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Journal of Experimental Botany, Vol. 51, No. 347, pp. 1127-1133, June 2000
© 2000 Oxford University Press

Antagonistic action of low-fluence and high-irradiance modes of response of phytochrome on germination and ß-mannanase activity in Datura ferox seeds

L. de Miguel, M.J. Burgin, J.J. Casal and R.A. Sánchez1

IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Av. San Martín 4453, 1417, Buenos Aires, Argentina

Seed germination is often induced by a pulse of red light perceived by phytochrome and cancelled by a subsequent pulse of far-red light. When the pulse of red light is followed by several hours of darkness, a pulse of far-red light is no longer effective and prolonged far-red is necessary to block germination. The aim was to investigate whether the red light pulse and prolonged far-red light act on the same or different processes during germination of Datura ferox seeds. Forty-five hours after the inductive red light pulse, germination could not be blocked by one pulse or six hourly pulses of far-red light, but was significantly reduced by 6 h of continuous far-red light. The pulse of red light increased embryo growth potential and the activities of ß-mannanase and ß-mannosidase extracted from the micropylar region of the endosperm. Continuous far-red light had no effect on embryo growth potential or ß-mannosidase activity, but severely reduced the activity of ß-mannanase. The effect of far-red light had the features of a high-irradiance response of phytochrome. Both germination and ß-mannanase activity were restored by a pulse of red light given after the end of the continuous far-red treatment. It is concluded that the low-fluence response and the high-irradiance response modes of phytochrome have antagonistic effects on seed germination and that the control of ß-mannanase activity is one process where this antagonism is established.

Key words: Germination, phytochrome, high-irradiance response.


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