Molecular And Biochemical Steps In Synthesis Of Auxin In Plant

Molecular And Biochemical Steps In Synthesis Of Auxin In Plant

1. MOLECULAR AND BIOCHEMICAL STEPS IN SYNTHESIS OF AUXIN IN PLANT Name- CHAVAN MAHADEO RAJARAM Reg. No.- ADPM/15 /2419 Class- Jr. M. Sc. Agriculture Genetics and Plant Breeding

2. Derived from Greek word ‘auxin’ means “to increase” or “to grow” “compounds that induce cell elongation in coleoptiles or resemble indole-3- acetic acid (IAA) in their physiological activities are considered as a uxin”

3. Went (1926) was successful in isolating this growth substance from Avena coleoptile tips which still retained the growth promoting activity. Later went (1928) developed a biossay for quantitative analysis of auxin. He suggested – The curvature of stem is proportional to the amount of growth substance in the block. This test – Avena curvature test

4. Early isolation of IAA In 1935 K ogl isolated auxintriolic acid from urine and named it as auxin -a . Kogl also isolated indole-3-acetic acid (IAA) from human urine

5. Natural Auxins : indole-3-acetic acid (IAA) 4-chloroindole-3-acetic acid (4-Cl-IAA) phenylacetic acid (PAA) indole-3-butyric acid (IBA) Type of auxin

6. Syntyetic auxin 2,4-Dichlorophenoxyacetic acid α-Naphthalene acetic acid 2-Methoxy-3,6-dichlorobenzoic acid 4-Amino-3,5,6-trichloropicolinic acid 2,4,5-Trichlorophenoxyacetic acid

7. Free auxin : - It is readily extractable - Immediately utilizable in growth Bound auxin : - Liberated from tissue when subjected to enzymolysis, hydrolysis, or autolysis - Storage form of hormone. - synthesized –seed maturation and - Hydrolyzed – seed germination Free and bound auxin

8. Auxin biosynthesis Two major pathways for IAA biosynthesis have been proposed in plants tryptophan (Trp)-independent Trp-independent IAA biosynthesis,indole-3- glycerol phosphate or indole is the likely precursor Trp dependent pathways

9. Auxin biosynthesis The indole-3-pyruvic acid pathway (IPAPathway) The tryptamine pathway (TAM Pathway) The indole-3-acetonitrile pathway (IAN Pathway) indole-3-acetamide (IAM pathway) Mechanisms:

10. Trytophan T ryptamine Indole -3-acetaldehyde Decarboxylation Oxidation and Deamination Indole-3-pyruvic acid Deamination Decarboxylation IAA Oxidation Indole-3-acetaldoxime Indole-3-acetonitrile IPA TAM IAN

11. The amino acid tryptophane losess the amino group (deamination) indol-3- acetic acid which thane loses CO2 to form indol -3-acetaldehyde The oxidation of indol -3- acetaldehyde result in the formation of IAA IPA Pathway (Indol -3- pyruvic acid)

12. It occurs in those species which lack IPA pathway. The tryptophan is first of all decarboxylated to form tryptamine. Which is than oxidized as well as deaminated to form indolacetaldehyde. Nonhhebel et al (1993) have found both IPA as well as TAM pathway in tomato. TAM Pathway

13. IAN and other components of the IAN pathway have been found primarily in the Brassicacae; therefore, this pathway has not been considered to be of general importance. Trp is converted to indole-3-acetaldoxime by an enzyme activity that has been detected in several plant species (Ludwig-Miiller and Hilgenberg,1988). Indole-3-acetaldoxime conversion to indole-3 acetonitrile has been demonstrated in plasma membranes of Chinese cabbage (Ludwig-Miiller and Hilgenberg, 1990). The nitrilase that converts indole-3-acetonitrile to IAA The IAN Pathway

14. Abbreviations IAA indole-3-acetic acid IAD indole-3-acetaldehyde IAM indole-3-acetamide IAN indole-3-acetonitrile IAOX indole-3-acetaldoxime IPA indole-3-pyruvic acid TAM tryptamine Trp tryptophan

15. Transport of auxin in plant The transport of auxin in plant is predominantly polar. In stems, polar transport of auxin is basipetal i.e ., it takes place from apex towards base. In roots also, the auxin transport is polar but is primarily acropetal. Jacobs (1961) found polar transport of auxin in coleus stem sections to be both basipetal and acropetal in the ratio of 3:1.

16. Case study The pathway of auxin biosynthesis in plants Yoshihiro Mano1,* and Keiichirou Nemoto2 Abstract The plant hormone auxin, which is predominantly represented by indole-3-acetic acid (IAA), is involved in the regulation of plant growth and development. Although IAA was the first plant hormone identified, the biosynthetic pathway at the genetic level has remained unclear. Two major pathways for IAA biosynthesis have been proposed: the tryptophan (Trp)-independent and Trp-dependent pathways. In Trp-dependent IAA biosynthesis, four pathways have been postulated in plants: (i) the indole-3-acetamide (IAM) pathway; (ii) the indole-3-pyruvic acid (IPA) pathway; (iii) the tryptamine (TAM) pathway; and (iv) the indole-3-acetaldoxime (IAOX) pathway.

17. Plants would be expected to share evolutionarily conserved core mechanisms for auxin biosynthesis because IAA is a fundamental substance in the plant life cycle, although different plant species may have unique strategies and modifications to optimize their metabolic pathways. Biochemical and molecular biological findings and bioinformatics studies indicate that the best candidate for the major pathway of IAA biosynthesis is the IAM pathway and/or the IPA pathway Conclusions and perspectives

18. Arai Y, Kawaguchi M, Syono K, Ikuta A. 2004 . Partial purification of an enzyme hydrolyzing indole-3-acetamide from rice cells. Journal ofPlant Research 117, 191–198. Bak S, Nielsen HL, Halkier BA. 1998 . The presence of CYP79homologues in glucosinolate-producing plants shows evolutionary conservation of the enzymes in the conversion of amino acid toaldoxime in the biosynthesis of cyanogenic glucosides and glucosinolates. Plant Molecular Biology 38, 725–734. Bak S, Tax FE, Feldmann KA, Galbraith DW, Feyereisen R. 2001. CYP83B1, a cytochrome P450 at the metabolic branch point in auxinand indole glucosinolate biosynthesis in Arabidopsis. The Plant Cell References

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