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Stimulation of 14C-Abscisic Acid Transport by IAA and Sucrose in Pea Epicotyls
Biochem. Physiol. Pflanzen 176, 852-858 (1981)
Stimulation of 14C-Abscisic Acid Transport by IAA and Sucrose in Pea Epicotyls VLADIMiR BORKOVEC and STANISLAV PROCHAZKA Department of Radiobiology, Department of Botany, University of Agriculture Brno, Czechoslovakia Key Term Index: abscisic acid, indoleacetic acid, transport; Pisum sativum.
Summary The effects of IAA and sucrose upon the transport of HC-ABA was studied in epicotyl segments of etiolated pea seedlings. It was found that 14C-ABA moved more intensively in the basipetal direction. Both IAA and sucrose promoted the basipetal transport of HC-ABA. This phenomenon is discussed with regard to the possible nature of ABA transport.
Introduction
The transport of abscisic acid (ABA) was studied earlier both in segments of plant organs (MILBORROW 1974; PILET 1972; DORFFLING et al. 1973; BELLAND and DORFFLING 1974) and in intact plants (HARTUNG 1977; PROCHAZKA 1981). In intact plants, ABA moves from leaves through phloem and xylem both to the stem apex and to the roots (WALTON 1980). From roots ABA moves towards the apex and the regulatory ability of intact apex can be stimulated by exogenous p-indole-3-acetic acid (IAA) (PROCHAZKA 1981). Experiments studying ABA transport in segments of plant organs showed that this transport is non-polar (VEEN 1975; JACOBS 1977). Some authors observed an acropetal polarity of this transport (DORFI'LING et al. 1973), others refer to a basipetal polarity (MILBORROW 1974; INGERSOLL and SMITH 1971; DORFFLING and BOTTGER 1968). It is, however, generally expected (MILLBORROW 1974) that the transport to short distances does not involve an active transport through the phloem but takes place via a metabolically controlled transfer from cell to cell, and that movement bv diffusion cannot be excluded (VEEN and FRISSEL 1975; DAVENPORT et al. 1977). The level of ABA in plant tissues can be affected by the concentration of IAA (ELIASSON 1975). A number of other factors arc also known to affect the ABA levels in plants. This paper deals with the effects of IAA and sucrose upon the transport of l4e-ABA in epicotyl segments of pea seedlings in relation to transport polarity and distribution of He-ABA within the transport system. ~
~
Material and Methods For the experiments 5-day-old, etiolated pea (Pisum sativum L., cv. "Smaragd") seedlings were used which have been precultivated in darkness on wet sawdust at 23°C and 85 % of relative humidity. Segments of the length of 10 mm were c.ut off from the basal part of etiolated epicotyls. Segments
853
Abscisic Acid Transport
were fixed in a vertical position. To determine the acropetal transport, the donor block was placed to the base of segment and the receiver block was situated at the physiological apex. To determine the basipetal transport both blocks were reversed without changing the normal orientation of segment. DL-cis, trans-[2-14C] abscisicacid(Amersham Co., U.K.) was used in the donor block in concentration of 0.69 x 10- 7 M. IAA was applied into the receiver block in concentration of 0.05 % (i. e. 2.8 X 10- 3 M). In the second experiment sucrose was applied in concentration of 1 % together with HC-ABA into the donor block. During the whole experiment plants were kept in darkness at 23°C. Considering the results of our earlier experiments (BORKOVEC and PROCHAZKA 1980), in which the effect of relative humidity upon the transport of HC-ABA was demonstrated, the relative humidity of air was adjusted to 100 %. Mter transport periods of 2, 4 and 8 h block were removed and segments were divided into two parts, one 2.5 mm long adjacent to the receiver block and the other of the length of 7.5 mm adjacent to the donor block. Thereafter they were dissolved in SOLUEN 100 and decoloured according to KALA (1980). Activity of 14 0 was estimated by liquid scintillation using Packard scintillation spectrometer, model 2425. The counted rates (in cpm) corrected according to quenching curves and expressed in disintegrations per minute (dpm). Data about 14C activity represent the average of 15 segments. Experiments were repeated three times and results were tested using t-test.
Results
Data about the 14C-ABA transport (Tables 1, 2) are presented in a similar way as in experiments by VEEN (1975). The total radioactivity (in dpm) in donor blocks at the time of application is expressed as Do; Dt and Rt represent radioactivities in donor and receivers within the time interval t and L1 D represent the difference between Do and
Dt .
Table 1. Time course of basipetal and acropetal movement and the apical and basal losses 0[140 applied as He-ABA on pea segments under the effect of IAA. The initial concentration of l4e-ABA in donor blocks was 0.69 x 10- 7 M, that of IAA in receiver blocks 2.8 x 10- 3 M. Background~corrected data are presented as an average of 15 samples (in dpm). For details see text
He-ABA x IAA acropetal transport
transport time in h
Do
Dt
D
2
41,723 39,883 38,752
39,333 37,366 35,310
2,390 2,517 3,442
5.73 6.31 8.88
0 0 100
39,402 35,861 34,194
1,780 2,579 3,415
4.32 6.71 9.07
0 0 53
0 0 1.55
4
8
100 DIDo Rt
100 Rtl LID 0 0 2.9
Control acropetal transport
4
8
41,182 38,440 37,609
He-ABA x IAA basipetal transport
2 4 8
41,357 42,925 40,685
38,899 38,195 33,877
2,458 4,730 6,808
5.94 11.02 16.73
588 1,490 2,613
23.92 31.50 38.38
Control basipetal transport
2
40,516 40,951 39,568
38,309 37,662 34,386
2,207 3,289 5,182
5.44 8.03 13.09
370 670 1,199
16.76 20.37 23.14
2
4 8
854
V. BORKovEc and S. PROCHAZKA
Table 2. Time course of basipetal and acropetal movement and the apical and basal losses of 14C applied as l4C-ABA on pea segments together with sucrose. The initial concentration of He-ABA in donor blocks was 0.69 X 10- 7 M, that of sucrose 1 %. Background-corrected data are presented as an average of 15 samples (in dpm). For details see text. transport time in h
Do
Dt
D
100 D/Do Rt
l4C-ABA + sucrose acropetal transport
2 4 8
30,822 30,009 29,415
29,578 28,108 26,411
1,244 1,901 3,004
4.03 6.33 10.21
0 45 29
0 2.36 0.96
Control acropetal transport
2 4 8
27,049 28,290 25,053
25,777 26,717 22,661
1,272 1,573 2,392
4.70 5.56 9.54
0 12 55
0 0.76 2.29
14C-ABA + sucrose basipetal transport
2 4 8
33,422 32,781 33,902
29,803 27.967 26,121
3,619 4,814 7,781
10.82 14.68 22.95
2,085 2,808 4,587
57.61 58.32 58.95
Control basipetal transport
2
35,862 35,838 34,441
34,116 33,301 30,320
1,746 2,537 4,121
4.86 7.07 11.96
301 545 1,425
17.23 21.48 34.57
dpm J
..r
""""
4 8
10- 3
dpm x /0-3
J ~------------------------
g-IAA
2 I--
-
100 Rt / LtD
rr-
IIr C-ABA
2
I-
!{
bh- fAA
---
f
11------
a o
,-
-
'---1- - - T- - -- ... --, 2
4-
-1
_ --I I
8
TI/'fE IN HOURS
1
O~--
o
__~____~____________- L - - J 2 8 TitrE IN HOURS
855-
Abscisic Acid Transport dpm x 10- 3
d,om .x 10- 3
sr---------------------------~
o.---------------------------~
t----
~
,I, C- ABA +-SIIO/OSE
-
s~-----------------------
Jr------I 2)---------
t ,- ,- ." ,.
I----
~;I
~- ' " C-ABA
, SUCROSE
_------'-_--I
JI-------
~!~."
J'?-;f
21----
I----~ - - - - - - - - - - - - - - ;
0 0
2
1
8
'" HOURS TI!'1E IN
0
3
-
;-""
0
4
t----!/ 2
,-
,-
;
,-
~
TINE IN HOURS
;
,-
8
Fig. 3. The effect of sucrose upon the acropetal transport of 14C-ABA into the pea segments. Sucrose + 14C-ABA ( ); control (-------). Fig. 4. The effect of sucrose upon the basipetal transport of 14C-ABA into the receiver block. Symbols as in Fig. 3.
Transport of HC-ABA It results from data about the transport of 14C-ABA (control values presented in Tables 1, 2) that its basipetal transport was more intensive than the acropetal one~ The polarity of transport is indicated above all by the comparison of activities foundin receiver blocks; the differences in activities of plant t_ssue segments are mostly not significant. Similarly, in the acropetal arrangement of experiment the receiver activity was found as late as after a 4- to 8 h transport period while in the basipetal arrangement about 16 % of transported activity was found there as early as after 2 h.
Effect of IAA upon the acropetal and basipetal transport of 14C-ABA IAA applied into the receiver block in conc. of 0.05 % (i.e. 2.8 X 10-3 M) promoted the basipetal transport of 14C-ABA (Table 1). The promotion of acropetal transport was Fig. 1. The effect of IAA upon the acropetal transport of14C-ABA into the receiver block and the adjacent
2.5 mm long part of pea segment. IAA
+ l4C-ABA (
); control
=
14C-ABA alone (-------).
Fig. 2. The effect of fAA upon the basipetal transport of 14C-ABA into the receiver block. Symbols as in Fig. 1.
·856
V.
BORKOVEC
and S.
PROCHAZKA
significant only in that case if the activity of receiver and its adjacent 2.5 mm long tissue segment were held for decisive (Fig. 1). In the case of acropetal transport no significant differences were demonstrated neither in receiver activities nor in the total transported activity. On the other hand, the effect of IAA upon the basipetal transport of 14C-ABA was highly significant, if only the receiver activity (i.e. R t or 100 Rt/Ll D) was held as decisive. Significant differences were observed as early as after a 2 h transport period (Fig. 2).
Effect of sucrose upon the acropetal and basipetal transport of 14 0_ ABA Sucrose (1 %) applied simultaneously with 14C-ABA into the donor block promoted the flow of 14C·ABA more intensively in the basipetal direction than in the acropetal one (Table 2). The effect of sucrose upon the acropetal transport of ABA was manifested above all in increased activities transported from donors (J D) or in an increased activity of tissue segments (Fig. 3). As compared with untreated controls the activity of receivers (Rt ) did not differ. In the basipetal direction the application of sucrose resulted in a marked accumulation of 14C-activity in receiver blocks (Fig. 4). Discussion
Our results suggest that in pea epicotyl tissues the basipetal flow of ABA is more intensive than the acropetal one. This corroborates earlier data about ABA transport observed in plant tissue segments of various species (MILBORROW 1968, 1974; INGERSOLL and Sl\lITH 1971; DORFFLING and BOTTGER 1968). Similarly as in experiments carried -out by VEEN (1975) the net loss of ABA from donor blocks was small and did not differ significantly in both treatments. However, different results were obtained in studies on ABA transport in the basipetal direction estimated on the base of radioactivity in receiver blocks. In this case the ABA transport into the receiver blocks was significantly higher. This could suggest that the acropetal and basipetal movement of ABA in plant tissues takes place through different pathways. It results from the evaluation of IAA effect upon the transport of 14e-ABA than IAA shows a lower effect on the acropetal transport than on the basipetal one. In the basipetal arrangement the accumulation of 14C-ABA was significantly higher than in both untreated controls and the acropetal arrangement, although it could be expected that the proper interaction with IAA took place mostly in that part of the segment which was adjacent to the source of IAA. When considering the above mentioned way of ABA transport, then a different affect of IAA upon the acropetal transport of ABA, as compared with the basipetal one, can be explained by the fact that IAA moves in the basipetal direction through different tissues than ABA moving in the opposite direction. This means that acropetally moving 14C-ABA (which is, moreover, transported acropetally in a less intensive manner) cannot be affected in the same way as ABA moving basipetally. A mor~ rapid basipetal transport of ABA through the segment is probably associated with the IAA-saturation of that part of segment which is adjacent to IAA source; this probably accelerates the unloading of ABA from conductive tissue into
Abscisic Acid Transport
857
the receiver. This is supported also by the observation that a higher intensity of transport results from its higher velocity. In general it can be said that these data support the findings by ELIASSON (1975) and PROCHAZKA (1981) that IAA shows a certain effect upon the ABA level in plant tissues. It results from studies on sucrose effect upon the transport of 14C-ABA that this sugar shows a similar effect as on IAA (NAQVr 1973). The promotion of 14C-ABA transport observed in our experiments after the application of sucrose corresponds with NAQvr's explanation. The promotion is again very different for both arrangements. The acropetal transport is less promoted and the promotion is manifested in an increased accumulation of 14e-ABA in the segme~t while in the basipetal arrangement this promotion is manifested in a faster accumulation of labelled compound in the receiver block. Sucrose served probably as an energetic source for the transport and a different response to the supplied energetic source also supports the expectation that ABA transport takes place in different ways in the acropetal and basipetal direction. The role of sucrose as an osmoticum was pratically eliminated by NAQvr (1973) who used different concentrations of different sugars with the same effect. The maintenance of a more intensive basipetal transport of 14C-ABA after the application of sucrose observed in our experiments supports this theory.
References BELLANDI, D. M., and DORFFLING, K.: Transport of Abscisic Acid-[2-C14] in Intact Pea Seedlings. Physiol. Plant. 32, 365-368 (1974). BORKOVEC, V., and PROCHAZKA, S.: Effect of indole-3-yl acetic Acid upon the Transport of DL-cis, trans-[2- 14 C] Abscisic Acid (ABA) in Pea Seedlings (czech). In: Symp. "Dny rostlinne fyziologie" pp. 113-116, Brno 1980. DAVENPORT, T. L., JORDAN, W. R., and MORGAN, P. W.: Movement and Endogenous Levels of Absci sic Acid during Water-stress-induced Abscission in Cotton Seedlings. Plant Physio1.59, 11651168 (1977). DORFFLING, K., and BOTTGER, M.: Transport von Abscisinsaure in Explantaten, Blattstiel- und Internodial Segmenten von Coleus rheneltianus. Planta 80, 299-308 (1968). - BELLANDI, D. M., BOTTGER, M., LUCKEL, H., and MENZER, V.: Abscisic Acid: Properties of Transport and Effect on Distribution of Potassium and Phosphorus. In: Symp. "Proceedings of the Research Institute of Pomology, Skierniewice, Poland", Series E, Nr. 3, 259-272 (1973). ELIASSON, L.: Effect of Indoleacetic Acid on the Abscisic Acid Level in Stem Tissue. Physiol. Plant. 34, 117-120 (1975). HARTUNG, W.: Der Transport von [2- 14 C]-Abscisinsaure aus dem Wurzelsystem intakter Bohnenkeimlinge in die oberirdischen Teile der Pflanze. Z. Pflanzenphysiologie 83, 81-84 (1977). INGERSOLL, R. B., and SMITH, O. E.: Transport of Abscisic Acid. Plant and Cell Physiol. 12, 301~ 309 (1971). JACOBS, W. P.: Regulation of Development by the Differential Polarity of Various Hormones as well as by Effects of One Hormone on the Polarity of Another. In: Symp. "Regulation of Developmental Processes in Plants" (eds. SHUTTE, H. R., and GROSS, D.), pp. 361-380, Jena 1977. KALA, A.: Decolourization of Plant Material for Detection of B-radioactivity by Liquid Scintilation Spectrometry (czech). In. Symp. "Vyuziti nuklearnfch metod a ionizujiciho zareni v genetice, slechteni a fyziologii rostlin" pp. 175-179, Bmo (1980).
858
V. BORKOVEO and S. PROCHAZKA, Abscisic Acid Transport
MILBORROW, B. V.: Identification and Measurement of (+ )-Abscisic Acid in Plants. In: Symp. "Biochemistry and Physiology of Growth Substances" (eds. WIGHTMAN, G., and SETTERFIELD, G.), pp. 1531-1546, Ottawa: Runge (1968). - The Chemistry and Physiology of Abscisic Acid. Ann. Rev. Plant Physiol. 25, 259-307 (1974). NAQVI, S. M.: The Effect of Sugar Supplement on the Kinetics of Indoleacetic Acid-[2-14C] Transport in Zea mays L. Coleoptile Segments. Z. Pflanzenphysiol. 71, 1-5 (1974). PILET, P. E.: ABA Effects on Growth in Relation to Auxin, RNA and Ultrastructure. In: Symp. "Hormonal Regulation in Plant and Development" (eds. KALDEWEY, H., and VARDAR, Y.), pp. 297-315, Weinheim 1972. PROCHAZKA, S.: Translocation of 14C-Abscisic Acid from Roots into the Aboveground Part of Pea (Pisum sativum L.) Seedlings. BioI. Plant. (1981) (in press). VEEN, H., and FRISSEL, M. J.: Stimulation of Hormone Transport in Petiole Segments of Coleus. Physiol. Plantar. 34, 208-215 (1975). - Non-polar Translocation of Abscisic Acid in Petiole Segments of Coleus. Acta Bot. Neerl. 24, 55-63 (1975). WALTON, D. C.: Biochemistry and Physiology of Abscisic Acid. Ann. Rev. Plant. Physiol. 31, 453489 (1980).
Received May 18, 1981. Authors' address: Dr. VLADIMIR BORKovEc and Doc. Dr. STANISLAV PROCHAZKA, University of Agriculture, ZemediHska 1, 66265 Brno, CSSR.
Stimulation of 14C-Abscisic Acid Transport by IAA and Sucrose in Pea Epicotyls VLADIMiR BORKOVEC and STANISLAV PROCHAZKA Department of Radiobiology, Department of Botany, University of Agriculture Brno, Czechoslovakia Key Term Index: abscisic acid, indoleacetic acid, transport; Pisum sativum.
Summary The effects of IAA and sucrose upon the transport of HC-ABA was studied in epicotyl segments of etiolated pea seedlings. It was found that 14C-ABA moved more intensively in the basipetal direction. Both IAA and sucrose promoted the basipetal transport of HC-ABA. This phenomenon is discussed with regard to the possible nature of ABA transport.
Introduction
The transport of abscisic acid (ABA) was studied earlier both in segments of plant organs (MILBORROW 1974; PILET 1972; DORFFLING et al. 1973; BELLAND and DORFFLING 1974) and in intact plants (HARTUNG 1977; PROCHAZKA 1981). In intact plants, ABA moves from leaves through phloem and xylem both to the stem apex and to the roots (WALTON 1980). From roots ABA moves towards the apex and the regulatory ability of intact apex can be stimulated by exogenous p-indole-3-acetic acid (IAA) (PROCHAZKA 1981). Experiments studying ABA transport in segments of plant organs showed that this transport is non-polar (VEEN 1975; JACOBS 1977). Some authors observed an acropetal polarity of this transport (DORFI'LING et al. 1973), others refer to a basipetal polarity (MILBORROW 1974; INGERSOLL and SMITH 1971; DORFFLING and BOTTGER 1968). It is, however, generally expected (MILLBORROW 1974) that the transport to short distances does not involve an active transport through the phloem but takes place via a metabolically controlled transfer from cell to cell, and that movement bv diffusion cannot be excluded (VEEN and FRISSEL 1975; DAVENPORT et al. 1977). The level of ABA in plant tissues can be affected by the concentration of IAA (ELIASSON 1975). A number of other factors arc also known to affect the ABA levels in plants. This paper deals with the effects of IAA and sucrose upon the transport of l4e-ABA in epicotyl segments of pea seedlings in relation to transport polarity and distribution of He-ABA within the transport system. ~
~
Material and Methods For the experiments 5-day-old, etiolated pea (Pisum sativum L., cv. "Smaragd") seedlings were used which have been precultivated in darkness on wet sawdust at 23°C and 85 % of relative humidity. Segments of the length of 10 mm were c.ut off from the basal part of etiolated epicotyls. Segments
853
Abscisic Acid Transport
were fixed in a vertical position. To determine the acropetal transport, the donor block was placed to the base of segment and the receiver block was situated at the physiological apex. To determine the basipetal transport both blocks were reversed without changing the normal orientation of segment. DL-cis, trans-[2-14C] abscisicacid(Amersham Co., U.K.) was used in the donor block in concentration of 0.69 x 10- 7 M. IAA was applied into the receiver block in concentration of 0.05 % (i. e. 2.8 X 10- 3 M). In the second experiment sucrose was applied in concentration of 1 % together with HC-ABA into the donor block. During the whole experiment plants were kept in darkness at 23°C. Considering the results of our earlier experiments (BORKOVEC and PROCHAZKA 1980), in which the effect of relative humidity upon the transport of HC-ABA was demonstrated, the relative humidity of air was adjusted to 100 %. Mter transport periods of 2, 4 and 8 h block were removed and segments were divided into two parts, one 2.5 mm long adjacent to the receiver block and the other of the length of 7.5 mm adjacent to the donor block. Thereafter they were dissolved in SOLUEN 100 and decoloured according to KALA (1980). Activity of 14 0 was estimated by liquid scintillation using Packard scintillation spectrometer, model 2425. The counted rates (in cpm) corrected according to quenching curves and expressed in disintegrations per minute (dpm). Data about 14C activity represent the average of 15 segments. Experiments were repeated three times and results were tested using t-test.
Results
Data about the 14C-ABA transport (Tables 1, 2) are presented in a similar way as in experiments by VEEN (1975). The total radioactivity (in dpm) in donor blocks at the time of application is expressed as Do; Dt and Rt represent radioactivities in donor and receivers within the time interval t and L1 D represent the difference between Do and
Dt .
Table 1. Time course of basipetal and acropetal movement and the apical and basal losses 0[140 applied as He-ABA on pea segments under the effect of IAA. The initial concentration of l4e-ABA in donor blocks was 0.69 x 10- 7 M, that of IAA in receiver blocks 2.8 x 10- 3 M. Background~corrected data are presented as an average of 15 samples (in dpm). For details see text
He-ABA x IAA acropetal transport
transport time in h
Do
Dt
D
2
41,723 39,883 38,752
39,333 37,366 35,310
2,390 2,517 3,442
5.73 6.31 8.88
0 0 100
39,402 35,861 34,194
1,780 2,579 3,415
4.32 6.71 9.07
0 0 53
0 0 1.55
4
8
100 DIDo Rt
100 Rtl LID 0 0 2.9
Control acropetal transport
4
8
41,182 38,440 37,609
He-ABA x IAA basipetal transport
2 4 8
41,357 42,925 40,685
38,899 38,195 33,877
2,458 4,730 6,808
5.94 11.02 16.73
588 1,490 2,613
23.92 31.50 38.38
Control basipetal transport
2
40,516 40,951 39,568
38,309 37,662 34,386
2,207 3,289 5,182
5.44 8.03 13.09
370 670 1,199
16.76 20.37 23.14
2
4 8
854
V. BORKovEc and S. PROCHAZKA
Table 2. Time course of basipetal and acropetal movement and the apical and basal losses of 14C applied as l4C-ABA on pea segments together with sucrose. The initial concentration of He-ABA in donor blocks was 0.69 X 10- 7 M, that of sucrose 1 %. Background-corrected data are presented as an average of 15 samples (in dpm). For details see text. transport time in h
Do
Dt
D
100 D/Do Rt
l4C-ABA + sucrose acropetal transport
2 4 8
30,822 30,009 29,415
29,578 28,108 26,411
1,244 1,901 3,004
4.03 6.33 10.21
0 45 29
0 2.36 0.96
Control acropetal transport
2 4 8
27,049 28,290 25,053
25,777 26,717 22,661
1,272 1,573 2,392
4.70 5.56 9.54
0 12 55
0 0.76 2.29
14C-ABA + sucrose basipetal transport
2 4 8
33,422 32,781 33,902
29,803 27.967 26,121
3,619 4,814 7,781
10.82 14.68 22.95
2,085 2,808 4,587
57.61 58.32 58.95
Control basipetal transport
2
35,862 35,838 34,441
34,116 33,301 30,320
1,746 2,537 4,121
4.86 7.07 11.96
301 545 1,425
17.23 21.48 34.57
dpm J
..r
""""
4 8
10- 3
dpm x /0-3
J ~------------------------
g-IAA
2 I--
-
100 Rt / LtD
rr-
IIr C-ABA
2
I-
!{
bh- fAA
---
f
11------
a o
,-
-
'---1- - - T- - -- ... --, 2
4-
-1
_ --I I
8
TI/'fE IN HOURS
1
O~--
o
__~____~____________- L - - J 2 8 TitrE IN HOURS
855-
Abscisic Acid Transport dpm x 10- 3
d,om .x 10- 3
sr---------------------------~
o.---------------------------~
t----
~
,I, C- ABA +-SIIO/OSE
-
s~-----------------------
Jr------I 2)---------
t ,- ,- ." ,.
I----
~;I
~- ' " C-ABA
, SUCROSE
_------'-_--I
JI-------
~!~."
J'?-;f
21----
I----~ - - - - - - - - - - - - - - ;
0 0
2
1
8
'" HOURS TI!'1E IN
0
3
-
;-""
0
4
t----!/ 2
,-
,-
;
,-
~
TINE IN HOURS
;
,-
8
Fig. 3. The effect of sucrose upon the acropetal transport of 14C-ABA into the pea segments. Sucrose + 14C-ABA ( ); control (-------). Fig. 4. The effect of sucrose upon the basipetal transport of 14C-ABA into the receiver block. Symbols as in Fig. 3.
Transport of HC-ABA It results from data about the transport of 14C-ABA (control values presented in Tables 1, 2) that its basipetal transport was more intensive than the acropetal one~ The polarity of transport is indicated above all by the comparison of activities foundin receiver blocks; the differences in activities of plant t_ssue segments are mostly not significant. Similarly, in the acropetal arrangement of experiment the receiver activity was found as late as after a 4- to 8 h transport period while in the basipetal arrangement about 16 % of transported activity was found there as early as after 2 h.
Effect of IAA upon the acropetal and basipetal transport of 14C-ABA IAA applied into the receiver block in conc. of 0.05 % (i.e. 2.8 X 10-3 M) promoted the basipetal transport of 14C-ABA (Table 1). The promotion of acropetal transport was Fig. 1. The effect of IAA upon the acropetal transport of14C-ABA into the receiver block and the adjacent
2.5 mm long part of pea segment. IAA
+ l4C-ABA (
); control
=
14C-ABA alone (-------).
Fig. 2. The effect of fAA upon the basipetal transport of 14C-ABA into the receiver block. Symbols as in Fig. 1.
·856
V.
BORKOVEC
and S.
PROCHAZKA
significant only in that case if the activity of receiver and its adjacent 2.5 mm long tissue segment were held for decisive (Fig. 1). In the case of acropetal transport no significant differences were demonstrated neither in receiver activities nor in the total transported activity. On the other hand, the effect of IAA upon the basipetal transport of 14C-ABA was highly significant, if only the receiver activity (i.e. R t or 100 Rt/Ll D) was held as decisive. Significant differences were observed as early as after a 2 h transport period (Fig. 2).
Effect of sucrose upon the acropetal and basipetal transport of 14 0_ ABA Sucrose (1 %) applied simultaneously with 14C-ABA into the donor block promoted the flow of 14C·ABA more intensively in the basipetal direction than in the acropetal one (Table 2). The effect of sucrose upon the acropetal transport of ABA was manifested above all in increased activities transported from donors (J D) or in an increased activity of tissue segments (Fig. 3). As compared with untreated controls the activity of receivers (Rt ) did not differ. In the basipetal direction the application of sucrose resulted in a marked accumulation of 14C-activity in receiver blocks (Fig. 4). Discussion
Our results suggest that in pea epicotyl tissues the basipetal flow of ABA is more intensive than the acropetal one. This corroborates earlier data about ABA transport observed in plant tissue segments of various species (MILBORROW 1968, 1974; INGERSOLL and Sl\lITH 1971; DORFFLING and BOTTGER 1968). Similarly as in experiments carried -out by VEEN (1975) the net loss of ABA from donor blocks was small and did not differ significantly in both treatments. However, different results were obtained in studies on ABA transport in the basipetal direction estimated on the base of radioactivity in receiver blocks. In this case the ABA transport into the receiver blocks was significantly higher. This could suggest that the acropetal and basipetal movement of ABA in plant tissues takes place through different pathways. It results from the evaluation of IAA effect upon the transport of 14e-ABA than IAA shows a lower effect on the acropetal transport than on the basipetal one. In the basipetal arrangement the accumulation of 14C-ABA was significantly higher than in both untreated controls and the acropetal arrangement, although it could be expected that the proper interaction with IAA took place mostly in that part of the segment which was adjacent to the source of IAA. When considering the above mentioned way of ABA transport, then a different affect of IAA upon the acropetal transport of ABA, as compared with the basipetal one, can be explained by the fact that IAA moves in the basipetal direction through different tissues than ABA moving in the opposite direction. This means that acropetally moving 14C-ABA (which is, moreover, transported acropetally in a less intensive manner) cannot be affected in the same way as ABA moving basipetally. A mor~ rapid basipetal transport of ABA through the segment is probably associated with the IAA-saturation of that part of segment which is adjacent to IAA source; this probably accelerates the unloading of ABA from conductive tissue into
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the receiver. This is supported also by the observation that a higher intensity of transport results from its higher velocity. In general it can be said that these data support the findings by ELIASSON (1975) and PROCHAZKA (1981) that IAA shows a certain effect upon the ABA level in plant tissues. It results from studies on sucrose effect upon the transport of 14C-ABA that this sugar shows a similar effect as on IAA (NAQVr 1973). The promotion of 14C-ABA transport observed in our experiments after the application of sucrose corresponds with NAQvr's explanation. The promotion is again very different for both arrangements. The acropetal transport is less promoted and the promotion is manifested in an increased accumulation of 14e-ABA in the segme~t while in the basipetal arrangement this promotion is manifested in a faster accumulation of labelled compound in the receiver block. Sucrose served probably as an energetic source for the transport and a different response to the supplied energetic source also supports the expectation that ABA transport takes place in different ways in the acropetal and basipetal direction. The role of sucrose as an osmoticum was pratically eliminated by NAQvr (1973) who used different concentrations of different sugars with the same effect. The maintenance of a more intensive basipetal transport of 14C-ABA after the application of sucrose observed in our experiments supports this theory.
References BELLANDI, D. M., and DORFFLING, K.: Transport of Abscisic Acid-[2-C14] in Intact Pea Seedlings. Physiol. Plant. 32, 365-368 (1974). BORKOVEC, V., and PROCHAZKA, S.: Effect of indole-3-yl acetic Acid upon the Transport of DL-cis, trans-[2- 14 C] Abscisic Acid (ABA) in Pea Seedlings (czech). In: Symp. "Dny rostlinne fyziologie" pp. 113-116, Brno 1980. DAVENPORT, T. L., JORDAN, W. R., and MORGAN, P. W.: Movement and Endogenous Levels of Absci sic Acid during Water-stress-induced Abscission in Cotton Seedlings. Plant Physio1.59, 11651168 (1977). DORFFLING, K., and BOTTGER, M.: Transport von Abscisinsaure in Explantaten, Blattstiel- und Internodial Segmenten von Coleus rheneltianus. Planta 80, 299-308 (1968). - BELLANDI, D. M., BOTTGER, M., LUCKEL, H., and MENZER, V.: Abscisic Acid: Properties of Transport and Effect on Distribution of Potassium and Phosphorus. In: Symp. "Proceedings of the Research Institute of Pomology, Skierniewice, Poland", Series E, Nr. 3, 259-272 (1973). ELIASSON, L.: Effect of Indoleacetic Acid on the Abscisic Acid Level in Stem Tissue. Physiol. Plant. 34, 117-120 (1975). HARTUNG, W.: Der Transport von [2- 14 C]-Abscisinsaure aus dem Wurzelsystem intakter Bohnenkeimlinge in die oberirdischen Teile der Pflanze. Z. Pflanzenphysiologie 83, 81-84 (1977). INGERSOLL, R. B., and SMITH, O. E.: Transport of Abscisic Acid. Plant and Cell Physiol. 12, 301~ 309 (1971). JACOBS, W. P.: Regulation of Development by the Differential Polarity of Various Hormones as well as by Effects of One Hormone on the Polarity of Another. In: Symp. "Regulation of Developmental Processes in Plants" (eds. SHUTTE, H. R., and GROSS, D.), pp. 361-380, Jena 1977. KALA, A.: Decolourization of Plant Material for Detection of B-radioactivity by Liquid Scintilation Spectrometry (czech). In. Symp. "Vyuziti nuklearnfch metod a ionizujiciho zareni v genetice, slechteni a fyziologii rostlin" pp. 175-179, Bmo (1980).
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MILBORROW, B. V.: Identification and Measurement of (+ )-Abscisic Acid in Plants. In: Symp. "Biochemistry and Physiology of Growth Substances" (eds. WIGHTMAN, G., and SETTERFIELD, G.), pp. 1531-1546, Ottawa: Runge (1968). - The Chemistry and Physiology of Abscisic Acid. Ann. Rev. Plant Physiol. 25, 259-307 (1974). NAQVI, S. M.: The Effect of Sugar Supplement on the Kinetics of Indoleacetic Acid-[2-14C] Transport in Zea mays L. Coleoptile Segments. Z. Pflanzenphysiol. 71, 1-5 (1974). PILET, P. E.: ABA Effects on Growth in Relation to Auxin, RNA and Ultrastructure. In: Symp. "Hormonal Regulation in Plant and Development" (eds. KALDEWEY, H., and VARDAR, Y.), pp. 297-315, Weinheim 1972. PROCHAZKA, S.: Translocation of 14C-Abscisic Acid from Roots into the Aboveground Part of Pea (Pisum sativum L.) Seedlings. BioI. Plant. (1981) (in press). VEEN, H., and FRISSEL, M. J.: Stimulation of Hormone Transport in Petiole Segments of Coleus. Physiol. Plantar. 34, 208-215 (1975). - Non-polar Translocation of Abscisic Acid in Petiole Segments of Coleus. Acta Bot. Neerl. 24, 55-63 (1975). WALTON, D. C.: Biochemistry and Physiology of Abscisic Acid. Ann. Rev. Plant. Physiol. 31, 453489 (1980).
Received May 18, 1981. Authors' address: Dr. VLADIMIR BORKovEc and Doc. Dr. STANISLAV PROCHAZKA, University of Agriculture, ZemediHska 1, 66265 Brno, CSSR.