AUXIN AND OTHER SIGNALS ON THE MOVE IN PLANTS

1. AUXIN AND OTHER SIGNALS ON THE MOVE IN PLANTS Chairman: Student: Dr. P. Balasubramanian S. Saravanan Professor. 08-807-003.

2. Auxin • They are a class of plant growth substance and morphogens • An essential role in coordination of many growth and behavioral processes in the plant life cycle • Auxins and their role in plant growth were first revealed by the Dutch scientist Frits went

3. About the Auxin • Derive their name from the Greek word "auxano“ -"I grow/increase”. • The first of the major plant hormones to be discovered • Their patterns of active transport through the plant are complex • They typically act in concert with, or in opposition to other plant hormones

4. Molecular level • An aromatic ring and a carboxylic acid group. • The most important member of the auxin family is Indole – 3 - acetic acid(IAA). • It generates the majority of auxin effects in intact plants, and is the most potent native auxin. However, molecules of IAA are chemically labile in aqueous solution, so IAA is not used commercially as a plant growth regulator. (Taiz and Zeiger, 1998)

5. Naturally-occurring auxins include 4-chloro-indoleacetic acid,phenylacetic acid (PAA) and indole-3-butyric acid (IBA). • Synthetic auxin analogs include 1-napthaleneacetic acid (NAA),2,4-dichlorophenoxyacetic acid (2,4-D), and others.

6. Gallery of native Auxins • Indole -3-acetic acid (IAA) • Indole -3-butyric acid (IBA) • 4-chloroindole-3-acetic acid (4-CI-IAA) • 2-phenylacetic acid (PAA)

7. Gallery of synthetic Auxins • 2,4-dichlorophenoxyacetic acid (2,4-D) • α-napthaleneacetic acid (α-NAA) • 2-Methoxy-3,6-dichlorobenzoic acid(dicamba) • 4-Amino-3,5,6-trichlorolinic acid (tordon or picloram) • α-(p-Chlorophenoxy)isobutyric acid (PCIB, an antiauxin)

8. Molecular mechanism • Auxins directly stimulate or inhibit the expression of specific genes • It induces transcription by targeting for degradation members of the Aux/IAA family of transcriptional repressor proteins, The degradation of the Aux/IAAs leads to the derepression of Auxin Respose Factors -mediated transcription. • Aux/IAAs are targeted for degradation by ubiquitination, catalysed by an SCF-type ubiquitin-protein ligase

9. Cellular level • Is essential for cell growth, affecting both cell division and cellular expansion • Specific tissue, auxin may promote axial elongation (as in shoots), lateral expansion (as in root swelling), or isodiametric expansion (as in fruit growth) • Promoted cell division and cell expansion may be closely sequenced within the same tissue (root initiation, fruit growth)

10. Location of Auxin • In shoot and root meristematic tissue • In young leaves • In mature leaves in very tiny amounts • In mature root cells in even smaller amounts • Transported throughout the plant more prominently downward from the shoot apices

11. Biosynthesis of Auxin • Indole pyruvic acid pathway • Tryptamine pathway • Indole acetaldoxime pathway

12. Indolepyruvic acid pathway

13. Tryptamine pathway

14. Indoleacetaldoxime pathway

15. Effects • Wounding response • Root growth and development • Apical dominance • Ethylene biosynthesis • Fruit growth and development • Flowering

16. Brief view • The plants have specialized transport pathway • Xylem flow from root to shoot • phloem flow from photosynthetic active tissue • Process based on inter cellular transport mechanism

17. Plant life strategy • Regulation of plant size and architecture • Regulating and coordinating plant growth and development process • Transport mechanism include; • Vascular networks • Intercellular transport

18. Transported substances • The substances get transported plant by one or several transport mechanism • The mineral elements to form inorganic to organic • Transported mechanism regulated by external and internal factors

19. Types of transport • Long distance transport • Short range transport

20. Long distance transport • The xylem and phloem constitute vasculature based transport and continuous tubular columns • Xylem essential for structural and maintain body height • Phloem sieve elements connected into long sieve tube • In shoot system- collateral vascular bundles • In root system- bilateral symmetry

21. Long distance transport

22. Short range transport • Apoplastic transport • Symplastic transport • Transcellular transport

23. Apoplastic transport • The transport of molecules through from root surface to endodermis • It can control by casparian strip • This structure restrict entry of pathogen, nutrients into out from the vasculature • An example of ABA

24. Symplastic transport • Connect the cytoplasm of two neighboring cells directly through the plasmodesmata • Symplastic domain vary in size during development • It is important in non-cell autonomous signaling • It is control by plasmodesmata pore

25. Transcellular transport • The movement of molecule from cell to cell • It regulate and integration of various signal • Signal regulating the expression or activity of transporter • There are two main transmembrane transport mechanism viz, • Import epidermal cell and export from endodermal cell • Polarly localized plasma membrane

26. Intercellular pathway

27. Boron transport

28. Phloem based transport chemiosmotic model for polar auxin transport

29. PIN polar localization during embryo and root development

30. Conclusion

31. Thank you..