photoassimilate movement in petioles of intact plants of Cyclamen persicum and Primula obconica in the presence of inhibitors affecting sucrose retrieval (PCMBS, CCCP). Inhibitor solutions were applied by rinsing locally isolated petiole bundles or by injection into the petiole parenchyma. PCMBS and CCCP reduced [14C]sucrose retrieval from the petiole apoplast by the vascular cells and altered the distribution pattern of 14C-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 surrounding the translocating phloem. It was concluded that assimilate movement in the petiole of Cyclamen and Primula was independent of apoplastic retrieval.