SHYAM S. SHAR~A and DAVID N. SEN

Botany Department, University of Jodhpur, Jodhpur, India

Effect of Light on Seed Germination and Seedling Growth of Merremia Species

A b s t r a c t

The seeds of iVierremia aegyptia are indifferent to light conditions for germination, which becomes I00 % in the first 24 hrs. On the contrary, in M. disseeta the highest percentage was found in red light within the first 24 hrs. This difference was lost later on except in far-red. The seedling growth of tho two species was least in blue and red lights, respectively. However, the growth of hypoeotyl in the former species was faster than the latter.

I N T R O D U C T I O N

The effects of different wave leng ths of l ight on seed ge rmina t ion and seedling g rowth have been s tud ied (CROCKER 1936). Cer ta in k inds of seeds requi re l ight for ge rmina- t ion, while o thers a p p a r e n t l y have no such requ i rement . SE~ (1968) r epo r t ed t h a t the seeds of Cryptostegia grandiflora e i ther d id no t ge rmina t e or exh ib i t ed de l a ye d and poor ge rmina t ion in cont inuous whi te l ight , bu t others, l ike Calot~vpis procera and Leptadenia pyrotechnica, a p p a r e n t l y had no l ight requi rements . I t has been re- po r t ed t h a t ge rmina t ion of m a n y seeds and spores was c lear ly d e p e n d e n t upon the ac t ion of phy tochrome , bu t such ac t ion was found to be absen t or no t obvious in o thers (MA~TCINELLI et ]~ORTHWICK 1964, MANCII~ELLI et al. 1966). I t has been repor- t ed ear l ie r t h a t t e m p e r a t u r e and l ight are i m p o r t a n t fac tors affect ing ge rmina t i on and seedl ing g rowth of Ruellia tuberosa (SEN et CHATTERJI 1966) and Asteracantha longifolia (SEN et CHAWA~ 1970). The r ed region of the spec t rum (590 and 680 {zm) is the most effective for the ge rmina t i on of l ight requi r ing seeds. R e d r ad i a t i ons have been sho~m to be effective in the ge rmina t ion of seeds of Verbascum thapsus (TOOLE et al. 1955). Fa r - red , the l ight of longer wave leng ths (700 to 800 ~m), has been r epo r t ed to reverse the response induced b y red l ight (MA~cI~ELLI et BO~THWICK 1964). P h y t o c h r o m e ac t ion has been s tud ied ma in ly on le t tuce b y a number of workers and inves t iga t ions have been e x t e n d e d to o ther species (JO~ES et BAILEY 1956, KOLLER et al. 1964, and MA~ClNELLI et al. 1966). The effect of l ight on the ge rmina-

Folia Geobot. l'hytotax., l~raha, 10: 265-269, 1975

266 F()LIA GEOBOTANICA ET PHYTOTAXO~'OMI(?A, 10,1975

t ion of a r id zone seeds and seedl ing growth has no t been fu l ly s tud ied except for a few repor t s (SEN 1968, 1969, AGARWAL et VYAS 1970; BHANDARI et SE~ 1973, CHAWAN et SEN 1973).

F o r the presen t inves t iga t ion two p l a n t species of the f a m i l y Convolvulaceae growing in the I n d i a n a r id zone were se lected

Merremia aegyptia (L.) URBAN, comes up wi th the ra ins hu t r emains t i l l ea r ly winter , when i t s t a r t s d i sappear ing , a l though i t has been r epo r t ed to pe renna te b y roots tock (SEN 1973). S imi la r ly , M. dissecta HALHER. f. is a c l imber , well a d a p t e d for the hot and ar id condi t ions of western R a j a s t h a n . The seeds when fu l ly m a t u r e and d r y exh ib i t ha rd coatedness (SEN et SHARMA 1972). SHARMA et SEN (1974) have r epor t ed t h a t the seeds possess a novel t y p e of s econdary do rmancy , as the f reshly ha rves t ed ones ge rmina t e up to 100 ~ bu t l a t e r become d o r m a n t .

F o r the presen t paper , the role of different wavelengths of l ight and the effect of red and far - red have been s tud ied for the seeds of the two species.

M A T E R I A L S A N D M E T H O D S

The seeds of both the species were collected from the University New Campus at Bhagat-ki-Kothi in O c t . - Nov., 1973. Fully mature and dried seeds which exhibit hard seed coat dormancy were treated with eonc. H2SO4 for 45--150 minutes for M. aegyptia and M. dissecta, respectively, to make them permeable. After acid scarification the seeds were thoroughly washed in running water for four hours. The pretreated seeds were then put for germination in petri-dishes containing filter paper moistened with distilled water. The different eolours of light were obtained by wrap- ping petrLdishes with differently coloured cellophane paper and placing them under six fluorescent tube lights of 40 watts each fitted at a distance of one metre, maintained at 28 ~ i 2 ~ Far-red was obtained by wrapping dishes with two layers each of standard blue and red cellophane paper. For continuous white light, the seeds were kept as such below the tube light and for total dark- ness, they were kept in a dark chamber. These different light conditions were supplied continuously till the observations were completed. Each petri-dish contained 10 seeds and each experiment was set in triplicate, repeated twice. The germination percentage was noted each day, the length of hypoeotyl and radicle were measured after 5 days of setting the experiment for both the species.

O B S E R V A T I O N S

The observa t ions on seed ge rmina t ion of the two species are shown in Tab. 1. I t is ev iden t from th is t ab le t h a t t he seeds of M. aegyptia are indi f ferent to a n y l ight as far the percentage of ge rmina t i on was concerned. The seeds showed nea r ly 100 ~o g e r m i n a t i o n even wi th in 24 hrs. in all cases. The percentage of ge rmina t ion in M. dissecta was highest in red as compared to o thers wi th in the first 24 hrs. However , no ge rmina t i on took place in to ta l darkness dur ing th is per iod. A t the end of the fou r th day , th is percentage increased to n e a r l y 100 ~ in all the l ight condi t ions except in far-red. I n v a r i a b l y a 100 ~ ge rmina t ion took place in t o t a l darkness , whereas some seeds e i ther d id no t ge rmina t e or r o t t ed in o ther l ight condi t ions (Tab. 1).

Seedl ing g rowth under different l ight condi t ions showed d i s t inc t va r ia t ions , which have been t a b u l a t e d in Tab. 2. I n M. aegyptia, the length of the radic le was m a x i m u m in red l ight . However , the radic le in al l the o the r l ights r ema ined lesser t h a n in whi te l ight . I t a p p e a r e d t ha t far - red spec ia l ly inh ib i t ed radicle growth. On the o ther hand the hypoco ty l l ength was found to be m a x i m u m in far-red.

SHARMA AND SEN: EFFECT OF LIGHT ON SEED GERMINATION 267

Table 1. Effect of different wavelengths of l ight on the percentage of germinat ion in Merremia spp.

M. aegyptia M. dissects

Wavelengths Percentage of germinat ion af ter of l ight

Percentage of germinat ion after

1 2 1 2 3 4 day days day days days days

Whi te 100 -- 5 4- 5 40 :~ 0 55 ~: 0 85 4- 5 Blue 100 -- 15 i 5 65 ~ 5 80 ~ 0 95 ~ 5 Green 100 -- 10 4- 0 70 ~ 5 80 • 0 85 4- 5 Red 100 -- 25 ~ 5 60 4- 5 85 4- 0 95 4- 0 Far- red lO0 -- 10 ~ 0 35 -: 0 50 :~: 5 75 ~ 0 Dark 100 -- 0 ! 0 70 ~ 5 90 • 5 100 ~ 0

Table 2. Effect of different wavelengths of l ight on seedling growth (in cm) of Merremia spp. at the end of five days,

M. aegyptia M. dissects Wavelengths

of l ight Radicle Hypocotyl Radicle Hypocotyl length length length length

White 6.2 _l 1.3 5.8 4- 0.7 5.8 ~J- 0.3 0.7 4- 0.3 Blue 4.6 -~-_ 0.8 6.1 4- 1.4 5.0 _~ 0.5 0.6 _~J- 0.1 Green 5.7 ~ 0.4 8.7 • 0.7 5.6 • 1.0 0.8 4- 0.2 Red 7.1 :z 0.9 6.8 4- 0.8 3.3 ~ 0.8 0.5 =t= 0.0 Far-red 3.0 4- 1.0 10.0 ~ 2.5 4.4 • 0.4 0.3 ~= 0.2 Dark 5.5 4- 1.0 7.6 4- 0.9 5.3 i 0.5 0.5 4- 0.2

I t is i n t e r e s t i n g to n o t e t h a t h y p o c o t y l b e c a m e l o n g e r i n a l l t h e l i gh t s , w h e n c o m p a r - e d w i t h w h i t e l igh t . S u r p r i s i n g l y , t h e f a r - r e d is m o s t bene f i c i a l for h y p o c o t y l b u t l e a s t fo r r a d i c l e g r o w t h . I n M. dissecta, w h i t e l i g h t is f o u n d t o b e t h e b e s t for r a d i c l e w h e r e a s i t s g r o w t h is s u p p r e s s e d i n a l l t h e l i g h t c o n d i t i o n s , r e m a r k a b l y so i n r ed . I t t a k e s a l o n g e r t i m e ( 4 - - 5 d a y s ) i n t h e case o f M. dissecta for t h e c o t y l e d o n s t o c o m e o u t o f t h e s eed coa t , w h i c h is n o t so i n M . aegyptia (2 d a y s ) . T h e g r o w t h o f t h e h y p o c o t y l i n M. dissecta is e x t r e m e l y s low. T h e h y p o c o t y l g r o w t h is f o u n d t o b e m a x i m u m i n w h i t e l i g h t as c o m p a r e d t o o t h e r s , b e i n g t h e l e a s t i n f a r - r ed .

I n M. dissects, a l l e x c e p t w h i t e l i g h t i n h i b i t e d t h e s e e d l i n g g r o w t h . F a r - r e d i n h i b i t e d to t h e m a x i m u m t h e r a d i c l e g r o w t h b u t e n h a n c e d t h a t o f h y p o c o t y l i n M . aegyptia. O n t h e c o n t r a r y f a r - r e d i n h i b i t e d t h e s e e d l i n g g r o w t h t o t h e m a x i m u m i n M . dissecta.

268 FOLIA GEOBOTANICA ET PIIYTOTAXONOMICA, 10,1975,

DISCUSSION AND CONCLUSION

Light plays an impor tant role in regulation of various ecophysiologieal aspects of plants including seed germination. The effect of different wavelengths of light on seed germination and seedling growth has been reported to be different for different species in the Indian arid zone (SEX et CItATTERJI 1966, S]~N 1969). Some similar results were also observed for Asteracantha longifolia by SEX et CHAWA~ (1970). In the presenv investigation, the germination of seeds in M. aegyptia was indifferent to different light conditions; while it was not so in M. dissevta.

AGXRWAL et VYAS (1970) have found maximum inhibition in white light; while maximum germination was obtained in white and red, but yellow, blue and green spectra have an inhibitory effect on seeds of Indigofera astragalina, an arid zone species. The present s tudy shows a promoting effect of hypocotyl in green light only. In M. dissecta, germination was delayed in total darkness and white light in the first 24 hours but this difference was lost in all the lights where germination became nearly 100 ~ except for far-red at the end of the experimental period. The inhibitory effect of red light on the hypocotyl elongation in lettuce seedlings has been reported by MATER et al. (1959). Here, the red light inhibited the growth of radicle and hypocotyl in M. dissevta; while red light enhanced the radicle and hy- pocotyl growth in M. aegyptia, when compared with white light. CHAWA~ et al. (1971) have reported that in A. longifolia and R. tuberosa, the radicle growth was inhibited and that of hypocotyl was promoted in blue and red light when compared with white light. This is confirmed by the present work for M. aegyptia in blue light. Red light enhanced the growth of both radicle and hypocotyl, but they are inhibited in M. dissecta, in both blue and red lights.

The present study on M. dissecta confirms the work of SEN (1969) where more radicle growth than of hypocotyl took place in all the spectral regions in the seedlings of Calotropis procera.

CHAWAN et SEN (1973) have reported tha t the germination percentage in seeds of Sida grewioides, a hard seed coat species, was poor as compared to S. spinosa. The pace of germination was enhanced in total darkness and far-red, whereas it was delayed in red and blue lights. In case of M. dissecta, germination was more in total darkness and red light; while in M. aegyptia the seeds exhibited a high percentage of germination almost in all the spectral regions tested within the period of 24 hrs. These results coincide with those of S. spinosa studied by CHAWA~ et SE~ (1973).

Acknowledgements

The authors are grateful to the authori t ies of Jodhpur Univers i ty for facilities. Help received from co-workers in the ecology laboratory of this univers i ty is gratefully acknowledged.

SUMMARY

The authors studied the effect of different lights and total darkness on seed germina- tion and early seedling growth of M. aegyptia and M. dissecta, growing in the Indian arid zone. The seeds of M. aegyptia are indifferent to light conditions as regards germination percentage because they germinated 100 ~/o within the first 24 hrs.

;SHARMA AND SEN: EFFECT OF LIGHT ON SEED GERMI]~,~ATION 269

I n M . dissecta , t h e h i g h e s t p e r c e n t a g e w a s f o u n d in r e d l i gh t w i t h i n t h e f i rs t 24 hrs . , b u t t h i s d i f f e r ence w a s los t l a t e r o n w h e n t h e p e r c e n t a g e g e r m i n a t i o n rose t o n e a r l y 100 % in all t h e l i g h t c o n d i t i o n s e x c e p t i n f a r - r ed . T h e s e e d l i n g g r o w t h d i d n o t s h o w a la rge v a r i a t i o n i n a n y o f t h e t w o spec ies e x c e p t t h a t i t w a s l ea s t i n b lue a n d r e d l i g h t s i n M . a e g y p t i a a n d M . dissecta, r e s p e c t i v e l y . G r o w t h o f t h e h y p o c o t y l i n t h e l a t e r spec ies is v e r y m u c h s l ower as c o m p a r e d t o t h e f o r m e r a n d h e n c e i t is d i f f icu l t t o c o m p a r e t h e t w o w i t h r e g a r d to t h e s eed l ing g r o w t h .

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Received 19 July 1974