Kurze Mitteilungen' Short Communications

Isotopen-Laboratorium, Forschungsanstalt fiir Landwirtschaft, Braunschweig, Federal Republic of Germany

Inhibition of Rb+ Absorption and Transport by Ethrel in Wheat Seedlings

SESHADRI KANNAN

With 3 figures

Received April 26, 1977 . Accepted May 14, 1977

Summary

The effects of different concentrations of ethrel (2-chloroethane phosphonic acid) on the absorption and transport of Rb+ in wheat seedlings grown in low salt (0.2 mM CaCI2) or high salt (dilute nutrient) solutions were studied. The presence of ethrel (20 ppm) was found to be very inhibitory to both the absorption and transport of Rb+ during a 24 hours absorption period, in general. A time course uptake pattern revealed that the rate of inhibition increased with time. Pretreatment of the roots with ethrel (20 ppm) for 48 hours was also effective in reducing the absorption and transport particularly in seedlings grown in low salt medium. It is suggested that ethrel resembles the respiratory inhibitors in their action on ion uptake.

Key words: Growth substances, ethrel, inhibition of ion uptake, Triticum aestivum.

Introduction

The concept of hormone directed transport has been widely applied for the trans­port of organic substances (SETH and WAREING, 1967), especially photosynthates, from the «source» to «sink" region. However, several studies have shown that inorganic ion transport could also be directed and modified by the external application of cer­tain growth substances like gibberellic acid, kinetin, and abscisic acid (KANNAN and MATHEW, 1970; LUTTGE et ai., 1968; PANDEY and KANNAN, 1976; WIENEKE et aI., 1971; WIENEKE, 1973). Ethrel is an ethylene releasing compound and ethylene has been implicated in various growth processes (BURG and BURG, 1966). The effects of ethrel on Rb+ absorption and transport in wheat seedlings raised in low salt and high salt media have been investigated and the findings are reported here.

z. PJlanzenphysiol. Bd. 85. S. 83-87. 1977.

84 SESHADRI KANNAN

Material and Methods

Seeds of wheat (Triticum aestivum L. cv. CARIBIO) were germinated and grown for 7-10 days in low salt (0.2 mM CaCI2) or high salt (dilute nutrient) solution, and the details of culture and experimentation were the same <JS described earlier (KANNAN and KEPPEL, 1976). The effects of ethrel were studied by exposing the roots of seedlings to solutions containing 0.1 mM 86RbCl and different concentrations of ethrel, for 24 hours. In another experiment, the absorption of Rb+ from 0.1 mM RbCl in the absence and presence of ethrel (20 ppm) was measured during a 6 hour period. The effects of pretreatment of the roots with ethrel were also investigated by exposing the roots of seedlings for 48 hours to ethrel (20 ppm) and then transferring them to 0.1 mM 86RbCl for 8 hours. At the end of the experiments, the roots were allowed to desorb in equimolar solutions of unlabelled RbCl (5 0q, for 30 minutes. Triplicate sets of 10 seedlings each were radioassayed in a gamma-ray spectrometer. The amounts of Rb estimated in the root and shoot represented the absorption and transport respectively. Since the experimental protocols were not the same, comparisons of results are more meaningful only within an experiment.

Results

It is found that both Rb+ absorption by root and transport to shoot are signifi­cantly reduced in plants grown in high salt solution, the maximum inhibition being at a concentration of 20 ppm ethrel. The transport to shoot is not very much affected in plants grown in low salt medium (Fig. 1). The inhibition is found to begin from the first hour of absorption (Fig. 2). In low salt plants, there is no further inhibition of both absorption and transport after about 3 hours. On the other hand, the inhibi­tion of absorption by root in high salt plants increased with time. There is no signif­icant effect on transport for 5 hours, although it is found to be slowly reduced at 6 hours.

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z. PJlanzenphysiol. Bd. 85. S. 83-87. 1977.

Fig. 1: Absorption and transport of 86Rb+ from 0.1 mM 86RbCl, in wheat seedlings grown in low (0---0), and high .---e salt solutions, as affected by different concentrations of ethrel.

Fig. 2: Time course of absorption and transport of 86Rb+ from 0.1 mM 86RbCI in the absence and presence of 20 ppm ethrel. Absorption was measured with plants grown in low salt medium in the absence (0-----0), and presence (.-----'.) of ethrel. The high salt plants were also allowed to absorb 86Rb+ in the absence (0---0) and presence (e---e) of ethrel.

Inhibition of Rb+ uptake by ethrel 85

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In the experiment where the roots were pretreated with 20 ppm ethrel for 48 hours, it is found that the absorption in both the low and high salt plants is reduced, while the transport is affected only in low salt plants (Fig. 3).

Discussion

A number of growth substances have been tested for their effects on the absorp­tion and transport of both mobile and immobile nutrient elements (KANNAN and MATHEW, 1970; WIENEKE et aI., 1971), and the results have been of diverse nature, ranging from enhancement to inhibition of ion uptake and transport. The effects were also found to depend on the concentration and mode of application of growth substances. WIENEKE et al. (1971) found that gibberellic acid (20 ppm) and triiodo­benzoic acid (30 ppm) depressed Ca++ absorption in pea and bean plants, and indole­acetic acid (20 ppm) increased Ca++ translocation to bean shoot, and depressed it in pea. However, the results clearly indicated that the effects of growth substances on ion absorption and transport are independent of those on plant growth per se (KANNAN and MATHEW, 1970; WIENEKE et aI., 1971). In the present investigation, ethrel is found to inhibit the absorption and transport of Rb+ in wheat seedlings, in general. The time course shows that the inhibition of absorption was rapid in the first 2 hours and continued at a slow rate thereafter (Fig. 2). The inhibitory effect is found to continue even after the removal of ethrel, especially in low salt plants

Z. Pjlanzenphysiol. Bd. 85. S. 83-87. 1977.

86 SESHADRI KANNAN

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Fig. 3: Absorption and transport of 86Rb+ from 0.1 mM 86RbCl in wheat seedlings grown in low and high salt media. A set of plants was pre­treated with 20 ppm ethrel before transferring to the absorption medium.

(Fig. 3). The finding that it has no effect on transport in high salt plants suggests that the presence of ethrel is necessary in this system, in order to cause the inhibition.

Ethylene has been implicated in the inhibitory effects caused by low concentra­tions of indole-acetic acid on the growth of root and stem sections of pea plants (BURG and BURG, 1966), and ethrel is reported to severely inhibit the nodulation of inoculated pea plants (DRENNEN and NORTON, 1972). The exact mechanism of in­hibition of Rb+ absorption and transport by ethrel is not known. It appears to differ from the type of inhibition obtained with growth substances like triiodobenzoic acid (KANNAN and MATHEW, 1970).

It is interesting to note that typical biphasic patterns of Rb+ absorption are ob­tained here (Fig. 2). The rate of absorption in the high salt plants is however much less than that in low salt ones. According to HOOYMANS (1974) the biphasic pattern represents the cytoplasmic and vacuolar filling up of ions. It is seen that in high salt plants, the phase II uptake begins from 2 hours (Fig. 2) when the roots are treated with ethrel. It is possible that ethrel has a specific effect in decreasing the process of vacuolar accumulation, or, alternatively, arrests the filling up of cytoplasm after 2 hours.

The author is grateful to the International Atomic Energy Agency and the Government of India Bhabha Atomie Research Centre, Bombay for financial support and sponsorship. Thanks are also expressed to Dr. H. KEPPEL for kindly providing facilities, and to Dr. PERKOW, Pflanzensehutz Urania GmbH, Hamburg, for the generous gift of ethrel.

References

BURG, S. P. and F. A. BURG: Interaction of auxin and ethylene and its role in plant growth. Proe. Nat!' Acad. Sci. U.s.A. 55,262-269 (1966).

Z. Pjlanzenphysiol. Bd. 85. S. 83-87. 1977.

Inhibition of Rb+ uptake by ethrel 87

DRENNAN, D. S. H. and C. NORTON: The effect of ethrel on nodulation in Pisum sativum L. Plant and Soil 36, 53-57 (1972).

HOOYMANS, J. J. M.: Role of cell compartments in the redistribution of K+ and Na+ ions ab­sorbed by the roots of intact barley plants. Z. Pflanzenphysiol. 73,234-242 (1974).

KANNAN, S. and H. KEPPEL: A study on the cytoplasmic and vacuolar accumulation of Fe and Mn in excised wheat roots. Comm. Soil Sci. and Plant Anal. 7, 763-775 (1976).

KANNAN, S. and T. MATHEW: Effects of growth substances on the absorption and transport of iron in plants. Plant Physiol. 45, 206-209 (1970).

LUTTGE, U., K. BAUER und D. KOHLER: Friihwirkungen von Gibberellinsaure auf Membran­transport in jungen Erbsenpflanzen. Biochim. Biophys. Acta 150,452-459 (1968).

PANDEY, D. P. and S. KANNAN: Action of ABA and some cytokinins on the transport of foliar and root absorbed Rb+ and Fe++ in bean plants. Z. Pflanzenphysiol. 78, 95-102 (1976 ).

SETH, A. K. and P. F. WAREING: Hormone-directed transport of metabolites and its possible role in plant senescence. J. Exp. Bot. 18, 65-77 (1967).

WIENEKE, J.: Investigations of secondary translocation of root absorbed 45Ca in bean plants. Z. Pflanzenernahr. u. Bodenkunde 134, 157-166 (1973).

WIENEKE, J., O. BIDDULPH, and C. G. WOODBRIDGE: Influence of growth regulating sub­stances on absorption and translocation of calcium in bean and pea plants. J. Amer. Soc. Hort. Sci. 96, 721-724 (1971).

SEHADRI KANNAN, Biology and Agriculture Division, Bhabha Atomic Research Centre, Bombay 400085, India.

Z. P/lanzenphysiol. Bd. 85. S. 83-87. 1977.