The Growth and Development of Plants

CS 482 Lecture, Dr. Lawlor

Stages in the development of an orchid flower:
green orchid bud spike
The orchid bud begins as a tiny "spike", which develops from an undifferentiated rounded growth.
green bud forming
The spike fattens into a smooth bud.
external ridges on bud
The bud develops ridges running toward the tip.
bud is about to flower
The bud swells and darkens as the flower develops inside.
The flower opens
The flower opens.
The flower, showing internal structure
These intricate guard structures formed inside the bud, around the pollen.

This is a Moth Orchid (Phalaenopsis).  Its genome was recently sequenced, and seems to be approximately similar to the human genome in size (about 1 billion nucleotide base pairs) and complexity (about 30,000 genes).  (Unrelated: the Bee Orchid story (xkcd), photos.)

As the bud grows, these complex structures are formed through simple cell division or growth, causing swelling, and cell shrinkage or death, separating structures.  These events are orchestrated by chemical signals that diffuse between the cells.

Morphogenesis

The actual biological signaling pathways involved in growth are complicated, but the general process typically begins with a small smooth bump: a bud or meristem (for plants), an imaginal disk (for insects), or a limb bud (for animals).  The development of complex features like limbs results from the execution of genetic subroutines, which are activated by chemical signaling compounds called morphogens, and can be disrupted by chemical disruptors in the environment called teratogens.

Simple growth models can provide beautiful simulations of plant growth or edge folding, resulting in very strange shapes reminiscent of Xenophyophores or leafy lichen.

For more details on the overall process, see Prusinkiewicz & Runions 2011.  The role of cell orientation or "polarity" has recently been proposed as a key part of cell-to-cell signaling.

Why do you care?