Effect of red, far-red radiations on germination of cotton seed

Transcription

1 Plant & Cell Physiol. 12: (1971) Effect of red, far-red radiations on germination of cotton seed GURBAKSH SINGH and O. P. GARG Department of Botany, Haryana Agricultural University, Hissar, India (Received November 4, 1970) Seeds of two cultivars, H-14 and J-34 of Gossypium hirsutum L. soaked in the dark for durations of 8, 12 and 16 hr were exposed to red and far-red radiations alone and in different successions. While cv. J-34 was unresponsive to all light treatments, seed germinaiton in cv. H-14 was promoted by darkness and by exposure to far-red radiation and was inhibited by red and white light. Seed germination depended upon what treatment was given at the end. The effect of red light was reversed by far-red and vice versa. Although instances of light inhibition of seed germination are known, the authors are not aware of any clear cut instance in the literature on far-red promotion of seed germination. Since the first demonstration of clear cut promotion of germination by red and of inhibition by far-red radiation in lettuce seeds (1), excellent reviews on the effects of light and temperature on germination have appeared (2-6). Further investigation culminated in the postulation of a red, far-red reversible pigment systems, named phytochrome (7, 8). Photoperiodic control in light promoted seed germination of birch (Betula pubescens) and in light inhibited seed germination of Nemophila insignis has been shown (9-11). Interrelationships between photoperiod, light quality and temperature in the germination of Chenopodium seeds has also been reported (12). A listing of seeds whose germination is stimulated by light and of those whose germination is inhibited by light has been published (13, 14). Therefore, we considered it worthwhile to study the effects of red and far-red radiation on seed germination in a large seeded plant, like cotton, whose germination is not completely inhibited by light. Material and methods Two agriculturally important cultivars, H-14 and J-34, of upland cotton (Gossypium hirsutum L.) were used in these studies. The procedure followed for studying the effects of red and far-red radiation on the germination of cotton seeds was that given for the germination of lettuce and Lepidium seeds (8, 15). Light source: Three 40 w fluorescent tubes fitted to a growth chamber were wrapped with two layers of red cellophane paper to provide an adequate source of red light in the region of A. A 100-w tungsten lamp covered with two layers of red and two layers of blue cellophane paper served as an effective source 411

2 412 G. SINGH and O. P. GARO for far-red radiation allowing light energy of wavelengths greater than 7000 A to pass through. The light sources were kept 30 cm from the surface of the Petri dishes. This whole set up was confined to a controlled environment laboratory maintained at 27 C and provided with a small dark chamber. Petri dishes, cotton wool and the water used in this trial were all autoclaved. A thin layer of cotton wool was placed at the bottom of Petri dishes 10 cm in diameter, and was moistened with 25 ml of water. Twenty seeds were arranged in each dish with four replicate Petri dishes used in each treatment. Petri dishes were arranged in the dark chamber. The imbibition periods tried were 8, 12 and 16 hr. After imbibition for the required period, seeds were given the various treatments shown in Table 1 ; then they were returned to the dark chamber. In the dark room, green light was used for brief periods, whenever needed. Germination counts were taken 72 hr after the start of imbibition. Elongation of the radicle was taken as germination. Experiments were repeated 3 times. Results Germination of seeds in cv H-14 was influenced by the three imbibition periods and the eleven radiation treatments. Average germination percentages for the various treatments are given in Table 1. Data were significant for imbibition periods, radiation treatments and their interactions. An increase in the imbibition period to 16 hr, preceding radiation treatments, improved seed germination. There was no difference between the 8 and 12 hr soaking periods. It is interesting to note that red light inhibited and far-red promoted germination. The highest germination, above 68%, was observed with exposure of seeds Table 1 Effect of different regimes of red and far-red radiations, following varying periods of water soaking, on the germination (%) of cv H-14 of cotton Imbibition period (hr) xvauiation treatments Q 1 O C O IZ Complete darkness throughout 2. Red 1 min 3. Red 4 min 4. Red 8 min 5. Far-red 4 min 6. Far-red 8 min 7. Red 1 min, far-red 4 min 8. Red 1 min, far-red 4 min, red 1 min 9. Red 4 min, far-red 4 min 10. Red 4 min, far-red 4 min, red 4 min 11. White light throughout Mean of imbibition periods: CD. at 5% (2.16) C. D. at 5% for body of the table: (7.05) Mean of radiation treatments (C. D. at 5% : 4.06)

3 Effect of red, far-red light on cotton seed germination 413 to far-red, which was 68.6% and 68.3% respectively, with far-red treatment for 4 and 8 min. Exposure to red light depressed germination. There was a decrease in germination when far-red was followed by red and an improvement in germination when red was followed by far-red. In fact, far-red given last in any combination promoted germination. Likewise, red given at the end decreased germination. Treatment of seeds with continuous light significantly depressed germination, to 38.3%, whereas in complete darkness throughout it was 56.3%. The effect of red was reversed when far-red followed it and vice versa. Thus, seed germination in cv H-14 clearly depends upon the ratio of the red absorbing to the far-red absorbing form of phytochrome. There were no significant differences in germination of seeds of cv J-34 in darkness or in any of the light treatments following the three imbibition periods; the germination percentage remained around 70% in all cases. Discussion Data presented in this work show that seed germination in cv H-14 is promoted by far-red and inhibited by red or white light. Promotion of germination by far-red radiation in variety H-14 is peculiar in the sense that no clear cut instance of this could be found in any plant after a thorough search of the literature. There are instances in the literature of odier seeds whose germination is promoted by dark (16-18). The well known promotion of seed germination by red light has been reported for a large variety of plants (7-9, 15, 19-21). There are a few instances in the literature of far-red promotion of germination; but under highly specific conditions, and in seeds that completely fail to germinate in the dark. Thus, against the usual pattern of inhibition and the reversal of promotive effects of red by far-red radiation in most of the Bromeliaceae, continuous far-red promoted the germination of two other members of this family as did a brief exposure to red (22). Far-red given alone or following 4 min of red did not suppress germination, but produced a third of the germination obtained with red light. Similarly, repeated brief irradiations with far-red promoted germination of excised axial portions of lettuce seed, although they inhibited germination of the whole seed (23). In seeking an explanation of the difference in germination response of cotton seed to red and far-red radiation, it should be borne in mind that this was not a light requiring seed, but one whose germination is actually inhibited, though not completely, by light (Table 1). The inhibitory effect of red light on cotton seed germination is, therefore, understandable in the context of the established similarity between the effects of red and white light. Since, however, 4 or 8 min of red inhibited germination less than continuous light did, it may be presumed that the conversion of P r into Pt r is a comparatively slower process in this seed, and that such short durations of red light are not able to tilt the balance as effectively, as does continuous white light, towards an unfavourably low Pfr/Pr ratio. Effects of far-red radiation are known to be akin to those of darkness, i.e. conversion of the far-red absorbing form of phytochrome to the red absorbing form. Since complete darkness promoted germination in cv H-14 of cotton, one might expect a promotion of germination by far-red as well. Since thermal conversion of the far-red absorbing form of phytochrome in the dark is a comparatively slower process, treatment with

4 414 G. SINGH and O. P. GARG far-red resulted in greater enhancement of germination than did complete darkness, by producing a more favourable P fr /Pr ratio. Seed germination in the other cultivar, viz. J-34, was not affected by any of the light treatments given, thus, indicating that the phytochrome system does not operate in seed germination of this cultivar. References ( / ) Flint, L. H. and E. D. McAlister: Wavelengths of radiation in the visible spectrum inhibiting the germination of light sensitive lettuce seed. Smithsonian Misc. Coll. 94: 1-11 (1935). (2) Evenari, M.: Seed germination. In Radiation Biology 3. Edited by A. Hollander, p McGraw Hill, New York, (3) Evenari, M.: Light and seed dormancy. Handb. Pflazenphysiol. Edited by W. Ruhland. 15: , Berlin-Gottingen-Heidelberg, Springer, ( 4 ) Toole, E. H., S. B. Hendricks, H. A. Borthwick and V. K. Toole: Physiology of seed germination. Ann. Rev. Plant Physiol. 7: (1956). (5) Koller, D., A.M.Mayer, A. P. Mayber and S.Klein: Seed germination. Ann. Rev. Plant Physiol. 13: 437^67 (1962). (6) Lang, A.: Effect of some internal and external conditions on seed germination. Handb. Pflanzenphysiol. Edited by W. Ruhland. 15: Berlin-Gottingen-Heidelberg, Springer, ( 7 ) Borthwick, H. A., S. B. Hendricks, M. W. Parker, E. H. Toole and V. K. Toole: A reversible photoreaction controlling seed germination. PTOC. Natl. Acad. Sci. U. S. 38: (1952). ( 8) Borthwick, H. A., S. B. Hendricks, E. H. Toole and V. K. Toole: Action of light on lettuce seed germination. Bot. Caz. 115: (1954). ( 9) Black, M. and P. F. Wareing: Photoperiodic control of germination in seed of birch (Betula pubescens). Nature 174: (1954). (10) Black, M. and P. F. Wareing: Growdi studies in woody species VII. Photoperiodic control of germination in Betula pubescens. Physiol. Plant. 8: (1955). (11) Black, M. and P. F. Wareing: Sensitivity of light inhibited seeds to certain spectral regions. Nature 180: 395 (1957). (12) Cumming, B. G.: The dependence of germination on photoperiod, light quality and temperature in Chenopodium species. Can. J. Bot. 41: (1963). (13) Mayer, A. M. and A. P. Mayber: The germination of seeds. International Series of Monographs on Pure and Applied Biology, Plant Physiology Division. Pergamon Press, New York, (14) Wareing, P. F.: The germination of seeds. In Vistas in Botany 3. Edited by W. B. Turril. p Pergamon Press, London, (15) Toole, E. H., V. K. Toole, H. A. Borthwick and S. B. Hendricks: Photocontrol of Lepidium seed germination. Plant Physiol. 30: (1955). (16) Mancinelli, A. L., H. A. Borthwick and S. B. Hendricks: Phytochrome action in tomato seed germination. Bot. Gaz. 127: 1-5 (1966). (17) Yaniv, Z. and A. L. Mancinelli: Phytochrome and seed germination II. Changes of P (r requirement for germination in tomato seeds. Plant Physiol. 42: (1967). (18) Yaniv, Z., A. L. Mancinelli and P. Smith: Phytochrome and seed germination III. Action of prolonged far-red irradiation in the germination of tomato and cucumber seeds, ibid. 42: (1967). (19) Toole, E. H., H. A. Borthwick, S. B. Hendricks and V. K. Toole: Physiological studies of the effects of light and temperature on seed germination. Proc. Int. Seed Testing Assoc. 18: (1953). (20) Toole, E. H., V. K. Toole, S. B. Hendricks and H. A. Borthwick: Effect of temperature on germination of light sensitive seeds, ibid. 22: (1957).

5 Effect of red, far-red light on cotton seed germination 415 (21) Varshney, C. K.: Germination of the light sensitive seeds of Odmum americanum L. New Phytol. 67: (1968). (22) Downs, R. J.: Photocontrol of germination of seeds of the Bromeliaceae. Ohylon 21:1 6 (1964). (23) Scheibe, J. and A. Lang: Lettuce seed germination: Effects of high temperature and of repeated far-red treatment in relation to phytochrome. Photockem. Photobiol. 9: (1969).

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