Biol 156 Discussion 2

Structure with 7 cells and 8 nucleii

• Egg cell
• Synergid cells
• Antipodal cells
• Central cell

the distal tip of the nucellus. The auxin output was traced to megasporogenesis.

Auxin is localized (concentrated) in early development but is more dispersed during gametophyte development.

the process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external variable. An increase of a cellular component is called upregulation.

• Restricted down regulation of ARF to embryo sac.
• Looked at GFP expression in developing embryos.
• Cells lacked identity

• Looked at auxin efflux facilitators called PINs
• No PIN expression in gametophyte, but there was PIN expression in nucellus until first stage
• SO auxin flux may occur in nuccellus during early stages of development

• Encode key enzymes in auxin biosynthesis
• YUCCA expression first appears in micropylar region of nucellus outside embryo sac in first stage
• Suggests auxin might be synthesized initially at the nucellus and subsequently at the micropylar pole of the embryo sac

• Cell identity problems. Too many synergid cell?
• Would attract 2 pollen tubes

1. Sphorophytic signals lead to auxin source specified within gametophyte at the micropylar pole that result in a gradient of auxin along the micropylar-chalazal axis

2. Gametophytic auxin might not be the primary signal but instead might be the result of a patterning caused by unknown X factor which induces YUC expression in micropylar nuclei resulting in asymetric auxin distribution.

so seems to be controlled.