Figure 1.

Effects of UV radiation on the relative variable fluorescence of S. punctata ecotypes 203 and 760. Plants were raised phototrophically on standard Hutner's medium (203 and 760 non-treated) or on medium supplemented with 10 μm dicamba, 0.1 μm 2,4 dichlorophenoxyacetic acid (2,4D), 1 μm tri-iodobenzoic acid (TIBA), 0.1 μm morphactin, or 1 μm 6-benzylaminopurine (6-BAP). Intact fronds (▪) were exposed to 4.4 W m⁻² UV for 24 h. Cells (░⃞) isolated from fronds that had been raised on supplemented medium were exposed to 4.4-W m⁻² UV for 1 h. Following the UV treatment the minimal fluorescence (F_o) and the maximal fluorescence (F_m) were measured on dark-adapted samples. The relative variable fluorescence (F_v/F_m) was normalized to that of the non-treated control (intact fronds 100% = 0.80 ± 0.02 or isolated cells 100% = 0.76 ± 0.02). Values represent averages of nine to 10 (intact fronds) or seven (isolated cells) measurements. ses of the mean are given. Statistical analysis (Student's t test) reveals differences between intact fronds of ecotypes 203 and 760 (P < 0.01) and between fronds of non-treated 203 and 203-dicamba (P < 0.05), 203-TIBA (P < 0.05), and 203-BAP (P < 0.10). Differences between cells isolated from ecotypes 203 and 760, and between non-treated 203 and 203-TIBA and 203-dicamba were all significant (P < 0.05). The UV effect on isolated morphactin cells was not determined.