AUXIN AND OTHER SIGNALS ON THE

MOVE IN PLANTS

Chairman: Student:Dr. P. Balasubramanian S. SaravananProfessor. 08-807-003.

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

About the AuxinDerive their name from the Greek word

"auxano“ -"I grow/increase”.The first of the major plant hormones to be

discoveredTheir patterns of active transport through

the plant are complexThey typically act in concert with, or in

opposition to other plant hormones

Molecular levelAn 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)

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.

Gallery of native AuxinsIndole -3-acetic acid (IAA)

Indole -3-butyric acid (IBA)

4-chloroindole-3-acetic acid (4-CI-IAA)

2-phenylacetic acid (PAA)

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)

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

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)

Location of AuxinIn 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

Biosynthesis of AuxinIndole pyruvic acid pathway

Tryptamine pathway

Indole acetaldoxime pathway

Effects

Wounding response

Root growth and development

Apical dominance

Ethylene biosynthesis

Fruit growth and development

Flowering

Brief viewThe plants have specialized transport

pathway

Xylem flow from root to shoot

phloem flow from photosynthetic active tissue

Process based on inter cellular transport mechanism

Plant life strategy Regulation of plant size and architecture

Regulating and coordinating plant growth and development process

Transport mechanism include;1.Vascular networks2.Intercellular transport

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

Types of transport

Long distance transport

Short range transport

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

Long distance transport

Short range transport

Apoplastic transport

Symplastic transport

Transcellular transport

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

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

Transcellular transport

The movement of molecule from cell to cellIt regulate and integration of various signalSignal regulating the expression or activity

of transporterThere are two main transmembrane

transport mechanism viz,1.Import epidermal cell and export from

endodermal cell2.Polarly localized plasma membrane

Intercellular pathway

Boron transport

Phloem based transport chemiosmotic model for

polar auxin transport

PIN polar localization during embryo and root

development

Conclusion