Figure 1.

The Arabidopsis plants and the representative transmission electron micrograph (TEM) of cells in the late growth stage Arabidopsis stems. (A) The Arabidopsis plants used for CaCl₂-extraction of plant stem cell walls at late growth stage (i.e., pods beginning to desiccate). (B) An enlarged image showing siliques turning color from green to yellow, an indicator that the plant is at the late stage of growth. (C) TEM image for sclerenchyma cells of a vascular bundle undergoing senescence. Cell I retains a largely intact cytoplasm, indicating cell is in pre- or very early stages of senescence. Cell II and the others in the field of view are in later stages of senescence, exhibiting deconstructed membranes and organelles. Scale bar 2 μm. (D) Membrane and organelle fragments adhere to secondary cell wall surfaces during senescence. Scale bar 1 μm. CML, compound middle lamella; S1, first layer of secondary cell wall; S2, second layer of secondary cell wall. Note that Arabidopsis stem segments used for TEM analysis is indicated by black box in (A).