COMPETITIVE CANALIZATION OF AUXIN IN PEA CAN BE INVOLVED IN INITIATION OF AXILLARY BUD OUTGROWTH

In many plants the growing shoot apex inhibits the outgrowth of axillary buds, a phenomenon termed apical dominance. Removal of the shoot apex, the starting point of polar auxin transport (PAT), leads to release of inhibited or dormant axillary buds to form branches. PAT system is necessary to establish various developmental processes in plants and has an essential role also in apical dominance. One of the latest theories explaining the mechanism of apical dominance is the theory of competitive auxin canalization, by which canalization from the lateral auxin source is possible only if the primary source is removed or weakened. After decapitation axillary buds in pea (Pisum sativum L.) establish directional auxin export by subcellular polarization of PIN1 auxin efflux transporters. In this work, initiation of bud outgrowth based on the polar auxin export was characterized by expression profiles of PsPIN1 and PsAUX1 genes coding auxin transmembrane carriers, and of the dormancy marker gene PsDRM1. Application of auxin efflux (NPA, TIBA) or protein synthesis (cycloheximide) inhibitors to the second axillary bud of decapitated plants reduces bud outgrowth. Inhibition of outgrowth of the second axillary bud in these plants caused outgrowth of the first bud. This competition between the second and first axillary buds as new potential sources of auxin after decapitation is associated also with changes in expression profiles of PsAUX1, PsPIN1 and PsDRM1 genes. The obtained results are in accordance with the competitive auxin canalization theory.