Initiation of vascular cambium derivatives produces new branch roots in a woody parental axis: Effect on root architecture

The anatomical differences of traces formed in woody parental roots enable the formation of two categories of branch roots: “primary branch roots” (PBR) and “secondary branch roots” (SBR). PBR are those roots hypothesized to be formed by primary tissues such as perycycle, endoderm or xylary parenchyma. SBR are roots hypothesized to be formed by cambium initials and/or phloem derivatives. After their formation the SBR primordia elongate through the secondary phloem, cortex, and phellogen before protruding externally from a swelling bark. A proteomic approach is used to produce a map of woody root axis, and to puts in evidence the occurrence of quantitative variations in a number of proteins in relation to SBRs production. The identities and possible physiological roles of these differentially expressed proteins is discussed in relation to root branching in woody roots. We suggest that SBRs emission improves the adaptation of woody plants to their rooting environment thorough a modification of root architecture.