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Uptake and Translocation of Radioactive Phosphorous in Wheat (Triticum aestivum L.)



Rashida Perveen, Irfan Wahid , Iftikhar Imam Naqvi and S. Shahid Shaukat
 
ABSTRACT

The study deals with a series of experiments to investigate absorption of radioactive phosphate from different parts of young Triticum aestivum L. (wheat variety Sutlej-86) plants. Considerable transport of P32 occurred when the labelled phosphate was fed through roots. The plants showed considerable variation in the rate of absorption and translocation of P32 with respect to time. Absorption through leaves was found at a lower level compared to roots. Downward movement of P32 was minimal. Therefore it can be concluded that only root has the capability to provide feeding route for plant.

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  How to cite this article:

Rashida Perveen, Irfan Wahid , Iftikhar Imam Naqvi and S. Shahid Shaukat , 2003. Uptake and Translocation of Radioactive Phosphorous in Wheat (Triticum aestivum L.). Pakistan Journal of Biological Sciences, 6: 1966-1970.

DOI: 10.3923/pjbs.2003.1966.1970

URL: https://scialert.net/abstract/?doi=pjbs.2003.1966.1970

INTRODUCTION

Phosphorous is the second most important nutrient for plants, next to nitrogen and is taken up by the roots. It is found in plants as a constituent of nucleic acids, phospholipids, the coenzymes NAD and NADP and most importantly, as a constituent of ATP (Mohar and Schopfer, 1995).

Heavy concentration of phosphorous is found in the meristematic region of actively growing plant where it is involved in the synthesis of nucleo-proteins. Sugahara et al. (1972) investigated the incorporation of P32 into the protein fraction of Spinacea oleracea fragments through cyclic and non-cyclic photophosphorylation. Phospholipids, along with proteins, may be important constituents of cell membrane. The coenzyme NAD and NADP are important in oxidation-reduction reactions in which hydrogen transfer reaction takes place and in many other important processes like photosynthesis, glycolysis, respiration and fatty acid synthesis. Green plants absorb water and inorganic salts from soil by unicellular root hairs and translocate to the plant by the processes of diffusion, imbibition and osmosis. The translocation of minerals in plants, when considered in its entirety, involves the upward movement of inorganic materials acquired by the roots, their distribution within the shoot and any redistribution via the vascular tissue from the initial site of deposition to any other part of the plant. Uptake and translocation of phosphorous also depends upon salinity of the soil. Flade (1973) and Attumi et al. (1999) studied the effect of salinity of soil on the distribution of P32 in runner bean and tomato, soya bean plants respectively. The absorption of water in both vapor and liquid form occurs to small extent through aerial part of the plant and its translocation depends upon the water potential of the leaf cells and permeability of the cutin layer ( Breazeale et al., 1950).

By using autoradiography one can measure the distribution of radio-nuclide in any substance. Shuakat et al. (1975) adopted this technique for the study of distribution of C14 and the effect of triazine herbicides on Pinus spp. Since roots tend to smear the activity while the plant is being prepared for the radiograph therefore, Overman et al. (1958) suggested that the root be cut off and thrown away.The present work is aimed to study the uptake and translocation behavior of P32 in wheat plant through root and the aerial parts of the plant.

MATERIALS AND METHODS

Ten to fifteen seeds of wheat were soaked in distilled water for 1 h and surface sterilized for five minutes with calcium hypochlorite. Pot experiment was adopted for germination in a growth chamber (26°C day and 20°C night) in February 2001 for one week. Sterilized seeds were distributed per pot containing half strength Hoagland solution (Chapman, 1976). After one week plants were carefully washed without damaging tender roots. The tube was masked with masking tape and placed in a lead container. The masked test tube was then clamped on a stand and the whole assembly was later erected in a zinc tray, which contained 7.48x 10-3 thick absorbing layer of wax.

Uptake of P32: 10 μ Ci P32 (phosphoric acid) solution was poured into the tube and the solution diluted until all the roots were dipped completely. The Gieger Muller tube was placed near any one leaf of the plant. The G.M. counter was operated at a predetermined plateau 760 volt (Skoog and West, 1976). The counts were recorded at the intervals of 15, 30,45 and 60 min.

Translocation of P32: In the second method plants parts, either roots (feeding from root) or the leaf (feeding from aerial part of plant) were completely dipped into 10 μ Ci P32 solution. These plants were left for 1.5 h and subsequently they were washed properly. They were transferred to the pot again. To obtain time scan data, plants were analyzed after 4, 6, 8, 12 h (for short term) and 24, 48, 72 h (for long term) translocation pattern. Powdered plant material was used for the analysis (Alvi et al., 2003).

Autoradiographic study: Autoradiography was performed to study the tagged phosphate among the roots, stem and leaves. For this purpose the P32 solution was poured into the test tube. The roots of the plants were placed into the solution for 1/ 2, 1, 8 and 24 h. After the time had elapsed the plant was carefully withdrawn and taken into a dark room. It was wrapped in wrapping paper of thickness of 1.97x10-3 inches and sandwiched by enveloping it in between photographic films and dark colour sheet for over-night and the autoradiograph was developed.

RESULTS AND DISCUSSION

Uptake of P32: The absorption of tagged phosphate in wheat plants showed that absorption of P32 increased with the passage of time (Fig. 1a-d). After 4 h, the activity of P32 acquired a constant level. Some fluctuations are observed in the activity vs time graph shown in Fig. a, the precise picture of this graph was obtained by increasing the interval between two observations, such as 30, 45, 60 min. These fluctuations may be attributed due to the random phenomena of activity (Naqvi, 1990). Sud et al. (1998) demonstrated that the uptake of P32 differs widely from soil to soil.

Translocation of P32 by root: The translocation of P32 when taken up by the root, showed that initially translocation of P32 from root to shoot is very rapid. However, after 12 h it gets slower and most of P32 gets accumulated in the leaves (Fig. 2a). Change of the rate of movement of P32 is due to the change in water potential gradient in plant (Biddulph and Markle, 1944). Initially potential gradient is high within the plant. As the upward movement of water takes place this becomes low and movement of water along with mineral (P32) gets slow. Distribution of P32 in the plants was studied by many workers and has been reported (Alvi et al., 2003; Attumi et al., 1999; Shaukat et al., 1975).

Fig. 1:Absorption of P32 by roots at different time intervals in min (a) 15 (b) 30 (c) 45 and (d) 60

Fig. 2:Percentage of radioactivity (P32) in different parts of the plant following uptake of P32 by (a) roots (b) leaves

Plate 1:
Autoradiograph of wheat plant representing uptake of radio-active P32 after ½ and 1 hour

Plate 2:
Autoradiograph of wheat plant representing uptake of radio-active P32 after 8 hour

Plate 3:
Autoradiograph of wheat plant representing uptake of radio-active P32 after 24 hours

Translocation of P32 by leaves: Translocation of P32 by the leaves showed (Fig. 2b) that most of the P32 accumulated in the leaves and downward movement was slow. Biddulph and Markle (1944) showed that this downward movement of inorganic salts from leaves requires living cells i.e pholoem acts as as a channel for translocation. Some upward movement also occurs which is erratic and up to 40%. Our results showed that the movement of P32 is considerably slow in downward direction (Fig. 2b). Sosebee et al. (1971) and Breazlea el al. (1950) concluded that translocation of P32 decreases with the increase in water stress.

Autoradiographic study: Autoradiographic study also supports the absorption and distribution mechanism (Plates 1-3). Portion that exhibits thicker tracks on the photographic plates indicates enhanced absorption of tagged phosphorous, in the particular region. Results shown in Plate 1 exhibit activity of absorbed P32 by the plant after half and 1 h of incorporation. There is appreciably more activity at 1 h compared to 1/2 h subsequent to P 32 supply in the rooting medium. Plate 2 shows that most of the activity concentrates in the stem. Root and leaves have small quantity of the P32. Plate 3 indicates the maximum transport of P32 in the shoot and leaves of the plant, whereas root has very low level of P32

ACKNOWLEDGEMENTS

Thanks are due to Director PINSTECH, Islamabad for providing P32 and Dean Faculty of Science University of Karachi for the provision of a research grant.

REFERENCES
Alvi, S., P. Rashida, N. Iftikhar Imam and S. Shahid Shaukat, 2003. Effect of atrazine on absorption and translocation of p32, chlorophyll, carbohydrate, protein and potassium contents in bean Vigna radiata (L.) wilczek. Pak. J. Biol. Sci., 6: 249-251.
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Attumi, A.A., N.N. Barthakur, R.T. Bajgai and F. Hashinaga, 1999. Phosphorous and sodium distribution in soyabean plants subjected to the salt stress. Jap. J. Soc. Hortic. Sci., 68: 746-752.

Biddulph, O. and J. Markle, 1944. Translocation of radiophosphorous in the phloem of the cotton plant. Am. J. Bot., 31: 65-70.
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Breazeale, J.A., W.T. Mcgeorge and J.F. Breazeale, 1950. Moisture absorption by plants from an atmosphere of high humidity. Plant Physiol., 25: 413-419.

Chapman, S.B., 1976. Methods in Plant Ecology. Ist Edn., Blackwell Scientific Publication, Oxford.

Flade, J.A., 1973. The effect of bicarbonate on P32 uptake by tomato and runner bean. Ann. Bot., 37: 341-344.
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Mohr, H. and P. Schopfer, 1995. Plant Physiology. Springer Verlag, Berlin, pp: 698.

Naqvi, S.I.I., 1990. Radiochemistry. 1st Edn., University Grants Commission, Islamabad, Pakistan.

Overman, R.T., L.D. Coffey and L.A. Muse, 1958. Radioisotope experiment in the Orin summer institute programmes. J. Chem. Educ., 35: 296-298.
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Shaukat, S.S., K.G. Moore and P.H. Lovell, 1975. Some effects of triazine herbicides on the growth, photosynthesis and translocation of phosphate in Pinus species. Physiol. Plant, 33: 295-299.

Skoog, D. and D. West, 1976. Fundamentals of Analytical Chemistry. 3rd Edn., Saunder Golden Sunburst Series, Philadelphia.

Sosbee, R.E. and H.H. Wiebe, 1971. Effect of water stress and clipping on photosynthate translocation in two grasses. Agron. J., 63: 14-17.

Sud, K.C., R.C. Sharma, B.C. Verma and N.K. Sharma, 1998. Studies on the movement of phosphate in some soils of Himachal Pardash. Nucl. Agric. Biol., 27: 200-206.

Sugahara, K. and T. Oku, 1972. Oligomycine-insensitive incorporation of P32 into chloroplast protein by illumination. Plant Cell Physiol., 13: 549-561.
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