LIGHT QUALITY AND VERNALIZATION INTERACT IN CONTROLLING LATE FLOWERING ARABIDOPSIS ECOTYPES AND MUTANTS

The late flowering ecotypes of Arabidopsis titaliana L. (Heyn.) Eifel, Pitztal and Innsbruck responded to 10 d vernalization (cold treatment) by flowering earlier with less than half the number of leaves of non-induced plants. The vernalization response was cumulative: increased numbers of days of vernalization induced earlier flowering up to an apparent saturation in response after 30 to 40 d. The ratio of red:far-red (R:FR) light also affected non-vernalized time-to-flower. When grown under fluorescent plus incandescent lamps (R;FR = tO), time-to-flower was approximately half that required by plants grown under fluorescent lamps (R:FR = 5-8) at the same photon flux density and photoperiod. Leaf production rate was unaffected by either vernalization or light quality changes and time-to-flower and leaf number were highly correlated (r2= 0-973). The late flowering mutants of Landsberg erecta were grown under lighting which displayed a gradient of R: FR. Some mutants like co, flowered at the same time in all R:FR treatments, while others like fca took nearly twice as long to flower, with double the number of leaves at R;FR ratios of 5-8 compared with the R:FR = 1 treatment. The ranking of the response from least to most responsive was co, fe, gi, WT, fd, fwa, ft, flta, fpa, fy, fve and fca. Vernalization of these Landsberg mutants always resulted in earlier flowering, although only fca, fve, fy and fpa were significantly more sensitive to thermoinduction than the wild type parent. There was a high correlation (r2 = 0-89) between the response to thermoinduction and to R:FR ratio. Vernalization of fca for 24 d largely eliminated the R: FR time-to-flower response. Vernalization and photoinduction similarly affect late flowering and can substitute for each another. © 1993 Annals of Botany Company.