Cell fate may depend on lineage and position within a tissue; since plant cell position is fixed within a tissue, communication between cells is integral for patterning events. There are a myriad of ways that neighbouring cells can communicate with each other but we might break them down into two distinct categories: molecular signalling and mechanical signalling. Molecular signalling involves cellular molecules such as proteins and hormones as signals, whereas mechanical signalling relies on differential stress/strain as a signal; however, we will see that these are not distinct phenomenon. In a spatial sense, we might also consider communication occurring on two levels, locally between neighbours and globally across a tissue. Again, we will see that while useful, these categorizations are simplifications of a beautiful complexity. In this article we will examine the communication processes (local, global, mechanical and molecular) required for the plant patterning event known as phyllotaxis, the organization of aerial organs about the stem.

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