Diurnal temperature alternations (DIF/drop) affect chlorophyll content and chlorophyll a/chlorophyll b ratio in Melissa officinalis L. and Ocimum basilicum L., but not in Viola x wittrockiana Gams.

DIF, defined as day temperature (DT) minus night temperature (NT), influences plant morphology in a wide range of species. A controlled climate experiment was conducted to elucidate whether negative DIF (-6 degreesC) or positive DIF ( -6 degreesC) treatments or a 2-h temperature drop or increase at different times during the day, would affect chlorophyll concentration in Melissa officinalis L. (lemon balm), Ocimum basilicum L. (basil) and Viola x wittrockiana Gams. (pansy). With negative DIF treatment, lower concentrations of chlorophyll a and chlorophyll b were observed in Melissa and Ocimum. The reduction in chlorophyll b was more pronounced than for chlorophyll a, resulting in a higher chlorophyll a/chlorophyll b ratio than in control plants (constant temperature). The results support the theory that DIF treatments may influence phytochrome controlled chlorophyll synthesis and chlorophyll a/chlorophyll b ratio in lemon balm and basil, but that 2 It is too short time or 6 degreesC DIF too little to produce the same effect. In Viola, DIF had no effect on leaf chlorophyll content, except for the first 2-h period of the day. (C) 2002 Elsevier Science B.V. All rights reserved.