Introduction 2001 1998 2002 2002 2003 2002 2 1992 1997 2005 6 + − − A B + z + 2+ − + − + Z + 1996 1998 2000 1996 2006 z  1997 Chenopodium album a a 1995 2000 Materials and methods Plant growth Chenopodium album 2006 −2  −1 UV-B radiation treatments 2 UV-B irradiations were performed using a Vilber Lourmat lamp with filter (VL-115M, Marne-la-Vallée, France). This lamp has a peak emission at 312 nm. UV-B irradiance was measured with an optometer (United Detector Technology Inc, Baltimore, USA) equipped with a probe specific for UV radiation. a a a o −2 −1 m o m −2  −1 o 1986 1989 1990 v m v m o m s v v m o v m m o m o 1991 a −2  −1 1995 2000 2005 o 2000 a v m t m o t a a 2001 2000 Results and discussion o m 1 v m 1 2003 m o o B v m Fig. 1 o m v m −2  −1  −2 −1 2 1993 −2 −1 −2  −1 −2 −1 v m −2  −1 m m 1993 −2  −1 Fig. 2 Effects of 6 h irradiation, at various levels, of detached leaves on some fluorescence parameters. CO is control; control is white light (PAR); UV-B is given by the Vilber lamp (zero PAR). Each value is the average of 4 measurements and the bars indicate ±S.D.; bars not shown are within the symbols  a 3 3 −2  −1 o m 3 o o o B o 1993 B Fig. 3 A −2  −1 B −5  −2  −1 −5   4 4 2000 2001 A − B −2  −1 5 A −  B − +  1 2 5 5 Fig. 4 A −2  −1 B A B  Fig. 5 2000 −2  −1 −2  −1  5 2006 A − 2006 1996 A 2+ 1996 1996