The eight stages (roman numbers, see S6 Fig) of LR primordium development in the roots of 10 day old cep1 ko mutant seedlings expressing pro-EGFP-CEP1 under the control of the endogenous promoter (PCEP1::pre-pro-3xHA-EGFP-AtCEP1-KDEL) were analyzed in vivo by CLSM (Olympus Fluoview FV 1000). No EGFP-CEP1 expression could be observed from developmental stage I-VI. (A-D) Stage VII of LR primordium development. (E-H) Stage VIII of LR primordium development. (I-M) Stage LR exhibiting the adult lateral root in LR primordium development. Arrow head in A, B and C indicates the LR primordium just emerging and separating the epidermis cells. The asterisk in B, F and K marks the epidermis cell expressing pro-EGFP-CEP1 at LR emergence sites. A, E and I: Focus is on the LR primordium. B-D, F-H, K-M: Focus is on the epidermis cells. A, B, E, F, I, K: Differential interference contrast. D, H, M: EGFP; C, G, L: merge.