Plant cell-wall growth is the underlying mechanism by which really small seedlings can grow to really large trees. It’s the cellular basis for the way leaves expand. ~ American biologist Daniel Cosgrove
Animals and their cells are typically motile. In contrast, plant cells are immobile. Plant development and growth depend upon cell expansion rather than cell migration.
Cell expansion is a basic aspect of plant growth. Its rate and direction are dynamically regulated, adapting to perceived internal and environmental conditions.
Growth occurs when water moves into a cell and inflates it. The speed of most growth responses is determined by the rate of water movement in a tissue. ~ American botanist Wendy Silk
The scaffolding for a plant cell is provided by its cytoskeleton, which comprises an array of tubule protein fibers (microtubules). Along with structural support, microtubules guide oriented deposition of cell wall components.
Along with augmentation, microtubular arrays move during cell growth in the expansion direction, which is determined by exposure to blue light.
To maintain appropriate cell expansion, plant cells fine-tune signaling pathways. This is an ongoing interpretive exercise, based upon an extensive information network.
To properly distribute nutrients and other needed molecules, the contents of plants cells are continuously mixed. Cytoplasmic streaming – the directed flow of cytosol through plant cells – is the distribution process.
The stirring of cytosol is achieved by the motor protein myosin xi. Molecular motors like myosin can move the surface of a specific substrate.
Myosin xi slides along actin filaments in the cell’s skeleton. The velocity of myosin xi movement determines the rate of cytoplasmic streaming, which ordains how quickly plant cells can expand.
The pace of plant cell expansion is a key determinant in plant size. Accordingly, the tempo of myosin xi is a critical factor in plant growth rate, and limits how large a plant may become.