- Email: [email protected]
Kinetin ( 6 Furfurylaminopurine) Inhibits the Replication Cycle of Potato Virus X at a Distinct Event
Biochem. Physiol. Pt1anzen 186,403-407 (1990) Gustav Fischer Yerlag Jena
Kinetin (6 Furfurylaminopurine) Inhibits the Replication Cycle of Potato Virus X at a Distinct Event GOTTFRIED SCHUSTER and SYLVIA HUBER Department of Life Sciences of the Karl Marx University Leipzig, Division of Plant Pathology and Microbiology , Leipzig, F.R.G.
Key Term Index : Cytokinins , kinetin, mode of action, virus inhibition; Nicotiana tabacum
Summary The time course of inhibition of PYX (potato virus X) synthesis by kinetin was determined in synchronously infected disks from leaves of Nicotiana tabacum L. 'Samsun' . Synchrony was obtained in one series of experiments by the differential temperature inoculation method. In a second series the synchrony of the first replication cycle was used. The results of both series demonstrate that kinetin (0.1 mM) inhibits an event of the replication cycle of PYX, which occurs later than the early event influenced by the reference substance 2-thioracil and earlier than the late event inhibited by the reference substance cycloheximide. It coincides with the event inhibited by the amino acid analogue ethionine. These data suggest that kinetin may inhibit the initiation of the synthesis of virus coat protein.
Introduction Cytokinins such as kinetin and benzyladenine influence the augmentation of plant viruses . But there are conflicting reports as to whether exogenously supplied cytokinins increase or decrease virus replication and local lesion formation (for surveys see SCHUSTER 1967; 1972; 1988) . The main reason for this may be seen in the dependence of the effects of treatments with cytokinins on the time distance to the virus inoculation and frequency of treatments as well as on the concentration of the cytokinins, the age of the treated virus infected leaves and other factors (ALDWINCKLE and SELMAN 1967; SCHUSTER 1967; 1972). For instance, kinetin promotes the multiplication of TMV in older leaves of Nicotiana tabacum L. 'Samsun' apparently indirectly because of its juvenating and substance attracting effects , thus providing a better virus multiplication in senescing leaves, whereas in younger leaves , as a rule, the virus multiplication is inhibited (SCHUSTER 1967) . Hitherto the question is open whether this virus inhibition by cytokinins is the consequence of indirect cytokinin effects upon host processes as it seems to be the fact with natural or artificial auxins (HUBER and SCHUSTER 1990) , or whether cytokinins inhibit a distinct step of the virus replication cycle. To clarify this question we have determined the time course of inhibition of PYX (potato virus X) multiplication by kinetin in synchronously infected leaf disks, which can give some hints at a possible mode of action of kinetin in the replication cycle of the virus.
BPP 186 (1990) 5/6
403
Material and Methods Chemicals Kinetin (6-furfurylaminopurine) was purchased from Chemapol, Praha). As reference substances were included 2-thiouracil (a gift of the research institute 'Manfred von Ardenne', Dresden), ethionine (purchased from Serva Feinbiochemica GmbH & Co, Heidelberg, BRD) and cycloheximide (purchased from the Upjohn Company, Kalamazoo, Mich., USA). Virus and virus host, synchronous virus synthesis. substance application. virus assay Synchronous multiplication of PYX (potato virus X), ringspot strain H 19, was achieved in leaves of Nicotiana tabacum J. 'Samsun' by the differential temperature inoculation (= DTI) procedure (DAWSON and SCHLEGEL 1973; DAWSON et al. 1975) in the modification described by SCHUSTER and ARENHOVEL (1984). Immediately after their inoculation with PYX the leaves were cut off and transmitted into a plant growth chamber with temperatures of 5 ± 2°e. Under these conditions the virus multiplication is arrested at a very early event. When the leaves are shifted to permissive temperatures (as a rule 5 days post infection), virus multiplication starts synchronously from the inhibited event. Immediately after the shift disks (lO-mm diameter) were punched out with a cork borer. 20 disks were combined into samples. A disk pattern was used to equalize possible differences in virus infection or multiplication between different plants, leaves or regions of leaves. Immediately after this procedure or %
-.--_. 100 -,,". '. ,
A
--
\
...c
60·
"?"'1
40
t....
C!.! Q..
'9
40
"
"'¢.L'
20 0
0
12
'
\~
•1\, \
',1'
"
C!.! t)
\ \
\
60
-.C
,£
\
80
\
C
D
B
00
'. ,
80 0
%
24
\
\
,t,
\
20 36
(h)
0
0
12
24
36
. ,,
48
.. , j \.
'\,,·,1
60
Time of treatment initiation (h after shift from 5° to 20°C) (h after mechanical inoculation) Fig. I, Time course of inhibition of PYX synthesis by 0.1 mM kinetin (0-0), 0.5 mM ethionine ( •.. - .. - .. • ), 5 mM 2-thiouracil (0 ........ 0) as well as by 5 X 10- 4 % cycloheximide (e· - . - ·e) in disks inoculated with PYX and preincubated for 5 d at 5 °C (A) or maintained at permissive temperatures after inoculation (B). after having floated on water for different time (see Fig. 1 A) the disks were vacuum infiltrated with kinetin solutions or reference substances and then laid on top of the solutions in lO-cm diameter petri dishes. 72 h after the shift to permissive temperature PYX yield (concentration) was assayed serologically by endpoint determination in the precipitation drop test as described by SCHUSTER et aI. (1979). The proportional long time interval between shift and virus assay is necessary for a further virus mUltiplication, which provides for a measurable PYX concentration in the uninhibited or only partially inhibited samples. All experiments were performed four times.
404
BPP 186 (1990) 5/6
In a second series of experIments (Fig. I B) the synchrony of the first replieation cycle was used. In this case the disks were punched out immediately after inoculation and the treatments started under permissive temperatures as described above. The virus concentration was assayed 96 h after inoculation. The significance of the observed differences was determined by STUDENT's t-test.
Results As shown in Table I, 0.05 mM kinetin inhibits the multi cation of PYX significantly whereas lower doses are less effective. After application of 0.1 mM and 0.5 mM kinetin no PYX is detectable in the precipitation drop test. Higher doses caused damage to the leaf disks. Table 1. Inhibition of potato virus X in leaf disks of Nicotiana tabacum L. "Samsun", which were infiltrated immediately after virus inoculation with increasing doses of kinetin. The virus content of the kinetin-treated samples is given relative to that of control samples (= 100%). - - x = leaf disks damaged Kinetin Concentration
Virus Content (control = 100%)
Virus Inhibition %
(mM)
0.01 0.05 0.1
0.5 1.0 5.0
97 32 0
± 8' ± 10+++
0
--x --x
+++ 1-++
3 68 100
± 8' ± 10+++
100
+++ +++
--x --x
The lowest dose of kinetin causing 100 % inhibition (0.1 mM) was used to determine the time course of inhibition of PYX with (Fig. 1 A) and without (Fig. 1 B) preincubation of the virus infected leaf disks for 5 days at 5°C. After synchronization of the virus multiplication by low temperatures, the PYX inhibition declined rapidly when kinetin was added 12 h after the shift to premissive temperatures or later (Fig. 1 A) thus indicating that kinetin inhibits the replication cycle of PYX at a distinct event. Within the range of error this event coincides with the event influenced by the amino acid analogue ethionine (0,5 mM). But it occurs later than the event influenced by 5 mM 2-thiouracil and earlier than the event influenced by 5 X 10- 4 % cycloheximide. When the synchrony of the first replication cycle was used, a slow decrease of the inhibition began 12 h p.i. and a rapid one 24 h p.i. Within the range of error the time course of inhibition coincides again with that caused by 0.5 mM ethionine (Pig. 1 B). It is later than that caused by 5 mM 2-thiouracil and earlier than that caused by 5 X 10- 4 % cycloheximide. The time difference between the time courses of inhibition obtained after synchronization by the DTI method or under permissive conditions, respectively, using the first replication cycle is thought to be caused by the time necessary for PYX to attain the replication stage which is inhibited by low temperatures.
27
BPP 186 (1990) 5/6
405
Discussion
The time course of inhibition of kinetin ist, within the range of error, identical with that of the amino acid analogue ethionine, the PVX inhibition of which can be reversed totally by methionine (SCHUSTER 1990). This gives rise to take into consideration that the middle late event inhibited by kinetin as well as by ethionine could concern the synthesis of late virus proteins, particularly of coat protein. Likewise, the time courses of inhibition caused by 50 mM 5-azadihydrouracil as well as by 0.02 mM ribavirin (SCHUSTER and HUBER 1990) are identical with that of kinetin. But the time courses of inhibition caused by 5 mM 5-azadihydrouracil (2,4-dioxohexahydro-l,3,5-triazine) and 0.002 mM ribavirin (1-B-ribofuranosyl-l ,2,4,-triazole-3-carboxamide) are identical with the time course of inhibition caused by 5 mM thiouracil (SCHUSTER and HUBER 1990). As the inhibition of TMV caused by ribavirin or thiouracil occurs before or at the beginning of the nucleic acid replication (DAWSON and GRANTHAM 1983; DAWSON and LOZOYA-SALDANA 1984), SCHUSTER and HUBER (1990) took into consideration that 5-azadihydrouracil and ribavirin inerfere with the beginning of the formation of RNA dependent RNA polymerase and, possibly, other early proteins as well as of late proteins, above all coat protein. As we hitherto did not find any hint for the inhibition of the formation of early proteins by kinetin, this substance and possibly other cytokinins may only inhibit the synthesis of virus coat protein. As experiments of CHEN and LEISNER (1985), CHEN et al. (1987), TEYSSENDIER DE LA SERVE and others (1987) gave evidence that cytokinins modulate the gene expression, it seems probable for kinetin and cytokinins to modulate in quite a similar manner the translation of virus coat proteins. Vice versa the virus inhibitors ribavirin and 5-azadihydrouracil exhibit considerable cytokinin activities (HOHNE et al. 1987), thus indicating that, besides the inhibition of the formation of virus coat protein and, possibly, other late and early viral proteins, host translation and/or transcription processes are influenced by these substances, quite similar to cytokinins. These and other similarities may contribute to a deepended understanding of these effects. But supplementary biochemical research is necessary to confirm the mentioned conclusions. References ALDWINCKLE, H. S., and SELMAN, I. W.: Some effects of supplying benzyladenine to leaves and plants inoculated with viruses. Ann. AppI. BioI. 60,49-58 (1967). CHEN, C.-M., ERTL, J., YANG, M.-S., LEISNER, S., and CHANG, C.-C.: Modulation of gene expression by cytokinin and anticytokinin. Proc. of the IV International Symposium of Plant Growth Regulators, Part 2, 123-130 (1987). CHEN, C.-M., and LEISNER, S. M.: Cytokinin-modulated gene expression in excised pumpkin cytyledons. Plant PhysioI. 77, 99-103 (1985). DAWSON, W.O., and GRANTHAM, L. G.: Effect of 2-thiouracil on RNA and protein synthesis in synchronous and asynchronous infections of tobacco mosaic virus. Intervirology 19, 155-161 (1983). DAWSON, W.O., and LOZOYA-SALDANA, H.: Examination on the mode of action of ribavirin against tobacco mosaic virus. Intervirology 22, 77-84 (1984). DAWSON, W.O., and SCHLEGEL, D. E.: Differential temperature treatment of plants greatly enhances multiplaction rates. Virology 53, 476-478 (1973). DAWSON, W.O., SCHLEGEL, D. E., and LUNG, M. C. Y.: Synthesis of tobacco mosaic virus in
406
BPP 186 (1990) 5/6
intact tobacco leaves systemically inoculated by different temperature treatment. Virology 65, 565-573 (1975). HOHNE, c., SCHUSTER, G., and FROMMHOLD, 1.: Wachstumsregulatorische Wirkungen von 5Azadihydrouracil und Ribavirin. Biochem. Physiol. Pflanzen 182, 375-384 (1987). HUBER , S . , and SCHUSTER , G.: Zum EinfluB natUrlicher und synthetischer Auxine auf die Vermehrung des Kartoffel-X- Virus . Arch . Phytopath . u. Pflanzenschutz, in press (1990) . SCHUSTER , G.: Umwelt und Versuchsanordnung als modifizierende Faktoren der Kinetinwirkung auf die Virusvermehrung. Flora (A) 158, 325 - 342 (1967). SCHUSTER, G.: Umwelt und Versuchsanordnung als modifizierende Faktoren der Wirkung von Kinetin auf die Ausbildung von Viruslokallassionen. Arch. Pflanzen schutz 8, 89-102 (1972). SCHUSTER , G.: Synthetic antiphytoviral substances. App!. Virology Res. 1,265-283 (1988). SCHUSTER , G.: Investigations into the inhibition of potato virus X by amino acid analogues . in preparation. SCHUSTER, G., and ARENHOVEL, C.: On the mode of action of the antiphytoviral compound 2,4dioxohexahydro-I,3,5-triazine (5-azadihydrouracil). Intervirology 21, 134-140 (1984) . SCHUSTER , G., HORINGKLEE , W . , WINTER, H. , ESSER , G., STEINKE , U. , KOCHMANN , W., KRAMER, W. , and STEINKE, W .: Antiphytoviral activity of 2 ,4 dioxo hexahydro triazine, Acta virol. 23, 412-420 (1979). SCHUSTER, G., and HUBER, S.: Evidence for the inhibition of potato virus X replication at two stages dependent on the concentration of ribavirin , 5-azadihydrouracil as well as 1,5-diacetyl-5-azadihydrouracil . in preparation. TEYSSENDIER D ELA SERVE , B. , AXELOS , M . , and PEAUD-LENOEL, c.: Modulation of gene expression by cytokinins in tobacco cell suspensions . Proc. of the IV International Symposium of Plant Growth Regulators, Pamporovo, Bulg., Part 2, 131-140 (1987).
Received February 6, 1990; revised form accepted April 9, 1990. Author' s address: Prof. Dr. sc . G. SCHUSTER , Department of Life Sciences of the Karl Marx University Leipzig , Divi sion of Plant Pathology and Mikrobiology, 0 - 7010 Leipzig, BRO .
BPP 186 (1990) 5/6
407
Kinetin (6 Furfurylaminopurine) Inhibits the Replication Cycle of Potato Virus X at a Distinct Event GOTTFRIED SCHUSTER and SYLVIA HUBER Department of Life Sciences of the Karl Marx University Leipzig, Division of Plant Pathology and Microbiology , Leipzig, F.R.G.
Key Term Index : Cytokinins , kinetin, mode of action, virus inhibition; Nicotiana tabacum
Summary The time course of inhibition of PYX (potato virus X) synthesis by kinetin was determined in synchronously infected disks from leaves of Nicotiana tabacum L. 'Samsun' . Synchrony was obtained in one series of experiments by the differential temperature inoculation method. In a second series the synchrony of the first replication cycle was used. The results of both series demonstrate that kinetin (0.1 mM) inhibits an event of the replication cycle of PYX, which occurs later than the early event influenced by the reference substance 2-thioracil and earlier than the late event inhibited by the reference substance cycloheximide. It coincides with the event inhibited by the amino acid analogue ethionine. These data suggest that kinetin may inhibit the initiation of the synthesis of virus coat protein.
Introduction Cytokinins such as kinetin and benzyladenine influence the augmentation of plant viruses . But there are conflicting reports as to whether exogenously supplied cytokinins increase or decrease virus replication and local lesion formation (for surveys see SCHUSTER 1967; 1972; 1988) . The main reason for this may be seen in the dependence of the effects of treatments with cytokinins on the time distance to the virus inoculation and frequency of treatments as well as on the concentration of the cytokinins, the age of the treated virus infected leaves and other factors (ALDWINCKLE and SELMAN 1967; SCHUSTER 1967; 1972). For instance, kinetin promotes the multiplication of TMV in older leaves of Nicotiana tabacum L. 'Samsun' apparently indirectly because of its juvenating and substance attracting effects , thus providing a better virus multiplication in senescing leaves, whereas in younger leaves , as a rule, the virus multiplication is inhibited (SCHUSTER 1967) . Hitherto the question is open whether this virus inhibition by cytokinins is the consequence of indirect cytokinin effects upon host processes as it seems to be the fact with natural or artificial auxins (HUBER and SCHUSTER 1990) , or whether cytokinins inhibit a distinct step of the virus replication cycle. To clarify this question we have determined the time course of inhibition of PYX (potato virus X) multiplication by kinetin in synchronously infected leaf disks, which can give some hints at a possible mode of action of kinetin in the replication cycle of the virus.
BPP 186 (1990) 5/6
403
Material and Methods Chemicals Kinetin (6-furfurylaminopurine) was purchased from Chemapol, Praha). As reference substances were included 2-thiouracil (a gift of the research institute 'Manfred von Ardenne', Dresden), ethionine (purchased from Serva Feinbiochemica GmbH & Co, Heidelberg, BRD) and cycloheximide (purchased from the Upjohn Company, Kalamazoo, Mich., USA). Virus and virus host, synchronous virus synthesis. substance application. virus assay Synchronous multiplication of PYX (potato virus X), ringspot strain H 19, was achieved in leaves of Nicotiana tabacum J. 'Samsun' by the differential temperature inoculation (= DTI) procedure (DAWSON and SCHLEGEL 1973; DAWSON et al. 1975) in the modification described by SCHUSTER and ARENHOVEL (1984). Immediately after their inoculation with PYX the leaves were cut off and transmitted into a plant growth chamber with temperatures of 5 ± 2°e. Under these conditions the virus multiplication is arrested at a very early event. When the leaves are shifted to permissive temperatures (as a rule 5 days post infection), virus multiplication starts synchronously from the inhibited event. Immediately after the shift disks (lO-mm diameter) were punched out with a cork borer. 20 disks were combined into samples. A disk pattern was used to equalize possible differences in virus infection or multiplication between different plants, leaves or regions of leaves. Immediately after this procedure or %
-.--_. 100 -,,". '. ,
A
--
\
...c
60·
"?"'1
40
t....
C!.! Q..
'9
40
"
"'¢.L'
20 0
0
12
'
\~
•1\, \
',1'
"
C!.! t)
\ \
\
60
-.C
,£
\
80
\
C
D
B
00
'. ,
80 0
%
24
\
\
,t,
\
20 36
(h)
0
0
12
24
36
. ,,
48
.. , j \.
'\,,·,1
60
Time of treatment initiation (h after shift from 5° to 20°C) (h after mechanical inoculation) Fig. I, Time course of inhibition of PYX synthesis by 0.1 mM kinetin (0-0), 0.5 mM ethionine ( •.. - .. - .. • ), 5 mM 2-thiouracil (0 ........ 0) as well as by 5 X 10- 4 % cycloheximide (e· - . - ·e) in disks inoculated with PYX and preincubated for 5 d at 5 °C (A) or maintained at permissive temperatures after inoculation (B). after having floated on water for different time (see Fig. 1 A) the disks were vacuum infiltrated with kinetin solutions or reference substances and then laid on top of the solutions in lO-cm diameter petri dishes. 72 h after the shift to permissive temperature PYX yield (concentration) was assayed serologically by endpoint determination in the precipitation drop test as described by SCHUSTER et aI. (1979). The proportional long time interval between shift and virus assay is necessary for a further virus mUltiplication, which provides for a measurable PYX concentration in the uninhibited or only partially inhibited samples. All experiments were performed four times.
404
BPP 186 (1990) 5/6
In a second series of experIments (Fig. I B) the synchrony of the first replieation cycle was used. In this case the disks were punched out immediately after inoculation and the treatments started under permissive temperatures as described above. The virus concentration was assayed 96 h after inoculation. The significance of the observed differences was determined by STUDENT's t-test.
Results As shown in Table I, 0.05 mM kinetin inhibits the multi cation of PYX significantly whereas lower doses are less effective. After application of 0.1 mM and 0.5 mM kinetin no PYX is detectable in the precipitation drop test. Higher doses caused damage to the leaf disks. Table 1. Inhibition of potato virus X in leaf disks of Nicotiana tabacum L. "Samsun", which were infiltrated immediately after virus inoculation with increasing doses of kinetin. The virus content of the kinetin-treated samples is given relative to that of control samples (= 100%). - - x = leaf disks damaged Kinetin Concentration
Virus Content (control = 100%)
Virus Inhibition %
(mM)
0.01 0.05 0.1
0.5 1.0 5.0
97 32 0
± 8' ± 10+++
0
--x --x
+++ 1-++
3 68 100
± 8' ± 10+++
100
+++ +++
--x --x
The lowest dose of kinetin causing 100 % inhibition (0.1 mM) was used to determine the time course of inhibition of PYX with (Fig. 1 A) and without (Fig. 1 B) preincubation of the virus infected leaf disks for 5 days at 5°C. After synchronization of the virus multiplication by low temperatures, the PYX inhibition declined rapidly when kinetin was added 12 h after the shift to premissive temperatures or later (Fig. 1 A) thus indicating that kinetin inhibits the replication cycle of PYX at a distinct event. Within the range of error this event coincides with the event influenced by the amino acid analogue ethionine (0,5 mM). But it occurs later than the event influenced by 5 mM 2-thiouracil and earlier than the event influenced by 5 X 10- 4 % cycloheximide. When the synchrony of the first replication cycle was used, a slow decrease of the inhibition began 12 h p.i. and a rapid one 24 h p.i. Within the range of error the time course of inhibition coincides again with that caused by 0.5 mM ethionine (Pig. 1 B). It is later than that caused by 5 mM 2-thiouracil and earlier than that caused by 5 X 10- 4 % cycloheximide. The time difference between the time courses of inhibition obtained after synchronization by the DTI method or under permissive conditions, respectively, using the first replication cycle is thought to be caused by the time necessary for PYX to attain the replication stage which is inhibited by low temperatures.
27
BPP 186 (1990) 5/6
405
Discussion
The time course of inhibition of kinetin ist, within the range of error, identical with that of the amino acid analogue ethionine, the PVX inhibition of which can be reversed totally by methionine (SCHUSTER 1990). This gives rise to take into consideration that the middle late event inhibited by kinetin as well as by ethionine could concern the synthesis of late virus proteins, particularly of coat protein. Likewise, the time courses of inhibition caused by 50 mM 5-azadihydrouracil as well as by 0.02 mM ribavirin (SCHUSTER and HUBER 1990) are identical with that of kinetin. But the time courses of inhibition caused by 5 mM 5-azadihydrouracil (2,4-dioxohexahydro-l,3,5-triazine) and 0.002 mM ribavirin (1-B-ribofuranosyl-l ,2,4,-triazole-3-carboxamide) are identical with the time course of inhibition caused by 5 mM thiouracil (SCHUSTER and HUBER 1990). As the inhibition of TMV caused by ribavirin or thiouracil occurs before or at the beginning of the nucleic acid replication (DAWSON and GRANTHAM 1983; DAWSON and LOZOYA-SALDANA 1984), SCHUSTER and HUBER (1990) took into consideration that 5-azadihydrouracil and ribavirin inerfere with the beginning of the formation of RNA dependent RNA polymerase and, possibly, other early proteins as well as of late proteins, above all coat protein. As we hitherto did not find any hint for the inhibition of the formation of early proteins by kinetin, this substance and possibly other cytokinins may only inhibit the synthesis of virus coat protein. As experiments of CHEN and LEISNER (1985), CHEN et al. (1987), TEYSSENDIER DE LA SERVE and others (1987) gave evidence that cytokinins modulate the gene expression, it seems probable for kinetin and cytokinins to modulate in quite a similar manner the translation of virus coat proteins. Vice versa the virus inhibitors ribavirin and 5-azadihydrouracil exhibit considerable cytokinin activities (HOHNE et al. 1987), thus indicating that, besides the inhibition of the formation of virus coat protein and, possibly, other late and early viral proteins, host translation and/or transcription processes are influenced by these substances, quite similar to cytokinins. These and other similarities may contribute to a deepended understanding of these effects. But supplementary biochemical research is necessary to confirm the mentioned conclusions. References ALDWINCKLE, H. S., and SELMAN, I. W.: Some effects of supplying benzyladenine to leaves and plants inoculated with viruses. Ann. AppI. BioI. 60,49-58 (1967). CHEN, C.-M., ERTL, J., YANG, M.-S., LEISNER, S., and CHANG, C.-C.: Modulation of gene expression by cytokinin and anticytokinin. Proc. of the IV International Symposium of Plant Growth Regulators, Part 2, 123-130 (1987). CHEN, C.-M., and LEISNER, S. M.: Cytokinin-modulated gene expression in excised pumpkin cytyledons. Plant PhysioI. 77, 99-103 (1985). DAWSON, W.O., and GRANTHAM, L. G.: Effect of 2-thiouracil on RNA and protein synthesis in synchronous and asynchronous infections of tobacco mosaic virus. Intervirology 19, 155-161 (1983). DAWSON, W.O., and LOZOYA-SALDANA, H.: Examination on the mode of action of ribavirin against tobacco mosaic virus. Intervirology 22, 77-84 (1984). DAWSON, W.O., and SCHLEGEL, D. E.: Differential temperature treatment of plants greatly enhances multiplaction rates. Virology 53, 476-478 (1973). DAWSON, W.O., SCHLEGEL, D. E., and LUNG, M. C. Y.: Synthesis of tobacco mosaic virus in
406
BPP 186 (1990) 5/6
intact tobacco leaves systemically inoculated by different temperature treatment. Virology 65, 565-573 (1975). HOHNE, c., SCHUSTER, G., and FROMMHOLD, 1.: Wachstumsregulatorische Wirkungen von 5Azadihydrouracil und Ribavirin. Biochem. Physiol. Pflanzen 182, 375-384 (1987). HUBER , S . , and SCHUSTER , G.: Zum EinfluB natUrlicher und synthetischer Auxine auf die Vermehrung des Kartoffel-X- Virus . Arch . Phytopath . u. Pflanzenschutz, in press (1990) . SCHUSTER , G.: Umwelt und Versuchsanordnung als modifizierende Faktoren der Kinetinwirkung auf die Virusvermehrung. Flora (A) 158, 325 - 342 (1967). SCHUSTER, G.: Umwelt und Versuchsanordnung als modifizierende Faktoren der Wirkung von Kinetin auf die Ausbildung von Viruslokallassionen. Arch. Pflanzen schutz 8, 89-102 (1972). SCHUSTER , G.: Synthetic antiphytoviral substances. App!. Virology Res. 1,265-283 (1988). SCHUSTER , G.: Investigations into the inhibition of potato virus X by amino acid analogues . in preparation. SCHUSTER, G., and ARENHOVEL, C.: On the mode of action of the antiphytoviral compound 2,4dioxohexahydro-I,3,5-triazine (5-azadihydrouracil). Intervirology 21, 134-140 (1984) . SCHUSTER , G., HORINGKLEE , W . , WINTER, H. , ESSER , G., STEINKE , U. , KOCHMANN , W., KRAMER, W. , and STEINKE, W .: Antiphytoviral activity of 2 ,4 dioxo hexahydro triazine, Acta virol. 23, 412-420 (1979). SCHUSTER, G., and HUBER, S.: Evidence for the inhibition of potato virus X replication at two stages dependent on the concentration of ribavirin , 5-azadihydrouracil as well as 1,5-diacetyl-5-azadihydrouracil . in preparation. TEYSSENDIER D ELA SERVE , B. , AXELOS , M . , and PEAUD-LENOEL, c.: Modulation of gene expression by cytokinins in tobacco cell suspensions . Proc. of the IV International Symposium of Plant Growth Regulators, Pamporovo, Bulg., Part 2, 131-140 (1987).
Received February 6, 1990; revised form accepted April 9, 1990. Author' s address: Prof. Dr. sc . G. SCHUSTER , Department of Life Sciences of the Karl Marx University Leipzig , Divi sion of Plant Pathology and Mikrobiology, 0 - 7010 Leipzig, BRO .
BPP 186 (1990) 5/6
407