The Characteristics of Shoot Meristems in Arabidopsis Change with Development

During the vegetative phase of growth, the Arabidopsis vegetative apical meristem produces phytomeres with very short internodes, resulting in a basal rosette of leaves (see Figure 24.1A). (Recall from Chapter 16 that a phytomere consists of a leaf, the node to which the leaf is attached, the axillary bud, and the internode below the node.)

As plants initiate reproductive development, the vegetative meristem is transformed into an indeterminate primary inflorescence meristem that produces floral meristems on its flanks (Figure 24.2). The lateral buds of the

Flower,

Secondary inflorescence

Flower,

Secondary inflorescence

Primary inflorescence

Rosette leaf

Cauline leaf

Primary inflorescence

Cauline leaf

Rosette leaf

FIGURE 24.1 (A) The shoot apical meristem in Arabidopsis thaliana generates different organs at different stages of development. Early in development the shoot apical meristem forms a rosette of basal leaves. When the plant makes the transition to flowering, the shoot apical meristem is transformed into a primary inflorescence meristem that ultimately produces an elongated stem bearing flowers. Leaf primordia initiated prior to the floral transition become cauline leaves, and secondary inflorescences develop in the axils of the cauline leaves. (B) Photograph of an Arabidopsis plant. (Photo courtesy of Richard Amasino.)

FIGURE 24.2 Longitudinal sections through a vegetative (A) and a reproductive (B) shoot apical region of Arabidopsis. (Photos courtesy of V. Grbic' and M. Nelson, and assembled and labeled by E. Himelblau.)

cauline leaves (inflorescence leaves) develop into secondary inflorescence meristems, and their activity repeats the pattern of development of the primary inflorescence meristem, as shown in Figure 24.1A.

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