Plant Structure, Growth, and Development

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Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm.

Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air.

Slide 57

Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body

Morphogenesis is the development of body form and organization.

The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant.

Slide 58

Growth: Cell Division and Cell Expansion

By increasing cell number, cell division in meristems increases the potential for growth.

Cell expansion accounts for the actual increase in plant size.

Slide 59

The plane and symmetry of cell division influence development of form

Plane of

cell division

(a) Planes of cell division

Developing

guard cells

Guard cell

“mother cell”

Unspecialized

epidermal cell

(b) Asymmetrical cell division

Slide 60

Orientation of Cell Expansion

Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles.

Plant cells expand primarily along the plant’s main axis.

Cellulose microfibrils in the cell wall restrict the direction of cell elongation.

Slide 61

The plane and symmetry of cell division influence development of form

Cellulose

microfibrils

Nucleus

Vacuoles

5 µm

Slide 62

Morphogenesis and Pattern Formation

Pattern formation is the development of specific structures in specific locations.

It is determined by positional information in the form of signals indicating to each cell its location.

Positional information may be provided by gradients of molecules.

Polarity, having structural or chemical differences at opposite ends of an organism, provides one type of positional information.

Slide 63

Morphogenesis in plants, as in other multicellular organisms, is often controlled by homeotic genes

Slide 64

Gene Expression and Control of Cellular Differentiation

In cellular differentiation, cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome.