Figure 5.

PIN1 Expression and DR5 Auxin Response during Embryogenesis.

(A) and (B) PIN1 is expressed throughout both wild-type (A) and kan1 kan2 kan4 (k124) (B) globular embryos.

(C) and (D) In wild-type embryos (C), PIN1 is expressed during the transition stage at the sites of incipient cotyledons and developing vasculature, whereas in kan1 kan2 kan4 embryos (D), PIN1 expression can also be seen in the embryonic cells of the L1 layer that will give rise to the hypocotyl (arrows).

(E) to (G) At the heart stage, PIN1 is excluded from the hypocotyl cells in the wild type (E) but continues to be expressed in these cells in kan1 kan2 kan4 embryos ([F] and [G]). A transverse section through the hypocotyl region of the kan1 kan2 kan4 embryo at the heart stage (G) exhibits ectopic expression of PIN1 in the L1 cells, whereas no changes in cell division are evident at this stage.

(H) to (M) By the late heart (H) and later (L) stages, PIN1 expression in wild-type embryos is restricted to the SAM, vasculature, and tips of the cotyledons. In kan1 kan2 kan4, ectopic expression of PIN1 in the hypocotyl is maintained through the late heart ([I] and [J]) and later (M) stages, correlating with the aberrant phenotype. An abnormal polar arrangement of PIN1 in the hypocotyl cells with protein at the base of more apical cells and at the apex of more basal cells (K) leads to ectopic auxin maxima within the hypocotyl.

(N) and (P) In phb phv rev embryos, PIN1 is expressed throughout the apical part of the embryo and in the provasculature cells from the globular through the heart stages.

(Q) and (R) At later stages, PIN1 expression is lacking from the single radialized cotyledon (cot) and expressed only in the central and basal regions of the vasculature.

(S) and (T) GFP expression driven by the artificial DR5 promoter can be seen in kan1 kan2 kan4 embryos (T) during the torpedo stage in the hypocotyl and cotyledon outgrowths (arrows), indicating areas of auxin accumulation not present in wild-type embryos (S).