SYMPLASTIC COMMUNICATION BETWEEN PRIMARY AND DEVELOPING LATERAL ROOTSOF ARABIDOPSIS-THALIANA

The functional symplastic connections between primary and developing l ateral roots of Arabidopsis were studied non-invasively using confocal laser scanning microscopy (CLSM), following ester-loading of the phlo em with carboxyfluorescein (CF). Prior to the formation of lateral pri mordia in the pericycle, the phloem of the primary root behaved as an isolated conducting domain. However, the differentiation of phloem con nector elements within the dividing pericycle allowed the rapid establ ishment of intercellular communication between the phloem and the cell s of the lateral primordium. This communication was often established prior to the complete emergence of the lateral root from the parent ro ot. Shortly after its emergence, functional conducting phloem became d ifferentiated within the developing lateral root. A progressive isolat ion between the phloem and surrounding cells at the base of the latera l root was observed as the lateral continued to grow; the new phloem c onducting CF to the elongation zone where it was unloaded symplastical ly from the protophloem into surrounding cells of the cortex and stele , a feature mirroring the pattern found near the apex of growing prima ry roots. Anomalous patterns of intercellular communication were found which indicated that previously functional symplastic pathways may ha ve become sealed off following the emergence of some of the lateral ro ots.