Mesure des photoequilibres du phytochrome dans les plantules de courge

Abstract

measurement of photoequilibria of phytochrome in pumpkin seedlings The photoequilibria P fr/P tot have been measured in the pumpkin hook after a short irradiation at different wavelengths between 660 nm and 710 nm. The values obtained are above those indicated by Hartmann for the mustard hypocotyls. Furthermore the results depend on the conditions during the irradiation and the preparation of the material. In a first case, the irradiation is given to the whole seedlings. The organs are cut off and the photoequilibria are measured. In a second case the hooks are cut off from the etiolated seedlings and the samples are illuminated before measuring. The photoequilibria are depresse d if the hooks are cut off after irradiation of the whole seedling. The same phenomenon is observed for the pumpkin cotyledons but not for the whole seedlings of Amaranthus caudatus. It is suggested that these differences are not due to a destruction of P fr but to an “inter-organ action”. At 25° a P fr→P r reversion can be observed during the 10 min following the light exposure. This dark reversion only concerns 6% of the pool of phytochrome and only takes place if sufficient molecules of P r have been transformed into P fr during the irradiation.