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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.