Mineral Nutrition and Ion Transport

7/24/2019 Mineral Nutrition and Ion Transport

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CHAPTER 7:

Mineral nutrition and ion transport

Section "A"

Introduction

The supply and absorption of specific chemical compounds needed for normal growth and

metabolism of plants is defined asnutrition while the chemical compounds that functions as

raw material for synthesis of different structural and functional substance of plants are

termednutrients. The inorganic material obtained from soil which are used as raw material

by plants are calledmineral nutrients. Absorption utilization and assimilation of inorganic

compound or minerals by plants for synthesis of essential material for their growth,

development, structure and physiology is called mineral nutrition.

Essential elements The mineral nutritional elements are available to the plant as ion presentin soil water absorbed through root. Nutrient elements may occur in the soil (a) in the aueous

solution, (b) adsorbed on organic or inorganic soil colloids, (c) in the form of an insoluble

inorganic compound, and (d) as a constituent of organic compounds, either as a residue of

plants or animals or in living organisms. The upta!e of nutrients by the plant roots is closely

related to the form in which the elements occur. Many factors influence nutrient upta!e for

plants. "ons can be readily available to roots or could be #tied up# by other elements or the

soil itself. $oil too high in p% (al!aline) or too low (acid) ma!es minerals unavailable to

plants.

Liebig (!#$proposed the law of minimum which states that productivity of a soil is

dependent upon the proportionate occurrence of deficient mineral.

%ulius &on Sac's( !#$)&erman botanist, demonstrated, for the first time, that plants could

be grown from seedling to maturity in a defined nutrient solution in complete absence of soil.

This techniue of growing plants in a nutrient solution is !nown as '*dro+onics.

Arnon and Stout (,-,$physiologists have given three criteria for plant nutrient

essentiality '

. $ome elements are essential for supporting normal growth and reproduction. "n the

absence of the element the plants do not complete their life cycle or set the seeds.

*. The reuirement of the element must be specific and the element cannot be replaced bythe presence of another element. "n other words, deficiency of any one element cannot be

met by supplying some other element.

+. The element must be directly involved in the metabolism of the plant.

Two criteria by pstein, *--'


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i. The element is part of a molecule that is an intrinsic component of the structure or

metabolism of a plant.

ii. The plant can be so severely deprived of element that it e/hibits abnormalities in itsgrowth, development or reproduction that is, its 0performance1 in comparison with

plants not so deprived.

2or e/ample, agnesium is a constituent of the chlorophyll molecule and is essential for

photosynthesis, so it cannot be replaced by any other element for the same function . "t is also

reuired as aco/actorby many enzymes involved in cellular res+iration and metabolic

+at' 0a*s.

Si1teen c'emical elements are important in which carbon) '*drogen) and o1*genare

supplied by air and water, which comprise about 345 of the fresh weight of the plant, at least

+ other chemical elements, called the essential inorganic nutrients, are needed for plant6s

growth and survival. The si/teen chemical elements are divided into two main groups'

a. 2on3ineral 2utrients'The NonMineral Nutrients are'*drogen (H$) o1*gen (4$)and carbon (C$."n a process called +'otos*nt'esis)plants use energy from the sun tochangecarbon dio1ide (C45 3 carbon and o1*gen$ and 0ater (H543 '*drogen and

o1*gen$into starches and sugars.

b. ineral + other chemical elements,which come from the soil, are dissolved in water

and absorbed through a plant6s roots called the essential inorganic nutrients, are neededfor plant growth.

7n the basis of average concentration in plants , Hoagland (,$ divided essential elements

into two categories'

. acronutrients:Macronutrients are generally present in plant tissues in largeconcentrations o/ .#3#.# mg +er gram o/ dr* matter.The macronutrientsincludeCarbon (C$ ) '*drogen (H$) o1*gen(4$) nitrogen)(2$ +'os+'orous(P$)

sul+'ur(S$) +otassium (6$) Calcium (Ca$and magnesium(g$.

*. 2itrogen) Potassium) and P'os+'orousare obtained from the soil and are the +rimar*macronutrients.Calcium) agnesium) and Sul+'urare the secondar*

macronutrientsneeded in lesser uantity.

+. icronutrients or trace elements:Micronutrients are present in very small amounts inplant body in concentration ofeual or less t'an #. mg +er gram o/ dr* matter.These

includeiron (8e$) manganese (n$ ) Co++er (Cu$) mol*bdenum (o$) 9inc (n$)

boron) (;$ c'lorine (Cl$ .Many of them arecom+onents or co/actors o/

en9*mes.$ome are essential for electron trans/er.

There are some beneficial elements such as sodium) silicon) cobalt and selenium) in addition

to the 8 essential elements named above They are reuired by higher plants.


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ssential elements can also be grouped into following types on the basis of their diverse

functions '

i. 8rame0or< elements:3 Carbon (C $) H*drogen (H$) 41*gen (4$synthesize the

cellulose and other components of cell walls. 9alcium (9a) is component of middle

lamella.

ii. Proto+lasmic elements :3 Carbon (C$ ) '*drogen (H$) o1*gen(4$) nitrogen)(2$+'os+'orous(P$) sul+'ur(S$) iron (8e$and magnesium(g$give rise to protoplasmic

constituents li!e proteins, nucleic acids, hormones, vitamins, phospholipids,,photosynthetic pigments, etc.

iii. 4smotic +otential :3$ome essential elements, e. g., nitrate, potassium, sulphate etc. can

alter the osmotic potential of a cell.Potassiumplays an important role in the opening and

closing of stomata and turgor movements in various plants.

iv. Energ* transducers :3agnesium occurs in c'loro+'*ll and +'os+'orous in ATP areessential elements that are components of energyrelated chemical compounds in plants,

converting one form of energy into another.

v. En9*matic e//ects:3$ome elements that acti&ate or in'ibit en9*mes) e.g.

6)Ca)g)n)n)Cl)2i)Cu) etc. g5=is an activator for both ribulose bisphosphate

carbo/ylaseo/ygenase and phosphoenol pyruvate carbo/ylase, both of which are critical

enzymes in photosynthetic carbon fi/ation,n5=is an activator of alcohol

dehydrogenase and oof nitrogenase during nitrogen metabolism.

vi. ;alancing elements :3 Calcium ) magnesium +otassium counteract the to/ic effect of

other minerals by ion balancing.

vii. 8e) n) Cu) n and o are function as co enzymes

Section ";"

Role o/ acro3 and icro3nutrients and T'eir >e/icienc* s*m+toms

.

2ame o/

elements

Element

obtained in t'e/orm o/

Regions o/

+lant 0'ere

element

reuired

8unctions >e/icienc* s*m+toms

Macronutrient

s


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Nitrogen (N)

Nitrogen cane/ist in a soil

organic form, or

as anammonium ion

(N%:;)nitrite

ion (N7*),ornitrate ion

(N7+).

Nitrogen isreuired by all

parts of a

plant,particularly the

meristematic

tissues and themetabolically

active cells.

Nitrogen is one of

the mahosphorus

(>)

>hosphorus is

absorbed by the

plants from soilin the form of

phosphate ionsas %*>7:

orthophosphate.

>hosphate is

easilyredistributed in

most plants

from one organto another and

is lost from

older leaves,

accumulatingin younger

leaves,developing

flowers and

seeds.The

meristemregion of

growing plants

is high inphosphorus.

>hosphorus is aconstituent of cell

membranes, certain

proteins, all nucleicacids and

nucleotides,

involved in energytransfer such as

AT> and A?>. "t

activates

coenzymes foramino acid

production used in

proteinsynthesis@and it is

involved in many

other metabolicprocesses reuired

for normal growth,

such as

photosynthesis,

glycolysis,respiration, and

fatty acid synthesis.

$tunted growth, dar!

green leaves with aleathery te/ture, and

reddish purple leaf tips

and margins.Maturity isoften delayed.

>otassium () "t is absorbed as

potassium ion(;).

=euired in

more abundantuantities in

the

%elps to determine

an anioncationbalance in cells and

activates enzymes

$mall plants, brown

margins on lower leaves,small wea! stems,

lodging of plants, poor


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meristematic

tissues, buds,

leaves and root

tips.

to metabolize

carbohydrates for

the manufacture of

amino acids andproteins, opening

and closing of

stomata, activationof enzymes and in

the maintenance of

the turgidity ofcells, facilitates cell

division and growth

by helping to move

starches and sugarsbetween plant

parts,disease

resistance.

yield and uality.As in Nand >, ; is easily

redistributed from mature

to younger organs, so

symptoms first appear inolder leaves.

Magnesium

(Mg)

"t is absorbed as

magnesium ion

(Mg*;).

"t is used forfruit and nut

formation and

essential forgermination of

seeds. Beaves'

withdrawn

from ageingleaves and

e/ported to

developingseeds

is a critical

structuralcomponent of the

chlorophyll

molecule and isnecessary for

functioning of plant

enzymes to produce

carbohydrates,sugars and fats."t is

an enzyme activator

in the synthesis ofnucleic acids (?NA

and =NA).

/tensiveinterveinalc'lorosiswhic

h starts with basal leaves

and progresses to younger

leaves (it is mobile).

9alcium

(9a*;)

"t is absorbed as

calcium ion

(9a*;).Adsorbe

d 9a*; is

important forsoil structure by

promoting theaggregation of

soil particles.

This improveswater and root

penetration

Meristematic

and

differentiating

tissues. "t is

immobile(non

translocatable)within plants

and remains in

the older tissuethroughout the

growing

9alcium is involved

in many plant

processes, including

cell elongation, cell

division,germination, pollen

growth, activatesenzymes,and is a

structural

component of cellwalls, . 7ne of its

most important

"nhibition of bud growth,

death of root tips,

cupping of mature leaves,

wea! growth.,


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through the soil

and maintains

the stability ofsoil particles.

season.9alciu

m is easily

leached.

functions is the

maintenance of

membrane

permeability andcell integrity.

$ulphur ($)

$ulfate ($7:C)

from the soil isthe primary

source of

$.$ulfur is also

ta!en up byleaves in

gaseous form as$7*.

$tem and roottips young

leaves@

remobilizedduring

senescence

(the growth

phase in aplant or plant

part as a leaffrom fullmaturity to

death).

"t is a structuralcomponent of

amino acids,

proteins, vitamins

and enzymes and isessential to produce

chlorophyll.

&eneral chlorosis of leaf,

including vascularbundles.$ulfur is not

easily mobilized within

theplant.Therefore,chlorosis,

occur in young tissues

before older ones.

Micronutrient

Dinc Dn

(immobile)

Most zinc in soilis found in

different

minerals withonly a smallpercentage

being adsorbed

in ionic form onsoil and organic

matter e/change

sites.

verywhere

"t activates various

enzymes especially

carbo/ylases, partof carbonicanhydrase and

various

dehydrogenases,needed for au/in

synthesis.

"nterveinal chlorosis of

the upper (youngest)leaves. Afterwards, shootgrowth slows down,

giving the affected plant

parts a rosetteli!eappearance.

Manganese

Mn

("mmobile)

The most

important form

for upta!e byroots is Mn;;,

but it is also

commonlyfound as o/ides

of Mn;;; and

Mn ;;;;(Mn*7+,

Beaves and

seeds

Manganese in the

plant participates in

several importantprocesses including

photosynthesis and

nitrogen andcarbohydrate

metabolism.

The absence of

Manganese causes

disorganization ofchloroplast thyla!oid

membranes. 9hlorosis


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Mn7*, etc.).

"ron, 2e

("mmobile)

>lants obtain

iron in the formof ferric ions

(2e+;). "t is

reuired inlarger amounts

as compare to

other

micronutrients.

verywhere ,

collects alongleaf veins.

"mportant

constituent of

proteins involved inthe transfer of

electrons li!eferredo/in and

cytochromes,

reversibly o/idisedfrom 2e*; to 2e+;

during electron

transfer,activates

catalase enzyme,reuired for

synthesis ofchlorophyll.

/tensive interveinal

chlorosis, starting with

younger leaves (iron isrelatively immobile).

9opper (9u)

"t is absorbed as

cupric ions

(9u*;).

verywhere

ssential for the

overall metabolismin plants.More than

half of the copper is

located in thechloroplasts and

participates in

photosynthetic

reactions. "t is alsofound in other

enzymes involved

with protein andcarbohydrate

metabolism.

?iebac! of shoots

Molybdenum

(Mo)

>lants obtain it

in the form of

molybdate ions.

verywhere,

the synthesis

of proteins is

bloc!ed andplant growth

ceases. =oot

nodule(nitrogen

fi/ing) bacteria

also reuire it.$eeds may not

ssential

component of two

enzymes involved

with nitrogenmetabolism.

>ale green leaves with

rolled or cupped margins.


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form

completely,

and nitrogen

deficiency mayoccur if plants

are lac!ing

molybdenum.

Eoron (E)

The soluble

form isprimarily boric

acid (E(7%)+).

"n neutral to

acid soils, boricacid has no

charge and can,therefore, beeasily leached.

At higher p%

values,conversion to

E(7%): occurs.

The resultingnegative charge

on the molecule

causes its

absorption bysoil particles.

Beaves and

seeds

Eoron is reuiredfor upta!e and

utilisation of 9a*;,membranefunctioning, pollen

germination, cell

elongation, celldifferentiation and

carbohydrate

translocation.

Terminal buds are

damaged, leaving arosette effect on the plant.Beaves are thic!, curled

and brittle. 2ruits, tubers

and roots are discolored,crac!ed and flec!ed with

brown spots.

9hlorine (9l)

9hloride (9lF),

the ionic form of

chlorine used by

plants, is usuallyfound in soluble

forms and is lost

by leaching..

verywhere

"nvolved in osmosis(movement of water

or solutes in cells),

the ionic balancenecessary for plants

to ta!e up mineral

elements and in

photosynthesis.

=educed growth@ stubby

roots, interveinal

chlorosis, nonsucculenttissue (in leafy

vegetables)

Hunger Signs' Ghen plants do not get sufficient amount of one or more essential nutrient

elements ,they show poor growth and develop specific deficiency symptoms Ghich is !nown

as'unger signs.

Section "C"


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Ion trans+ortThe plant absorb minerals nutrient from the soil mostly by the rootsbut in

some plants bylea&es((carni&orous +lants) bromeliads) etc. $ in ionized form.=oots absorb

some mineral nutrients selectively , including some which may not be essential for them.

>lants absorb minerals from soil through the root, passes the membrane, in two ways'

. Passi&e trans+ort'Movement of molecules from high to low concentration. Needs no

energy input. "ncluding Passi&e di//usion and 8acilitated di//usion

*. Acti&e trans+ort:3 o&ement o/ molecules /rom lo0 to 'ig' concentration (o++osite

t'e /lo0 o/ di//usion$. 2eeds in+ut o/ energ* (ATP$.

>assive transport ' The main theories and concepts of passive transport are '

. >onann euilibrium t'eor* (>onann ,$' ntry of ions into the cell across theplasma membrane to maintain electrical euilibrium is !nown as ?onann euilibrium

*. Interce+tion and contact or Ion e1c'ange t'eor*:3 %enn* and 4&erstreet(,-?$ /change of anions and cations absorbed to the root surface with similarly

charged ions of soil solution is !nown as ion e/change.

+. ass /lo0 (6ramer ,?$when solute are transported with the conventional flow of

water from the soil to the plant root under the influence of transpiration .

ec'anism o/ +assi&e trans+ort

A. >i//usion'All molecules are in constant motion. As molecules collides into each other,

directions are changed, causing random dispersal of the molecules. The randommovement of molecules results in diffusion.

E. >i//usion is t'e mo&ement o/ molecules /rom an area o/ 'ig' concentration to one o/

lo0 concentration.

9. This difference in the concentration of molecules across a space is called

theconcentration gradient)is the difference between the concentration of a solute in

one place and its concentration in an ad


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imageH-+

. ?iffusion occurs due to the


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in their vacuoles. The solutes cause an influ/ of water. "n this way can plant cells build up

a large positive internal pressure, the turgor +ressure."t has a decisive influence on the

maintenance of the rigidity and stability of plant tissues. ach cell e/erts a pressure on itsneighbouring cells. The pressures add up to a large tissue tension.

imageH-:

:. H*+ertonic'concentration of solutes outside cell is higher than concentration of solutesinside cell cytosol. Ghen a plant cell is immersed in a'*+ertonic solution,water is

e/tracted from the protoplasm, it shrin!s. This phenomenon is called +lasmol*sis.The

process is reversed as soon as the cells are transferred into a hypotonic

solution (de+lasmol*sis$.

. Isotonic'. concentrations of solutes outside and inside cell are eual. "n isotonic

condition)there is no movement of water into the cell of plant. The cell becomes/laccid(lim+$) and the plant may wilt.

8acilitated di//usion

>lasma membranes of plant made up of +'os+'oli+id bila*erinterspersed with two type

of proteins. "t is selectivepermeable and allows the passage of specific molecules needed

by cell.


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imageH-*

Bipid bilayer isim+ermeable to some o/ t'e &ital molecules li


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"n general, channels are uite s+eci/ic for the type of solute they will transport and

transport through channels is uite a bit faster than by carrier proteins.

Three ssential characteristics' . $pecific (selective for single nutrient molecule) *.

>assive (reuires no input of energy) +. $aturates (nonlinear dependence on

concentration).

$ome ion channels are always open, but others have gatesthat open to allow ions to pass

or close to stop their passage and control t'e c'annel@s +ermeabilit*.The gate can

controlled by &oltage or ion concentration) e&en b* lig't) 'ormones or ot'er

stimuli."on channels '

. Ioltagegated channels

*. Mechanical gated channels

+. Bigandgated channels

imageH-

Carrier +roteins(also


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same direction, and anti+orters, where transfer of one solute depends on the

simultaneous or seuential transfer of a second solute, but in the opposite direction.

Section ">"

Acti&e trans+ort (using ATP energ*$B'en a molecule mo&es /rom lo0er concentration

to 'ig'er concentration ) reuires in+ut o/ energ* (uses ATP$) and is driven active transport systems ' %ydrolysis of AT> ta!es place by

o Na; ,; transport (sodium pump),Na; is maintained at low concentrations inside

the cell and ; is at higher concentrations.

o 9a;; transport

o %;,; transport iv AE9 transporter superfamily, v osteocast proton pumps.

*. "on gradient driven active transport systems or9otransport @The gradients of ions(cations or anions) established by AT>ase or by light driven transport may lead to

secondary active transport of substance li!e amino acid and sugar. These molecules move

in same directionS*m+ort or in o++osite directions Anti+ort .


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imageH-H

"n plants, active transport enables roots to absorb mineral ions from the soil, which are

therefore more concentrated inside plant cells than in the soil. This reuires AT> energy

from aerobic respiration, and therefore roots need o/ygen to allow mineral upta!e and a

waterlogged (thus anaerobic) soil will !ill most roots.

;ul< trans+ortBarge molecules, such as polysaccharides and proteins,are too large to

cross the cell membrane and cross the membrane via vesicles, occurs bye1oc*tosis

(substances lea&ing t'e cell.$ or endoc*tosis.

.

imageH-4

ineral nutrients u+ta


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vessels.The passive movement of ions into the apoplast usually occurs through

ionchannels, the transmembrane proteins that function as selective pores. .

o S*m+lastic( or inner s+ace $"t is a living continuous system formed by

cytoplasm and plasmodesmata from epidermis to /ylem parenchyma. An ion enter

the cell wall of the root hair and pass between the wall and plasma membrane andmoves across the cytoplasm, corte/, endodermis, pericycle through

plasmodesmata endodermis, a layer of cells that they must pass through to enter

the /ylem.The entry or e/it of ions to and from the symplast reuires thee/penditure of metabolic energy, which is an process.

The mineral ions stored in the root hairs pass into /ylem from where these are

translocated through /ylem along with the ascending stream of water, which is pulled

up through the plant by transpiration stream. Mineral elements brought to the leaves

are subseuently assimilated into organic molecules and are redistributed to other

parts of the plant through the phloem.

Mineral Nutrition and Ion Transport

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