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Salinity, temperature, and growth regulator effects on seed germination of Salicornia europaea L.
Aquatic Botany, 3 (1977) 329--335 329 © Elsevier Scientific Publishing Company, Amsterdam --Printed in The Netherlands
SALINITY, TEMPERATURE, AND GROWTH REGULATOR EFFECTS O N S E E D G E R M I N A T I O N O F S A L I C O R N I A E U R O P A E A L.
IRWIN A. UNGAR Department of Botany, Ohio University, Athens, Ohio 45701 (U.S.A.) (Received 1 September 1976)
ABSTRACT
Ungar, I.A., 1977. Salinity, temperature, and growth regulator effects on seed germination of Salicornia europaea L. Aquat. Bot., 3: 329--335. Temperature optima for Salicornia europaea L. seed germination at different salinities were investigated. Maximum germination occurred in distilled water at 25 ° C. Lowest germination percentages for all salinities were at 10 ° C. Even though S. europaea is the most salt tolerant of the species growing on the salt pan in which it occurs, an increase in salinity stress proved to be inhibitory to seed germination for all temperature regimes investigated. Treatments with 1 X 10-3 M gibberellic acid (GA 3 ) stimulated germination in salinities with up to 5.0% NaCl concentrations; germination increased from 5.0% in the control to 42.0% in the growth regulator treatment. Kinetin did not stimulate germination of S. europaea seeds.
INTRODUCTION Salicornia europaea L. is a highly salt t o l e r a n t h a l o p h y t i c species occurring in coastal m a r s h e s o f N o r t h A m e r i c a ( C h a p m a n , 1 9 7 4 ) . U n g a r ( 1 9 7 3 ) f o u n d S. europaea g r o w i n g in p u r e stands o n t h e m o s t highly saline l o c a t i o n s o f an inland saline p a n at R i t t m a n , O h i o . I t was also a s s o c i a t e d w i t h H o r d e u m j u b a t u m L. and A t r i p l e x triangularis Willd. at sites with r e d u c e d salinity. S e e d s c o l l e c t e d f r o m a R h o d e Island coastal locality c o n t a i n i n g S. europaea were f o u n d t o h a v e an o p t i m a l r a t e a n d t o t a l p e r c e n t a g e g e r m i n a t i o n in distilled water, a n d i n c r e m e n t s o f salinity d e c r e a s e d b o t h t h e r a t e a n d t o t a l n u m b e r o f seeds g e r m i n a t i n g (Ungar, 1962). O t h e r r e s e a r c h e r s s t u d y ing t h e g e r m i n a t i o n o f seeds o f a n n u a l species o f Salicornia h a v e d e m o n s t r a t e d a v a r i e t y o f i n t e r a c t i o n s b e t w e e n t e m p e r a t u r e , salinity, a n d germin a t i o n (Langlois, 1 9 6 6 ; Rivers a n d Weber, 1 9 7 1 ; G r o u z i s e t al., 1 9 7 6 ) . Rivers a n d W e b e r ( 1 9 7 1 ) f o u n d t h a t Salicornia bigelovii T o r t . r e s p o n d e d similarly t o S. europaea at 2 6 . 6 ° C , w h e r e a s at 1 5 . 5 ° C t h e y o b t a i n e d relatively high g e r m i n a t i o n p e r c e n t a g e s in s o l u t i o n s w i t h u p t o 8.0% NaC1. Langlois ( 1 9 6 6 ) f o u n d t h a t t h r e e a n n u a l species, including S. stricta D u m . ,
330 S. disarticulata Moss, and S. radicans Smith, had optimal germination percentages in low NaC1 concentrations. The rate of germination depended on the incubation temperature. Seeds of S. emerici Duval-Jouve, S. brachystachya Meyer, and S. patula Duval-Jouve were found to be very sensitive to salt stress if they did not receive a cold stratification treatment (Grouzis et al., 1976). The influence of temperature on the germination of S. europaea seeds will be examined in this investigation. It will also be determined if any synergistic effect on seed germination exists between temperature and salinity stress. Exogenous treatments with growth regulators will be used in order to determine how these substances influence dormancy of seeds induced by salt stress. METHODS An experiment using a temperature gradient bar was carried out in order to identify temperature optima for germination and to determine if any interaction influencing seed germination occurred between temperature and salinity. Salicornia europaea seeds were collected from plants growing in an inland saline pan at Rittman, Ohio. Two samples containing 25 seeds were placed in 5 cm diameter petri dishes containing 4 ml of test solution and two sheets of Whatman No. 2 filter paper. Seeds were soaked for seven days at 5°C prior to being placed on the temperature gradient bar at temperatures of 10, 15, 20, 25, and 30°C. Salinity concentrations of 0.0, 1.0, 2.0, 3.0, and 5.0% NaC1 were used. All experiments were repeated at least twice. The influence of gibberellic acid (GA3) and kinetin on germination of seeds at different salinities was determined. Kinetin concentrations of I × 10 -4 M and 1 × 10- s M, GA3 concentrations of 1 × 10 -3 M amd 1 × 10 -4 M, and NaC1 concentrations ranging from 0.0 to 4.0% were utilized in this experiment. GA3 used in these experiments was obtained from Eastman Organic Chemicals (No. 7444) and kinetin Nutritional Biochemicals (No. 1838). Five samples containing 25 seeds each were placed in 9 cm diameter petri dishes containing two sheets of Whatman No. 2 filter paper and 8 ml of test solution. Germination of seeds was observed for 40 days at a temperature of 15 ° C. The effect of alternating temperatures at 12 h at 5°C and 12 h at 25°C on the germination of S. europaea seeds was observed for 40 days. In this study we used a salinity series of 0.0, 1.0, 3.0, and 5.0% NaCI, and growth regulator concentrations of 1 × l f f 3 M GA3 and 1 × 10 -4 kinetin. Procedures and number of replications are the same as in the previous experiment. RESULTS Optimal germination for seeds of Salicornia europaea occurred in distilled water treatments at 25 ° C (Fig. 1). The treatments at 10 ° C had the lowest
331
70
60
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z nr (.9
30
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I0
15
20
TEMPERATURE
25
30
(°C)
Fig. 1. T h e i n t e r a c t i o n b e t w e e n t e m p e r a t u r e a n d salinity o n g e r m i n a t i o n o f seeds o f Salicornia europaea a f t e r 20 days. NaCl c o n c e n t r a t i o n s : m 0.0%, u:] 1.0%, e~ 2.0%,
3.0%. LSD (0.05)=8.8, maximum SE=-+3.5. germination percentages at all salinity regimes tested. Salinity increments inhibited germination of seeds in all temperature treatments. The smallest decrease in germination from the control occurred in the 1.0% NaC1 treatment at 25°C (Fig. 1). No seeds could germinate in the 5.0% NaC1 solutions at any of the temperatures used. Figure 2 illustrates the percentage germination for seeds incubated for 20 days at 25°C in salt solutions ranging from 0.0 to 3.0% NaC1. These data indicate a t w o day delay of the germination of seeds in the 3.0% NaCl treatment. There appeared to be no long delay in germination for S. europaea seeds soaking at high salinities, as has been reported for other species of halophytes (Ungar, 1974). Nearly maximal levels of seed germination occurred after 15 days incubation at all salinities, indicating that this environmentally induced inhibition of germination was n o t overcome with time and that an alleviation of salt stress was necessary. A treatment of seeds with gibberellic acid (GA3) was attempted at a temperature of 15°C in order to determine if dormancy o f seeds induced by salinity treatments could be overcome. Exogenous GA3 applications would be successful if the d o r m a n c y induced by salt stress was because of either low growth regulator production or a rapid turnover of gibberellins. Only the results o f the 1 × 10 -3 M GA3 test will be reported here because 1 X
332 70 0.0% No Cl
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• 1.0% Na CI
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Z
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2.0% NaCI
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=E iz i,i (9
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5.0% No CI 2
4
6
8
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12
14
16
18
20
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Fig. 2. The influence of salinity on the germination of seeds of Salicornia europaea during 20 days at 25°C. LSD(0.05) for 20 day data=13.2, maximum SE=-+I.7.
10-4M GA3 treatments produced nearly identical results (Fig. 3). These data indicate an increase in the percentage of seeds germinating when they were treated with GA3. The percentage of seeds germinating in a 4.0% NaC1 solution increased from 6.0% in the control treatment to 30.0% in the GA3 treated sample (Fig. 3). Kinetin solutions alone were not stimulatory to the germination of S. europaea seeds at 15°C and did n o t overcome the inhibitory effect of NaC1 concentrations ranging from 1.0 to 5.0% (Fig. 4). Only at 3.0% NaC1 is there a slight stimulation of germination percentage of seeds.Treatments with 1 X 10 -3 M GA3 were highly stimulatory at all salinities and a combined treatment of 1 × 10-3 M GA3 and 1 X 10-4 M kinetin yielded increased germination percentages, ranging from 5.0% in the 5.0% NaC1 control to 42.0% in the combined growth regulator treatment. The influence of the effect of growth regulator treatments at a more stimulatory temperature regime for germination, 5°C for 12 h and 25°C for 12 h, was tested. Significant increases in seed germination occurred when 1 X 10-4 M GA3 was added to the 1.0 and 3.0% NaCl treatments, equalling 32.0% greater than the control in both cases (Fig. 5). Kinetin treatments alone were n o t stimulatory to germination. DISCUSSION
Although Salicornia europaea occupied the most saline sites in an inland saline pan at Rittman, Ohio, increased salinity caused a reduction in the percentage germination of its seeds. Other researchers who have studied halop h y t e seed germination have also found that optimal germination occurs under reduced salinity stress even in the case of the most highly salt tolerant species (Binet, 1964; Ungar, 1962, 1974; Seneca, 1969; Williams and Ungar, 1972; Chapman, 1974). This could be of ecological significance since get-
333
80
70
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No CI I%1 F i g 3. T h e e f f e c t o f s a l i n i t y a n d G A 3 o n t h e g e r m i n a t i o n o f Salicornia europaea a t 1 5 ° C a f t e r 4 0 d a y s a t v a r i e d s a l i n i t i e s . M e a n s -+ S E . - - - -1 × 1 0 - 3 M G A 3 , control. LSD (0.05)=12.5.
mination of seeds in early spring, when salinity stress is reduced by high soil moisture levels, probably assures that some individuals would survive until the end of the growing season. Later in the summer salt stress would be t o o high for germination of seeds to occur on inland saline pans (Ungar, 1973) and seedling mortality would be high. Odegbaro and Smith (1969) and Kaufmann and Ross (1970) have demonstrated that there is an interaction between kinetin and the dormancy induced in seeds by osmotic stress. They found that glycophytes such as lettuce and wheat would respond to treatments with kinetin and the osmotically induced seed dormancy would be alleviated. In their studies with various halophytic species, Ungar and Binet (1975) and Boucaud and Ungar (1976) could n o t stimulate seeds of salt stressed halophytes to germinate with kinetin. Gibberellic acid was found to overcome the dormancy induced by salt stress in seeds of several species of Suaeda and in Spergularia media. In these experiments with S. europaea kinetin did n o t p r o m o t e the rate or total percentage germination of seeds, b u t treatments with GA3 or a combination of GA3 and kinetin proved to be stimulatory to both aspects of germination. These data indicate that probably more than one mechanism is involved in
334
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Fig. 4. Percentage germination of Salicornia europaea seeds after 40 days at ] 5 ° C with varied NaCl concentrations and growth regulators.- - - - 1 × 10-4 M kinetin + 1 × 10-3 M GA 3 , - 1 × 1 0 - 3 M G A 3 , . . . . . . 1 × 10-4 M kinetin, - control. LSD(0.05)= 20.2, maximum SE=± 7.9. Fig. 5. The effect of a 40 day treatment with alternating temperatures of 5°C for 12 h and 25°C for 12 h, growth regulators, and salinity on the germination o f seeds of Salicornia europaea. -- - - 1 × 10-3M GA 3 , - . . . . 1 × 10 -4 M kinetin, - control. LSD (0.05)=21.8, maximum SE=_+4.4. o v e r c o m i n g i n h i b i t i o n o f s e e d g e r m i n a t i o n i n d u c e d b y s a l i n i t y stress. In t h e case of glycophytes kinetin appears to alleviate osmotically induced dormancy, whereas halophytes appear to respond to GA3 treatments. ACKNOWLEDGEMENTS This research was supported by National Science Foundation research grants B M S 7 4 - 1 9 4 3 5 a n d D E B 7 6 - 0 0 4 4 4 . I w i s h t o a c k n o w l e d g e s u p p o r t f o r part o f t h i s w o r k f r o m t h e O h i o U n i v e r s i t y R e s e a r c h C o m m i t t e e , r e s e a r c h grant No. 457.
335
REFERENCES Binet, P., 1964. La germination des semences des halophytes. Bull. Soc. Fr. Physiol. Veg., 10: 253--263. Binet, P., 1968. Dormances et aptitude ~ germer en milieu sale chez les halophytes. Bull. Soc. Fr. Physiol. Veg., 4: 115--124. Boucaud, J. and Ungar, I.A., 1976. Hormonal control of germination under saline conditions of three halophytic taxa in the genus Suaeda. Physiol. Plant., 37: 143--148. Chapman, V.J., 1974. Salt Marshes and Salt Deserts of the World. J. Cramer, West Germany, 494 pp. Grouzis, M., Berger, A. and Helm, G., 1976. Polymorphisme et germination des gaines chez trois esp~ces annuelles du genre Salicornia. Oecol. Plant., 11 : 41--52. Kaufmann, M.R. and Ross, K.J., 1970. Water potential, temperature and kinetin effects on seed germination in soil and solute systems. Am. J. B o t . , 57 : 413--419. Langlois, J., 1966. Etude compar~e de l'aptitude ~ germer des gaines de Salicornia stricta Dumort., Salicornia disarticulata Moss. and Salicornia radicans Moss. Rev. Gen. Bot., 73:25--39. Lesko, G.L. and Walker, R.B., 1969. Effect of seawater on seed germination in two Pacific atoll beach species. Ecology, 50: 730--734. Odegbaro, O.A. and Smith, O.E., 1969. Effect of kinetin, salt concentrations and temperature on germination and early seedling growth of Lactuca sativa L. Am. Soc. Hort. Sci., 94: 167--170. Rivers, W.G. and Weber, D.J., 1971. The influence of salinity and temperature on seed germination in Salicornia bigelovii.Physiol. Plant., 24:73--75. Seneca, E.D., 1969. Germination response to temperature of four dune grasses from the outer banks of North Carolina. Ecology, 50: 45--53. Ungar, I.A., 1962. Influence of salinity on seed germination in succulent halophytes. Ecology, 43: 763--764. Ungar, I.A., 1973. Salinity tolerance of inland halophytic vegetation of North America. Bull. Soc. Bot. Fr., 120:217--222. Ungar, I.A., 1974. The effect of salinity and temperature on seed germination and growth of Hordeum jubatum. Can. J. Bot., 52 : 1357--1362. Ongar, I.A. and Binet, P., 1975. Factors affecting seed dormancy in Spergularia media. Aquat. Bot., 1: 45--55. Williams, M.D. and Ungar, I.A., 1972. The effect of environmental parameters on the germination, growth, and development of Suaeda depressa (Pursh) Wats. Am. J. Bot., 59: 912--918.
SALINITY, TEMPERATURE, AND GROWTH REGULATOR EFFECTS O N S E E D G E R M I N A T I O N O F S A L I C O R N I A E U R O P A E A L.
IRWIN A. UNGAR Department of Botany, Ohio University, Athens, Ohio 45701 (U.S.A.) (Received 1 September 1976)
ABSTRACT
Ungar, I.A., 1977. Salinity, temperature, and growth regulator effects on seed germination of Salicornia europaea L. Aquat. Bot., 3: 329--335. Temperature optima for Salicornia europaea L. seed germination at different salinities were investigated. Maximum germination occurred in distilled water at 25 ° C. Lowest germination percentages for all salinities were at 10 ° C. Even though S. europaea is the most salt tolerant of the species growing on the salt pan in which it occurs, an increase in salinity stress proved to be inhibitory to seed germination for all temperature regimes investigated. Treatments with 1 X 10-3 M gibberellic acid (GA 3 ) stimulated germination in salinities with up to 5.0% NaCl concentrations; germination increased from 5.0% in the control to 42.0% in the growth regulator treatment. Kinetin did not stimulate germination of S. europaea seeds.
INTRODUCTION Salicornia europaea L. is a highly salt t o l e r a n t h a l o p h y t i c species occurring in coastal m a r s h e s o f N o r t h A m e r i c a ( C h a p m a n , 1 9 7 4 ) . U n g a r ( 1 9 7 3 ) f o u n d S. europaea g r o w i n g in p u r e stands o n t h e m o s t highly saline l o c a t i o n s o f an inland saline p a n at R i t t m a n , O h i o . I t was also a s s o c i a t e d w i t h H o r d e u m j u b a t u m L. and A t r i p l e x triangularis Willd. at sites with r e d u c e d salinity. S e e d s c o l l e c t e d f r o m a R h o d e Island coastal locality c o n t a i n i n g S. europaea were f o u n d t o h a v e an o p t i m a l r a t e a n d t o t a l p e r c e n t a g e g e r m i n a t i o n in distilled water, a n d i n c r e m e n t s o f salinity d e c r e a s e d b o t h t h e r a t e a n d t o t a l n u m b e r o f seeds g e r m i n a t i n g (Ungar, 1962). O t h e r r e s e a r c h e r s s t u d y ing t h e g e r m i n a t i o n o f seeds o f a n n u a l species o f Salicornia h a v e d e m o n s t r a t e d a v a r i e t y o f i n t e r a c t i o n s b e t w e e n t e m p e r a t u r e , salinity, a n d germin a t i o n (Langlois, 1 9 6 6 ; Rivers a n d Weber, 1 9 7 1 ; G r o u z i s e t al., 1 9 7 6 ) . Rivers a n d W e b e r ( 1 9 7 1 ) f o u n d t h a t Salicornia bigelovii T o r t . r e s p o n d e d similarly t o S. europaea at 2 6 . 6 ° C , w h e r e a s at 1 5 . 5 ° C t h e y o b t a i n e d relatively high g e r m i n a t i o n p e r c e n t a g e s in s o l u t i o n s w i t h u p t o 8.0% NaC1. Langlois ( 1 9 6 6 ) f o u n d t h a t t h r e e a n n u a l species, including S. stricta D u m . ,
330 S. disarticulata Moss, and S. radicans Smith, had optimal germination percentages in low NaC1 concentrations. The rate of germination depended on the incubation temperature. Seeds of S. emerici Duval-Jouve, S. brachystachya Meyer, and S. patula Duval-Jouve were found to be very sensitive to salt stress if they did not receive a cold stratification treatment (Grouzis et al., 1976). The influence of temperature on the germination of S. europaea seeds will be examined in this investigation. It will also be determined if any synergistic effect on seed germination exists between temperature and salinity stress. Exogenous treatments with growth regulators will be used in order to determine how these substances influence dormancy of seeds induced by salt stress. METHODS An experiment using a temperature gradient bar was carried out in order to identify temperature optima for germination and to determine if any interaction influencing seed germination occurred between temperature and salinity. Salicornia europaea seeds were collected from plants growing in an inland saline pan at Rittman, Ohio. Two samples containing 25 seeds were placed in 5 cm diameter petri dishes containing 4 ml of test solution and two sheets of Whatman No. 2 filter paper. Seeds were soaked for seven days at 5°C prior to being placed on the temperature gradient bar at temperatures of 10, 15, 20, 25, and 30°C. Salinity concentrations of 0.0, 1.0, 2.0, 3.0, and 5.0% NaC1 were used. All experiments were repeated at least twice. The influence of gibberellic acid (GA3) and kinetin on germination of seeds at different salinities was determined. Kinetin concentrations of I × 10 -4 M and 1 × 10- s M, GA3 concentrations of 1 × 10 -3 M amd 1 × 10 -4 M, and NaC1 concentrations ranging from 0.0 to 4.0% were utilized in this experiment. GA3 used in these experiments was obtained from Eastman Organic Chemicals (No. 7444) and kinetin Nutritional Biochemicals (No. 1838). Five samples containing 25 seeds each were placed in 9 cm diameter petri dishes containing two sheets of Whatman No. 2 filter paper and 8 ml of test solution. Germination of seeds was observed for 40 days at a temperature of 15 ° C. The effect of alternating temperatures at 12 h at 5°C and 12 h at 25°C on the germination of S. europaea seeds was observed for 40 days. In this study we used a salinity series of 0.0, 1.0, 3.0, and 5.0% NaCI, and growth regulator concentrations of 1 × l f f 3 M GA3 and 1 × 10 -4 kinetin. Procedures and number of replications are the same as in the previous experiment. RESULTS Optimal germination for seeds of Salicornia europaea occurred in distilled water treatments at 25 ° C (Fig. 1). The treatments at 10 ° C had the lowest
331
70
60
5O Z O Q
4o
z nr (.9
30
I0
I0
15
20
TEMPERATURE
25
30
(°C)
Fig. 1. T h e i n t e r a c t i o n b e t w e e n t e m p e r a t u r e a n d salinity o n g e r m i n a t i o n o f seeds o f Salicornia europaea a f t e r 20 days. NaCl c o n c e n t r a t i o n s : m 0.0%, u:] 1.0%, e~ 2.0%,
3.0%. LSD (0.05)=8.8, maximum SE=-+3.5. germination percentages at all salinity regimes tested. Salinity increments inhibited germination of seeds in all temperature treatments. The smallest decrease in germination from the control occurred in the 1.0% NaC1 treatment at 25°C (Fig. 1). No seeds could germinate in the 5.0% NaC1 solutions at any of the temperatures used. Figure 2 illustrates the percentage germination for seeds incubated for 20 days at 25°C in salt solutions ranging from 0.0 to 3.0% NaC1. These data indicate a t w o day delay of the germination of seeds in the 3.0% NaCl treatment. There appeared to be no long delay in germination for S. europaea seeds soaking at high salinities, as has been reported for other species of halophytes (Ungar, 1974). Nearly maximal levels of seed germination occurred after 15 days incubation at all salinities, indicating that this environmentally induced inhibition of germination was n o t overcome with time and that an alleviation of salt stress was necessary. A treatment of seeds with gibberellic acid (GA3) was attempted at a temperature of 15°C in order to determine if dormancy o f seeds induced by salinity treatments could be overcome. Exogenous GA3 applications would be successful if the d o r m a n c y induced by salt stress was because of either low growth regulator production or a rapid turnover of gibberellins. Only the results o f the 1 × 10 -3 M GA3 test will be reported here because 1 X
332 70 0.0% No Cl
60
• 1.0% Na CI
50
z O I-
40
Z
50
2.0% NaCI
I
=E iz i,i (9
20 I0 0
5.0% No CI 2
4
6
8
I0
12
14
16
18
20
DAYS
Fig. 2. The influence of salinity on the germination of seeds of Salicornia europaea during 20 days at 25°C. LSD(0.05) for 20 day data=13.2, maximum SE=-+I.7.
10-4M GA3 treatments produced nearly identical results (Fig. 3). These data indicate an increase in the percentage of seeds germinating when they were treated with GA3. The percentage of seeds germinating in a 4.0% NaC1 solution increased from 6.0% in the control treatment to 30.0% in the GA3 treated sample (Fig. 3). Kinetin solutions alone were not stimulatory to the germination of S. europaea seeds at 15°C and did n o t overcome the inhibitory effect of NaC1 concentrations ranging from 1.0 to 5.0% (Fig. 4). Only at 3.0% NaC1 is there a slight stimulation of germination percentage of seeds.Treatments with 1 X 10 -3 M GA3 were highly stimulatory at all salinities and a combined treatment of 1 × 10-3 M GA3 and 1 X 10-4 M kinetin yielded increased germination percentages, ranging from 5.0% in the 5.0% NaC1 control to 42.0% in the combined growth regulator treatment. The influence of the effect of growth regulator treatments at a more stimulatory temperature regime for germination, 5°C for 12 h and 25°C for 12 h, was tested. Significant increases in seed germination occurred when 1 X 10-4 M GA3 was added to the 1.0 and 3.0% NaCl treatments, equalling 32.0% greater than the control in both cases (Fig. 5). Kinetin treatments alone were n o t stimulatory to germination. DISCUSSION
Although Salicornia europaea occupied the most saline sites in an inland saline pan at Rittman, Ohio, increased salinity caused a reduction in the percentage germination of its seeds. Other researchers who have studied halop h y t e seed germination have also found that optimal germination occurs under reduced salinity stress even in the case of the most highly salt tolerant species (Binet, 1964; Ungar, 1962, 1974; Seneca, 1969; Williams and Ungar, 1972; Chapman, 1974). This could be of ecological significance since get-
333
80
70
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\b-
2
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kZ
~ 30 2O
eO
olo
i.o
;.o
2.0
No CI I%1 F i g 3. T h e e f f e c t o f s a l i n i t y a n d G A 3 o n t h e g e r m i n a t i o n o f Salicornia europaea a t 1 5 ° C a f t e r 4 0 d a y s a t v a r i e d s a l i n i t i e s . M e a n s -+ S E . - - - -1 × 1 0 - 3 M G A 3 , control. LSD (0.05)=12.5.
mination of seeds in early spring, when salinity stress is reduced by high soil moisture levels, probably assures that some individuals would survive until the end of the growing season. Later in the summer salt stress would be t o o high for germination of seeds to occur on inland saline pans (Ungar, 1973) and seedling mortality would be high. Odegbaro and Smith (1969) and Kaufmann and Ross (1970) have demonstrated that there is an interaction between kinetin and the dormancy induced in seeds by osmotic stress. They found that glycophytes such as lettuce and wheat would respond to treatments with kinetin and the osmotically induced seed dormancy would be alleviated. In their studies with various halophytic species, Ungar and Binet (1975) and Boucaud and Ungar (1976) could n o t stimulate seeds of salt stressed halophytes to germinate with kinetin. Gibberellic acid was found to overcome the dormancy induced by salt stress in seeds of several species of Suaeda and in Spergularia media. In these experiments with S. europaea kinetin did n o t p r o m o t e the rate or total percentage germination of seeds, b u t treatments with GA3 or a combination of GA3 and kinetin proved to be stimulatory to both aspects of germination. These data indicate that probably more than one mechanism is involved in
334
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5.0
N a Cl (%]
Fig. 4. Percentage germination of Salicornia europaea seeds after 40 days at ] 5 ° C with varied NaCl concentrations and growth regulators.- - - - 1 × 10-4 M kinetin + 1 × 10-3 M GA 3 , - 1 × 1 0 - 3 M G A 3 , . . . . . . 1 × 10-4 M kinetin, - control. LSD(0.05)= 20.2, maximum SE=± 7.9. Fig. 5. The effect of a 40 day treatment with alternating temperatures of 5°C for 12 h and 25°C for 12 h, growth regulators, and salinity on the germination o f seeds of Salicornia europaea. -- - - 1 × 10-3M GA 3 , - . . . . 1 × 10 -4 M kinetin, - control. LSD (0.05)=21.8, maximum SE=_+4.4. o v e r c o m i n g i n h i b i t i o n o f s e e d g e r m i n a t i o n i n d u c e d b y s a l i n i t y stress. In t h e case of glycophytes kinetin appears to alleviate osmotically induced dormancy, whereas halophytes appear to respond to GA3 treatments. ACKNOWLEDGEMENTS This research was supported by National Science Foundation research grants B M S 7 4 - 1 9 4 3 5 a n d D E B 7 6 - 0 0 4 4 4 . I w i s h t o a c k n o w l e d g e s u p p o r t f o r part o f t h i s w o r k f r o m t h e O h i o U n i v e r s i t y R e s e a r c h C o m m i t t e e , r e s e a r c h grant No. 457.
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