The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome

Abstract

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m‐2) promotes flowering, while far‐red (730 nm, 0.31 W m‐2) and irradiation with combined red + far‐red (0.20 + 0.41 W m‐2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m‐2, 12 min) at regular intervals, although these are counteracted by far‐red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.