PLANT PHYSIOLOGY
Cell wall biogenesis and expansion
Regulation of plant growth and development by
environmental factors
Overview
1. The structure and biosynthesis of plant cell wall
2. Cell wall elongation and degradation 3. Factors regulating plant growth and
development
4. The effect of environmental factors in a plant's
life cycle
1. The structure and biosynthesis of plant cell wall
1.1. The architecture, mechanics and function of plants depend on the structure of the cell wall
1.2. Plant cell walls vary greatly in form and composition, depending cell type and species
1.3. Primary cell wall is a network of cellulose microfibrils embedded in a matrix of hemicelluloses, pectins, and
structural proteins
1.4. Secondary walls in woody tissues contain more cellulose, xylans, and lignin
Diversity of plant cell wall structure
(A) primary, and (B)-(C) secondary cell walls
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 428.
Schematic diagram of the major structural components of the primary cell wall
A structural model of a cellulose microfibril
2. Cell wall elongation and degradation
2.1. Microfibril orientation influences growth directionality of cells with diffuse growth
2.2. The actions of hormones and environmental conditions modulate cell expansion
2.3. Acid-induced cell wall extension is characteristic of primary walls and is mediated by the protein expansin 2.4. Plant cell walls play a major role in carbon flow through ecosystems
2.5. Cell wall degradation and plant defense
The orientation of newly deposited cellulose microfibrils determines the direction of cell expansion
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 447.
Reduction of cell turgor pressure (water potential) by stress relaxation
Acid-induced extension of isolated cell walls, measured in an extensometer
Scheme for the production of oligosaccharins during fungal or oomycete invasion of plant cells
Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web material, http://5e.plantphys.net
3. Factors regulating plant growth and development
3.1. Plant cells are able to sense and respond to a wide range of external and internal signals
3.2. The signals can be grouped into: a) external, and b) internal (intracellular and extracellular) ones
3.3. The main external signals are light and temperature
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 404.
Generic scheme for signal transduction with examples
4. The effect of environmental factors in a plant's life cycle
4.1. Light provides the signal for photomorphogenesis 4.2. Phytochrome mediates several aspects of vegetative and reproductive development
4.3. Chracteristics of phytochrome-induced responses 4.4. Phytochrome responses can be distinguished by the amount of light required
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 494.
Corn and mustard seedlings grown either in the light (A and C) or the dark (B and D)
Lettuce seed germination is a typical photoreversible response controlled by phytochrome
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 498.
Low-fluence response (LFR) action spectra for the photoreversible stimulation and inhibition of seed germination in Arabidopsis
4. The effect of environmental factors in a plant's life cycle
4.7. The early phytochrome-induced gene products are transcription factors that activate other genes
4.8. Most organisms display endogenous circadian rhythms governed by an internal oscillator or clock 4.9. In the natural environment, phytochrome enables plants to respond shading
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 512.
Phytochromes appear to play a predominant role in controlling stem elongation rate in sun plants, but not in shade plants
(A) Seedlings of Datura ferox growing at increasing densities show larger stem elongation
(B) As an even canopy develops with time, perception of the neighbors stimulates stem elongation
Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web material, http://5e.plantphys.net
4. The effect of environmental factors in a plant's life cycle
4.11. The responses to blue light signals are distinct from phytochrome responses
4.12. Blue light stimulates transcription and translation, yielding gene products that are required for the
morphogenetic response to light
4.13. Plants can be classified according to their photoperiodic responses
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 522.
Blue-light signals are used in many responses, allowing the plant to sense the presence of light and its direction
The effect of latitude on day length at different times of the year in the northern hemisphere
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 735.
The photoperiodic regulation of flowering: effects on short-day and long-day plants
Phytochrome control of flowering by red (R) and far-red (FR) light
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 742.
The duration of exposure to low temperature increases the stability of the vernalization effect
