Auxin hormones
•Download as PPTX, PDF•
1 like•167 views
Auxin is a plant hormone that promotes growth. It is produced by plant tips and occurs in extremely low concentrations throughout the plant. Charles Darwin first concluded that a growth stimulus is produced in plant tips and transmitted downward. Later, experiments showed that this stimulus could pass through gelatin but not barriers, and it was called "auxin". F.W. Went isolated auxin from plant tips in 1926. Auxin is transported polarly from tips downward through cells using pH gradients and carrier proteins. It regulates gene expression and cell elongation to promote vertical plant growth.
More Related Content
What's hot
What's hot (20)
Similar to Auxin hormones
Similar to Auxin hormones (20)
More from vidan biology
More from vidan biology (20)
Recently uploaded
Recently uploaded (20)
Auxin hormones
- 1. CSIR POINT ACADEMY LIFE SCIENCE PLANT HORMONES (AUXIN) OPPOSITE A.N. JHA HOSTEL, NEAR SCIENCE FACULTY KATRA PRAYAGRAJ
- 3. • Plant hormones (also known as phytohormones) are signal molecules produced within plants, that occur in extremely low concentrations. • Unlike in animals each plant cell is capable of producing hormones. • The term ‘Phytohormone' was coined by Went & Thimann and used in the title of their book in 1937. • Phytohormones are found across the Plant kingdom , and even in algae, where they have similar functions to those seen in Higher plant. • Some phytohormones also occur in microorganism, such as unicellular Fungi and Bacteria, however in these cases they do not play a hormonal role and can better be regarded as secondary metabolites.
- 4. Hormones As a Signal molecules Binding with Receptor Activated Enzyme Second messenger Transcription Effect on cellular function
- 5. IsolationDiscovery Distribution Transportation Auxin (from the Greek auxin=to grow ) is a generic name given to growth hormones produced by the tip of the coleoptile and specifically required for elongation process Charles Darwin Peter Boysen F.W. Went Isolate from dutch patient suffering from pellagra disease (human urine)Trihydroxy carboxylic acid Auxin A Auxin B Heteroauxin Isolated from corn germ oil Hydroxy-keto carboxylic acid Isolated from Human urine Beta indole acetic acid Found in all Parts of plant Highest amount(in growing region) Lowest in non meristematic region Polar transport Auxin Influx (Uptake) Auxin Efflux
- 6. A.From experiments on coleoptile phototropism, Darwin concluded in 1880 that a growth stimulus is produced in the coleoptile tip and is transmitted to the growth zone. Root Seed coleoptile
- 7. In 1913, P. Boysen Jensen discovered that the growth stimulus passes through gelatin but not through water impermeable barriers such as mica. Mica sheet inserted on dark side Mica sheet inserted on light side Tip removed Gelatin
- 8. coleoptile Tip Agar Block Without auxin Transfer tip to agar block and leave for several hour Then transfer a piece of agar block to fleshy decapitated coleoptile Agar with auxin
- 9. F.W. Went (1926) by simple experiments demonstrated that the tip of the coleoptile synthesizes some growth causing substance. He cut the tips of oat coleoptiles and replaced them in a regularly arranged manner on rectangular blocks of 5% agar. After an hour the tips were removed and the agar block was sliced into equal square pieces. When one of these pieces was placed on a decapitated coleoptile, growth was resumed exactly in a similar manner as if the coleoptile itself has been replaced. But if ordinary agar blocks were kept on decapitated tip, growth was not resumed It was thus concluded that some chemicals migrate down from the coleoptile to the agar blocks and when the agar block was placed on the decapitated tip these again migrated downwards and induced growth. He called this chemical substance as auxin.
- 10. CH2-COOH N H
- 12. CH2-COOH N H CH2-COOH N H Cl CH2-COOH indole-3-acetic acid 4-chloroindole-3-acetic acid phenylacetic acid
- 13. Precursor IPA IANTAM Indole-3-pyruvic acid pathway Indole-3-acetonitrile acid pathway Tryptamine (Most common pathway) Eg-Tomato Brassicaceae Poaceae Musaceae
- 14. Tryptophan Indole-3-pyruvic acid Indole-3-acetaldehyde Indole-3-acetic acid (IAA) Transaminase IPA Decorboxylase Dehydrogenase Tryptophan Indole-3-acetaldehyde Indole-3-acetic acid (IAA) Decorboxylation Dehydrogenase Tryptamine Tryptophan Indole-3-acetaldoxime Indole-3-acetalnitrite Tryptophan monooxygenase Indole-3-acetic acid (IAA) Nitrilase
- 15. Meristematic zone Auxin moves down the stem Auxin is made here Auxin diffuses down the shoot stimulating If one side of shoot is in the sunlight Auxin diffuses away from the light Due to more auxin present at shady zone shoot to bend towards light
- 17. IAAˉ IAAˉ IAAH H+ H+ 2H+ IAAH IAAˉ IAAˉ IAAˉ IAAH H+ H+ H+ H+ PH 7 PH 5 ATP ATP ATP Plasma membrane Cell wall Cytosol Vacuole H+ 1. IAA enters the cell either passively in the undissociated form (IAAH) or by secondary active cotransport in the anionic form (IAAˉ) 3. In the cytosol which has a neutral pH, the anionic form (IAAˉ) predominates 2. The cell wall is maintained at an acidic pH by the activity of the plasma membrane H+ ATpase 4. The anions exit the cell via auxin anion efflux carriers that are concentrated at the basal ends of the each cell in the longitudinal pathway ATP ATP H+ influx carrier protein (AUX1) efflux Carriers Pin protein
- 18. Auxin Influx (Uptake): According to chemiosmotic model the auxin uptake by plant cells may take place from any direction. IAA may exist in two forms; one is protonated or un-dissociated form (IAAH) which is highly lipophilic and can cross the plasma-membrane easily. The other form is dissociated or anionic form (IAA–) that does not cross plasma-membrane unaided. i. In more acidic pH (low pH), the IAAH form predominates such as that exists in cell- wall space (apoplast). The low apoplastic pH (about 5) is maintained due to activities of ATPases present all around in the plasma-membrane. Any IAA that may be present in cell wall, rapidly associates with H+ to form IAAH. The latter diffuses passively across the plasma-membrane easily. ii. The anionic form (IAA ) may also cross the plasma-membrane from cell wall by secondary active co-transport mechanism through 2H+/IAA– symporter (i.e., influx carrier protein) which is uniformly distributed around the cell, These permease type of influx carrier proteins or 2H+/IAA– symporters have been called as AUX1 and were first identified in Arabidopsis roots by Bennett et al (1996).
- 19. In cytosol, the pH is relatively higher or neutral (about 7) in comparison to cell wall so that IAAH dissociates into H+ and IAA. It is in this dissociated form that auxin predominates in cytosol. In the dissociated or anionic form, the IAA” exits the cell only through basally located auxin efflux carriers called as PIN proteins The exit of IAA from the cell is driven by inside negative membrane potential. The basal location of auxin efflux carriers in each cell in longitudinal pathway establishes polarity in auxin transport and as mentioned earlier, is one of the two main features of chemiosmotic model of polar auxin transport. (Geldner et al (2001) have recently shown experimentally that although PIN proteins are stable but they do not remain permanently on plasma membrane. Instead, there is actin filaments- dependent cycling of PIN proteins from plasma membrane to some endosomal compartment through endocytotic vesicles and their recycling back to plasma membrane).
- 20. Activation theory Synthesis theory Intracellular cell Receptor (ABP) Intracellular cell Receptor (ABP) Intracellular 2nd messenger H+ transport from cytoplasm to cell wall &P.M Activation expensin protein Activate cell wall loosening Cell expension Activate H+ pump of P.M I.S.M
- 21. Cell wall Plasma membrane Expansins Auxin stimulates H+ H+ pump H+ Cell wall Cytoplasm Activates Cell elongation H2O Cellulose loosens Cell can elongate Ankit Mishra