This image is from a figure in a research article by Reddy & Meyerowitz 2005. (A related article is our featured paper of the month in October). This image is a reconstructed view of the L1 layer of the shoot apical meristems (SAM)s.
To study the immediate effect of loss of CLV3 function, the authors utilized dex-inducible clv3 RNAi lines to conditionally silence CLV3 expression in the meristems. To follow cell lineages in SAMs, they marked CZ by CLV3:GFP, and all of the cells in SAM were marked by a plasma membrane–localized yellow fluorescent protein (YFP).
In this figure, the authors mock-treated (top row) or treated with Dex (bottom row). Quoting from the figure legend, “Expansion of the CZ continues as more of the PZ cells begin to acquire CZ identity (arrows point to the same cells in images acquired at successive intervals) along with an increase in SAM size”. These results provided critical data to show that CLV3 restricts its own domain of expression (the central zone, CZ) by preventing the differentiation of peripheral zone cells (PZ), which surround the CZ, into CZ cells.