Photoinhibition of hypocotyl growth in white cabbage (Brassica oleracea L., cv "Bianco Brunswick") is controlled by UV absorbing receptor(s) and the phytochrome system, while in red cabbage (cv "Rosso Olandese tardivo invemale") phytochrome can act without any requirement for the action of a specific UV receptor. Similar results have been obtained for the photoregulation of anthocyanin production. Twenty-four hour preirradiations with UV light or 692 nanometers light lead to the same increase in responsiveness of the system toward Pfr in a following dark period, suggesting a phytochrome promotion of subsequent light induction for both.A considerable number of studies have been reported on the effects of UV radiation on higher plants (2,3,10,23). Nevertheless, the nature and the mode of interaction between the photoreceptors involved in the control of the photomorphogenic responses induced by UV irradiation, is still an open question. UV may induce both negative (damaging) and positive (nondamaging) effects in higher plants, and the same response can be differently affected (positively or negatively) depending on the fluence rate (1 1). UV light is absorbed by phytochrome, the red-far red reversible photoreceptor of plants, causing photoconversion of Pr to Pfr and vice versa, both in vitro (see 13 for the relevant literature) and in vivo (15). A specific blue-UV receptor known as cryptochrome, with one of its peaks at about 370 nm has been characterized by action spectroscopy (16). In addition, a little studied UV-