MECHANISMS OF NUTRIENT UPTAKE FROM SOIL

DIFFERENT MECHANISMS OF NUTRIENT UPTAKE

1. Mechanisms of Nutrient uptake of plant root cells from soil Presented by M. Shravan kumar M.Sc. Agronomy - 1 st year RAM/16 – 03.

2. PASSIVE / NON – MEDIATED UPTAKE Passive absorption : It is the absorption of minerals without direct expenditure of metabollic energy . Also called as the Non mediated uptake . In passive absorption 1. mineral salt absorption is not affected by temperature and metabollic inhibitors . 2. Rapid uptake of ion occures when plant tissues are transferred from a medium of low concentration to higher concentration.

3. Passive absorption may takes place by 5 mechansims 1. Mass flow 2. Diffusion. 3.Root interception 4 . Ion Exchange a) The contact exchange theory b) the carbonic acid theory 5 . Gannon equilibrium ..

4. 1 . Mass flow : is the movement of plant nutrients along with water to the roots . It is a convective process in which plant nutrient ions and other dissolved substances are transported in the flow of water to the root due to transpirational water uptake by the plant. Some mass flow can also occur due to evaporation and percolation of soil water Movement of ions in the soil solution to the surfaces of roots is an important factor in satisfying the nutrient requirement of plants. This movement is accomplished largely by mass flow and diffusion.

5. Karmer (1956) , Russel ( 1960 ) believe that ions are absorbed by the root along with the mass flow of water taking place under the influence of transpiration. Lopushinsky ( 1964) working with detopped plants supported the concept that an increase in transpiration could increase the absorption of salts ..

6. Mass flow

7. Mass flow & root interception & Diffusion

8. 2. Diffusion: Diffusion process operates when an ion moves from an area of high concentration to one of low concentration by random thermal motion . As plant roots absorb nutrients from the surrounding soil solution, a diffusion gradient is set up . A high plant requirement or a high root “absorbing power” results in a strong sink or a high diffusion gradient favouring ion transport. Mainly 3 soil factors which influence the movement of nutrient ions into the root through diffusion namely diffusion coefficient, concentration of the nutrient in the soil solution and the buffering capacity of the solid phase of the soil for the nutrient in the soil s olution phase.

9. Diffusion comes into operation when the concentration at the root surface is either higher or lower than that of the surrounding solution. It is directed towards the root when the concentration at the root surface is decreased , and away from the roots when it is increased. Diffusion follows Fick's first law: F = -D . dc/ dx F =Diffusion rate (quantity diffused per unit cross section and per unit time), dc/ dx =concentration gradient C=concentration D = diffusion coefficient x =distance

10. The concentration of certain ions under some conditions may build up at the root surface because the root is unable to absorb ions at a sufficiently faster rate. Under such conditions the phenomenon of “back diffusion” occurs due to concentration gradient where the movement of certain ions will be away from the root surface and back toward the soil solution. Normally such a condition will not occur, but as root do not absorb all nutrient ions at the same rate, there may on occasion be a buildup of those ions that are less rapidly absorbed, particularly during period of rapid absorption of moisture by the plant.

11. If diffusion is the main process by which a plant nutrient is transported to the root surface, the quantity of the nutrient absorbed by the root can be described approximately by the following equation (Drew et at. 1969): Q=2 π a α c t Q = Quantity of nutrient absorbed per cm root length a = Root radius in cm α = Nutrient absorbing power of the root in cm root length c = Average nutrient concentration at the root surface t =Time of nutrient absorption.

12. Nutrients taken up rapidly by plant roots and which are generally present in the soil solution in low concentrations such as NH 4 + , K+, and phosphate are mainly transported to plant roots by diffusion . The contribution of mass flow to the transport of these nutrients can be calculated as the product of solution concentration and transpiration rate. Values thus obtained are far too low to meet the needs of the plant in any of these elements (Barber et at. 1963). Diffusion also dominates when transpiration is low. Mass flow plays an important role for nutrients present in soil solution in high concentration and when transpiration is high.

13. Occasionally ion accumulations can even occur around roots as is sometimes the case with Ca2+ (Barber 1974). In the case of N03 -, transport can take place either by mass flow or diffusion. Investigations of Strebel et at. (1983) with sugar beet have shown that under field conditions at the beginning of the growth period mass flow is the major process in transporting N03 - towards plant roots. In the later stages of growth, however, when the N03 - concentration in the soil solution is low , diffusion becomes the more important process.

14. Nutrients such as phosphorus and potassium are absorbed strongly by soils and are only present in small quantities in the soil solution. These nutrients move to the root by diffusion . Diffusion is responsible for the majority of the P, K and Zn moving to the root for uptake.

15. 3. Root Interception: Root interception is the extension (growth) of plant roots into new soil areas where there are untapped supplies of nutrients in the soil solution. All these three processes are in constant operation during growth. As the root system develops and exploits the soil more completely, soil solution and soil surfaces retaining adsorbed ions are exposed to the root mass and absorption of these ions by the contact exchange phenomenon is accomplished.

16. For a nutrient element to cross a cell membrane into the cell, it is necessary for each nutrient element to be attached to some carrier. The carrier nutrient complex can pass through the membrane into the cell. The necessary carriers are different for many of the nutrients. Some nutrient elements can be partially but not entirely excluded from absorption, others can be preferentially absorbed, even against a concentration gradient.

17. 4. Ion Exchange : In ionic exchange mechanism ,,anions or cations from within cells are exchanged with anions or cations of equivalent charge of the external solution. The process of ion exchange can be explained by 2 theories . A) the contact exchange theory : according to this theory an ion may be absorbed by the plant root without being first dissolved in the soil solution . An ion adsorbed electrostatically to a solid particle such as plant root or clay particle , is not held too tightly ,,but oscillates within a certain small volume of space .. Exchange of ions takes place when the oscillation volume of one ion overlaps the oscillation volume of another ion .

18. Today it is well known that the plasmalemma pumps h H ions out of the cell into the root medium. This H+ released by the pump, however, does not come in direct contact with the surface of clay minerals . shows the sites and dimensions of the cell membrane (plasmalemma) and the surface of a clay mineral. It is evident that, if at all, only cations at the very outer surface of the cell wall can exchange for cations adsorbed to the clay mineral. By an exchange of H+ from the cell wall, K+ or other cation species can be mobilized from a clay mineral . Even if this does occur, however, the exchanged K+ is still at the outer surface of the cell wall of an epidermal cell and far from the real sites of uptake systems located in the outer cell membrane (plasmalemma).

19. Cation exchange

20. The thickness of a cell wall is in the range of 500 to 1000 nm. There is no evidence that K+ is able to move across the cell wall by further exchange processes but rather moves by diffusion from the soil solution adjacent to the cell wall surface along pores and intercellular spaces to the plasma membrane. The carboxyl and phosphate groups of the cell wall structures represent a strong buffer to the H+ released by the plasmalemma H+ pump

21. Ion uptake mechanisms

22. B ) Carbonic acid exchange theory : according to this theory CO2 released during the respiration of root cells combines with water to form carbonic acid .. Carbonic acid dissociates into H+ ions may be exchanged for cations adsorbed on clay particles . the cations thus released into the soil solution from the clay particles ,,may be adsorbed on root cells in exchange for H+ ions or as ion pairs with bicarbonate .. Thus soil solution plays an important role in Carbonic acid exchange theory. Ion exchange theory allows faster rate of absorption of ions from the external medium by the cells of the root .

23. Carbonic acid exchange theory

24. 4. Donnans’ Equilibrium Theory of Ion Uptake: The accumulation of ions inside the cells without involving expenditure of the metabolic energy can be explained by Donnan’s equilibrium theory. According to this theory there are certain pre-existing ions inside the cell which cannot diffuse outside through membrane. Such ions are called as indiffusible or fixed ions. However, the membrane is permeable to both anions and cations of the outer solutions. Suppose there are certain fixed anions in the cell which is in contact with outer solution containing anions and cations. Normally equal number of anions and cations would have diffused into the cell through an electrical potential to balance each other, but to balance the fixed anions more cations will diffuse into the plant cell.

25. This equilibrium is known as Donnan’s equilibrium . In this particular case, there would be an accumulation of cations inside the cell. If however, there are fixed cations inside the plant cell, the Donnan’s equilibrium will result in the accumulation of anions inside the plant cell.

26. ACTIVE OR MEDIATED UPTAKE OF IONS The concentration of ions in the cytoplasm is often much higher than that in soil solution ,,in extreme cases ,,10,000 fold higher ..Therefore ,,the roots must be able to take up ions againest a considerable concentration gradient . Uptake againest a concentration gradient or strictly speaking , againest an electrochemical gradient requires metabollic energy ,,and the process is called active uptake.. At present there are 2 principal theories of ion transport across the membrane 1. The carrier theory 2 . Ion pump theory .

27. 1. Carrier theory : Carrier is commonly used to refer to an agent responsible for transporting ions from one side of the membrane to the other . Carriers have properties similer to those of enzymes , but unlike enzymes , carriers have not been isolated and characterized . Isolation of a carrier will not necessarily entail its removal from the membrane, but there is no way of measurig its activity . In the transport process a carrier meets the particular ions for which it has affinity ,, form a carrier ion complex ,, and moves across the membrane . The enzyme phosphatage ,, which is located at the inner membrane boundary ,, splits off phosphate group from the carrier complex ,,and the ion is released

28. In this process of ion transport energy is required and involvement of ATP is reported . The ATP is generated from ADP plus inorganic phosphate ( Pi) via respiration ( Oxidative phosphorylation ) The whole uptake may be described as follows ( Mengel and kirkby ,,1982) Carrier + ATP → Carrier p + ADP Carrier p + ion → Carrier p – ion complex Carrier p – ion complex →carrier + pi + ion ( in the presence of phosphatage) Net ion + ATP →Ion + ADP + pi

29. The carrier theory

30. 2 . ATP ase theory of ion transport : Hodges proposed the ATP ase theory of ion transport in plants . ATP ase is a group of enzymes that have the capacity to dissociate ATP into ADP and inorganic phosphate. Energy liberated by this process can be utilized in ion transport across the membrane . In plants the phenomenon is known as the activity of ATP ,,which is associated with the plasmalemma and is activated by cations A detailed description of this process of ion transport is given by Hodges ,,Mengel and kirkby , and clarkson.

31. ATP ase theory of ion uptake

32. Table 1 : Percentages of nutrient supply to the plant roots from soil solution Nutrient Root interception Mass flow Diffusion movement Percentages in supply N 1 99 P 2 4 94 K 2 20 78 Ca 12 88 Mg 27 73 S 4 94 2 (Halvin et al ,,2005.)

33. Table 2 .Ion absorption and proton extrusion by banana roots Bruno et al ,,2005 ,U.P

34. Table 3 .Ion absorption and proton extrusion by banana roots Bruno et al ,,2005 ,U.P

35. Table 4 . Kinetics of chloride ions absorption by plant sprouts in the presence of NaNO3, Ca(NO3)2 and NaSO4 concentration Ca(NO3)2 (mM) 100 Mm Nacl Control 3.1 ± 0.1 50 2.3 ± 0.08 100 1.7 ± 0.07 150 1.1 ± 0.05 200 0.6 ± 0.04 The decrease of Cl - ions (mg) from the solution of 100 mM NaC1 as a result of their absorption by the roots of barley during 20 min ( t - 20°C). Bashir et al ,, 2012 , Cameroon

36. Fig 5 . Absorption of chloride ions by the roots of Barley from the solution of 100 mM NaC1 in the presence of NaNO3 and Ca(NO3)2 .. Bashir et al ,, 2012 , Cameroon

37. Fig.6 . ( 4 ) Quantity of the absorbed Cl - ions out of solutions 100mm (a) and 50mm (b) NaCl by roots of barley depending on temperature within 160minutes. 1 – 1 C 2 – 10 C 3 – 20 c ( control ) 4 – 30 C 5 - 40 C Int Jr. of Agril innovations and research,,2009 ,,3 ( 5 ) Vilayet , 2005

38. Fig7 . K content in sunflower seedlings under different Nacl concentrations Agril. Science and Tech Vol .12 no. 3 ,,2011. . Yang et al ,, Beijing ,,China .

39. Fig 8 . Mg content in sunflower seedlings under different Nacl concentrations Agril. Science and Tech Vol .12 no. 3 ,,2011 .. Yang et al ,, Beijing ,,China .

40. Fig 9 . Ca content in sunflower seedlings under different Nacl concentrations Agril. Science and Tech Vol .12 no. 3 ,,2011 . . Yang et al ,, Beijing ,,China .

41. Fig 10 . Na content in sunflower seedlings under different Nacl concentrations Agril. Science and Tech Vol .12 no. 3 ,,2011. . Yang et al ,, Beijing ,,China .

42. Fig 11 . Evaluation potential of Lemna triscula in the absorption of Zn. Environment conservational journal ,,2012 ,,vol 11 no 3 Krupa et al,,China

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45. Zhang et al , 2012 . Effects of NaHCO3 stress on Na+ absorption in tobacco ( Nicotiana tabacum Linn .). Australian journal of crop sciences 6 ( 10 ) : 1455 – 1461 .