UPTAKE OF POTASSIUM BY RICE PLANTAT DIFFERENT STAGES OF GROWTH N. K.

UPTAKE OF POTASSIUM BY RICE PLANTAT DIFFERENT STAGES OF GROWTH

N. K. FAGERIA*

Faculty of Agronomy, Catholic University of Louvain, Belgium

Received on February 11, 1974

SUMMARY

Uptake of potassium by rice plants at different stages of growth can be described by a biphasic isotherm in the range of 5 X 10-5_{M to 1.5 X 10-}3_{M and is probably mediated by a} multiphasic mechanism in the plasmalemma.

INTRODUCTION

The mechanism of absorption of nutrients by plant cells has eeen investigated ex-tensively in recent years. It is pointed out that ion absorption by plant roots involves a dual

mechanism when uptake is studied over a wide range of concentrations (Edwards, 1968 ; Barber, 1972 ; Fageria, 1974) The system one is located in plasmalemma and system two either in plasmalemma (Welch and Epstein, 1968, 1969; Epstein, 1972) or in tonoplast (Torii and Laties, 1966; Laties, 1969). The idea of parallel mechanisms requires the uptake at any one concentration to be the sum of two or more Michaelis- Menten terms, while the concept of serial mechanisms includes the postulation of a diffusive component across the plasmalemma at high external salt concentrations. But recently, a theory propo-sed by Nissen (1973), suggestes that the uptake of ions is described by single multiphasic isotherms, i.e. by a series of phases following Michaelis· Men ten kinetics and separated by discontinuous transitions. He reanalysed the data of potassium uptake by Epstein et a!.,

(I 963) and chloride uptake by Torii andLaties (1966) and confirmed the concept of multiphasic uptake mechanisms.

Although dual or multiphasic patterns of ion absorption have been recorded for a number of ions in tissues of higher plants (Kannan, 1971; Nissen, 1971, 1973), it has not been demonstrated for potassium in intact rice plants. The present investigation was under-taken to examine the mechanism involved in the uptake of potassium by rice plants at different stages of growth.

MATERIALS AND METHODS

Rice ( Oryza sativa L) variety IR 8 was used as the test plant in the present investi-gation. Seeds were soaked in distilled water for 24 hr and were germinated on

cheese-* Present address: Department of Agronomy, University of Udaipur (Rajasthan), India.

54 N.K. FAGERIA

cloth in plastic vessels ( 4 litre) containing solutions of desired potassium concentrations. After one week, five healthy seedlings were placed in plant-supported discs which were positioned in a black painted vessel of 4 litre capacity. The nutrient solution was changed daily to maintain the desired concentration uniform within narrow limits. The growth of the plants was good under these conditions. No aeration was found necessary as mentioned by Tang and Laudelout (1966) since sufficient oxygen was provided by the nutrient solu-tion. When plants were 25, 50, 75, 100 and 125 day-old they were transferred to culture vessels through which a complete nutrient solution containing potassium concentrations from 51 to 1543 tLM was passed at a flow rate of 110 to 115 ml/hr as is described earlier (Tang et a!., 1972). Potassium uptake was measured by monitoring its concentration before entering and after leaving the culture vessel by atomic absorption spectrometer. The rate of uptake was studied by the continuous flow technique as detailed in Fag.eria (1974) and the rate was calculated by the following formula:

Cs

1-- C

0.F.C

Rate of uptake

Dry root weight

Where Cs is the concentration of out-going solution from culture vessel; Co, the con-centration of in-going solution in culture vessel; F, the flow rate (mljhr); C, the concen-tration of the stable ion in the nutrient solution (mg/1).

1

v

1

v

o l

-o 000 6 - - • .

_________..--~ _________..--~·_________..--~:_________..--~_________..--~

QL-~5LQ--100L--1L~--2L00_

UPTAKE OF POTASSIUM BY RICE PLANTS ₅₅ The concentration of nutrient solution (tJ.M) consisted of Ca (N03) 2AH20, 125; KH2P04 , 32; MgS04.7H20, 41; (NH4hS04 , 227; Fe(EDTA)Na, 9.5; CuS04.5H,O, 0.2; H3B03 ; 9.7; MnCI.24H20, 0.2; (NH4) 6Mo70z4.4H:.O, 0.004; ZnS04.7H~O, 0.17 and KCI

in concentrations 51.14, 1022.9, 127.87, 179.00, 225.74, 511.48, 767.22 and 1534.44. The pH of the solution was 5.6±0.2.

The climatic conditions of the growth chamber were as follows: day temperature 30°C± I; night temperature 22°C± 1; relative humidity 80%±2 during the day and 85%±2 at night. Twelve hr day light was supplied with photo tubes at an intensity of 12000 lux at 20 em bench level. The results represent the average data of three replications.

Kinetic constants were calculated by a Fortran program minimizing log v (Cleland, 1963). Kinetic constants based on more than 2 points are given with 95% confidence intervals provided the entire interval remains positive (Table I).

RESULTS AND DISCUSSION

Data for potassium uptake by intact rice plants at different growth stages are pre-sented in double reciprocal plots in Fig. 1 and the kinetic constants are given in Table I. By

Table I. Kinetic constants and transition points for uptake of potassium by rice plant at different growth stages

Time _{Phase V max (flg.g-r.h-r) Km (M)}

Transition (M) (days)

8735±7814 2.4x

to-•

25 _{1.79 X 10-}4 _(chosen)*

2 3586± 1 1.9±0.8x

w-'

1233 ± 38 t.7±0.3x

w-

50

1.79x to-• (chosen)**

2 1130± 1 5.6±2.9x

w-'

635± 13 _1.2±0.2x

_w-'

75 _{1.79x J0-}4 _(chosen)n.s.

2 630±4 8.9± 2.5 x

w-•

738± 125 1.6±0.5Xl0-4

100

2.56 X 10-4 _(chosen)*

2 492±4 _{1.4 ± o.4 x 1 o-}s

1126 3.9 x

w-•

125

1.79X 10-4 _{(chosen) *or***}

2 365±9 _1.7±0.7x

_w-•

n.s.=not significant (P>0.05); * = -01 <P<0.05; ** _{-0.001 < P<O.Ol;}

...

concentra-56 N. K. FAGERIA

tions of about 10-3_{M (Nissen 1971). According to Nissen (1971) the high affinity}

mechan-isms of ion uptake are generally assumed to be in the plasmalemma. While the plasmalemma may be more permeable above 10-3_{M at least to alkali cations and halide ions, it still seems}

improbable that the cytoplasmic concentrations of potassium could reflect the external con-centration with sufficient accuracy to give the observed kinetics. The nature of the transi-tions taking place at the inflection points may be related to sudden change in membrane resistance caused by changes in ionic strength of the nutrient solution at the increasing con-centrations. Elzam and Epstein (1969) also noted similar jumps in potassium influx by wheat grass. If the observed jumps are related to membrane resistance, then two phases separated by a jump must be located in the same membrane, namely the plasmalemma (Nissen, 1971). If so, this would strengthen the concept of a single structure in the plasma-lemma as being rate limiting for uptake of potassium. The existence of separate transition sites has also been demonstrated with other Ions. Reanalysis of data for alkali cations-chlo-ride and boric acid reveals remarkably similar multiphasic patterns (Nissen, 1973). The patterns for the uptake of phosphate and sulphate are also similar in a variety of plants and tissues (Nissen 1973). This suggests that multiphasic patterns may be caused by transi-tions in a structure common to ions exhibiting the same pattern.

ACKNOWLEDGEMENTS

The author is highly thankful to Dr. Per Nissen, Botanical Laboratory, University of Bergen, Norway, for his generous help in calculating the kinetic constants by Fortran Program, going through the manuscript and for his valuable comments. Author is also thank-ful to Professor H. Laudelout, Catholic University of Louvain, Belgium, for providing necessary facilities in his laboratory and to Dr. Tang Van Hai for his help in experimen-tation.

REFERENCES

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Elzam, C.E. and E. Epstein. (1969). Salt relation of two grass species differing in salt tolerance. II. kinetics of the absorption of K, Na and Cl by their excised roots. Agrochiemica, 13 : 196-206.

Epstein, E. (1972). Mineral nutrition of plants: Principles and Perspectives. John Wiley and Sons, Inc. New York.

- - - , Rains, D.W. and Elzam, O.E. (1963). Resolution of dual mechanisms of potassium absorp-tion by barley roots. Proc. Nat. A cad. Sci., 49: 684-92.

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- - - (1974). Kinetics of phosphate absorption by intact rice plants. Submitted to Australian .T. Agri. Research.

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UPTAKE OF POTASSIUM BY R.ICE PLANTS ₅₇

Nissen, P. (1971). Uptake of sulfate by roots and leaf slices of barley: ~ediated by single multiphasic mechanisms. Physiol. Plant., 24: 315-24.

- - - (1973). Multiphasic ion uptake in roots. Ion transport in plants. Academic Press, pp. 539-53.

- - - (1973). Multiphasic uptake in plants. Physiol. Plant., 28: 304-16.

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- - - , Fageria, N.K. and Laudelout, H. (1972). Root electrical potential and phosphate uptake of rice as determined by pH. IAEA-SM-151/3: 81-86.

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