SYMPLASTIC COMMUNICATION BETWEEN PRIMARY AND DEVELOPING LATERAL ROOTS OF ARABIDOPSIS-THALIANA

The functional symplastic connections between primary and developing lateral roots of Arabidopsis were studied non-invasively using confocal laser scanning microscopy (CLSM), following ester-loading of the phloem with carboxyfluorescein (CF). Prior to the formation of lateral primordia in the pericycle, the phloem of the primary root behaved as an isolated conducting domain. However, the differentiation of phloem connector elements within the dividing pericycle allowed the rapid establishment of intercellular communication between the phloem and the cells of the lateral primordium. This communication was often established prior to the complete emergence of the lateral root from the parent root. Shortly after its emergence, functional conducting phloem became differentiated within the developing lateral root. A progressive isolation between the phloem and surrounding cells at the base of the lateral root was observed as the lateral continued to grow; the new phloem conducting CF to the elongation zone where it was unloaded symplastically from the protophloem into surrounding cells of the cortex and stele, a feature mirroring the pattern found near the apex of growing primary roots. Anomalous patterns of intercellular communication were found which indicated that previously functional symplastic pathways may have become sealed off following the emergence of some of the lateral roots.