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Auxins and gibberellins in 2-chloroethylphosphonic acid-induced femaleness of Cucurbita pepo L.
Institute of Biology, Copernicus University, Toruil, Poland
Auxins and Gibberellins in 2-Chloroethylphosphonic Acid-Induced Femaleness of Cucurbita pepo L. ANDRZEJ CHROMINSKI and JAN KOPCEWICZ With 2 figures Received May 2, 1972
Summary High level of gibberellin was associated with maleness of squash plants while alteration of sex expression toward femaleness, resulting from the treatment with 2-chloroethylphosphonic acid, was not followed by consistent changes in auxin content. The specificity of auxin participation in endogenous regulation of sex expression is discussed.
Introduction Sex expression in both monoecious and dioecious plants can be modified by soil fertility, temperature, day length as well as exogenously applied chemicals of various nature. Moist, high in nitrogen soil, short day and low temperature of a dark period (HESLOP-HARRISON, 1957), combustion gases from closed wood stoves (NhNINA, 1938), carbon monoxide (MININA and TYLKINA, 1947; HESLOP-HARRISON and HESLop-HARRISON, 1957), acetylene (MEKHANIK, 1958), auxins (LAIBACH and KRIBBEN, 1950; ITO and SAITO, 1956; GALUN, 1959; GALUN et al., 1963); growth retardants (MITCHELL and WITTWER, 1962; HALEVY and RUDICH, 1967), ethylene (MININA and TYLKINA, 1947; MININA, 1952) as well as 2-chloroethylphosphonic acid an ethylene releasing compound (McMuRRAY and MILLER, 1968; KENDER and REMAlLY, 1970), cytokinins (CATARINO, 1964; HASHIZUME and IrZUKA, 1971) and estrogens (LOVE and LOVE, 1945; KOPCEWICZ, 1971 a; GAWIENOWSKI et al., 1971) increase femaleness, while dry, low in nitrogen soil, long day and high temperature of a dark period (HESLOP-HARRISON, 1957) as well as gibberellins (ATAL, 1959; WITTWER and BUKOVAC, 1962) - maleness of the plant.
It was also observed that monoecious cucumber plants have more endogenous gibberellin-like substances than gynoecious ones (ATSMON et al., 1968), while hermaphrodite plants have more extractable auxins than andromonoecious plants (GALUN et al., 1965). Likewise, female Cannabis plants were reported to contain more auxins than male ones (CONRAD and MOTHES, 1961). Consequently, the hypothesis has been proposed that environmental as well as chemical factors exert their effects on sex expression by manipulating the balance of endogenous auxins and gibberellins, with high auxins tending to produce femaleness (ATSMON et al., 1968; IWAHORI et al., 1969; SPLITTSTOESSER, 1970). Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
Auxins, GibberelJins and Sex Expression of Cucurbita
185
Nevertheless, the role of auxins in sex differentiation seems to be debatable since the possibility exists that they promote femaleness due to the enhancement of ethylene production (SHANNON and DE LA GUARDIA, 1969). The latter, however, is not solely attributed to the action of endogenous auxins. In fact, there are data showing that an ethylene-forming system can also be stimulated by other growth regulators (FUCHS and LIEBERMAN, 1968; LOVEYS and WAREING, 1971; GAMBORG and LARuE, 1971). The problem has become even more complicated when reports on the interference of ethylene with auxin translocation within plant tissues (ABELES, 1966; BURG and BURG, 1966 a, 1967; MORGAN and GAUSMAN, 1966) culminated in the work of ERNEST and VALDOVINOS (1971) presenting the ethylene inhibition of both auxin transport and biosynthesis. It was therefore thought desirable to test whether endogenous auxins and gibberellins are directly involved in modification of sex expression in squash.
Material and Methods Monoecious squash plants (Cucurbita pepo L., cultivar Weiser Bush) were grown during spring and summer (March 10 to July 13, 1971) in clay pots in the greenhouse at maximum and minimum temperature of 26 and 17° C, respectively. 2-Chloroethylphosphonic acid (CEPA), a substitute for ethylene, was applied as an aqueous run-off foliar spray in twO treatments, each at a concentration of 200 ppm. Plants were sprayed when the 4th leaf was 1 cm in diameter, and again when the 7th leaf reached that size. Under the conditions described this occured when the plants were 42 and 49 day old, respectively. Control plants were sprayed with distilled water. Number of male and female flowers produced by each plant were recorded with observations being made every second day. Material for growth regulator determinations was taken as indicated in Table 1. Derooted plants deprived of all generative organs were used. GibberelJins and auxins were extracted and fractioned ace. to the methods previously described (KOPCEWICZ, 1968, 1970 a) . Descending chromatography on Whatman No.3 paper in isopropanol-ammonia-water (10 : 1 : 1) follo wed by Avena coleoptile straight growth bioassay (NITSCH, 1956) for auxins, and TLC in benzene-acetic acid (10: 3) followed by both lettuce hypocotyl (FRANKLAND and WAREING, 1960) and dwarf pea (MCCOMB and CARR, 1958) bioassays for gibberellins were applied. Results and Discussion GALUN et al. (1963) on the basis of the experiments with cucumber buds cultured in vitro claimed that the local concentration balance of auxin and gibberellin is important for sex differentiation. From the latter work of GALUN et al. (1965), however, it can be seen that auxin content in the sections of both andromonoecious and hermaphrodite cucumber plants resembled proportionally the total content of auxin in the whole plant of the respective lines, with more auxin being always presl:nt in the hermaphrodite one. Our results demonstrate that CEPA altered sex expression of squash to complete femaleness at the 2nd and 3rd samplings (Table 1). At the same samplings CEPA-treated Z. PJlanzenphysiol. Ed. 68. S. 184-189. 1972.
186
A. CHROMINSKI and
J.
KOPCEWICZ
Table 1. CEPA-modified sex expression of Cucurbita pepo L. at the time of sa mpling for endogenous auxins and gibberellins
Samplings
1/ 4 May l 2/ 16 May l 3/27 Mayl 4/ 13 Julyl
Total no. of flowers per plant':· Control CEP A
14.2 39.9 109.9
Ofo of female flowers Control
CEPA
flower buds visible 13.2 0.0 29.4 2.5 100.7 9.0
100.0 100.0 47.8
" opened and unopened flowers recorded until prevalence of the male ones on the CEPAtreated plants. Each result is the mean of six replicates.
plants contained smaller or roughly similar amounts of auxins and considerably smaller amounts of gibberellins than control plants (Figs. 1 and 2). Moreover, when the CEPA-treated plants started producing male flowers (4 th sampling), an increase of gibberellin content was found (Fig. 2). The results presented here show a positive correlation between maleness and endogenous gibberellin content and a lack of correlation between femaleness and endoge-
II
10
~
i
>-
5'1. r/.
i;
LSD
C!
0
52 .~
"l!
.51 to
l
~ 5 C!
'"
2
3
SAMPLINGS
4
Fig. 1. Auxin content in control and CEPA-treated plants of Cucurbita pepo L. For details on sex expression of analyzed plants see Table 1.
z.
Pjlanzenphysiol. Ed. 68. S. 184-189. 1972.
Auxins, Gibberellins and Sex Expression of Cucurbita
187
nous auxin content in squash. Increased femaleness in other cucurbita, viz. muskmelon, was reported to be caused by a growth retardant (B-995; cf. HALEVY and RuDICH, 1967) known to reduce endogenous auxin content (REED et a!., 1965). It was also stated that ethylene which promotes femaleness in several plant species stimulates the peroxidase and IAA-oxidase activity thus potentially contributing to the
II
5'101'10 LSD
3
SAMPLINGS
4
Fig. 2. Gibberellin content in control and CEPA-treated plants of Cucurbita pepo L. For details on sex expression of analyzed plants see Table 1.
increase of auxin destruction (HALL and MORGAN, 1964). Auxin inactivation may be also caused by interference of ethylene with its transport and biosynthesis (ERNEST and VALDOVINOS, 1971). It is likely, therefore, that production of staminate flowers is associated with high amounts of endogenous gibberellins but formation of pistillate flowers need not necessarily be correlated with an increase in endogenous auxin content. The latter does not confirm the hypothesis on a causal relationship between endogenous auxins and sex expression in plants (CONRAD and MOTHES, 1961; GALUN, 1959; GALUN et a!., 1963, 1965). It has already been suggested that many physiological effects of auxins, including induction of flowering in pineapple (BURG and BURG, 1966 b), abscission (ABELES and RUBINSTEIN, 1964), and bud growth inhibition (BURG and BURG, 1968), are realized via ethylene. Although the application of exogenous auxins promotes femaleness, most probably through an enhancement of ethylene production (SHANNON and DE LA GUARDIA, 1969), the lack of correlation between the shift toward femaleness and auxin content shown in the present work indicates the unspecificity of endogenous auxins in control of sex differentiation. Thus it well may be true that sex differentiation of the examined plants is regulated by ethylene-gibberellin balance. Similar explanation was proposed earlier for the results obtained with Cucurbita moschata (SPLITTSTOESSER, 1970) and Cucumis melo (Loy, 1971), however, no measurements of internal growth regulator content were made at that time to support the suggestion. Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
188
A. CHROMINSKI and
J.
KOPCEWICZ
In addition to the above, it seems of interest that our other work (KOPCEWICZ and CHROMINSKI, 1972) carried out simultaneously on the same samples of plant material, indicates that the experimentally induced femaleness of squash is correlated with high content of endogenous estrogens. There are also other data pointing to the possible participation of steroidal hormones in the induction of flowering (CHOUARD, 1937 ; CZYGAN, 1962; LEsHEM, 1967; KOPCEWICZ, 1970b, 1971 b) and in sex differentiation (LovE and LovE, 1945; KOPCEWICZ, 1971 a; GAWIENOWSKI et aI., 1971) of plants. Assuming the regulation of sex expression by ethylene-gibberellin balance, the possibility cannot be excluded that ethylene exerts its effects through endogenous steroidal hormones. Acknowledgement We are grateful to Amchem Products, Inc., Ambler, Pa., USA, for providing the sample of 2-chloroethylphosphonic acid.
References ABELES, F. B.: PI. Physiol. 946 (1966) . ABELES, F. B., and B. RUBINSTEI N: PI. Physio!. 39, 963 (1964). ATAL, C. : Current Sci. 28, 408 (1959) . ATSMON, D ., A. LANG and N . LIGHT: PI. Physiol. 43 , 806 (1968) . BURG, S. P., and E. A. BURG: Proc. Nat. Acad. Sci. 55, 262 (1966 a). - Science 152,1269 (1966 b). - PI. Physio!. 42, 1224 (1967) . - PI. Physiol. 43, 1069 (1968) . CATARINO, F. M.: Portug. Acta BioI., ser. A, 8,267 (1964). CONRAD, K., and K. MOTHES: Naturwissenschaften 48, 26 (1961). CHOUARD, P.: C. R. Seanc. Soc. Bio!. 126,509 (1937). CZYGAN, F . c.: Naturwissenschaften 49, 285 (1962). ERNEST, L. c., and J. G. VALDOVINOS: PI. Physiol. 48, 402 (1971). FRANKLAND, B., and P . F . WAREING: Nature 185, 255 (1960) . FUCHS, Y ., and M. LIEBERMAN: PI. Physiol. 43, 2029 (1968). GALUN, E.: Physiologia PI. 12, 48 (1959). GALUN, E ., S. IZHAR and D. ATSMON: PI. Physiol. 40, 321 (1965). GALUN, E., Y. JUNG and A . LANG : Develop. BioI. 6, 370 (1963). GAMBOURG, 0., and T. A. G. LARUE: P!. Physio!. 48, 399 (1971). GAWIENOWSKI, A. M., R. W. CHENEY, Jr. and H. V. MARSH: Phytochemistry 10, 2653 (1971). HALEVY, A. H., and Y. RUDICH: Physiologia PI. 20,1052 (1967). HALL, W. c., and P. W. MORGAN: in: Regulateurs naturels de la croissance vegetale, p. 727. ColI. Intern. CNRS, Paris (1964). HASHIZUME, T., and M. hZUKA: Phytochemistry 10,2653 (1971). HESLOP-HARRISON, J.: BioI. Rev. 32, 38 (1957). HESLOP-HARRISON, J., and Y. HESLOP-HARRISON : New Phytol. 56, 352 (1957) . ITO, H ., and T. SAITO: J. Hort. Assoc. Jap. 25, 101 (1956). In Japanese. IWAHORI, S., J. M. LYONS and W. L. SIMS: Nature 222, 271 (1969). KENDER, W. J. and G. REMAILY: HoTtScience 5, 491 (1970). KOPCEWICZ, J.: Acta Soc. Bot. Pol. 37, 579 (1968). - Acta Soc. Bot. Pol. 39, 339 (1970 a).
Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
Auxins, Gibberellins and Sex Expression of Cucurbita
189
- Naturwissenschaften 57, 136 (1970 b). - Z. Pflanzenphysiol. 65,92 (1971 a). - Phytochemistry 10, 1423 (1971 b). KOPCEWICZ, J., and A. CHROMINSKI: Experientia 28, 603 (1972). LAIBACH, F., and F. J. KRIBBEN: Ber. Dtsch. Bot. Ges. 62,53 (1950). LESHEM, Y.: Phyton 24, 25 (1967). LOVEYS, B., and P. F. WAREING: Planta 98, 117 (1971). Loy, J. B.: J. Amer. Soc. Hort. Sci. 96, 641 (1971). LOVE, A., and D. LOVE: Ark. Bot 32 A, 1 (1945). MCCOMB, A. J., and D. J. CARR: Nature 181, 1548 (1958). McMURRAY, A. L., and C. H. MILLER: Science 162, 1397 (1968). MEKHANIK, F. Ia.: C. R. All Union Agric. Acad. Moscow 23, 20 (1958). In Russian. MININA, E. G.: C. R. Acad. Sci. USSR (Doklady) 21, 298 (1938). In Russian. - Modification of sex expression in plants under the influence of environmental factors, p. 74. Publ. Acad. Sci. USSR, Moscow (1952). In Russian. MININA, E. G., and L. G. TYLKINA: C. R. Acad. Sci. USSR (Doklady) 55, 169 (1947). In Russian. MITCHELL, W. D., and S. H. WITTWER: Science 136,880 (1962). MORGAN, P. W., and H. W. GAUSMAN: PI. Physiol. 41, 45 (1966). NITSCH, J. P.: in: The chemistry and mode of action of plant growth substances (Ed. R. L. WAIN and F. WIGHTMAN), p. 3. Butterworths Sci. Publ., London (1956). REED, D. J., T. C. MOOR and J. D. ANDERSON: Science 148, 1469 (1965). SHANNON, S., and M. D. DE LA GUARDIA: Nature 223, 186 (1969). SPLITTSTOESSER, W. E.: Physiologia PI. 23, 762 (1970). WITTWER, S. H., and M. J. BUKOVAC: Naturwissenschaften 49, 305 (1962). Dr. ANDRZEJ CHROMINSKI, Copernicus University, Institute of Biology, Centre of Applied Biology, Piwnice, P. O. Lulkowo, Poland. Dr. JAN KOPCEWICZ, Copernicus University, Institute of Biology, Department of Plant Physiology, Torun, Poland.
z.
Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
Auxins and Gibberellins in 2-Chloroethylphosphonic Acid-Induced Femaleness of Cucurbita pepo L. ANDRZEJ CHROMINSKI and JAN KOPCEWICZ With 2 figures Received May 2, 1972
Summary High level of gibberellin was associated with maleness of squash plants while alteration of sex expression toward femaleness, resulting from the treatment with 2-chloroethylphosphonic acid, was not followed by consistent changes in auxin content. The specificity of auxin participation in endogenous regulation of sex expression is discussed.
Introduction Sex expression in both monoecious and dioecious plants can be modified by soil fertility, temperature, day length as well as exogenously applied chemicals of various nature. Moist, high in nitrogen soil, short day and low temperature of a dark period (HESLOP-HARRISON, 1957), combustion gases from closed wood stoves (NhNINA, 1938), carbon monoxide (MININA and TYLKINA, 1947; HESLOP-HARRISON and HESLop-HARRISON, 1957), acetylene (MEKHANIK, 1958), auxins (LAIBACH and KRIBBEN, 1950; ITO and SAITO, 1956; GALUN, 1959; GALUN et al., 1963); growth retardants (MITCHELL and WITTWER, 1962; HALEVY and RUDICH, 1967), ethylene (MININA and TYLKINA, 1947; MININA, 1952) as well as 2-chloroethylphosphonic acid an ethylene releasing compound (McMuRRAY and MILLER, 1968; KENDER and REMAlLY, 1970), cytokinins (CATARINO, 1964; HASHIZUME and IrZUKA, 1971) and estrogens (LOVE and LOVE, 1945; KOPCEWICZ, 1971 a; GAWIENOWSKI et al., 1971) increase femaleness, while dry, low in nitrogen soil, long day and high temperature of a dark period (HESLOP-HARRISON, 1957) as well as gibberellins (ATAL, 1959; WITTWER and BUKOVAC, 1962) - maleness of the plant.
It was also observed that monoecious cucumber plants have more endogenous gibberellin-like substances than gynoecious ones (ATSMON et al., 1968), while hermaphrodite plants have more extractable auxins than andromonoecious plants (GALUN et al., 1965). Likewise, female Cannabis plants were reported to contain more auxins than male ones (CONRAD and MOTHES, 1961). Consequently, the hypothesis has been proposed that environmental as well as chemical factors exert their effects on sex expression by manipulating the balance of endogenous auxins and gibberellins, with high auxins tending to produce femaleness (ATSMON et al., 1968; IWAHORI et al., 1969; SPLITTSTOESSER, 1970). Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
Auxins, GibberelJins and Sex Expression of Cucurbita
185
Nevertheless, the role of auxins in sex differentiation seems to be debatable since the possibility exists that they promote femaleness due to the enhancement of ethylene production (SHANNON and DE LA GUARDIA, 1969). The latter, however, is not solely attributed to the action of endogenous auxins. In fact, there are data showing that an ethylene-forming system can also be stimulated by other growth regulators (FUCHS and LIEBERMAN, 1968; LOVEYS and WAREING, 1971; GAMBORG and LARuE, 1971). The problem has become even more complicated when reports on the interference of ethylene with auxin translocation within plant tissues (ABELES, 1966; BURG and BURG, 1966 a, 1967; MORGAN and GAUSMAN, 1966) culminated in the work of ERNEST and VALDOVINOS (1971) presenting the ethylene inhibition of both auxin transport and biosynthesis. It was therefore thought desirable to test whether endogenous auxins and gibberellins are directly involved in modification of sex expression in squash.
Material and Methods Monoecious squash plants (Cucurbita pepo L., cultivar Weiser Bush) were grown during spring and summer (March 10 to July 13, 1971) in clay pots in the greenhouse at maximum and minimum temperature of 26 and 17° C, respectively. 2-Chloroethylphosphonic acid (CEPA), a substitute for ethylene, was applied as an aqueous run-off foliar spray in twO treatments, each at a concentration of 200 ppm. Plants were sprayed when the 4th leaf was 1 cm in diameter, and again when the 7th leaf reached that size. Under the conditions described this occured when the plants were 42 and 49 day old, respectively. Control plants were sprayed with distilled water. Number of male and female flowers produced by each plant were recorded with observations being made every second day. Material for growth regulator determinations was taken as indicated in Table 1. Derooted plants deprived of all generative organs were used. GibberelJins and auxins were extracted and fractioned ace. to the methods previously described (KOPCEWICZ, 1968, 1970 a) . Descending chromatography on Whatman No.3 paper in isopropanol-ammonia-water (10 : 1 : 1) follo wed by Avena coleoptile straight growth bioassay (NITSCH, 1956) for auxins, and TLC in benzene-acetic acid (10: 3) followed by both lettuce hypocotyl (FRANKLAND and WAREING, 1960) and dwarf pea (MCCOMB and CARR, 1958) bioassays for gibberellins were applied. Results and Discussion GALUN et al. (1963) on the basis of the experiments with cucumber buds cultured in vitro claimed that the local concentration balance of auxin and gibberellin is important for sex differentiation. From the latter work of GALUN et al. (1965), however, it can be seen that auxin content in the sections of both andromonoecious and hermaphrodite cucumber plants resembled proportionally the total content of auxin in the whole plant of the respective lines, with more auxin being always presl:nt in the hermaphrodite one. Our results demonstrate that CEPA altered sex expression of squash to complete femaleness at the 2nd and 3rd samplings (Table 1). At the same samplings CEPA-treated Z. PJlanzenphysiol. Ed. 68. S. 184-189. 1972.
186
A. CHROMINSKI and
J.
KOPCEWICZ
Table 1. CEPA-modified sex expression of Cucurbita pepo L. at the time of sa mpling for endogenous auxins and gibberellins
Samplings
1/ 4 May l 2/ 16 May l 3/27 Mayl 4/ 13 Julyl
Total no. of flowers per plant':· Control CEP A
14.2 39.9 109.9
Ofo of female flowers Control
CEPA
flower buds visible 13.2 0.0 29.4 2.5 100.7 9.0
100.0 100.0 47.8
" opened and unopened flowers recorded until prevalence of the male ones on the CEPAtreated plants. Each result is the mean of six replicates.
plants contained smaller or roughly similar amounts of auxins and considerably smaller amounts of gibberellins than control plants (Figs. 1 and 2). Moreover, when the CEPA-treated plants started producing male flowers (4 th sampling), an increase of gibberellin content was found (Fig. 2). The results presented here show a positive correlation between maleness and endogenous gibberellin content and a lack of correlation between femaleness and endoge-
II
10
~
i
>-
5'1. r/.
i;
LSD
C!
0
52 .~
"l!
.51 to
l
~ 5 C!
'"
2
3
SAMPLINGS
4
Fig. 1. Auxin content in control and CEPA-treated plants of Cucurbita pepo L. For details on sex expression of analyzed plants see Table 1.
z.
Pjlanzenphysiol. Ed. 68. S. 184-189. 1972.
Auxins, Gibberellins and Sex Expression of Cucurbita
187
nous auxin content in squash. Increased femaleness in other cucurbita, viz. muskmelon, was reported to be caused by a growth retardant (B-995; cf. HALEVY and RuDICH, 1967) known to reduce endogenous auxin content (REED et a!., 1965). It was also stated that ethylene which promotes femaleness in several plant species stimulates the peroxidase and IAA-oxidase activity thus potentially contributing to the
II
5'101'10 LSD
3
SAMPLINGS
4
Fig. 2. Gibberellin content in control and CEPA-treated plants of Cucurbita pepo L. For details on sex expression of analyzed plants see Table 1.
increase of auxin destruction (HALL and MORGAN, 1964). Auxin inactivation may be also caused by interference of ethylene with its transport and biosynthesis (ERNEST and VALDOVINOS, 1971). It is likely, therefore, that production of staminate flowers is associated with high amounts of endogenous gibberellins but formation of pistillate flowers need not necessarily be correlated with an increase in endogenous auxin content. The latter does not confirm the hypothesis on a causal relationship between endogenous auxins and sex expression in plants (CONRAD and MOTHES, 1961; GALUN, 1959; GALUN et a!., 1963, 1965). It has already been suggested that many physiological effects of auxins, including induction of flowering in pineapple (BURG and BURG, 1966 b), abscission (ABELES and RUBINSTEIN, 1964), and bud growth inhibition (BURG and BURG, 1968), are realized via ethylene. Although the application of exogenous auxins promotes femaleness, most probably through an enhancement of ethylene production (SHANNON and DE LA GUARDIA, 1969), the lack of correlation between the shift toward femaleness and auxin content shown in the present work indicates the unspecificity of endogenous auxins in control of sex differentiation. Thus it well may be true that sex differentiation of the examined plants is regulated by ethylene-gibberellin balance. Similar explanation was proposed earlier for the results obtained with Cucurbita moschata (SPLITTSTOESSER, 1970) and Cucumis melo (Loy, 1971), however, no measurements of internal growth regulator content were made at that time to support the suggestion. Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
188
A. CHROMINSKI and
J.
KOPCEWICZ
In addition to the above, it seems of interest that our other work (KOPCEWICZ and CHROMINSKI, 1972) carried out simultaneously on the same samples of plant material, indicates that the experimentally induced femaleness of squash is correlated with high content of endogenous estrogens. There are also other data pointing to the possible participation of steroidal hormones in the induction of flowering (CHOUARD, 1937 ; CZYGAN, 1962; LEsHEM, 1967; KOPCEWICZ, 1970b, 1971 b) and in sex differentiation (LovE and LovE, 1945; KOPCEWICZ, 1971 a; GAWIENOWSKI et aI., 1971) of plants. Assuming the regulation of sex expression by ethylene-gibberellin balance, the possibility cannot be excluded that ethylene exerts its effects through endogenous steroidal hormones. Acknowledgement We are grateful to Amchem Products, Inc., Ambler, Pa., USA, for providing the sample of 2-chloroethylphosphonic acid.
References ABELES, F. B.: PI. Physiol. 946 (1966) . ABELES, F. B., and B. RUBINSTEI N: PI. Physio!. 39, 963 (1964). ATAL, C. : Current Sci. 28, 408 (1959) . ATSMON, D ., A. LANG and N . LIGHT: PI. Physiol. 43 , 806 (1968) . BURG, S. P., and E. A. BURG: Proc. Nat. Acad. Sci. 55, 262 (1966 a). - Science 152,1269 (1966 b). - PI. Physio!. 42, 1224 (1967) . - PI. Physiol. 43, 1069 (1968) . CATARINO, F. M.: Portug. Acta BioI., ser. A, 8,267 (1964). CONRAD, K., and K. MOTHES: Naturwissenschaften 48, 26 (1961). CHOUARD, P.: C. R. Seanc. Soc. Bio!. 126,509 (1937). CZYGAN, F . c.: Naturwissenschaften 49, 285 (1962). ERNEST, L. c., and J. G. VALDOVINOS: PI. Physiol. 48, 402 (1971). FRANKLAND, B., and P . F . WAREING: Nature 185, 255 (1960) . FUCHS, Y ., and M. LIEBERMAN: PI. Physiol. 43, 2029 (1968). GALUN, E.: Physiologia PI. 12, 48 (1959). GALUN, E ., S. IZHAR and D. ATSMON: PI. Physiol. 40, 321 (1965). GALUN, E., Y. JUNG and A . LANG : Develop. BioI. 6, 370 (1963). GAMBOURG, 0., and T. A. G. LARUE: P!. Physio!. 48, 399 (1971). GAWIENOWSKI, A. M., R. W. CHENEY, Jr. and H. V. MARSH: Phytochemistry 10, 2653 (1971). HALEVY, A. H., and Y. RUDICH: Physiologia PI. 20,1052 (1967). HALL, W. c., and P. W. MORGAN: in: Regulateurs naturels de la croissance vegetale, p. 727. ColI. Intern. CNRS, Paris (1964). HASHIZUME, T., and M. hZUKA: Phytochemistry 10,2653 (1971). HESLOP-HARRISON, J.: BioI. Rev. 32, 38 (1957). HESLOP-HARRISON, J., and Y. HESLOP-HARRISON : New Phytol. 56, 352 (1957) . ITO, H ., and T. SAITO: J. Hort. Assoc. Jap. 25, 101 (1956). In Japanese. IWAHORI, S., J. M. LYONS and W. L. SIMS: Nature 222, 271 (1969). KENDER, W. J. and G. REMAILY: HoTtScience 5, 491 (1970). KOPCEWICZ, J.: Acta Soc. Bot. Pol. 37, 579 (1968). - Acta Soc. Bot. Pol. 39, 339 (1970 a).
Z. Pjlanzenphysiol. Bd. 68. S. 184-189. 1972.
Auxins, Gibberellins and Sex Expression of Cucurbita
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