Summary
The possibility that phytochrome is involved in the promotion of flowering by far-red light was investigated. The addition of far-red (FR) to a day extension with red (R) light promotes inflorescence initiation in Lolium. A 2-hour interruption with darkness also promoted flowering compared with the uninterrupted red light control; apex length was further increased by a 10-minute FR irradiation given before the 2-hour dark interruption and was decreased by 10-minutes of R light given in the middle: both FR promotion and R inhibition were reversed by R and FR respectively. Apex length increased approximately linearly with increasing duration of dark interruption up to at least 2 1/2 hours. When varying ratios of R:FR light were substituted for a 2-hour dark period, apex length was increasingly depressed as the % R was increased above 25%; no difference between 25% R/75% FR and 100% FR could be detected. Apex length was inversely linearly related to the calculated [Pfr]/[P] ratios above about 40% Pfr.
FR promoted flowering when given during a 5-hour interruption of a day extension with R light but, between 0.25 and 0.90 J m2 s-1, there was no effect of intensity of FR; at 0.11 J m-2 s-1 apex length was shorter than at 0.25 J m-2 s-1 but longer than in darkness. When the duration of FR (from the beginning of a dark interruption of a day extension with R) was varied, apex length increased with increasing duration of FR up to 1 1/4 to 2 hours but further increasing the duration of FR did not promote flowering more.
The results implicate phytochrome in the promotion of flowering by FR light. It has been demonstrated that a low [Pfr]/[P] ratio (less than present in 25% R/75% FR) is needed over a relatively long period of time: this explains why a relatively high proportion of FR light must be added to R for several hours in order to give maximum promotion of flowering. It is concluded that, in Lolium, the increased flowering response to FR light is brought about by a reduction of [Pfr]/[P] ratio at the appropriate time, although the possibility that another effect of far-red is also involved has not been rigorously excluded.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Aspinall, D.: The effects of day length and light intensity on the growth of barley. VI. Interactions between the effects of temperature, photoperiod, and the spectral composition of the light source. Aust. J. biol. Sci. 22, 53–67 (1969).
Butler, W. L., Hendricks, S. B., Siegelman, H. W.: Action spectra of phytochrome in vitro. Photochem. and Photobiol. 3, 521–528 (1964).
Evans, L. T.: Inflorescence initiation in Lolium temulentum L. Effect of plant age and leaf area on sensitivity to photoperiodic induction. Aust. J. biol. Sci. 13, 112–131 (1960).
—, Borthwick, H. A., Hendricks, S. B.: Inflorescence initiation in Lolium temulentum L. VII. The spectral dependence of induction. Aust. J. biol. Sci. 18, 745–762 (1965).
—, King, R. W.: Role of phytochrome in photoperiodic induction of Pharbitis nil. Z. Pflanzenphysiol. 60, 277–288 (1969).
Friend, D. J. C.: The promotion of floral initiation of wheat by far-red radiation. Physiol. Plantarum (Cph.) 17, 902–920 (1964).
Holland, R. W. K.: The effects of red and far-red light on floral initiation in Lolium temulentum and other long-day plants. Ph. D. Thesis University of Reading (1969).
Lane, H. C., Cathey, H. M., Evans, L. T.: The dependence of flowering in several long-day plants on the spectral composition of light extending the photoperiod. Amer. J. Bot. 52, 1006–1014 (1965).
Moshkov, V. S., Pumpyanskaya, S. L., Fukshanskii, L. Ya.: Certain quantitative results of an analysis of a photoperiodism model. Fiziol. Rastenii 16, 41–48 (1948).
Schneider, M. J., Borthwick, H. A., Hendricks, S. B.: Effects of radiation on flowering of Hyoscyamus niger. Amer. J. Bot. 54, 1341–1249 (1967).
Vince, D.: The promoting effect of far-red light on flowering in the long-day plant Lolium temulentum. Physiol. Plantarum (Cph.) 18, 474–482 (1965).
—: An interpretation of the promoting effect of far-red light on the flowering of long-day plants. Photochem. and Photobiol. 5, 449–450 (1966a).
Vince, D.: Spectral distribution of light affecting growth and development: Angiosperms, Part I. Phytochrome response. In: Environmental biology (P. L. Altman and D. S. Dittmer, edit.). Federation of American societies for Experimental Biology (1966b).
—, Blake, J., Spencer, R.: Some effects of wavelength of the supplementary light on the photoperiodic behaviour of the long-day plants carnation and lettuce. Physiol. Plantarum (Cph.) 17, 119–125 (1964).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Holland, R.W.K., Vince, D. Floral initiation in Lolium temulentum L.: the role of phytochrome in the responses to red and far-red light. Planta 98, 232–243 (1971). https://doi.org/10.1007/BF00387068
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00387068