BIO 250 Asgmnt UITM

8/19/2019 BIO 250 Asgmnt UITM

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BIO 250

PLANTS HORMONES AND RESPONSE TO

INTERNAL AND EXTERNAL SIGNALS

NAME : MUHAMMAD HASIF BIN MOHAMAD

SUZAINI

ID NUMBER : 2011890782

CLASS : AS1204G2

LECTURE’S NAME : AHMAD ZAIMI BIN MOHDZAAI



PLANTS HORMONES

In general, plant hormones take control in plant growth and development. Plants cells use

hormones to communicate with one another. Plants hormonesare signaling molecules that can

stimulate or inhibit plant development, including growth. Environmental cues such as the

availability of water,temperature and gravity influence plants by triggering the production and

dispersal of hormones. When a plants hormone binds to a target cell, it may modify gene

expression, solute concentration, enzyme activity or activity another molecule in the cytoplasm.

ome ma!or classes of plant hormones are auxin "I##$, cytokinins, gibberellins, abscisic acid"#%#$ and ethylene.



Auxin (Indoleacetic acid, IAA)

&he term auxin is derived from the 'reek word, auxein which mean to grow. &herefore, any

chemical substance that have ability and promotes cell elongation can be considered as auxin.

&he natural auxin in plants is indoleacetic acid, or I##. #uxins are plants hormones that promote

or inhibit cell division and elongation, depending on the target tissue.

#uxins that are produced in apical meristems result in elongation of shoots. &hey also induce cell

division and differentiation in vascular cambium, fruit development in ovaries and lateral root

formation in roots. #uxins also have inhibitory effect. (or example, auxins produced in shoot tip

prevents the growth of lateral buds along a lengthening stem, an effect called apical dominance.

• )hemical structure of #uxins.



Cytokinins

'enerally, cytokinins take control in the cell division and differentiation. )ytokinins are

compounds with a structure resembling adenine which promote cell division and have other

similar functions to kinetin. *inetin was the first cytokinin discovered and so named because of

the compounds ability to promote cytokinesis "cell division$. )ytokinins have been found in

almost all higher plants as well as mosses, fungi, bacteria, and also in t+# of many prokaryotes

and eukaryotes.

)ytokinins are produced in actively growing tissues, particularly in roots. )ytokinins produced

in the root reach their target tissues by moving up the plant in the xylem sap.

)ytokinins interact with auxins to stimulate cell division and differentiation. In the absence of cytokinins, a piece of parenchyma tissue grows large, but the cells do not divide. In the presence

of cytokinins and auxins, the cells divide, while cytokinins alone have no effect.

If the ratio of cytokinins and auxins is at a specific level, then the mass of growing cells, called a

callus, remains undifferentiated. If cytokinin levels are raised, shoot buds form from the callus. If

auxin levels are raised, roots form.

)ytokinins, auxins, and other factors interact in the control of apical dominance, the ability of the

terminal bud to suppress the development of axillary buds.

)ytokinins retard the aging of some plant organs. &hey inhibit protein breakdown by stimulating+# and protein synthesis and by mobilizing nutrients from surrounding tissues. -eaves

removed from a plant and dipped in a cytokinin solution stay green much longer than otherwise.

• )hemical structure of cytokinins.



Ethylene

Ethylene the only gaseous hormone. It produced by damaged cells in response such as drought,

flooding, in!ury, and infection. It also produced in autumn in deciduous plants or near the end of the life cycle as part of a plant/s normal process of aging.

Ethylenes initiate a seedling to perform a growth called the triple response that enables a

seedling to avoid an obstacle as it grows through soil. In the triple response, stem elongation

slows, the stem thickens, and curvature causes the stem to start growing horizontally. It is

ethylene and not the physical obstruction that induces the stem to grow horizontally. In simple

words, the response of ethylene is mediates fruit ripening.

&he uses of ethylene in commercial is allows shipping of green, still0hard fruit. )arbon dioxide

application stops ripening of fruit in transit to market, then ethylene is applied to ripen

distributed fruit 1uickly.

)hemical structure of ethylene



Abscisic acid (ABA)

#bscisic acid is a hormone that was inhibits growth, and has little to do with abscission. #%# is

part of a stress response that causes stomata to close. It also diverts photosynthetic products from

leaves to seeds, an effect that overrides growth0stimulating effects of other hormones as the

growing season ends. #%# inhibits seed germination in some species, such as apple. uch seeds

do not germinate before most of the #%# they contain has been broken down, for example by a

long periods of cold and wet conditions.

ome cormmercial uses of #%# is induces nursery stock to enter dormancy before shipment to

minimize damage during handling.

C!"#$%&' ()*+%)+*" ,- #bscisic acid



ormones Primary souce Effect ite of effects

#uxins tem tip, young

leaves

timulates cell

elongation

'rowing tissues

Initiate formation of lateral roots

+oots

Inhibits growth

"apical dominance$

#xillary buds

timulate

differentiation of

xylem

)ambium

Inhibit abscission -eaves, fruits

2eveloping embryos timulates fruit

development

ovary

'ibberellins tem tip, youngleaves

timulates celldivision,elongation

tem inertnode

Embryo timulates

germination

eed

Embryo "grass$ timulates starch

hydrolysis

Endosperms

#bscisis acid leaves )loses stomata 'uard cells

timulate formation

of dormant buds

tem tip

ovule Inhibits germination eed coat

)ytokinins +oot tip timulate cell division tem tip, axillary buds

Inhibit senescence

"aging$

-eaves

Ethylene 2amaged or aged

tissue

Inhibits cell

elongation

tem

timulate senescence

"aging$

-eaves

timulate ripening (ruits

Major plants hormones and some o their eects!



PLANTS RESPONSE TO INTERNAL AND

EXTERNAL SIGNALS

Plants respond to environment stimuli by ad!usting the growth of roots and shoots. &hese

response are called tropisms and they are mediated bythe plants hormones. (or example, a root

or shoot bends because of differences in auxin concentration. #uxin that accumulates in cells on

side of a shoot causes the cells to elongate more than the cells on the other side. &he results is

that the shoot bends away from the side with more auxin. #uxin has the opposite effect in roots.

It inhibits elongation of root cells. &hus, a root will bend towards the side with more auxin.

"hototropism

-ight streaming in from one direction causes stem to curve towards its surce. &his response is

called phototropism. In this response, phototropism, orients certain parts of the plants in the

direction that will maximize the amount of light intercepted by its photosynthetic cells.

Phototropism in plants occurs in response to blue light. onphotosynthetic pigment called

phototropins absorb blue light and translate its energy into a cascade of intercellular signals. &he

ultimate effect of this cascade is that auxin is redistributed to the shaded side elongate of a shoot

or coleoptile. #s a result, cell on the shaded side elongate faster than cells on the illuminated

side. 2ifferences in growth rates between cells on opposite sides of a shoot or coleoptiles cause

the entire structure to bend toward the light.



Gra#itropism

o matter how aseed is positioned in the soil when it germinates, the radical always grows down,

and the primary shoot always grows up. Even if a seedling is turned upside down !ust after

germination, the primary root and shot will curve so the root grows down and the shoot grows

up. # growth response to gravity is called gravitropism.

&he plant know which direction up by gravity0sensing mechanismsof many organisms are based

on statoliths. In plants, statoliths are starch0grainstuffed amyloplasts that occur in root cap cells,

and also in specialized cells at the periphery of vascular tissue in the stem.

tarch grains are heavier than cytoplasm, so statoliths tend to sink to the lowest region of the

cell, wherever that is. When statoliths move, they put tension on actin microfilamens of the cell,s

cytoskeleton. &he filaments are connected to the cell,s membrane, and the change in tension is

thought to stimulate certain ion channels in the membranes. &he result is that the cell,s auxin

efflux carriers move to the new bottom of the cell within minutes of a change in orientation.&hus, auxin is always transported to down0facing side of roots and shoots.

$hi%motropism

# plant/s contact with a solid ob!ect may result in a change in the direction of its growth, a

response called thigmotropism. &he mechanism that gives rise to the response is not wellunderstood, but it involves the products of calcium ions and at least five genes called touch.

We can see thigmotropism after a plant/s tendril touches an ob!ect. &he cells near the area of

contact stop elongating, and the cells on the opposite sideof the shoot keep elongating. &he result

of une1ual growth rates of cells on opposite sides of the shoot is cause to curl around the ob!ect.

# similar mechanismcauses roots togrow away from contact, which allows them to feel their way

around rock and other impassable ob!ects in the soil.

A+.$/ $( )*&/(,*)"

), )!" (!&" ($"

3!"*" $) %&+(" %"''(

S+/'$!)

()*$6" ,/'

,/" ($" ,- &



"hototaxis

Phototaxis is the ability of organisms to move directionally in response to a light source. 3any

cyanobacteria exhibit phototaxis, both towards and away from a light source. In the

environment, the ability to move into optimal light conditions for photosynthesis is likely to be

an advantage. We are particularly interested in how cells perceive light of different wavelengths4the photoreceptors involved and the signal transduction cascade involved in this process.

Chemotaxis

)hemotaxis, movement toward or away from chemicals, is a universal attribute of motile cells

and organisms. &he cells swim toward amino acids "serine and aspartic acid$, sugars "maltose,

ribose, galactose, glucose$, dipeptides, pyrimidines and electron acceptors "oxygen, nitrate,

fumarate$. (igure 5 shows two simple methods for assessing attractant responses. &he capillary

assay relies on diffusion0generated gradients and is more 1uantitative, but also more laborious.

oft agar assays involve metabolism0generated chemoeffector gradients and provide a more

1ualitative, but expedient, measure of chemotactic ability. )ell also swims away from potentially

noxious chemicals, such as alcohols and fatty acids, but repellent responses haven6t been as

extensively studied.

(igure 57 &he test chemical diffuses from the capillary mouth, establishing a steep gradient that

attracts bacteria to the entrance. &he cells enter the capillary and are subse1uently documented by colony counts.



&erences

• &he unity and 2iversity of life, 58 th edition.

• )ampbell %iology, 9th edition.

• http7::chemotaxis.biology.utah.edu:Parkinson;-ab:pro!ects:ecolichemotaxis:ecolichemot

axis.html• http7::dpb.carnegiescience.edu:labs:bhaya0lab:pro!ects:phototaxis

• http7::plantsinaction.science.u1.edu.au:edition5:<1=content:>08050gravitropism

• http7::dpb.carnegiescience.edu:article:lighting0plant0hormone0?E8?>@?9)command0

system?E8?>@?92

http://chemotaxis.biology.utah.edu/Parkinson_Lab/projects/ecolichemotaxis/ecolichemotaxis.html


http://dpb.carnegiescience.edu/labs/bhaya-lab/projects/phototaxis

http://plantsinaction.science.uq.edu.au/edition1/?q=content/8-2-1-gravitropism

http://dpb.carnegiescience.edu/article/lighting-plant-hormone-%E2%80%9Ccommand-system%E2%80%9D


http://dpb.carnegiescience.edu/labs/bhaya-lab/projects/phototaxis

http://plantsinaction.science.uq.edu.au/edition1/?q=content/8-2-1-gravitropism





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