PLANT PHYSIOLOGY. Az Agrármérnöki MSc szak tananyagfejlesztése TÁMOP /1/A

Transcription

1 PLANT PHYSIOLOGY Az Agrármérnöki MSc szak tananyagfejlesztése TÁMOP /1/A

2 Cell wall biogenesis and expansion Regulation of plant growth and development by environmental factors

3 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

4 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

5 Diversity of plant cell wall structure (A) primary, and (B)-(C) secondary cell walls Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 428.

6 Schematic diagram of the major structural components of the primary cell wall Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 428.

7 A structural model of a cellulose microfibril Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 431.

8 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

9 The orientation of newly deposited cellulose microfibrils determines the direction of cell expansion Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 441.

10 Reduction of cell turgor pressure (water potential) by stress relaxation Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 447.

11 Acid-induced extension of isolated cell walls, measured in an extensometer Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 447.

12 Scheme for the production of oligosaccharins during fungal or oomycete invasion of plant cells Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web material,

13 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 3.4. Extracellular factors are plant growth regulators (PGRs), which often called as hormones

14 Generic scheme for signal transduction with examples Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 404.

15 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 4.5. Very low-fluence responses ar nonphotoreversible 4.6. Low-fluence responses are photoreversible

16 Corn and mustard seedlings grown either in the light (A and C) or the dark (B and D) Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 494.

17 Lettuce seed germination is a typical photoreversible response controlled by phytochrome Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 495.

18 Low-fluence response (LFR) action spectra for the photoreversible stimulation and inhibition of seed germination in Arabidopsis Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 498.

19 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 Plants can detect the proximity of neighbors through phytochrome perception

20 Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 512.

21 Phytochromes appear to play a predominant role in controlling stem elongation rate in sun plants, but not in shade plants Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 513.

22 (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,

23 4. The effect of environmental factors in a plant's life cycle The responses to blue light signals are distinct from phytochrome responses Blue light stimulates transcription and translation, yielding gene products that are required for the morphogenetic response to light Plants can be classified according to their photoperiodic responses Floral development can be a response to changes in day length (photoperiodism) or to prolonged cold (vernalization)

24 Blue-light signals are used in many responses, allowing the plant to sense the presence of light and its direction Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 522.

25 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. 733.

26 The photoperiodic regulation of flowering: effects on short-day and long-day plants Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 735.

27 Phytochrome control of flowering by red (R) and far-red (FR) light Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 739.

28 The duration of exposure to low temperature increases the stability of the vernalization effect Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 742.

29 Summary The architecture, mechanics and function of plants depend on the structure of the cell wall. The wall is secreted and assembled as a complex structure that varies in form and composition as the cell differentiates. Plant cells are able to sense and respond to a wide range of external and internal signals. The main external factors are light and temperature. The integrating endogenous and environmental signals have crucial role in a plant's life cycle.

30 Questions What characteristics contribute strength and rigidity to a cell wall? What limitations does the cell wall place on the growth of plant cell? What is the physiological significance of physiological ecotypes, or photoperiodic races within a species that are chracterized by different critical daylengths?

31 THANK YOU FOR YOUR ATTENTION Next lecture: Auxin Compiled by: Prof. Vince Ördög Dr. Zoltán Molnár