Rucete ✏ Campbell Biology In a Nutshell
Unit 6 PLANT FORM AND FUNCTION — Concept 35.5 Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body
The formation of a plant’s body results from three overlapping developmental processes: growth, morphogenesis, and cell differentiation. Although all plant cells share the same genome, they develop into diverse forms and functions depending on their position, gene expression, and environmental signals.
Developmental Plasticity
- Developmental plasticity: ability of plants to alter form based on environment.
- Example: Cabomba aquatica produces different leaf types under water vs. above water.
- Plasticity helps stationary plants cope with environmental variation.
Key Developmental Processes
1. Growth
- Irreversible increase in size.
- Driven by:
- Cell division: increases cell number.
- Cell expansion: mainly via vacuole water uptake.
2. Morphogenesis
- Determines shape and spatial organization of cells.
- Key mechanism: asymmetrical cell division.
- Example: guard cells originate from asymmetric epidermal divisions.
3. Cell Differentiation
- Identical DNA, but different gene expression leads to specialized functions.
- Cell position often determines fate more than lineage.
- Example: GLABRA-2 gene is expressed in non-hair cells, depending on neighbors.
Genetic Tools in Plant Development
- Arabidopsis thaliana:
- Model organism for plant biology.
- Small genome, short life cycle, easy to grow.
- First plant genome sequenced (~27,000 genes).
- Tools like transgenes and CRISPR reveal gene function.
- Researchers aim to simulate development via “virtual plants.”
Pattern Formation and Positional Information
- Positional cues guide cell differentiation:
- Lineage-based hypothesis: fate is inherited.
- Position-based hypothesis: fate depends on location and neighbors (more likely).
- KNOTTED-1 gene in maize affects leaf shape.
- MADS-box transcription factors: determine floral organ identity.
Phase Changes
- Plants pass through:
- Juvenile → Adult Vegetative → Reproductive
- Controlled by shoot apical meristems, changing new organ traits.
- Example: Muehlenbeckia australis changes leaf shape with phase.
- Axillary buds retain the phase of their originating node.
Genetic Control of Flowering
- Flowering is a determinate phase, triggered by:
- External cues (e.g., light duration).
- Internal signals (e.g., hormones).
- Shoot apical meristems convert to floral meristems → sepals, petals, stamens, carpels.
The ABC Hypothesis
- Three gene classes (A, B, C) determine floral identity:
- A only: sepals
- A + B: petals
- B + C: stamens
- C only: carpels
- A and C inhibit each other’s expression.
- Mutations can lead to misplaced organs (e.g., extra petals or missing stamens).
In a Nutshell
Plant body development involves growth, morphogenesis, and differentiation—guided by both genes and environment. Cells gain identity through positional cues, not just lineage. Model species like Arabidopsis help uncover the genetic pathways of development. Flowering showcases the power of positional information through the ABC model, which determines floral organ formation.