Abstract
The interaction between phytochrome photoequilibrium (phi) and photon flux in the photoregulation of anthocyanin production under prolonged irradiation was studied in seedlings of Brassica oleracea L. and Lycopersicon esculentum Mill. In cabbage, anthocyanin production increases with decreasing phi, reaching a maximum at the lowest value (phi = 0.13) used in this study; in tomato, the extent of the response is higher at intermediate values, reaching a maximum at phi = 0.46. In cabbage, the response increases with increasing photon flux at all phi values; however, the response to changes in photon flux is minimal at phi = 0.85, and, at phi = 0.13, minimal at photon fluxes higher than 5 micromolar per square meter per second. In tomato, the response increases with increasing photon flux at phi = 0.46, 0.65, and 0.85, the response to changes in photon fluxes being minimal at phi = 0.85; at phi = 0.13 and 0.29 the response first increases (significantly at phi = 0.29 and minimally at phi = 0.13) and then decreases with increasing photon fluxes, the transition occurring at about 1 micromolar per square meter per second at phi = 0.13, and at 5 micromolar per square meter per second at phi = 0.29. The patterns of light quality-quantity interaction in the photoregulation of anthocyanin production are significantly different in cabbage and tomato and are also significantly different than those observed for other photomorphogenic responses to prolonged irradiations.