Metabolic cost involved in nutrient absorption in plant

1. Metabolic Cost involved in
Nutrient Absorption in Plant
BY
VAISHNAVI Y
19PGA504

2. Introduction
Nutrient uptake: the mechanism by which plants capture all those elements that
are essential for their growth.
Factors
for
Nutrient
uptake
plant
species
environmental
conditions
nutrient
supply
interrelationship
between plant and soil
Others
presence of
microorganisms

3. Nutrient uptake
• Shared by all young root parts and
zone of root hairs
• Root excretions influence the solubility
of some mineral substances
(phosphorus)
• Development of soil microflora
• Nutrients: small molecules without an
electric charge or positively or
negatively charged ions
Roots
• They can also pose a place where a
foliar nutrition of plants can take
place
• Amount of taken up nutrients is low
• Significantly affect the acceptability
of nutrients by soil
• Nutrient application + pesticides
(especially regarding nitrogen
fertilizers)
Foliar

4. Metabolism
 A series of chemical processes that occur within an organism, which include either
synthesis (anabolism) or breakdown (catabolism) of organic compounds.
 These two mechanisms are interrelated, as anabolism requires energy from catabolism
that links ion transport with electron flow in the respiration chain.
Greek word “metabolismos”, which means change in
movement/form
Synthesis (anabolism)
The set of metabolic
pathways that construct
molecules from smaller units
Breakdown (catabolism)
The set of metabolic
pathways that break down
molecules into smaller units
and release energy

5. Nitrogen Uptake
 Plants absorb nitrogen through their roots either in the form of ammonium ions or
nitrates which are available in the soil.
 Molecular nitrogen can be fixed directly by the nitrogen-fixing prokaryotes
(diazotrophs), which are either free living or growing in symbiotic associations with
plants.
 Within plants nitrogen is transported in the form of nitrates, amino acids, amines.

6. An overview of nitrogen metabolism

7. Metabolic Cost of Nitrogen Uptake
 Nitrate is the most common form in which nitrogen is absorbed by plants from the soil.
 Nitrate uptake, mediated by symporters present in plasma membrane, is driven by H+ gradient. It is a
2 H+ /NO3
- symport.
 H+ gradient is created across the plasma membrane by the ATPase-mediated H+ pumps.
 Flow of H+ in response to their gradient is coupled with nitrate uptake.
 NO3
- concentration in the cytosol is maintained by translocating excess nitrate through xylem or by
storing it in vacuoles.
 One class of nitrate transporters present in tonoplast belongs to chloride channel family (CLC).
 CLC can be either H+ gated anion channels or 2NO3
-/ H+ antiporter. It functions to transport nitrate
across tonoplast.

8. Flow of H+ in response to their gradient
is coupled with nitrate uptake

9. Sulphur Metabolism
 Sulphur is a constituent of sulphur-containing amino acids, cysteine, and methionine which are integral
to the protein structure.
 Sulphur is available to plants in oxidized form as sulphate ions from soil and/or as a pollutant from air in
the form of SO2.
 Plants absorb sulphate through their roots as well as through the stomatal chambers in the leaves.
 Once absorbed by roots, sulphate is transported to plastids where it is metabolized or translocated to
leaves where sulphur metabolism is significant and occurs in chloroplasts.

10. Overview of sulphur
metabolism

11. Metabolic Cost of Sulphur Uptake
 Plants absorb sulphur from the soil in the form of sulphates with the help of sulphate transporters.
These transporters are present in root epidermis, cortical cells, vascular systems, vacuoles, and also in
the membrane of plastids and chloroplasts in the mesophyll cells.
 In plasma membrane of root epidermal cells, high-affinity SO4
2- cotransporters are also present which
are H+/SO4
2- symporters. These transporters accumulate sulfate against electrochemical gradient and are
powered by ATPase-mediated proton pumps in the plasma membrane.
 Movement of 3H+ occurs in response to proton motive force (PMF), which is coupled with the transport
of one SO4
2-.

12. Sulphate uptake by
root cells

13. Phosphorus Metabolism
 Phosphorus is essential macronutrient which is central to plant metabolism. It is the constituent of nucleic
acids as phosphodiester linkages join two subsequent nucleotides.
 Phosphorus is an essential structural component of membranes as phospholipids.
 Phosphorus is found in soil solutions in the form of H2PO4
-, HPO4
2-, and PO4
3-, depending upon the pH of the
soil solution.
 In the pH range of 3–7, it is the H2PO4
- which dominates. This form of phosphorus (H2PO4
-) which is denoted
by inorganic phosphate (Pi) is absorbed by the plant.
 Unlike NO3
- and SO4
2- , phosphates are not reduced, and it is the oxidized form which is incorporated in the
biomolecules.

14. Metabolic Cost of Phosphorus Uptake
 H2PO4
- is the predominant form of phosphorus available in soil at pH 5–6. Plants absorb
phosphorus in the form of H2PO4
-.
 There are high-affinity and low-affinity transporters which work in the range of 2.5–12
μM and 50–100 μM, respectively.
 Energy demand is met through ATPase-mediated H+ pumps.
 Phosphate transporters are H+/Pi symporters with 2 or 4 H+ being transported for each
Pi transported.

15. Phosphorus uptake by root cells

16. Potassium Uptake
 Potassium (K+) is the most abundant ion in the plant cell.
 In Photosynthesis, potassium regulates the opening and closing of stomata, and therefore regulates CO2 uptake.
 Potassium triggers activation of enzymes and is essential for production of Adenosine Triphosphate (ATP). ATP is an
important energy source for many chemical processes taking place in plant issues.
 Potassium plays a major role in the regulation of water in plants (osmo-regulation). Both uptake of water through plant
roots and its loss through the stomata are affected by potassium.
 Known to improve drought resistance.
 Activation of enzymes – potassium has an important role in the activation of many growth related enzymes in plants.

17. Metabolic Cost of Potassium Uptake
 HATS (High affinity transport system) and LATS (Low affinity transport system):
 In the HATS mechanism, the thermodynamically uphill flux of K+ is driven by the
downhill flux of H+; charge balance is achieved by the outward pumping of two
H+ by the plasma membrane proton ATPase.
 In the LATS mechanism, by contrast, an electrogenic uniport of K+ is electrically
balanced by the ATP-driven efflux of one H+.

18. General mechanisms
proposed for K+ influx
into plant cells, via
the HATS (upper
diagram) and the LATS
(lower diagram).

19. Iron Uptake
 Iron is an essential element in all living beings.
 It is required as a component of various proteins and as an activator in various
enzyme-catalyzed reactions.
 It ranks fourth among all the elements which are available in the earth crust.
 Plants can absorb reduced form of iron (Fe2+) since transporters for these are
present in plasma membrane of the root epidermis.

20. Metabolic Cost of Iron Uptake
 Two strategies are adopted by plants for the uptake of iron: Phytosiderophores (PS) and Ferredoxin Reductase/Oxidase
(FRO)
 In grasses, plants release organic compounds known as phytosiderophores (PS) that efficiently chelate and solubilize
ferric ions.
 The Fe (III)-PS complex is the soluble form of the iron complexes which can be absorbed by high-affinity transporters
present in the plasma membrane of root epidermis.
 Function of phytosiderophores is less affected by pH.
 ATPase mediated H+ pumps in root epidermis pump out protons altering pH of rhizosphere adjacent to roots to acidic.

21. Iron uptake as complex
with phytosiderophore
released by the plant

22.  In many species of monocots other than grasses, enzymes of ferredoxin reductase/oxidase (FRO) family are
synthesized.
 These are flavocytochromes with intra-membrane heme moieties and large cytoplasmic loops having
binding sites for FAD and NAD(P)H. FROs facilitate electron transfer from NAD(P)H to Fe3+ mediated by
heme as a result of which Fe3+ is reduced to Fe2+.
 The presence of iron regulated transporter (IRT1) in root epidermis is responsible for the absorption of Fe2+
ions.
 Coordinated role of ATPase-mediated H+ pumps, FROs and IRT, is required for iron uptake by the monocots
and dicots.

23. Mechanism of iron
uptake in roots of the
plant. FRO, ferredoxin
reductase/oxidase;
IRT, iron-regulated
transporter

24. Calcium Uptake
 Calcium is an essential macronutrient in plants
 It exhibits a dual function, both as a structural component of cell walls and
membranes and as intracellular second messenger.
 Calcium is taken up from the soil solution through plasma membrane channels
expressed in roots
 Ca2+ permeable channels in root cells were first classified into depolarization-
activated channels (DACCs) and hyperpolarization-activated channels (HACCs).

25. OVERVIEW OF Ca2+ UPTAKE AND THE FUNCTIONS IT FULFILLS IN THE PLANT.
Ca2+ is taken up
by the root and
transported to
the shoot in a
mainly
apoplastic way
to avoid
interference
with its function
as second
messenger.

26. Ca2+ enters the cytosol from compartments of
higher concentration (apoplast, organelles) via
channel proteins (blue) to induce an increase in
the cytosolic calcium concentration [Ca2+], the
Ca2+ signal, which is decoded by downstream
components into an appropriate response. The
signal is terminated by transport of Ca2+ out of
the cytosol via Ca2+-ATPases (shown in orange)
or H+ /Ca2+ antiporters (purple) in the plasma or
organeller membranes.

27. Magnesium Uptake
 Magnesium is involved in the regulation of cell cycle progression.
 Magnesium (Mg) is the most abundant intracellular divalent cation, serving a
wide range of metabolic, structural, and regulatory functions.
 Mg2+ from the soil solution can diffuse or be carried passively by water flow in
the apoplast of the root cortex (apoplasmic pathway).

28. Metabolic Cost of Magnesium Uptake
 One possible way of Mg2+ entry could be through RCA calcium channels at the
plasma membrane of root cells, which are permeable to a wide variety of
monovalent and divalent cation.
 Another possibility is through the AtMRS2/ MGT family members, likely to function
as Mg2+ channels.
 Most of those genes follow partly overlapping tempo-spatial activity patterns, but six
members are expressed in root tissues, indicating a possible role in Mg2+ uptake.

29. Magnesium
uptake by root
cells

30. Zinc Uptake
 Zinc (Zn) is an essential micronutrient for plant growth and development
 Zn acts as cofactor of more than 300 proteins, among which majority are zinc finger
proteins, RNA polymerases and DNA polymerases
 It is the only metal present in all six enzyme classes (oxidoreductase, transferase,
hydrolases, lyases, isomerases and ligases).
 Zinc deficiency causes stunted growth, mental retardness, diarrhoea and pneumonia
in children.

31. Metabolic Cost of Zinc Uptake
 Zn is taken up mainly as divalent cation (Zn2+ ion) by plant roots.
 Strategy I involve efflux of reductants, organic acids and H+ ions,which enhance solubility of Zn-
complexes (Zn phosphates, hydroxides etc.) and release Zn2+ Ions for absorption by root
epidermal cells.
 Strategy II involves efflux of phytosiderophores (phytometallophores) which form stable
complexes with Zn and their subsequent influx into root epidermal cells.
 Passive Zn uptakes by these mechanisms involve participation of water (solvent) molecules and
difference in Zn concentrations across root cell-plasma membrane (RCPM).
 The RCPM H+-ATPase system actively pumps H+ ion extracellularly at the expense of ATP
hydrolysis.
 Release of H+ ion in rhizosphere causes hyperpolarization of RCPM on one hand while reduces
the soil pH on the other hand which results in increased cation uptake rate.

32. Copper Uptake
 Copper has a natural abundance of 60 mg/kg in the Earth’s Crust
 In plants, copper (Cu) acts as essential cofactor of numerous proteins.
 Under physiological conditions, the transition metal Cu is found in the two
common forms, the reduced Cu(I) state and the oxidized Cu(II) state.
 Plant absorbs copper as Cu2+

33. Metabolic Cost of Copper Uptake
 Copper is taken up in the roots in its reduced form Cu2+ by COPT proteins, highly
selective Cu-transporters.
 Cu uptake system may be non-selective ZIP proteins whereas Cu2+ -efflux is
mediated by H+ /Cu2+ antiporters.
 In case excessive Cu enters the roots, the massive generation of ROS activates
also the efflux of K+, causing activation of Programmed Cell Death(PCD).

34. Overview of the Cu-transport system
occurring at the root tip of dicots

35. Manganese Uptake
 Manganese (Mn) is an important micronutrient for plant growth and
development and sustains metabolic roles within different plant cell
compartments.
 The metal is an essential cofactor for the oxygen-evolving complex (OEC) of the
photosynthetic machinery, catalyzing the water-splitting reaction in photosystem
II (PSII).
 In many enzymes, Mn is interchangeable with other divalent cations such as Ca2+
, cobalt (Co), copper (Cu2+ ), Mg2+ , or Zn2+ .
 Availability of Mn to plants depends on its oxidation state: Mn2+ is the only plant-
available form and can be readily transported into root cells and translocated to
the shoot.

36. Metabolic Cost of Manganese Uptake
 At the pH of the cytoplasm (assumed pH-7) there
may be significant conversion of Mn(II) to Mn(III).
 The transport of Mn2+ into the ER is sheer
speculation but if it occurs it would be analogous to
Ca2+ sequestration by Ca2+ - transporting ATPase.
 The uphill transport of Mn2+ into the vacuole is
energized by an H+ antiport, analogous to the H+/Ca
antiport described by Schumaker & Sze
 In the long term it seems inevitable that some
mechanism which pumps or exchanges cytoplasmic
Mn2+ across the plasma membrane must be the
major defence against excessive accumulation.

37. Reference
 Alejandro, S., S. Höller, B. Meier and E. Peiter. 2020. Manganese in Plants: From Acquisition to Subcellular Allocation. Front. Plant Sci. 11:300.
 Bhatla, S.C. and M. A. Lal. 2018. Plant Physiology, Development and Metabolism. Springer Nature Singapore Pte Ltd. Gateway East, Singapore.
 Britto, D.T. and H. J. Kronzucker. 2008. Cellular mechanisms of potassium transport in plants. Physiol. Plant.
 Clarkson, D.T. 1988. The Uptake And Translocation Of Manganese By Plant Roots. In R. D. Graham Et Al. (Eds.), Manganese In Soils And Plants,
Kluwer Academic Publishers, Pp 101-111.
 Gupta, N., H. Ram and B. Kumar. 2016. Mechanism of Zinc absorption in plants: uptake, transport, translocation and accumulation. Rev.
Environ. Sci. Biotechnol.
 Hermans, C., J. Chen and N. Verbruggen. Magnesium in Plants.
 Liu D-Y, Liu Y-M, Zhang W, Chen X-P and C-Q Zou . 2019. Zinc Uptake, Translocation, and Remobilization in Winter Wheat as Affected by Soil
Application of Zn Fertilizer. Front. Plant Sci. 10:426.
 Printz, B., S. Lutts, J. H. Hausman and K. Sergeant. 2016. Copper Trafficking in Plants and Its Implication on Cell Wall Dynamics. Front. Plant Sci.
7:601.
 Thor, K. 2019. Calcium—Nutrient and Messenger. Front. Plant Sci. 10:440.